D.M. Raj Kumar

Influence of Ni/Mn concentration on the structural, magnetic and magnetocaloric properties in Ni50−xMn37+xSn13 Heusler alloys

We report the structure, magnetism and magnetic entropy change in a Mn-rich Ni50−xMn37+xSn13 Heusler alloy system in the composition range 0 ≤ x ≤ 4. An excess Mn content stabilizes the cubic austenite phase at room temperature. Martensitic transition decreases from 305 to 100 K with increasing Mn concentration (x: 0 → 4) and also it was found to shift to a lower temperature with the application of a higher magnetic field. The exchange bias blocking temperature was found to decrease drastically from 149 to 9 K with increasing Mn concentration. A large magnetic entropy change (ΔSM) of 32 J kg−1 K−1 has been achieved for a field change of 5 T in the x = 3 alloy.

Effect of annealing on the magnetic, magnetocaloric and magnetoresistance properties of Ni-Co-Mn-Sb melt spun ribbons

Abstract The structural, magnetic, magnetocaloric and magnetotransport properties of Ni 46 Co 4 Mn 38 Sb 12 melt spun ribbons have been systematically investigated. The partially ordered B2 phase of the as-spun ribbon transforms to fully ordered L2 1 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.

In-plane and out of plane magnetic properties in Ni46Co4Mn38Sb12 ribbons

Magnetic, magnetocaloric, and exchange bias properties have been systematically investigated in Ni46Co4Mn38Sb12 ribbon by applying magnetic field along in-plane (IP) and perpendicular out of plane (OP) to the ribbon plane. From the thermo-magnetization curves, the sharpness of the martensitic transition is observed to be nearly the same for both IP and OP ribbons. The thermomagnetic irreversibility region is found to be larger in the OP ribbon at 500 Oe, indicating that the magnetic anisotropy is larger in this case. The OP ribbon shows the Hopkinson maximum at 500 Oe, both for the field cooled cooled and zero field cooled modes. The magnetization curve for IP ribbon shows a faster approach to saturation, compared to the OP ribbon. Isothermal magnetic entropy change at 50 kOe has been found to be nearly same for both the ribbons. At 5 K, the coercivity and exchange bias values are larger for the OP ribbon. Crystallographic texturing of the ribbons and its effect in the easy magnetization direction are fou...

Effect of annealing on the structural, microstructural and magnetic properties in Ni46Co4Mn38Sb12 ribbons

The effects of annealing on the structural, microstructural and magnetic properties of Ni46Co4Mn38Sb12 alloy ribbons have been investigated. It was observed that the room temperature structure changes from partially ordered B2 to fully ordered L21 phase upon annealing. At low temperatures both the as spun and the annealed ribbons exhibit 5M modulated martensitic structure. Significant changes in the martensitic transition and the magnetic properties in the annealed ribbon arise due to structural changes brought after annealing the ribbon.