Rafik M'nassri - Academia.edu (original) (raw)
Papers by Rafik M'nassri
Journal of Materials Science: Materials in Electronics
In this work, we have exploited the magnetic entropy changes (DS) of Mn 5 Si 3type Mn 5-x Co x Ge... more In this work, we have exploited the magnetic entropy changes (DS) of Mn 5 Si 3type Mn 5-x Co x Ge 3 intermetallic compounds in order to explore their ability as magnetocaloric (MCE) materials near room temperature. The quantitative criterion derived from the local exponent (N), and the phenomenological universal behaviour were performed to distinguish the characteristic of second-order transition. The universal curves of the Mn 5-x Co x Ge 3 samples collapse onto a single curve for all the Co-compositions for any applied magnetic field where an average curve is obtained. The same behaviour is observed for the local exponent N(T). The existence of the universal curve of entropy changes (DS) and N indicates that Mn 5-x Co x Ge 3 system exhibited a universal behaviour. This implies that four samples have the same nature of phase transitions and belong to the same universality class. The average curve can be used to predict the response of materials in different conditions not available in the laboratory by extrapolations in field or temperature for Co-substituted samples. It is found that the predicted DS and N(T) based on average curves are in good agreement with the experimental results, indicating the reliability of this method for assessing MCE properties. This work is especially relevant in the sense that it quantifies the Mn 5-x Co x Ge 3 in terms of adiabatic temperatures changes (DT ad), temperature averaged entropy change (TEC), maximum refrigerant capacity (RC) and normalized refrigerant capacity (NRC) all at once. Accordingly, the addition of Co ion increases DS, DT ad , TEC, RC max and NRC max and thereby improves the MCE performance in Mn 5-x Co x Ge 3 samples. These metrics can help in identifying materials with high performance and clearly suggest that the
Applied Physics A
Based on the experimental data of the isothermal polarization P(T,E) of BaHf 0.11 Ti 0.89 O 3 bul... more Based on the experimental data of the isothermal polarization P(T,E) of BaHf 0.11 Ti 0.89 O 3 bulk ceramic, entropy change (∆S), temperature change (∆T), and heat carrying capacity (∆Q) of the material are evaluated in detail using an artificial neural network (ANN) procedure. As a result, the maximum ECE occurs above T C and shifts to higher temperatures with increasing applied field. The BaHf 0.11 Ti 0.89 O 3 ceramic exhibits large ECE parameters around the Curie temperature (T C) associated with a relatively broad electrocaloric temperature span. Furthermore, under different electric fields, many figures of merit such as relative cooling power, temperature-averaged entropy change, and normalized refrigerant capacity are explored, making the sample a promising material for green cooling devices. Such figures of merit increase monotonically with the enhancement of the applied field. In addition, the field dependence of the ∆S and ∆T is thoroughly investigated. The master curve and the exponent n controlling the field dependence of both magnitudes confirm the second-order character of the electric phase transition of the sample. The ANN method provides very accurate and fast predictions with a small amount of experimental data. Therefore, this method accelerates the characterization of novel electrocaloric materials by shortening the time necessary for experimentation.
Journal of Materials Science: Materials in Electronics
The main objective of this work is to explore the field dependence of the electrocaloric effect (... more The main objective of this work is to explore the field dependence of the electrocaloric effect (ECE) in KTa0.57Nb0.43O3 in terms of the entropy change (ΔS) and the temperature change (ΔT) for applied electric fields ranging from 5 to 15 kV cm−1. The artificial neural network (ANN) may be used as a reliable modeling method for simulating and predicting electrocaloric behavior under different thermoelectrical conditions. The experimental data collection was employed for this purpose to forecast the coefficient of performance and temperature span for KTa0.57Nb0.43O3 operating near room temperature. The large ECE, comparatively high relative cooling power (RCP), temperature-averaged entropy change (TEC), normalized refrigerant capacity (NRC), and low cost jointly make the present compound a promising candidate for cooling devices near room temperature. The electrical field dependence of ECE can help to predict the ECE characteristics of cooling devices and facilitate the design of highly efficient cooling devices.
In this work, we have exploited the magnetic entropy changes (DS) of Mn 5 Si 3type Mn 5-x Co x Ge... more In this work, we have exploited the magnetic entropy changes (DS) of Mn 5 Si 3type Mn 5-x Co x Ge 3 intermetallic compounds in order to explore their ability as magnetocaloric (MCE) materials near room temperature. The quantitative criterion derived from the local exponent (N), and the phenomenological universal behaviour were performed to distinguish the characteristic of second-order transition. The universal curves of the Mn 5-x Co x Ge 3 samples collapse onto a single curve for all the Co-compositions for any applied magnetic field where an average curve is obtained. The same behaviour is observed for the local exponent N(T). The existence of the universal curve of entropy changes (DS) and N indicates that Mn 5-x Co x Ge 3 system exhibited a universal behaviour. This implies that four samples have the same nature of phase transitions and belong to the same universality class. The average curve can be used to predict the response of materials in different conditions not available in the laboratory by extrapolations in field or temperature for Co-substituted samples. It is found that the predicted DS and N(T) based on average curves are in good agreement with the experimental results, indicating the reliability of this method for assessing MCE properties. This work is especially relevant in the sense that it quantifies the Mn 5-x Co x Ge 3 in terms of adiabatic temperatures changes (DT ad), temperature averaged entropy change (TEC), maximum refrigerant capacity (RC) and normalized refrigerant capacity (NRC) all at once. Accordingly, the addition of Co ion increases DS, DT ad , TEC, RC max and NRC max and thereby improves the MCE performance in Mn 5-x Co x Ge 3 samples. These metrics can help in identifying materials with high performance and clearly suggest that the
Based on the experimental data of the isothermal polarization P(T,E) of BaHf 0.11 Ti 0.89 O 3 bul... more Based on the experimental data of the isothermal polarization P(T,E) of BaHf 0.11 Ti 0.89 O 3 bulk ceramic, entropy change (∆S), temperature change (∆T), and heat carrying capacity (∆Q) of the material are evaluated in detail using an artificial neural network (ANN) procedure. As a result, the maximum ECE occurs above T C and shifts to higher temperatures with increasing applied field. The BaHf 0.11 Ti 0.89 O 3 ceramic exhibits large ECE parameters around the Curie temperature (T C) associated with a relatively broad electrocaloric temperature span. Furthermore, under different electric fields, many figures of merit such as relative cooling power, temperature-averaged entropy change, and normalized refrigerant capacity are explored, making the sample a promising material for green cooling devices. Such figures of merit increase monotonically with the enhancement of the applied field. In addition, the field dependence of the ∆S and ∆T is thoroughly investigated. The master curve and the exponent n controlling the field dependence of both magnitudes confirm the second-order character of the electric phase transition of the sample. The ANN method provides very accurate and fast predictions with a small amount of experimental data. Therefore, this method accelerates the characterization of novel electrocaloric materials by shortening the time necessary for experimentation.
Les travaux présentés dans ce manuscrit consistent à élaborer par la méthode céramique des oxydes... more Les travaux présentés dans ce manuscrit consistent à élaborer par la méthode céramique des oxydes ferromagnétiques de type pérovskite et à étudier leurs propriétés physiques (structurales, magnétiques, magnétocaloriques..). Nous avons commencé ce travail par la synthèse de séries de manganites à base de praséodyme ( Pr0.6-xEuxSr0.4MnO3 et Pr0.6-xErxSr0.4MnO3 ) et de lanthane ( La0.6Sr0.2Ba0.2-x□xMnO3 et (La0.6Sr0.2Ba0.2MnO3)1-x /(Co2O3)x ) en utilisant la méthode solide-solide à haute température. Les échantillons élaborés ont été caractérisés par diffractométrie de poudre RX. Les diffractogrammes obtenues ont été affinés par la méthode Rietveld en utilisant le logiciel Fullprof. L'affinement structural a montré que les manganites synthétisés se présentent sous forme de phases pures avec des raies fines et intenses sans phases parasites et cristallisent dans des structures déformées.Des mesures magnétiques (M(T) et M(H)) ont permis d'obtenir des informations sur le comportem...
Les travaux presentes dans ce manuscrit consistent a elaborer par la methode ceramique des oxydes... more Les travaux presentes dans ce manuscrit consistent a elaborer par la methode ceramique des oxydes ferromagnetiques de type perovskite et a etudier leurs proprietes physiques (structurales, magnetiques, magnetocaloriques..). Nous avons commence ce travail par la synthese de series de manganites a base de praseodyme ( Pr0.6-xEuxSr0.4MnO3 et Pr0.6-xErxSr0.4MnO3 ) et de lanthane ( La0.6Sr0.2Ba0.2-x□xMnO3 et (La0.6Sr0.2Ba0.2MnO3)1-x /(Co2O3)x ) en utilisant la methode solide-solide a haute temperature. Les echantillons elabores ont ete caracterises par diffractometrie de poudre RX. Les diffractogrammes obtenues ont ete affines par la methode Rietveld en utilisant le logiciel Fullprof. L'affinement structural a montre que les manganites synthetises se presentent sous forme de phases pures avec des raies fines et intenses sans phases parasites et cristallisent dans des structures deformees.Des mesures magnetiques (M(T) et M(H)) ont permis d'obtenir des informations sur le comportem...
Journal of Materials Science: Materials in Electronics, 2021
The critical behaviour and magnetic field dependence of magnetic entropy changes (ΔSM) for the fe... more The critical behaviour and magnetic field dependence of magnetic entropy changes (ΔSM) for the ferromagnetic La0.65Nd0.05Ba0.3Mn1−xCrxO3 (0 ≤ x ≤ 0.15) ceramics are systematically investigated in details. Upon Cr doping, the Curie temperature TC, ΔSM and the critical exponents (β, γ, and δ) are substantially influenced. As a result, the TC varies from 330 K for x = 0 to 275 K for x = 0.15 and the ΔSM decreases gradually with higher Cr substitution. The values of the critical exponents of the prepared samples lie between the Tricritical mean field model and 3D-Ising model. Thus, these results suggest that critical phenomena in La0.65Nd0.05Ba0.3Mn1−xCrxO3 (0 ≤ x ≤ 0.15) could not be explained on the conventional universality classes. However, the obtained results suggest an existence of FM short-range order in the prepared samples. To check the agreement with the scaling theory, m = f ± (h) is plotted for all samples. It was found that all data points fall into two separate branches above and below the critical temperature, TC, which confirmed that the critical exponents are reliable. The analysis of the field dependence of the ΔSM reveals the power law dependence at the transition temperature. Based on the value of critical exponents, one can find that all the magnetic entropy changes and heat capacity changes fall on a master curve for all measured fields and temperatures confirming the nature of second-order magnetic transition. This excellent overlap clearly indicates that the critical exponents obtained for the prepared system are reasonably accurate.
Journal of Magnetism and Magnetic Materials, 2020
Structure, magnetic and field dependence of magnetocaloric properties of Pr 0.5 RE 0.
Journal of Materials Science: Materials in Electronics, 2019
We report in this work the results of synthesis and characterization of La 0.8 Ca 0.2−x Na x MnO ... more We report in this work the results of synthesis and characterization of La 0.8 Ca 0.2−x Na x MnO 3 (0 ≤ x ≤ 0.2) prepared by the Pechini sol-gel method. We have investigated different effects of replacing Ca by Na on the magnetic properties and magnetocaloric effect of La 0.8 Ca 0.2 MnO 3 compounds using X-ray diffraction and magnetization measurements. We have observed an evolution from an orthorhombic to a rhombohedral symmetry caused by the addition of Na and that the rhombohedral phase is stable for x ≥ 0.1. The partial substitution of Ca by Na leads to a monotonic increase in the Curie temperature (T C) of the samples from 105 K for x = 0 to 330 K for x = 0.2. A second-order nature of the magnetic phase transition is established in all the prepared compounds with the help of the Banerjee criterion. At an applied field of 5T, the maximum magnetic entropy change (∆S M max) shows an enhancement with increasing Na + concentration. Moreover, the relative cooling power (RCP) values are found to vary between 203 and 300.5 J/kg in this series of materials. In order to compare the magnetocaloric performances of the prepared samples, we have used several figures of merit such as the temperature-averaged entropy change (TEC), refrigerant capacity (RC) and normalized refrigerant capacity (NRC). Accordingly, the addition of Na ion greatly increases TEC, RC and NRC and thereby improves the magnetocaloric performance in La 0.8 Ca 0.2−x Na x MnO 3 (0 ≤ x ≤ 0.2). These metrics can help in identifying materials with high performance and clearly suggest that the sol-gel-made samples with x ≥ 0.1 can be customized for use in magnetic cooling applications near room temperature.
Chemical Physics Letters, 2018
We investigated the effect of both lanthanum and strontium deficiencies upon the structural, magn... more We investigated the effect of both lanthanum and strontium deficiencies upon the structural, magnetic and magnetocaloric properties in La 0.7 Sr 0.3 MnO 3 mixed-valence manganite. Lacunar powder oxides La 0.7Àx h x Sr 0.3 MnO 3 and La 0.7 Sr 0.3Àx h x MnO 3 (x = 0, 0.01, 0.02 and 0.05), where h is a vacancy, were prepared by the sol-gel technique by sintering at 750°C and 850°C. Our synthetized samples crystallize in a rhomboedrically distorted perovskite structure with space group R-3C. Both these series of samples are ferromagnets and undergo second order paramagnetic-ferromagnetic transition with decreasing temperature. Magnetization measurements versus magnetic applied field at low temperature confirm the ferromagnetic behavior of our lacunars samples. Curie temperature decrease with increasing vacancy content for strontitum-deficient samples, while, its shows a maximum at about x = 0.01 (T C = 358 K) followed by a minimum for x = 0.03 (T C = 336 K) for lanthanum-deficient compounds. All compounds undergo a large magnetocaloric effect and have consequently potential applications in magnetic refrigeration domain around room temperature.
RSC Advances, 2016
The structure, magnetic properties, critical exponents and magnetocaloric effect (MCE) of La0.6Sr... more The structure, magnetic properties, critical exponents and magnetocaloric effect (MCE) of La0.6Sr0.4CoO3 cobaltite are studied.
Journal of Alloys and Compounds, 2016
Abstract A systematic study on the magnetic and magnetocaloric properties of a polycrystalline sa... more Abstract A systematic study on the magnetic and magnetocaloric properties of a polycrystalline sample of Pr 0.6 Ca 0.1 Sr 0.3 Mn 0.975 Fe 0.025 O 3 prepared by solid-state reaction has been studied. Structural study shows that our sample is of a single phase and crystallizes in the distorted orthorhombic system with Pbnm space group. The measurements of the temperature and field dependences of the magnetization clearly show that the Pr 0.6 Ca 0.1 Sr 0.3 Mn 0.975 Fe 0.025 O 3 ceramic exhibit a paramagnetic-ferromagnetic transition with decreasing temperature. The magnetic entropy change (-ΔS M ) is determined from isothermal magnetization curves. The field dependence of magnetic entropy change is analyzed and showing the power law dependence, ΔS max (T,H) = a(T)(μ 0 H) n(T,H) at the Curie temperature (T C ). It has been noted that the value of n obeys to the Curie-Weiss law above T C . The Landau theory (LT) for phase transitions framework is applied to describe the magnetocaloric effect (MCE) in Pr 0.6 Ca 0.1 Sr 0.3 Mn 0.975 Fe 0.025 O 3 manganite. The analysis of the MCE using the LT shows good agreement with the experimental data, indicating the importance of magneto-elastic coupling and electron interaction in the MCE properties of manganite. Based on the obtained magnetic entropy change (-ΔS M ) under different magnetic fields, we determined the spontaneous magnetization (M Sp ). For comparison, the M Sp has been also deduced from the classical extrapolation from the Arrott plot. An excellent agreement is found between the spontaneous magnetization determined from the entropy change (ΔS M vs. M 2 ) and the Arrot curves (H/M vs. M 2 ), confirming that the use of magnetic entropy change to get the spontaneous magnetization is valid.
Ceramics International, 2015
Influence of transition metal doping (Fe, Co, Ni and Cr) on magnetic and magnetocaloric propertie... more Influence of transition metal doping (Fe, Co, Ni and Cr) on magnetic and magnetocaloric properties of Pr 0.7 Ca 0.3 MnO 3 manganites, Ceramics International,
Ceramics International, 2015
Journal of Alloys and Compounds, 2015
ABSTRACT The structure, critical exponents and magnetocaloric effect (MCE) of Pr0.4Eu0.2Sr0.4MnO3... more ABSTRACT The structure, critical exponents and magnetocaloric effect (MCE) of Pr0.4Eu0.2Sr0.4MnO3 were investigated in detail. A solid state reaction method was used in the preparation phase. Phase purity, structure, size, and crystallinity were investigated using XRD and SEM. The Reitveld refinement of XRD pattern shows that the sample adopts an orthorhombic structure with Pnma space group. Analyzing temperature and field dependences of magnetization around the ferromagnetic-paramagnetic transition reveals the sample undergoing the second-order magnetic phase transition with the critical parameters TC ∼ 238K, β =0.310(3), γ = 1.264(1) and δ = 4.761(9).The exponents are close to 3D-Ising values. This reflects an existence of ferromagnetic short-range order in our sample. With these values one can scale the magnetization below and above TC following a single equation of state. However, it is noteworthy that the scaling relations are obeyed indicating renormalization of interactions around the TC. Temperature variation in effective exponents βeff and γeff resemble with those for disordered ferromagnet. In the vicinity of TC, the magnetic entropy change ΔS reached maximum values of 2.80 and 5.32 J/kg K under magnetic field variations of 2 and 5T, respectively. The field dependence of the magnetic entropy changes are also analyzed, which show power law dependence ΔSMmax≈a(μ0H)n at transition temperature. The critical exponent analysis related to magnetocaloric effect is described. Moreover, the temperature dependence of the exponent n for a different magnetic field is also studied. The values of n obey to the Curie Weiss law above the transition temperature. In particularly, n can be related to the critical exponents β, γ and δ at the magnetic transition. We used the scaling hypotheses to scale the magnetic entropy change and heat capacity changes to a single universal curve respectively for Pr0.4Eu0.2Sr0.4MnO3 sample.
Journal of Alloys and Compounds, 2015
This article covers the detailed study on the magnetic and magnetocaloric properties of Pr 0.5 Eu... more This article covers the detailed study on the magnetic and magnetocaloric properties of Pr 0.5 Eu 0.1 Sr 0.4 MnO 3 samples. The materials were synthesized through the sol-gel using nitrate-citrate route method by sintering at four different temperatures starting from 600 to 1000°C. Phase purity, structure, size, and crystallinity were investigated using XRD and SEM. The structure, magnetic properties and magnetocaloric effect of Pr 0.5 Eu 0.1 Sr 0.4 MnO 3 ceramics with different particle sizes have been investigated. Regardless of the sintering temperature, the orthorhombic crystal structure with the Pnma space group is stable. XRD analysis showed that the particle size increases with the increase in sintering temperature. The Curie temperature shifted from 90 K to 270 K. Magnetization, magnetic entropy change (∆S), and relative cooling power (RCP) also increased with size in the nanocrystalline samples. The magnetic entropy changes were about 0.89 J/kgK, 2.75J/kgK, 3.34J/kg K, and 3.82 J/kg K for the samples sintered at 600 °C, 800°C, 900°C and 1000°C, respectively when a magnetic field of 5 T was applied. It is shown that for Pr 0.5 Eu 0.1 Sr 0.4 MnO 3 the magnetic entropy change follows a master curve behavior.
Journal of Applied Physics, 2013
Structural, magnetic, and magnetocaloric properties of La0.6Sr0.2Ba0.2-x◻xMnO3 (0 ≤ x ≤ 0.15) whe... more Structural, magnetic, and magnetocaloric properties of La0.6Sr0.2Ba0.2-x◻xMnO3 (0 ≤ x ≤ 0.15) where ◻ is a barium deficiency have been investigated by X-ray diffraction and magnetic measurements. Our samples were synthesized using the solid-state reaction method at high temperatures. Structural studies show that our samples are single phase and crystallize in the rhombohedral system with R 3¯ c space group. Magnetization measurements as a function of temperature in a magnetic applied field of 0.05 T show that all our samples exhibit a paramagnetic-ferromagnetic transition with decreasing temperature. The Curie temperature TC shifts to lower values with increasing barium-deficiency. The Arrott plots show that the phase transition is of second order. The effect of barium deficiency on the magnetocaloric properties has been investigated. The values of the maximum of the magnetic entropy change, |−ΔSmax|, under a magnetic field change of 3.5 T are found to be 2.9, 2.92, 3.31, and 3.34 J/kg K for x = 0.0, 0.05...
Journal of Alloys and Compounds, 2014
Effect of iron substitution on the structural, magnetic and magnetocaloric properties of Pr 0.6 C... more Effect of iron substitution on the structural, magnetic and magnetocaloric properties of Pr 0.6 Ca 0.1 Sr 0.3 Mn 1-x Fe x O 3 (0 x 0.075) manganites, (2014),
Journal of Materials Science: Materials in Electronics
In this work, we have exploited the magnetic entropy changes (DS) of Mn 5 Si 3type Mn 5-x Co x Ge... more In this work, we have exploited the magnetic entropy changes (DS) of Mn 5 Si 3type Mn 5-x Co x Ge 3 intermetallic compounds in order to explore their ability as magnetocaloric (MCE) materials near room temperature. The quantitative criterion derived from the local exponent (N), and the phenomenological universal behaviour were performed to distinguish the characteristic of second-order transition. The universal curves of the Mn 5-x Co x Ge 3 samples collapse onto a single curve for all the Co-compositions for any applied magnetic field where an average curve is obtained. The same behaviour is observed for the local exponent N(T). The existence of the universal curve of entropy changes (DS) and N indicates that Mn 5-x Co x Ge 3 system exhibited a universal behaviour. This implies that four samples have the same nature of phase transitions and belong to the same universality class. The average curve can be used to predict the response of materials in different conditions not available in the laboratory by extrapolations in field or temperature for Co-substituted samples. It is found that the predicted DS and N(T) based on average curves are in good agreement with the experimental results, indicating the reliability of this method for assessing MCE properties. This work is especially relevant in the sense that it quantifies the Mn 5-x Co x Ge 3 in terms of adiabatic temperatures changes (DT ad), temperature averaged entropy change (TEC), maximum refrigerant capacity (RC) and normalized refrigerant capacity (NRC) all at once. Accordingly, the addition of Co ion increases DS, DT ad , TEC, RC max and NRC max and thereby improves the MCE performance in Mn 5-x Co x Ge 3 samples. These metrics can help in identifying materials with high performance and clearly suggest that the
Applied Physics A
Based on the experimental data of the isothermal polarization P(T,E) of BaHf 0.11 Ti 0.89 O 3 bul... more Based on the experimental data of the isothermal polarization P(T,E) of BaHf 0.11 Ti 0.89 O 3 bulk ceramic, entropy change (∆S), temperature change (∆T), and heat carrying capacity (∆Q) of the material are evaluated in detail using an artificial neural network (ANN) procedure. As a result, the maximum ECE occurs above T C and shifts to higher temperatures with increasing applied field. The BaHf 0.11 Ti 0.89 O 3 ceramic exhibits large ECE parameters around the Curie temperature (T C) associated with a relatively broad electrocaloric temperature span. Furthermore, under different electric fields, many figures of merit such as relative cooling power, temperature-averaged entropy change, and normalized refrigerant capacity are explored, making the sample a promising material for green cooling devices. Such figures of merit increase monotonically with the enhancement of the applied field. In addition, the field dependence of the ∆S and ∆T is thoroughly investigated. The master curve and the exponent n controlling the field dependence of both magnitudes confirm the second-order character of the electric phase transition of the sample. The ANN method provides very accurate and fast predictions with a small amount of experimental data. Therefore, this method accelerates the characterization of novel electrocaloric materials by shortening the time necessary for experimentation.
Journal of Materials Science: Materials in Electronics
The main objective of this work is to explore the field dependence of the electrocaloric effect (... more The main objective of this work is to explore the field dependence of the electrocaloric effect (ECE) in KTa0.57Nb0.43O3 in terms of the entropy change (ΔS) and the temperature change (ΔT) for applied electric fields ranging from 5 to 15 kV cm−1. The artificial neural network (ANN) may be used as a reliable modeling method for simulating and predicting electrocaloric behavior under different thermoelectrical conditions. The experimental data collection was employed for this purpose to forecast the coefficient of performance and temperature span for KTa0.57Nb0.43O3 operating near room temperature. The large ECE, comparatively high relative cooling power (RCP), temperature-averaged entropy change (TEC), normalized refrigerant capacity (NRC), and low cost jointly make the present compound a promising candidate for cooling devices near room temperature. The electrical field dependence of ECE can help to predict the ECE characteristics of cooling devices and facilitate the design of highly efficient cooling devices.
In this work, we have exploited the magnetic entropy changes (DS) of Mn 5 Si 3type Mn 5-x Co x Ge... more In this work, we have exploited the magnetic entropy changes (DS) of Mn 5 Si 3type Mn 5-x Co x Ge 3 intermetallic compounds in order to explore their ability as magnetocaloric (MCE) materials near room temperature. The quantitative criterion derived from the local exponent (N), and the phenomenological universal behaviour were performed to distinguish the characteristic of second-order transition. The universal curves of the Mn 5-x Co x Ge 3 samples collapse onto a single curve for all the Co-compositions for any applied magnetic field where an average curve is obtained. The same behaviour is observed for the local exponent N(T). The existence of the universal curve of entropy changes (DS) and N indicates that Mn 5-x Co x Ge 3 system exhibited a universal behaviour. This implies that four samples have the same nature of phase transitions and belong to the same universality class. The average curve can be used to predict the response of materials in different conditions not available in the laboratory by extrapolations in field or temperature for Co-substituted samples. It is found that the predicted DS and N(T) based on average curves are in good agreement with the experimental results, indicating the reliability of this method for assessing MCE properties. This work is especially relevant in the sense that it quantifies the Mn 5-x Co x Ge 3 in terms of adiabatic temperatures changes (DT ad), temperature averaged entropy change (TEC), maximum refrigerant capacity (RC) and normalized refrigerant capacity (NRC) all at once. Accordingly, the addition of Co ion increases DS, DT ad , TEC, RC max and NRC max and thereby improves the MCE performance in Mn 5-x Co x Ge 3 samples. These metrics can help in identifying materials with high performance and clearly suggest that the
Based on the experimental data of the isothermal polarization P(T,E) of BaHf 0.11 Ti 0.89 O 3 bul... more Based on the experimental data of the isothermal polarization P(T,E) of BaHf 0.11 Ti 0.89 O 3 bulk ceramic, entropy change (∆S), temperature change (∆T), and heat carrying capacity (∆Q) of the material are evaluated in detail using an artificial neural network (ANN) procedure. As a result, the maximum ECE occurs above T C and shifts to higher temperatures with increasing applied field. The BaHf 0.11 Ti 0.89 O 3 ceramic exhibits large ECE parameters around the Curie temperature (T C) associated with a relatively broad electrocaloric temperature span. Furthermore, under different electric fields, many figures of merit such as relative cooling power, temperature-averaged entropy change, and normalized refrigerant capacity are explored, making the sample a promising material for green cooling devices. Such figures of merit increase monotonically with the enhancement of the applied field. In addition, the field dependence of the ∆S and ∆T is thoroughly investigated. The master curve and the exponent n controlling the field dependence of both magnitudes confirm the second-order character of the electric phase transition of the sample. The ANN method provides very accurate and fast predictions with a small amount of experimental data. Therefore, this method accelerates the characterization of novel electrocaloric materials by shortening the time necessary for experimentation.
Les travaux présentés dans ce manuscrit consistent à élaborer par la méthode céramique des oxydes... more Les travaux présentés dans ce manuscrit consistent à élaborer par la méthode céramique des oxydes ferromagnétiques de type pérovskite et à étudier leurs propriétés physiques (structurales, magnétiques, magnétocaloriques..). Nous avons commencé ce travail par la synthèse de séries de manganites à base de praséodyme ( Pr0.6-xEuxSr0.4MnO3 et Pr0.6-xErxSr0.4MnO3 ) et de lanthane ( La0.6Sr0.2Ba0.2-x□xMnO3 et (La0.6Sr0.2Ba0.2MnO3)1-x /(Co2O3)x ) en utilisant la méthode solide-solide à haute température. Les échantillons élaborés ont été caractérisés par diffractométrie de poudre RX. Les diffractogrammes obtenues ont été affinés par la méthode Rietveld en utilisant le logiciel Fullprof. L'affinement structural a montré que les manganites synthétisés se présentent sous forme de phases pures avec des raies fines et intenses sans phases parasites et cristallisent dans des structures déformées.Des mesures magnétiques (M(T) et M(H)) ont permis d'obtenir des informations sur le comportem...
Les travaux presentes dans ce manuscrit consistent a elaborer par la methode ceramique des oxydes... more Les travaux presentes dans ce manuscrit consistent a elaborer par la methode ceramique des oxydes ferromagnetiques de type perovskite et a etudier leurs proprietes physiques (structurales, magnetiques, magnetocaloriques..). Nous avons commence ce travail par la synthese de series de manganites a base de praseodyme ( Pr0.6-xEuxSr0.4MnO3 et Pr0.6-xErxSr0.4MnO3 ) et de lanthane ( La0.6Sr0.2Ba0.2-x□xMnO3 et (La0.6Sr0.2Ba0.2MnO3)1-x /(Co2O3)x ) en utilisant la methode solide-solide a haute temperature. Les echantillons elabores ont ete caracterises par diffractometrie de poudre RX. Les diffractogrammes obtenues ont ete affines par la methode Rietveld en utilisant le logiciel Fullprof. L'affinement structural a montre que les manganites synthetises se presentent sous forme de phases pures avec des raies fines et intenses sans phases parasites et cristallisent dans des structures deformees.Des mesures magnetiques (M(T) et M(H)) ont permis d'obtenir des informations sur le comportem...
Journal of Materials Science: Materials in Electronics, 2021
The critical behaviour and magnetic field dependence of magnetic entropy changes (ΔSM) for the fe... more The critical behaviour and magnetic field dependence of magnetic entropy changes (ΔSM) for the ferromagnetic La0.65Nd0.05Ba0.3Mn1−xCrxO3 (0 ≤ x ≤ 0.15) ceramics are systematically investigated in details. Upon Cr doping, the Curie temperature TC, ΔSM and the critical exponents (β, γ, and δ) are substantially influenced. As a result, the TC varies from 330 K for x = 0 to 275 K for x = 0.15 and the ΔSM decreases gradually with higher Cr substitution. The values of the critical exponents of the prepared samples lie between the Tricritical mean field model and 3D-Ising model. Thus, these results suggest that critical phenomena in La0.65Nd0.05Ba0.3Mn1−xCrxO3 (0 ≤ x ≤ 0.15) could not be explained on the conventional universality classes. However, the obtained results suggest an existence of FM short-range order in the prepared samples. To check the agreement with the scaling theory, m = f ± (h) is plotted for all samples. It was found that all data points fall into two separate branches above and below the critical temperature, TC, which confirmed that the critical exponents are reliable. The analysis of the field dependence of the ΔSM reveals the power law dependence at the transition temperature. Based on the value of critical exponents, one can find that all the magnetic entropy changes and heat capacity changes fall on a master curve for all measured fields and temperatures confirming the nature of second-order magnetic transition. This excellent overlap clearly indicates that the critical exponents obtained for the prepared system are reasonably accurate.
Journal of Magnetism and Magnetic Materials, 2020
Structure, magnetic and field dependence of magnetocaloric properties of Pr 0.5 RE 0.
Journal of Materials Science: Materials in Electronics, 2019
We report in this work the results of synthesis and characterization of La 0.8 Ca 0.2−x Na x MnO ... more We report in this work the results of synthesis and characterization of La 0.8 Ca 0.2−x Na x MnO 3 (0 ≤ x ≤ 0.2) prepared by the Pechini sol-gel method. We have investigated different effects of replacing Ca by Na on the magnetic properties and magnetocaloric effect of La 0.8 Ca 0.2 MnO 3 compounds using X-ray diffraction and magnetization measurements. We have observed an evolution from an orthorhombic to a rhombohedral symmetry caused by the addition of Na and that the rhombohedral phase is stable for x ≥ 0.1. The partial substitution of Ca by Na leads to a monotonic increase in the Curie temperature (T C) of the samples from 105 K for x = 0 to 330 K for x = 0.2. A second-order nature of the magnetic phase transition is established in all the prepared compounds with the help of the Banerjee criterion. At an applied field of 5T, the maximum magnetic entropy change (∆S M max) shows an enhancement with increasing Na + concentration. Moreover, the relative cooling power (RCP) values are found to vary between 203 and 300.5 J/kg in this series of materials. In order to compare the magnetocaloric performances of the prepared samples, we have used several figures of merit such as the temperature-averaged entropy change (TEC), refrigerant capacity (RC) and normalized refrigerant capacity (NRC). Accordingly, the addition of Na ion greatly increases TEC, RC and NRC and thereby improves the magnetocaloric performance in La 0.8 Ca 0.2−x Na x MnO 3 (0 ≤ x ≤ 0.2). These metrics can help in identifying materials with high performance and clearly suggest that the sol-gel-made samples with x ≥ 0.1 can be customized for use in magnetic cooling applications near room temperature.
Chemical Physics Letters, 2018
We investigated the effect of both lanthanum and strontium deficiencies upon the structural, magn... more We investigated the effect of both lanthanum and strontium deficiencies upon the structural, magnetic and magnetocaloric properties in La 0.7 Sr 0.3 MnO 3 mixed-valence manganite. Lacunar powder oxides La 0.7Àx h x Sr 0.3 MnO 3 and La 0.7 Sr 0.3Àx h x MnO 3 (x = 0, 0.01, 0.02 and 0.05), where h is a vacancy, were prepared by the sol-gel technique by sintering at 750°C and 850°C. Our synthetized samples crystallize in a rhomboedrically distorted perovskite structure with space group R-3C. Both these series of samples are ferromagnets and undergo second order paramagnetic-ferromagnetic transition with decreasing temperature. Magnetization measurements versus magnetic applied field at low temperature confirm the ferromagnetic behavior of our lacunars samples. Curie temperature decrease with increasing vacancy content for strontitum-deficient samples, while, its shows a maximum at about x = 0.01 (T C = 358 K) followed by a minimum for x = 0.03 (T C = 336 K) for lanthanum-deficient compounds. All compounds undergo a large magnetocaloric effect and have consequently potential applications in magnetic refrigeration domain around room temperature.
RSC Advances, 2016
The structure, magnetic properties, critical exponents and magnetocaloric effect (MCE) of La0.6Sr... more The structure, magnetic properties, critical exponents and magnetocaloric effect (MCE) of La0.6Sr0.4CoO3 cobaltite are studied.
Journal of Alloys and Compounds, 2016
Abstract A systematic study on the magnetic and magnetocaloric properties of a polycrystalline sa... more Abstract A systematic study on the magnetic and magnetocaloric properties of a polycrystalline sample of Pr 0.6 Ca 0.1 Sr 0.3 Mn 0.975 Fe 0.025 O 3 prepared by solid-state reaction has been studied. Structural study shows that our sample is of a single phase and crystallizes in the distorted orthorhombic system with Pbnm space group. The measurements of the temperature and field dependences of the magnetization clearly show that the Pr 0.6 Ca 0.1 Sr 0.3 Mn 0.975 Fe 0.025 O 3 ceramic exhibit a paramagnetic-ferromagnetic transition with decreasing temperature. The magnetic entropy change (-ΔS M ) is determined from isothermal magnetization curves. The field dependence of magnetic entropy change is analyzed and showing the power law dependence, ΔS max (T,H) = a(T)(μ 0 H) n(T,H) at the Curie temperature (T C ). It has been noted that the value of n obeys to the Curie-Weiss law above T C . The Landau theory (LT) for phase transitions framework is applied to describe the magnetocaloric effect (MCE) in Pr 0.6 Ca 0.1 Sr 0.3 Mn 0.975 Fe 0.025 O 3 manganite. The analysis of the MCE using the LT shows good agreement with the experimental data, indicating the importance of magneto-elastic coupling and electron interaction in the MCE properties of manganite. Based on the obtained magnetic entropy change (-ΔS M ) under different magnetic fields, we determined the spontaneous magnetization (M Sp ). For comparison, the M Sp has been also deduced from the classical extrapolation from the Arrott plot. An excellent agreement is found between the spontaneous magnetization determined from the entropy change (ΔS M vs. M 2 ) and the Arrot curves (H/M vs. M 2 ), confirming that the use of magnetic entropy change to get the spontaneous magnetization is valid.
Ceramics International, 2015
Influence of transition metal doping (Fe, Co, Ni and Cr) on magnetic and magnetocaloric propertie... more Influence of transition metal doping (Fe, Co, Ni and Cr) on magnetic and magnetocaloric properties of Pr 0.7 Ca 0.3 MnO 3 manganites, Ceramics International,
Ceramics International, 2015
Journal of Alloys and Compounds, 2015
ABSTRACT The structure, critical exponents and magnetocaloric effect (MCE) of Pr0.4Eu0.2Sr0.4MnO3... more ABSTRACT The structure, critical exponents and magnetocaloric effect (MCE) of Pr0.4Eu0.2Sr0.4MnO3 were investigated in detail. A solid state reaction method was used in the preparation phase. Phase purity, structure, size, and crystallinity were investigated using XRD and SEM. The Reitveld refinement of XRD pattern shows that the sample adopts an orthorhombic structure with Pnma space group. Analyzing temperature and field dependences of magnetization around the ferromagnetic-paramagnetic transition reveals the sample undergoing the second-order magnetic phase transition with the critical parameters TC ∼ 238K, β =0.310(3), γ = 1.264(1) and δ = 4.761(9).The exponents are close to 3D-Ising values. This reflects an existence of ferromagnetic short-range order in our sample. With these values one can scale the magnetization below and above TC following a single equation of state. However, it is noteworthy that the scaling relations are obeyed indicating renormalization of interactions around the TC. Temperature variation in effective exponents βeff and γeff resemble with those for disordered ferromagnet. In the vicinity of TC, the magnetic entropy change ΔS reached maximum values of 2.80 and 5.32 J/kg K under magnetic field variations of 2 and 5T, respectively. The field dependence of the magnetic entropy changes are also analyzed, which show power law dependence ΔSMmax≈a(μ0H)n at transition temperature. The critical exponent analysis related to magnetocaloric effect is described. Moreover, the temperature dependence of the exponent n for a different magnetic field is also studied. The values of n obey to the Curie Weiss law above the transition temperature. In particularly, n can be related to the critical exponents β, γ and δ at the magnetic transition. We used the scaling hypotheses to scale the magnetic entropy change and heat capacity changes to a single universal curve respectively for Pr0.4Eu0.2Sr0.4MnO3 sample.
Journal of Alloys and Compounds, 2015
This article covers the detailed study on the magnetic and magnetocaloric properties of Pr 0.5 Eu... more This article covers the detailed study on the magnetic and magnetocaloric properties of Pr 0.5 Eu 0.1 Sr 0.4 MnO 3 samples. The materials were synthesized through the sol-gel using nitrate-citrate route method by sintering at four different temperatures starting from 600 to 1000°C. Phase purity, structure, size, and crystallinity were investigated using XRD and SEM. The structure, magnetic properties and magnetocaloric effect of Pr 0.5 Eu 0.1 Sr 0.4 MnO 3 ceramics with different particle sizes have been investigated. Regardless of the sintering temperature, the orthorhombic crystal structure with the Pnma space group is stable. XRD analysis showed that the particle size increases with the increase in sintering temperature. The Curie temperature shifted from 90 K to 270 K. Magnetization, magnetic entropy change (∆S), and relative cooling power (RCP) also increased with size in the nanocrystalline samples. The magnetic entropy changes were about 0.89 J/kgK, 2.75J/kgK, 3.34J/kg K, and 3.82 J/kg K for the samples sintered at 600 °C, 800°C, 900°C and 1000°C, respectively when a magnetic field of 5 T was applied. It is shown that for Pr 0.5 Eu 0.1 Sr 0.4 MnO 3 the magnetic entropy change follows a master curve behavior.
Journal of Applied Physics, 2013
Structural, magnetic, and magnetocaloric properties of La0.6Sr0.2Ba0.2-x◻xMnO3 (0 ≤ x ≤ 0.15) whe... more Structural, magnetic, and magnetocaloric properties of La0.6Sr0.2Ba0.2-x◻xMnO3 (0 ≤ x ≤ 0.15) where ◻ is a barium deficiency have been investigated by X-ray diffraction and magnetic measurements. Our samples were synthesized using the solid-state reaction method at high temperatures. Structural studies show that our samples are single phase and crystallize in the rhombohedral system with R 3¯ c space group. Magnetization measurements as a function of temperature in a magnetic applied field of 0.05 T show that all our samples exhibit a paramagnetic-ferromagnetic transition with decreasing temperature. The Curie temperature TC shifts to lower values with increasing barium-deficiency. The Arrott plots show that the phase transition is of second order. The effect of barium deficiency on the magnetocaloric properties has been investigated. The values of the maximum of the magnetic entropy change, |−ΔSmax|, under a magnetic field change of 3.5 T are found to be 2.9, 2.92, 3.31, and 3.34 J/kg K for x = 0.0, 0.05...
Journal of Alloys and Compounds, 2014
Effect of iron substitution on the structural, magnetic and magnetocaloric properties of Pr 0.6 C... more Effect of iron substitution on the structural, magnetic and magnetocaloric properties of Pr 0.6 Ca 0.1 Sr 0.3 Mn 1-x Fe x O 3 (0 x 0.075) manganites, (2014),