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Papers by sami kallel

La premiere partie de ce travail porte sur 1 'etude de couches minces de silicium deposees pa... more La premiere partie de ce travail porte sur 1 'etude de couches minces de silicium deposees par RT-LPCVD et dopees in situ au phosphore dans un reacteur a lampes halogene et a parois froides a partir du silane (SiH4) utilise comme gaz precurseur et la phosphine (PH3) comme source dopante. Nous avons etudie ces couches dans une gamme de temperatures allant de 600°C a 850°C (pour une pression de 2mbar) et nous avons mis en evidence 1 'effet de la phosphine sur la cinetique de depot ainsi que sur ses proprietes physiques (taille des grains, texture, contraintes residuelles, resistivite). Nous avons aussi montre que les traitements thermiques rapides ulterieurs (RTA) favorisent une augmentation de la taille des grains, une relaxation des contraintes et une amelioration de la resistivite. Dans la deuxieme partie du travail, nous avons applique les procedes thermiques rapides pour la realisation de cellules solaires a faible budget thermique. Pour cela nous avons etudie et optimise...

Indian Journal of Physics, 2016

Electrical and dielectric properties of a polycrystalline La 0.6 Nd 0.1 Sr 0.3 Mn 0.7 Ti 0.3 O 3 ... more Electrical and dielectric properties of a polycrystalline La 0.6 Nd 0.1 Sr 0.3 Mn 0.7 Ti 0.3 O 3 sample prepared by standard solid state reaction technique are presented. FTIR studies have showed the vibration of (Mn/Ti)O 6 octahedra. The complex impedance is investigated in a temperature range 120-340 K and in frequency range 40 Hz-10 MHz. The impedance spectra have indicated that the electrical properties are strongly dependent on temperature and frequency, showing a good correlation with the sample microstructure. Ac conductivity is found to obey Jonscher power law. The value of activation energy estimated from the conductivity analysis is slightly higher than that deduced from relaxation analysis.

Journal of Magnetism and Magnetic Materials, 2015

the magnetic isotherms of (La 0.56 Ce 0.14) Sr 0.30 MnO 3 by a mean-field scaling method and esti... more the magnetic isotherms of (La 0.56 Ce 0.14) Sr 0.30 MnO 3 by a mean-field scaling method and estimation of magnetic entropy c h a n g e , Journal of Magnetism and Magnetic Materials,

Canadian Journal of Physics, 2000

Low-pressure chemical vapor deposition (LPCVD) in halogen lamp-heated reactor (RTLPCVD: rapid the... more Low-pressure chemical vapor deposition (LPCVD) in halogen lamp-heated reactor (RTLPCVD: rapid thermal LPCVD) is a promising technique for silicon-based thin films deposition. Indeed, overall process time and gas consumption reduction in RTP reactors allows to project new device fabrication technologies (microsensors, solar cells) in order to reach a higher environmental safety with respect to classical technologies.Various gases available on our RTP installation (SiH4, NH3, N2O, O2, PH3, B2H6) enable several silicon-based thin films RTLPCVD deposition: intrinsic polycrystalline silicon (poly-Si) films or in situ doped poly-Si, silicon nitride (Si-N) and oxynitride (Si-O-N). In this paper, we discuss our results on deposition kinetics and physical properties of these thin films. It appeared that RTLPCVD silicon-based thin films with interesting structural, electrical, and optical properties can be synthesized in our lamp-heated reactor with a tight control of process parameters such ...

Current Applied Physics, 2011

This article appeared in a journal published by Elsevier. The attached copy is furnished to the a... more This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit: http://www.elsevier.com/copyright

Journal of Alloys and Compounds, 2016

The structural, magnetic and electrical prop- erties of (La0.70−xNdx)Sr0.30Mn0.70Ti0.30O3 perovsk... more The structural, magnetic and electrical prop- erties of (La0.70−xNdx)Sr0.30Mn0.70Ti0.30O3 perovskites (0 ≤ x ≤ 0.30) prepared by the usual ceramic proce- dure were investigated. Structural Rietveld refinements of the X-ray powder diffraction revealed that for x = 0t he compound crystallizes in a rhombohedral (R¯ 3c) perovskite structure, while for x = 0.10, 0.20 and 0.30 the struc- ture becomes orthorhombic (Pbnm). The field-cooled, zero- field-cooled and M(H) measurements lead to conclude that the samples with x ≥ 0.10 behave like spin-glass systems. The temperature dependence of the resistivity exhibits two transitions at two temperatures Tp1 and Tp2, with the same width for the two peaks. TP1 results from the competition between double-exchange and super-exchange mechanisms inside the grain (intrinsic effects) whereas TP2 arises due to the grain boundary effects (extrinsic effect). The resis- tivity of this system seems to be related to the competition between antiferromagnetic i...

Journal of Magnetism and Magnetic Materials, 2016

This work presents a Monte Carlo study of the phase transition in the perovskites La0.7Sr0.3Mn 3+... more This work presents a Monte Carlo study of the phase transition in the perovskites La0.7Sr0.3Mn 3+ 0.7 Mn 4+ 0.3−x TixO3 (x= 0.1, 0.2, and 0.25). We take into account nearest-neighbor (NN) interactions between magnetic ions Mn 3+ (S = 2) and Mn 4+ (S = 3/2) using a spin model describing a strong anisotropy on the z axis. We have calculated the uniform and staggered magnetizations as well as the Edwards-Anderson order parameter as functions of temperature, with and without an applied magnetic field. Fitting the experimental Curie temperature at x = 0, we estimated values of various exchange interactions in the system. The dominant one is that between Mn 3+ and Mn 4+ which is at the origin of the ferromagnetic ordering. Effects of the very small interaction J2 between NN Mn 3+ is analyzed: we show that it can cause an antiferromagnetic phase above Tc which disappears at smaller J2 or at Mn 3+ concentrations smaller than 0.55. Our results show a good agreement with experiments on the magnetizations for substitution concentration x = 0.1, 0.2 and 0.3. We also studied the applied-field effect on the magnetization and our obtained results are compared with experiments performed at x = 10%.

Journal of Alloys and Compounds, 2016

We present a simple analysis based on the molecular field theory and on the Bean-Rodbell model to... more We present a simple analysis based on the molecular field theory and on the Bean-Rodbell model to justify the magnetocaloric effect (MCE) on La 0.7 Sr 0.3 Mn 0.9 Ti 0.1 O 3. The modeling the magnetic properties of the La 0.7 Sr 0.3 Mn 0.9 Ti 0.1 O 3 was investigated. Using the Brillouin function we have determined the mean field exchange parameter λ and the total angular momentum J of the perovskite. The mean-field equation of state leads the system to second order ferromagnetic (FM)-paramagnetic (PM) phase transition. The expressions describing entropy and its change under the influence of magnetic field have been derived. A large magnetic entropy ሺ−∆S ሻ has been observed in our sample with a peak centered on the Curie temperature (T C = 210 K). The theoretical calculations are compared with experimental behavior.

Ceramics International, 2015

Polycrystalline samples of (Nd 1-x Ce x) 0.7 Sr 0.3 MnO 3 (x = 0, 0.10 and 0.20) were prepared by... more Polycrystalline samples of (Nd 1-x Ce x) 0.7 Sr 0.3 MnO 3 (x = 0, 0.10 and 0.20) were prepared by a high-temperature solid-state reaction technique. The X-ray diffraction study has shown that all the samples exhibit a single phase with orthorhombic structure (Space group Pnma). From the resistivity data, it is found that all the samples show metal to semiconductor transition and the transition temperature decreases with the Ce doping. The complex impedance has been investigated in the temperature range 80-320 K and in the frequency range 40 Hz-1 MHz. AC conductance analyses indicate that the conduction mechanism is strongly dependent on temperature and frequency. The impedance plane plot shows semicircle arcs at different temperatures and an electrical equivalent circuit has been proposed to explain the impedance results. The activation energies obtained from the conductance is slightly higher than that from time relaxation analyses.

Physica B: Condensed Matter, 2011

The electrical properties and the mechanism of conduction of the simultaneously substituted La0.7... more The electrical properties and the mechanism of conduction of the simultaneously substituted La0.7−xYxBa0.3Mn1−xFexO3 perovskite (0≤x≤0.30) have been studied. The insertion of Y3+ and Fe3+ ions in the parent compound La0.7Ba0.3MnO3 leads to an increase of the resistivity. The undoped sample (x=0) shows a metallic behavior, which can be fitted by the relation ρ(T)=ρ0+ρ2T2+ρ4.5T4.5, indicating the importance of electron–magnon scattering effects

Physica B: Condensed Matter, 2011

ABSTRACT

Materials Letters, 2010

ABSTRACT The effect of Ti substitution on the magnetocaloric effect of the La0.70Sr0.30MnO3 perov... more ABSTRACT The effect of Ti substitution on the magnetocaloric effect of the La0.70Sr0.30MnO3 perovskite was investigated. The magnetic entropy change (− ΔSM) was deduced by two methods: a Maxwell relation and the Landau theory. The magnetocaloric data displays a large value of the magnetic entropy change (− ΔSM) near the Curie temperature (TC = 210 K), which increases when increasing the applied magnetic field. A good agreement is found between the experimental (− ΔSM) and the one estimated by Landau theory. The relative cooling power values vary from 49 to 288 J kg− 1 upon variation of the applied magnetic field at 1 and 5 T. Under 5 T, the relative cooling power value for La0.70Sr0.30Mn0.90Ti0.10O3 is about 70% of the conventional refrigerant Gd material. As a result, the herein reported compound can be considered as a promising material in magnetic refrigeration technology.

Journal of Superconductivity and Novel Magnetism, 2013

The transport properties and conduction mechanism in La 0.6 Sr 0.4 Mn 1-2x Fe x Cr x O 3 (0 1 x 1... more The transport properties and conduction mechanism in La 0.6 Sr 0.4 Mn 1-2x Fe x Cr x O 3 (0 1 x 1 0.3) have been investigated. The undoped samples show metal-semiconductor transition with a peak of resistivity at a temperature T P , whereas for all doped compounds, the semiconducting behavior persists in the whole temperature range. The insertion of Cr 3+ and Fe 3+ ions leads to the increase of resistivity because the simultaneous substitution of Fe 3+ and Cr 3+ for Mn 3+ reduces the number of available hopping sites for the Mn e g2 electron and suppresses the double-exchange mechanism. It was found that the transport mechanism for substituted samples is dominated by the variable range hopping of small polarons between localized states model where the various parameters estimated from Mott's relation obey the variable range hopping (VRH) mechanism.

Journal of Magnetism and Magnetic Materials, 2010

The structural, magnetic and electrical properties of Cr and Fe simultaneously substituted in the... more The structural, magnetic and electrical properties of Cr and Fe simultaneously substituted in the perovskite La 0.6 Sr 0.4 Mn 1 À 2x Cr x Fe x O 3 have been studied. The presence of Cr and Fe had no significant effect on the structural properties. Curie temperature and saturation magnetization decrease with increase in Cr and Fe contents. For x ¼ 0.20 and 0.25, a steep drop of zero field-cooled (ZFC) magnetization at low temperature signifies the formation of cluster-or spin-glass state. A weak hysteresis at low fields seems to be an indication of phase separation. All the resulting magnetization curves can be explained by a superposition of both ferromagnetic and antiferromagnetic components. All the samples are semiconducting throughout the temperature range studied. Resistivity can be described by the adiabatic small polaron hopping and the variable range hopping model. It was found that the transport mechanism is dominated by the VRH model with an increase of Mott localization energy, which explains the increase of resistivity.

Journal of Magnetism and Magnetic Materials, 2009

The structural, magnetic and transport properties of La 0.5 Sr 0.5 MnO 2.88 and La 0.5 Sr 0.5 Mn ... more The structural, magnetic and transport properties of La 0.5 Sr 0.5 MnO 2.88 and La 0.5 Sr 0.5 Mn 0.5 Ti 0.5 O 3 samples have been investigated systematically. Indeed, this series has been considered to understand the influence of physical parameters such as oxygen deficiency and titanium doping effect in undoped La 0.5 Sr 0.5 MnO 3 sample. Ceramic material based on La 0.5 Sr 0.5 MnO 2.88 exhibits interesting behaviours of charge-ordering (CO), ferromagnetic (FM) states and a good conductivity down to the lowest temperatures. The substitution of Ti for Mn destroyed drastically the CO, damaged the motion of itinerant e g electrons and changed the local parameters of perovskite cell. A change of the structure from tetragonal to rhombohedral symmetry is observed causing a weakening of double-exchange interaction. The experiment results show that the suppression of the CO is sensitive to the variety of Mn 3+ /Mn 4+ ratio. In a field of 8 T at 10 K, FM and CO phase can be evaluated to be 20:80accordingtothemexp/mcalratioforLa0.5Sr0.5MnO2.88,whereastheCOstateissuppressedforLa0.5Sr0.5Mn0.5Ti0.5O3sample,FMandanti−ferromagnetic(AFM)phasearecoexistedandevaluatedtobe20:80 according to the m exp /m cal ratio for La 0.5 Sr 0.5 MnO 2.88 , whereas the CO state is suppressed for La 0.5 Sr 0.5 Mn 0.5 Ti 0.5 O 3 sample, FM and anti-ferromagnetic (AFM) phase are coexisted and evaluated to be 20:80accordingtothemexp/mcalratioforLa0.5Sr0.5MnO2.88,whereastheCOstateissuppressedforLa0.5Sr0.5Mn0.5Ti0.5O3sample,FMandanti−ferromagnetic(AFM)phasearecoexistedandevaluatedtobe54:46, respectively.

Journal of Magnetism and Magnetic Materials, 2014

We have studied the MagnetoCaloric Effect (MCE) in La 0.7 Sr 0.3 Mn 0.9 M 0.1 O 3 , M¼ Cr, Sn and... more We have studied the MagnetoCaloric Effect (MCE) in La 0.7 Sr 0.3 Mn 0.9 M 0.1 O 3 , M¼ Cr, Sn and Ti, prepared by a conventional solid state reaction. The temperature dependence of magnetization reveals that all compositions exhibit a ferromagnetic (FM) to paramagnetic (PM) transition at T C temperatures of 369, 326, 228 and 210 K, respectively for La 0.

Journal of Alloys and Compounds, 2012

The magnetic phase transition and the magnetic entropy change (ÀDS M) in the La 0.67 Ba 0.33 Mn 0... more The magnetic phase transition and the magnetic entropy change (ÀDS M) in the La 0.67 Ba 0.33 Mn 0.9 Cr 0,1 O 3 manganite were investigated by measuring the magnetization as a function of temperature. The maximum magnetic entropy change (ÀDS M) and the relative cooling power (RCP) are found to be, respectively, 4.20 J kg À1 K À1 and 238 J kg À1 for a 5-T field change, making of this material a promising candidate for magnetic refrigeration near room temperature. To investigate the nature of the paramagnetic (PM) to ferromagnetic (FM) phase transition, found to be of second-order, we performed a critical exponents study by dc-magnetization M(H,T) measurements around the Curie temperature T C , in a temperature range including the critical region |e| = |T À T C |/ T C 6 0.05. From the derived values of the critical exponents (b = 0.380, c = 1.345), we conclude that La 0.67 Ba 0.33 Mn 0.9 Cr 0.1 O 3 belongs to the three-dimensional Heisenberg class with short-range interaction. Scaling relations are obeyed, indicating renormalized interactions around T C. By investigating the field dependence of RCP and DS M , it was possible to evaluate the critical exponents of the magnetic phase transitions. Their values are in good agreement with those obtained from the critical exponents using a modified Arrott method.

Journal of Alloys and Compounds, 2010

We present the structural and magnetic properties of polycrystalline samples of the solid solutio... more We present the structural and magnetic properties of polycrystalline samples of the solid solution (La0.70−xYx)Ba0.30Mn1−xFexO3 (x=0.00, 0.10, 0.20 and 0.30). Samples have been prepared by a conventional solid-state reaction method in air. Rietveld refinements of the X-ray powder diffraction data show a structural transition from rhombohedral (R3¯c) to orthorhombic (Pbnm) symmetry when x≥0.10. The ZFC, FC and M(H) measurements lead

La premiere partie de ce travail porte sur 1 'etude de couches minces de silicium deposees pa... more La premiere partie de ce travail porte sur 1 'etude de couches minces de silicium deposees par RT-LPCVD et dopees in situ au phosphore dans un reacteur a lampes halogene et a parois froides a partir du silane (SiH4) utilise comme gaz precurseur et la phosphine (PH3) comme source dopante. Nous avons etudie ces couches dans une gamme de temperatures allant de 600°C a 850°C (pour une pression de 2mbar) et nous avons mis en evidence 1 'effet de la phosphine sur la cinetique de depot ainsi que sur ses proprietes physiques (taille des grains, texture, contraintes residuelles, resistivite). Nous avons aussi montre que les traitements thermiques rapides ulterieurs (RTA) favorisent une augmentation de la taille des grains, une relaxation des contraintes et une amelioration de la resistivite. Dans la deuxieme partie du travail, nous avons applique les procedes thermiques rapides pour la realisation de cellules solaires a faible budget thermique. Pour cela nous avons etudie et optimise...

Indian Journal of Physics, 2016

Electrical and dielectric properties of a polycrystalline La 0.6 Nd 0.1 Sr 0.3 Mn 0.7 Ti 0.3 O 3 ... more Electrical and dielectric properties of a polycrystalline La 0.6 Nd 0.1 Sr 0.3 Mn 0.7 Ti 0.3 O 3 sample prepared by standard solid state reaction technique are presented. FTIR studies have showed the vibration of (Mn/Ti)O 6 octahedra. The complex impedance is investigated in a temperature range 120-340 K and in frequency range 40 Hz-10 MHz. The impedance spectra have indicated that the electrical properties are strongly dependent on temperature and frequency, showing a good correlation with the sample microstructure. Ac conductivity is found to obey Jonscher power law. The value of activation energy estimated from the conductivity analysis is slightly higher than that deduced from relaxation analysis.

Journal of Magnetism and Magnetic Materials, 2015

the magnetic isotherms of (La 0.56 Ce 0.14) Sr 0.30 MnO 3 by a mean-field scaling method and esti... more the magnetic isotherms of (La 0.56 Ce 0.14) Sr 0.30 MnO 3 by a mean-field scaling method and estimation of magnetic entropy c h a n g e , Journal of Magnetism and Magnetic Materials,

Canadian Journal of Physics, 2000

Low-pressure chemical vapor deposition (LPCVD) in halogen lamp-heated reactor (RTLPCVD: rapid the... more Low-pressure chemical vapor deposition (LPCVD) in halogen lamp-heated reactor (RTLPCVD: rapid thermal LPCVD) is a promising technique for silicon-based thin films deposition. Indeed, overall process time and gas consumption reduction in RTP reactors allows to project new device fabrication technologies (microsensors, solar cells) in order to reach a higher environmental safety with respect to classical technologies.Various gases available on our RTP installation (SiH4, NH3, N2O, O2, PH3, B2H6) enable several silicon-based thin films RTLPCVD deposition: intrinsic polycrystalline silicon (poly-Si) films or in situ doped poly-Si, silicon nitride (Si-N) and oxynitride (Si-O-N). In this paper, we discuss our results on deposition kinetics and physical properties of these thin films. It appeared that RTLPCVD silicon-based thin films with interesting structural, electrical, and optical properties can be synthesized in our lamp-heated reactor with a tight control of process parameters such ...

Current Applied Physics, 2011

This article appeared in a journal published by Elsevier. The attached copy is furnished to the a... more This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit: http://www.elsevier.com/copyright

Journal of Alloys and Compounds, 2016

The structural, magnetic and electrical prop- erties of (La0.70−xNdx)Sr0.30Mn0.70Ti0.30O3 perovsk... more The structural, magnetic and electrical prop- erties of (La0.70−xNdx)Sr0.30Mn0.70Ti0.30O3 perovskites (0 ≤ x ≤ 0.30) prepared by the usual ceramic proce- dure were investigated. Structural Rietveld refinements of the X-ray powder diffraction revealed that for x = 0t he compound crystallizes in a rhombohedral (R¯ 3c) perovskite structure, while for x = 0.10, 0.20 and 0.30 the struc- ture becomes orthorhombic (Pbnm). The field-cooled, zero- field-cooled and M(H) measurements lead to conclude that the samples with x ≥ 0.10 behave like spin-glass systems. The temperature dependence of the resistivity exhibits two transitions at two temperatures Tp1 and Tp2, with the same width for the two peaks. TP1 results from the competition between double-exchange and super-exchange mechanisms inside the grain (intrinsic effects) whereas TP2 arises due to the grain boundary effects (extrinsic effect). The resis- tivity of this system seems to be related to the competition between antiferromagnetic i...

Journal of Magnetism and Magnetic Materials, 2016

This work presents a Monte Carlo study of the phase transition in the perovskites La0.7Sr0.3Mn 3+... more This work presents a Monte Carlo study of the phase transition in the perovskites La0.7Sr0.3Mn 3+ 0.7 Mn 4+ 0.3−x TixO3 (x= 0.1, 0.2, and 0.25). We take into account nearest-neighbor (NN) interactions between magnetic ions Mn 3+ (S = 2) and Mn 4+ (S = 3/2) using a spin model describing a strong anisotropy on the z axis. We have calculated the uniform and staggered magnetizations as well as the Edwards-Anderson order parameter as functions of temperature, with and without an applied magnetic field. Fitting the experimental Curie temperature at x = 0, we estimated values of various exchange interactions in the system. The dominant one is that between Mn 3+ and Mn 4+ which is at the origin of the ferromagnetic ordering. Effects of the very small interaction J2 between NN Mn 3+ is analyzed: we show that it can cause an antiferromagnetic phase above Tc which disappears at smaller J2 or at Mn 3+ concentrations smaller than 0.55. Our results show a good agreement with experiments on the magnetizations for substitution concentration x = 0.1, 0.2 and 0.3. We also studied the applied-field effect on the magnetization and our obtained results are compared with experiments performed at x = 10%.

Journal of Alloys and Compounds, 2016

We present a simple analysis based on the molecular field theory and on the Bean-Rodbell model to... more We present a simple analysis based on the molecular field theory and on the Bean-Rodbell model to justify the magnetocaloric effect (MCE) on La 0.7 Sr 0.3 Mn 0.9 Ti 0.1 O 3. The modeling the magnetic properties of the La 0.7 Sr 0.3 Mn 0.9 Ti 0.1 O 3 was investigated. Using the Brillouin function we have determined the mean field exchange parameter λ and the total angular momentum J of the perovskite. The mean-field equation of state leads the system to second order ferromagnetic (FM)-paramagnetic (PM) phase transition. The expressions describing entropy and its change under the influence of magnetic field have been derived. A large magnetic entropy ሺ−∆S ሻ has been observed in our sample with a peak centered on the Curie temperature (T C = 210 K). The theoretical calculations are compared with experimental behavior.

Ceramics International, 2015

Polycrystalline samples of (Nd 1-x Ce x) 0.7 Sr 0.3 MnO 3 (x = 0, 0.10 and 0.20) were prepared by... more Polycrystalline samples of (Nd 1-x Ce x) 0.7 Sr 0.3 MnO 3 (x = 0, 0.10 and 0.20) were prepared by a high-temperature solid-state reaction technique. The X-ray diffraction study has shown that all the samples exhibit a single phase with orthorhombic structure (Space group Pnma). From the resistivity data, it is found that all the samples show metal to semiconductor transition and the transition temperature decreases with the Ce doping. The complex impedance has been investigated in the temperature range 80-320 K and in the frequency range 40 Hz-1 MHz. AC conductance analyses indicate that the conduction mechanism is strongly dependent on temperature and frequency. The impedance plane plot shows semicircle arcs at different temperatures and an electrical equivalent circuit has been proposed to explain the impedance results. The activation energies obtained from the conductance is slightly higher than that from time relaxation analyses.

Physica B: Condensed Matter, 2011

The electrical properties and the mechanism of conduction of the simultaneously substituted La0.7... more The electrical properties and the mechanism of conduction of the simultaneously substituted La0.7−xYxBa0.3Mn1−xFexO3 perovskite (0≤x≤0.30) have been studied. The insertion of Y3+ and Fe3+ ions in the parent compound La0.7Ba0.3MnO3 leads to an increase of the resistivity. The undoped sample (x=0) shows a metallic behavior, which can be fitted by the relation ρ(T)=ρ0+ρ2T2+ρ4.5T4.5, indicating the importance of electron–magnon scattering effects

Physica B: Condensed Matter, 2011

ABSTRACT

Materials Letters, 2010

ABSTRACT The effect of Ti substitution on the magnetocaloric effect of the La0.70Sr0.30MnO3 perov... more ABSTRACT The effect of Ti substitution on the magnetocaloric effect of the La0.70Sr0.30MnO3 perovskite was investigated. The magnetic entropy change (− ΔSM) was deduced by two methods: a Maxwell relation and the Landau theory. The magnetocaloric data displays a large value of the magnetic entropy change (− ΔSM) near the Curie temperature (TC = 210 K), which increases when increasing the applied magnetic field. A good agreement is found between the experimental (− ΔSM) and the one estimated by Landau theory. The relative cooling power values vary from 49 to 288 J kg− 1 upon variation of the applied magnetic field at 1 and 5 T. Under 5 T, the relative cooling power value for La0.70Sr0.30Mn0.90Ti0.10O3 is about 70% of the conventional refrigerant Gd material. As a result, the herein reported compound can be considered as a promising material in magnetic refrigeration technology.

Journal of Superconductivity and Novel Magnetism, 2013

The transport properties and conduction mechanism in La 0.6 Sr 0.4 Mn 1-2x Fe x Cr x O 3 (0 1 x 1... more The transport properties and conduction mechanism in La 0.6 Sr 0.4 Mn 1-2x Fe x Cr x O 3 (0 1 x 1 0.3) have been investigated. The undoped samples show metal-semiconductor transition with a peak of resistivity at a temperature T P , whereas for all doped compounds, the semiconducting behavior persists in the whole temperature range. The insertion of Cr 3+ and Fe 3+ ions leads to the increase of resistivity because the simultaneous substitution of Fe 3+ and Cr 3+ for Mn 3+ reduces the number of available hopping sites for the Mn e g2 electron and suppresses the double-exchange mechanism. It was found that the transport mechanism for substituted samples is dominated by the variable range hopping of small polarons between localized states model where the various parameters estimated from Mott's relation obey the variable range hopping (VRH) mechanism.

Journal of Magnetism and Magnetic Materials, 2010

The structural, magnetic and electrical properties of Cr and Fe simultaneously substituted in the... more The structural, magnetic and electrical properties of Cr and Fe simultaneously substituted in the perovskite La 0.6 Sr 0.4 Mn 1 À 2x Cr x Fe x O 3 have been studied. The presence of Cr and Fe had no significant effect on the structural properties. Curie temperature and saturation magnetization decrease with increase in Cr and Fe contents. For x ¼ 0.20 and 0.25, a steep drop of zero field-cooled (ZFC) magnetization at low temperature signifies the formation of cluster-or spin-glass state. A weak hysteresis at low fields seems to be an indication of phase separation. All the resulting magnetization curves can be explained by a superposition of both ferromagnetic and antiferromagnetic components. All the samples are semiconducting throughout the temperature range studied. Resistivity can be described by the adiabatic small polaron hopping and the variable range hopping model. It was found that the transport mechanism is dominated by the VRH model with an increase of Mott localization energy, which explains the increase of resistivity.

Journal of Magnetism and Magnetic Materials, 2009

The structural, magnetic and transport properties of La 0.5 Sr 0.5 MnO 2.88 and La 0.5 Sr 0.5 Mn ... more The structural, magnetic and transport properties of La 0.5 Sr 0.5 MnO 2.88 and La 0.5 Sr 0.5 Mn 0.5 Ti 0.5 O 3 samples have been investigated systematically. Indeed, this series has been considered to understand the influence of physical parameters such as oxygen deficiency and titanium doping effect in undoped La 0.5 Sr 0.5 MnO 3 sample. Ceramic material based on La 0.5 Sr 0.5 MnO 2.88 exhibits interesting behaviours of charge-ordering (CO), ferromagnetic (FM) states and a good conductivity down to the lowest temperatures. The substitution of Ti for Mn destroyed drastically the CO, damaged the motion of itinerant e g electrons and changed the local parameters of perovskite cell. A change of the structure from tetragonal to rhombohedral symmetry is observed causing a weakening of double-exchange interaction. The experiment results show that the suppression of the CO is sensitive to the variety of Mn 3+ /Mn 4+ ratio. In a field of 8 T at 10 K, FM and CO phase can be evaluated to be 20:80accordingtothemexp/mcalratioforLa0.5Sr0.5MnO2.88,whereastheCOstateissuppressedforLa0.5Sr0.5Mn0.5Ti0.5O3sample,FMandanti−ferromagnetic(AFM)phasearecoexistedandevaluatedtobe20:80 according to the m exp /m cal ratio for La 0.5 Sr 0.5 MnO 2.88 , whereas the CO state is suppressed for La 0.5 Sr 0.5 Mn 0.5 Ti 0.5 O 3 sample, FM and anti-ferromagnetic (AFM) phase are coexisted and evaluated to be 20:80accordingtothemexp/mcalratioforLa0.5Sr0.5MnO2.88,whereastheCOstateissuppressedforLa0.5Sr0.5Mn0.5Ti0.5O3sample,FMandanti−ferromagnetic(AFM)phasearecoexistedandevaluatedtobe54:46, respectively.

Journal of Magnetism and Magnetic Materials, 2014

We have studied the MagnetoCaloric Effect (MCE) in La 0.7 Sr 0.3 Mn 0.9 M 0.1 O 3 , M¼ Cr, Sn and... more We have studied the MagnetoCaloric Effect (MCE) in La 0.7 Sr 0.3 Mn 0.9 M 0.1 O 3 , M¼ Cr, Sn and Ti, prepared by a conventional solid state reaction. The temperature dependence of magnetization reveals that all compositions exhibit a ferromagnetic (FM) to paramagnetic (PM) transition at T C temperatures of 369, 326, 228 and 210 K, respectively for La 0.

Journal of Alloys and Compounds, 2012

The magnetic phase transition and the magnetic entropy change (ÀDS M) in the La 0.67 Ba 0.33 Mn 0... more The magnetic phase transition and the magnetic entropy change (ÀDS M) in the La 0.67 Ba 0.33 Mn 0.9 Cr 0,1 O 3 manganite were investigated by measuring the magnetization as a function of temperature. The maximum magnetic entropy change (ÀDS M) and the relative cooling power (RCP) are found to be, respectively, 4.20 J kg À1 K À1 and 238 J kg À1 for a 5-T field change, making of this material a promising candidate for magnetic refrigeration near room temperature. To investigate the nature of the paramagnetic (PM) to ferromagnetic (FM) phase transition, found to be of second-order, we performed a critical exponents study by dc-magnetization M(H,T) measurements around the Curie temperature T C , in a temperature range including the critical region |e| = |T À T C |/ T C 6 0.05. From the derived values of the critical exponents (b = 0.380, c = 1.345), we conclude that La 0.67 Ba 0.33 Mn 0.9 Cr 0.1 O 3 belongs to the three-dimensional Heisenberg class with short-range interaction. Scaling relations are obeyed, indicating renormalized interactions around T C. By investigating the field dependence of RCP and DS M , it was possible to evaluate the critical exponents of the magnetic phase transitions. Their values are in good agreement with those obtained from the critical exponents using a modified Arrott method.

Journal of Alloys and Compounds, 2010

We present the structural and magnetic properties of polycrystalline samples of the solid solutio... more We present the structural and magnetic properties of polycrystalline samples of the solid solution (La0.70−xYx)Ba0.30Mn1−xFexO3 (x=0.00, 0.10, 0.20 and 0.30). Samples have been prepared by a conventional solid-state reaction method in air. Rietveld refinements of the X-ray powder diffraction data show a structural transition from rhombohedral (R3¯c) to orthorhombic (Pbnm) symmetry when x≥0.10. The ZFC, FC and M(H) measurements lead