Effect of Mn Concentration on Magneto-mechnaical Properties in Directionally Solidified Ferromagnetic Shape Memory Ni-Mn-Ga Alloys

Heusler type alloys Ni50Mn25+xGa25-x  (x=2,3,4 and 5) based on near stoichiometric Ni2MnGa compositions were directionally solidified using modified Bridgman method. The alloys thus prepared were characterized for their chemical composition, crystal structure, microstructure, phase transformation, magnetic  and magneto-mechanical properties. The directionally solidified Ni50Mn30Ga20 alloy rod exhibited maximum magnetocrystalline value of 95 kJm-3 and lowest detwinning stresses for martensite phase of about 5MPa. The reversible room temperature magnetic field induced strain of 0.2% under external magnetic field of 0.6T and 0.05kN bias load was obtained for the directionally solidified Ni50Mn30Ga20 alloy

An Experimental Evaluation of Quenched Fe-Ga Alloys: Structural Magnetic and Magnetostrictive Properties

This study examines the effect of quenching on Fe100-x-Gax (x – 20 & 25) alloys. The long range of D03 ordering causes a minor variation in unit cell, which reduces peak intensity. This existence of D03, coupled with the A2 phase, leads to a decrease in magnetostriction in the quenched 25 at.% Ga alloy, which promotes D03 ordering. An Fe-Ga alloy having 20 at.% Ga that has been quenched possesses the A2 phase, the production of D03 is a first-order transition. Continuous ordering attempts to suppress D03 in 25 at. % Ga alloys were ineffective. Quenched Fe80-Ga20 alloy's saturation magnetization is larger than Fe75-Ga25 alloy. This suggests that lowering the nonmagnetic element Ga promotes saturation magnetization. The rise in material flaws and dislocations is due to the increased Ga content and higher quenching temperature. In a single-phase region, Fe80-Ga20 has the greatest magnetostriction at 85 ppm. Magnetostriction diminishes as Ga content rises to 25%, the D03 structure is responsible for this drop

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

Magnetic, magnetocaloric and exchange bias properties have been systematically investigated in Ni46Co4Mn38Sb12 ribbon by applying magnetic field along (IP) and perpendicular (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 FCC and ZFC 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 found to be the reason behind the differences between the two ribbons.Comment: J. Appl. Phys. 113, 17A940 (2013

Effect of Fe on the Martensitic Transition, Magnetic and Magnetocaloric Properties in Ni-Mn-In Melt-spun Ribbons

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 (∆SM) of 50 Jkg-1K-1 has been achieved in the Ni47Mn38Fe2In13 (x = 1) ribbon at 282 K for an applied field of 5 T

Origin of spin gapless semiconductor behavior in CoFeCrGa: Theory and Experiment

Despite a plethora of materials suggested for spintronic applications, a new class of materials has emerged, namely spin gapless semiconductors (SGS), which offers potentially more advantageous properties than existing ones. These magnetic semiconductors exhibit a finite band gap for one spin channel and a closed gap for the other. Here, supported by electronic-structure calculations, we report evidence of SGS behavior in equiatomic quaternary CoFeCrGa, having a cubic Heusler (prototype LiMgPdSn) structure but exhibiting chemical disorder (DO3 structure). CoFeCrGa is found to transform from SGS to half-metallic phase under pressure, which is attributed to unique electronic-structure features. The saturation magnetization (MS) obtained at 8K agrees with the Slater-Pauling rule and the Curie temperature (TC) is found to exceed 400K. Carrier concentration (up to 250K) and electrical conductivity are observed to be nearly temperature independent, prerequisites for SGS. The anomalous Hall coefficient is estimated to be 185S/cm at 5K. Considering the SGS properties and high TC, this material appears to be promising for spintronic applications

Evidence for vortex state in Fe2CoGe thin films using FORC and magnetic imaging

We report on the evidence for the vortex state in the thin films of Fe2CoGe through first order reversal curves, magnetic force microscope, longitudinal magneto-optical Kerr effect and micro-magnetic simulations. Phase purity of the films confirmed through X-ray diffraction, which confirms the A2 type disorder Heusler alloy structure. Contour graph of first order reversal curves infers the formation of vortex state that is useful to understand magnetization reversal and switching process. We do observe the vortex state ∼1 μm with in – plane curling of the magnetization using magnetic force microscope phase analysis. We believe that realization of vortex state formation in Fe2CoGe thin films may cater applications in future magnetic data storage and microwave oscillators