Structural and magnetic properties of MnCo1−xFexSi alloys (original) (raw)
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Effect of Mn content on the austenite–martensite phases and magnetic properties in Fe–Mn–Co alloys
Materials Chemistry and Physics, 2011
The influence of the Mn content on the magnetic properties and microstructure of the Fe-Mn-Co alloys has been investigated by means of scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and Mössbauer spectroscopy. Experiments reveal that two types of thermal-induced martensites, (h.c.p.) and ␣ (b.c.c.) martensites, form in the as-quenched alloys. and ␣ martensites coexist in the Fe-Mn-Co alloys with 13.2-17.3 wt% Mn content while only martensite appears in the case of 20.7 wt% Mn. The amount of ␣ martensite decreases significantly while the amount of martensite increases with an increase in Mn content. The lattice parameters of austenite increase also with increasing Mn content. In addition, Mössbauer spectra of the alloys reveal a paramagnetic character with a singlet for the ␥ (f.c.c.) austenite and martensite phases and a ferromagnetic character with a broad sextet for ␣ martensite phase. The magnetic character of the Fe-Mn-Co alloys changes as Mn content increases and the ferromagnetic character disappears completely in case of 20.7 wt% Mn.
Journal of Magnetism and Magnetic Materials, 2016
The thermal, structural and magnetic properties were studied for the hexagonal MnCo 0.78 Fe 0.22 Ge alloys, which undergoes a first-order phase transformation from paramagnetic hexagonal phase into ferromagnetic orthorhombic martensite on cooling. Owing to the magnetostructural coupling, large magnetocaloric effect (∆S M =−10.97 J•kg-1 •K-1) was obtained at 254 K. In-situ synchrotron high-energy X-ray diffraction experiments were conducted to reveal the detailed change in crystallographic structure of phases and the effect of applied magnetic field on phase transformation behaviors. An anomalously huge strain of 11.89% and volume expansion of 4.35% in unit-cell was obtained between martensite and parent phase across the transformation. Furthermore, the magnetic field-induced martensitic transformation was directly evidenced at 250 K, which eventually demonstrates the possibility to achieve magnetic-field-induced strain and large magnetocaloric effect simultaneously.
Journal of Alloys and Compounds, 2009
The effects of the Mo and Co on the magnetic properties and the characteristics of martensitic transformation of the Fe–Mn alloy have been investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), differential scanning calorimeter (DSC), and Mössbauer spectroscopy. Experiments reveal that two types of thermal-induced martensites, ɛ(h.c.p.) and α′(b.c.c.) martensites, form in the as-quenched alloys and these transformations
Effect of Mo on the magnetic properties of martensitic phase in Fe–Ni–Mo alloys
Journal of Alloys and Compounds, 2006
The paramagnetic-magnetically ordered transition and the effect of Mo content on the magnetic properties of martensite phase in Fe-30% Ni-x% Mo alloys have been investigated by AC susceptibility and Mössbauer spectroscopy. The results show that martensitic transformation temperature (M S) indicates the magnetic transition from paramagnetic to magnetically ordered state. Hyperfine magnetic field, isomery shift and volume fractions of phases were determined by Mössbauer spectroscopy. It is also found that volume fraction of thermally induced martensite and M S temperature decreased with the increasing Mo content.
The Magnetic Properties of Mn x Fe1−x NiSi (x=0,0.25,0.5,0.75,1) Alloys
Journal of Superconductivity and Novel Magnetism, 2012
The magnetic properties of Mn x Fe 1−x NiSi (x = 0, 0.25, 0.5, 0.75, 1) alloys are studied using density functional theory and the WIEN2k package. The exchange correlation potential is treated by generalized gradient approximation (GGA). The total energy calculations of these alloys confirm the stability of the ferromagnetic phase as compared to a nonmagnetic phase. The total magnetic moment is not a linear function of x. By increasing x, it increases and then decreases. The peak position of the magnetic moment is near x = 0.75.
Magnetic and Structural Properties of Metamagnetic MnCo0.92Fe0.08Ge Compound
MATERIALS TRANSACTIONS, 2016
The magnetic and structural properties of ferromagnetic MnCo 0.92 Fe 0.08 Ge were investigated by magnetization and X-ray powder diffraction measurements in magnetic fields up to 5 T. The compound showed first-order transition between the paramagnetic and ferromagnetic state with a thermal hysteresis of approximately 24 K, which was accompanied by the martensitic transformation from the hexagonal Ni 2 In-type structure to the orthorhombic TiNiSi-type structure in the vicinity of 275 K. The cell volume expanded by 4.1% during the martensitic transformation. The magnetic moment of MnCo 0.92 Fe 0.08 Ge was estimated to be 111 Am 2 kg ¹1 (3.7 ® B /f.u.) at 10 K. The compound showed both metamagnetic transition and magnetic field-induced martensitic transformation. [
Journal of Physics D: Applied Physics, 2015
Detailed study of the Fe 2-x Co x MnSi (0 ≤ x ≤ 0.6) alloys has been carried out by investigating the samples with x-ray diffraction, Mössbauer spectroscopy, magnetization, transport and current spin polarization measurements. A perfectly ordered L2 1 phase is found to exist for x = 0.4. Competing magnetic interactions between ferromagnetic (FM) and antiferromagnetic (AFM) phases are found to exist in Fe 2-x Co x MnSi for x < 0.2 whereas the AFM phase completely disappears for x ≥ 0.2 as revealed by the magnetization and resistivity data. Anomalous, semiconducting-like behaviour is observed for x = 0.4. Current spin polarization has been estimated from different conductance curves obtained by using the point contact Andreev reflection technique. Alloys with x=0.2 and 0.4 show spin polarization values of 0.61±0.1 and 0.66 ± 0.1 respectively.
Materials, 2021
The aim of the present work is to study the influence of a partial substitution of Mn by Zr in MnCoGe alloys. The X-ray diffraction (XRD) studies revealed a coexistence of the orthorhombic TiNiSi-type and hexagonal Ni2In- type phases. The Rietveld analysis showed that the changes in lattice constants and content of recognized phases depended on the Zr addition. The occurrence of structural transformation was detected. This transformation was confirmed by analysis of the temperature dependence of exponent n given in the relation ΔSM = C·(BMAX)n. A decrease of the Curie temperature with an increase of the Zr content in the alloy composition was detected. The magnetic entropy changes were 6.93, 13.42, 3.96, and 2.94 J/(kg K) for Mn0.97Zr0.03CoGe, Mn0.95Zr0.05CoGe, Mn0.93Zr0.07CoGe, and Mn0.9Zr0.1CoGe, respectively. A significant rise in the magnetic entropy change for samples doped by Zr (x = 0.05) was caused by structural transformation.
Martensitic transition and magnetic properties in Ni–Mn–X alloys
Materials Science and Engineering: A, 2006
The structural and magnetic properties of Heusler alloy series Ni 50 Mn 50−x Sn x (numbers indicate at. %) and Ni 50 Mn 50−x In x have been studied. Magnetization and calorimetric measurements have been carried out in order to study the magnetic and structural transitions properties. The behaviour of the studied compounds is compared with that of the Ni-Mn-Ga alloy. Data for entropy and magnetization changes at the martensitic transition are reported. It is found that, as opposed to Ni-Mn-Ga, for Ni-Mn-In and Ni-Mn-Sn the magnetic moment in martensite is lower than in austenite.
Magnetic properties of mechanically alloyed MnO + FeCo
Journal of Alloys and Compounds, 2004
Isotropic nanocrystalline heterogeneous magnetic powders of MnO + FeCo were obtained by mechanical alloying in normal atmosphere from high-purity Mn, Fe and Co elements. After 120 h of milling, the material consists of micrometric particles with exchange-coupled nanocrystalline grains of MnO, ␣-Fe 40 Co 60 and minoritily non-magnetic ␥-Fe as determined by X-ray diffraction and Mössbauer spectroscopy. The hysteresis loop obtained by VSM in the as-milled powder showed exchange-bias phenomena when the temperature of the sample is smaller than the Néel temperature of the MnO, approximately 120 K. The as-milled powders were cold pressed and annealed at 700 K for different times in vacuum. Although the exchange-bias field is smaller in the annealed materials, samples with times of annealing below 3 h show a noticeable improvement of the coercivity, even to room temperature. The mechanism for this coercivity enhancement effect can be linked to the substantially high anisotropy field produced by the unidirectional anisotropy, and the favorable fine nanostructure originated during the ball milling, that produces an efficient isolation of the ferromagnetic grains.