Search

The effect of Fe on the martensitic transitions, magnetic and inverse magnetocaloric effect in Ni47Mn40-xFexIn13 ribbons (x = 1, 2, 3, and 5) has been investigated. All the ribbon compositions under study have shown the presence of austenite phase at room temperature. The variation of martensitic transition with the increase in Fe-content is non-monotonic. The thermal hysteresis of the martensitic transition increased with the increase in Fe-content. The martensitic transitions shifted to lower temperatures in the presence of high magnetic fields. A maximum magnetic entropy change (ΔSM) of 50 Jkg-1K-1 has been achieved in the Ni47Mn38Fe2In13 (x = 1) ribbon at 282 K for an applied field of 5 T. [ABSTRACT FROM AUTHOR]

Abstract: Effect of Fe-substitution on the phase formation, partitioning behaviour of Fe in the co-existing phases, magneto-structural transition, magnetic entropy change and associated hysteresis losses has been investigated in Gd5Si2Ge2 alloy. The virgin alloy crystallizes in monoclinic Gd5Si2Ge2-type phase, while Fe-substituted alloys form mixed monoclinic Gd5Si2Ge2-type and orthorhombic Gd5Si4-type phases. Electron probe microanalysis reveals that Fe does not dissolve in the matrix, but influences the magneto-structural transitions. Magneto-structural characterization of the Fe-containing alloys reveals that the Fe-substitution suppresses the structural transition observed at 273K in virgin alloy. A maximum magnetic entropy change, ΔS M of 6.5J/kg-K at 273K was observed for a field change of 2T in Gd5Si2Ge2 alloy. The Fe-substituted alloys exhibit lower value of ΔS M but with reduced hysteresis losses. [Copyright &y& Elsevier]

Abstract: Evolution of structure and magnetocaloric properties in ball-milled Gd5Si2Ge2 and Gd5Si2Ge2/0.1wt% Fe nanostructured powders were investigated. The high-energy ball-milled powders were composed of very fine grains (70–80nm). Magnetization decreased with milling time due to decrease in the grain size and randomization of the magnetic moments at the surface. The magnetic entropy change (ΔS M) was calculated from the isothermal magnetization curves and a maximum value of 0.45J/kgK was obtained for 32h milled Gd5Si2Ge2 alloy powder for a magnetic field change of 2T while it was still low in Fe-contained alloy powders. The thermo-magnetic measurements revealed that the milled powders display distribution of magnetic transitions, which is desirable for practical magnetic refrigerant to cover a wide temperature span. [Copyright &y& Elsevier]

Abstract: The structure, microstructure, magneto-structural transition and magnetocaloric effect have been investigated in series of (Gd5−x Zr x )Si2Ge2 alloys with 0≤x≥0.20. X-ray powder diffraction analysis revealed the presence of orthorhombic structure for Zr containing alloys at room temperature in contrast to the monoclinic structure observed in the parent Gd5Si2Ge2 alloy. The microstructural studies reveal that, low Zr addition (x≤0.1) resulted in low volume fraction of detrimental Gd5Si3-type secondary phase compared to that present in the parent alloy. All the Zr containing alloys have shown the presence of only second order magnetic transition unlike the parent alloy showing both first order structural and second order magnetic transition. A moderate (ΔS) M value of −5.5J/kgK was obtained for the x=0.05 alloy at an enhanced operating temperature of 292K compared to −7.8J/kgK at 274K of the parent alloy for an applied field of 2T. The interesting feature of Zr (x=0.05) containing alloy is the wide operating temperature range of ∼25K than that of ∼10–12K for the parent, which resulted in enhanced net refrigerant capacity of 103J/kg compared to that of 53J/kg for the parent alloy. [Copyright &y& Elsevier]

Abstract: Polycrystalline Gd5Si2−x Ge2−x Nb2x alloys (0≤2x ≤0.2) were investigated for microstructure and magnetocaloric effect. The 2x =0.05 and 0.1 alloys were mainly composed of monoclinic Gd5Si2Ge2-type and orthorhombic Gd5Si4-type phases whereas other alloys exhibit monoclinic Gd5Si2Ge2-type phase at room temperature. The microstructural studies reveal that Nb addition results in the formation of Nb5(Si,Ge)3 and α-Nb phases. The former promotes the nucleation of Gd5Si3-type phase while the latter suppresses it. At low Nb addition (2x ≤0.1) the microstructural modification results in low volume fraction of detrimental Gd5Si3-type phase leading to enhanced magnetocaloric effect (ΔS)M value compared to that of the parent compound. A maximum (ΔS)M value of −9.6J/kgK with refrigerant capacity of 98J/kg was obtained for the 2x =0.1 alloy for a field change of 2 T near room temperature. The magneto-structural transitions shifted to higher temperatures with increase in Nb content up to 2x =0.1. [Copyright &y& Elsevier]

The Gd 5 Si 2 Ge 2 B x (0 < x ≤ 0.125) alloys were investigated to study the influence of Boron addition on the structure, microstructure, magnetic and magnetocaloric properties. Except x = 0.05 alloy, all the other Boron containing alloys under study displayed the presence of major monoclinic Gd 5 Si 2 Ge 2 -type phase along with low volume fraction of hexagonal GdSi-type (5:5 H) secondary phase at room temperature (RT). In the case of alloy with x = 0.05, monoclinic Gd 5 Si 2 Ge 2 -type and orthorhombic Gd 5 (Si,Ge) 4 type mixed phases along with low volume fraction of Gd 5 Si 3 -type (5:3 H) secondary phase were observed at RT. The structural transition (T s ) (orthorhombic to monoclinic) and the Curie transition (T C ) of the monoclinic phase in the x = 0.05 alloy occurred at 293 K and 305 K respectively. These transitions occurred at relatively higher temperatures than those reported in parent Gd 5 Si 2 Ge 2 alloy. At higher concentrations of Boron (x > 0.05), both the transitions, T s and T C shifted to lower temperatures. A maximum magnetic entropy change of 13.6 J/(kg-K) (at 293 K) and refrigerant capacity (RC) of 378 J/kg were obtained in Gd 5 Si 2 Ge 2 B 0.05 alloy which conveys that this alloy has an edge over the parent alloy in terms of operating temperature and refrigeration capacity. [ABSTRACT FROM AUTHOR]

Highlights • The substitution of Fe in Ni 47 Mn 40 In 13 enhances the Curie temperature of martensitic phase. The martensitic transition shifts to low temperature with the increase of Fe concentration. • The present study reveals the enhancement of magnetic entropy change in Fe doped Ni-Mn-In alloy. • The huge increase of ΔS M value in Ni 47 Mn 40- x Fe x In 13 (x = 2) alloy at room temperature is expected to have an application in the modern magnetic refrigeration technology. Abstract We report the effect of Fe on the martensitic transitions in Ni 47 Mn 40- x Fe x In 13 (x = 1 and 2) alloys and associated magnetocaloric effect. Structural and magnetic transitions are observed in x = 1 and 2 alloys. The martensitic transition shifts to low temperature with the increase of Fe concentration. The maximum positive entropy change (ΔS M) with quite large magnitude of 22 Jkg−1K−1 (x = 1) and 51.2 Jkg-1K-1 (x = 2) are observed for a field change of 50 kOe. Substitution of Fe enhances the magnetization as well as increases the ΔS M more than a twice in the x = 2 system. [ABSTRACT FROM AUTHOR]

Highlights: [•] The pressure effects on ΔS M were investigated in Si doped Ni–Mn–Sn alloys. [•] The T m and Curie temperature of the austenitic phase changes with pressure. [•] The maximum ΔS M of 24.5Jkg−1 K−1 at 9.7kbar were observed for x =1 alloy. [•] The RC increases for x =1 alloy and can be used for magnetic refrigeration. [ABSTRACT FROM AUTHOR]

Abstract: The structural, magnetic, magnetocaloric and magnetotransport properties of Ni46Co4Mn38Sb12 melt spun ribbons have been systematically investigated. The partially ordered B2 phase of the as-spun ribbon transforms to fully ordered L21 phase upon annealing, which signifies a considerable change of the atomic ordering in the system. The presence of atomic disorder in the as-spun ribbon gives rise to a higher martensitic transition temperature and a lower magnetization as compared to the bulk sample. However, annealing the ribbons helps in regaining the bulk properties to a large extent. Significant changes in magnetocaloric effect, exchange bias and magnetoresistance have been observed between the as-spun and the annealed ribbons, indicating the role of atomic ordering on the functional as well as fundamental properties in the Heusler system. Importantly, the study shows that one can reduce the hysteresis loss by preparing melt spun alloys and subjecting them to appropriate annealing conditions, which enable them to become practical magnetic refrigerants. [Copyright &y& Elsevier]