Spin Stiffness Constant of Half-metallic Ferrimagnet in Mn-based Heusler Alloys

AbstractIn order to investigate the spin stiffness constant, D, of Mn-based Heusler alloys with half-metallic density of states, magnetic measurements were properly carried out. The Curie temperature, TC, of Mn2VAl, Mn50V20Al30 and Mn2CoGa were 768, 738 and 740K, respectively. The value of D was evaluated from the temperature, T, dependence of the spontaneous magnetization in each specimen below 150K, where linear dependence of T 3/2 was observed. The D values for these materials were obtained to be 5.34, 4.38 and 5.67 meV·(nm)2 and significantly larger than that for Co-based Heusler alloys reported previously. The strong exchange interaction would be the reason that the Mn-based Heusler alloys indicate high TC even though they have not so large total magnetic moment comparing to that of Co-based Heusler alloys

Evidence of Change in the Density of States during the Martensitic Phase Transformation of Ni-Mn-In Metamagnetic Shape Memory Alloys

Specific heat measurements were performed at low temperatures for Ni50Mn50−xInx alloys to determine their Debye temperatures (θD) and electronic specific heat coefficients (γ). For x ≤ 15, where the ground state is the martensite (M) phase, θD decreases linearly and γ increases slightly with increasing In content. For x ≥ 16.2, where the ground state is the ferromagnetic parent (P) phase, γ increases with decreasing In content. Extrapolations of the composition dependences of θD and γ in both the phases suggest that these values change discontinuously during the martensitic phase transformation. The value of θD in the M phase is larger than that in the P phase. The behavior is in accordance with the fact that the volume of the M phase is more compressive than that of the P phase. On the other hand, γ is slightly larger in the P phase, in good agreement with the reported density of states around the Fermi energy obtained by the first-principle calculations

Shape Memory Response in Ni_{40}Co_{10}Mn_{33}Al_{17} Polycrystalline Alloy

Shape memory response of the polycrystalline Ni 40 Co 10 Mn 33 Al 17 alloy were investigated. In the isobaric thermal cycling experiments, the measured transformation strain levels increased with increasing stress reaching about 3.6% under 200 MPa. The slope of the stress vs. transformation temperature diagram, constructed using the data from these experiments, almost coincided with the predicted one obtained using the Clausius-Clapeyron equation, and experimental entropy data and transformation strain. Perfect pseudoelasticity was observed up to 405 K during compressive straining up to 2.5%