We report on structural, magnetic, transport, and spin-polarization measurements of the Heusler alloys Co 2 MnSi and NiMnSb. Laue diffraction patterns confirm the single-crystal nature of Co 2 MnSi. Roomtemperature transport measurements show a negative magnetoresistance in NiMnSb. Point-contact Andreev reflection measurements of the spin polarization yield polarization values for Co 2 MnSi and NiMnSb of 56% and 45%, respectively. Temperature dependence of resistivity for Co 2 MnSi reveals a relatively large residual resistivity ratio ( 293 K / 5 K ) typical of single-crystal Heusler alloys. In NiMnSb, resistivity and magnetization as a function of temperature show evidence of a magnetic phase transition near 90 K.

In this Brief Report, we report on the observation of a giant positive ͑inverse͒ magnetic entropy change ͑about 28.6 J K −1 kg −1 at 5 T magnetic field͒ below 300 K and a modest negative ͑normal͒ entropy change ͑about 6.6 J K −1 kg −1 at 5 T͒ above 300 K in a Ni 50 Mn 33.13 In 13.90 single crystal. This temperature-dependent entropy change may suggest that both the magnetizing and demagnetizing processes can be employed for cooling.

The first-principles calculation within density-functional theory is used to search for new candidates of half-metallic ferromagnets in semi-Heusler alloys NiCrM (M = P, As, Sb, S, Se and Te). Our calculations predict that NiCrP, NiCrSe and NiCrTe are half-metallic ferromagnets (HMFs) with magnetic moments of nearly 3 or 4 µ B /fu and HM gaps of 0.263, 0.047 and 0.102 eV, respectively. Other compounds are so-called nearly HMFs. Substitution of the sp atoms cannot be responsible for the formation of the band gap, but results in a shift in the Fermi level and the loss of half-metallicity. The half-metallicity of NiCrP and NiCrTe can be retained when the lattice parameter is changed by about 2%-3%.

We calculated the energy consumed for phase boundary motion in a Ni 52 Mn 23 Ga 25 single-crystalline sample during martensitic transformation using a boundary friction phenomenological theory. It was found that the energy consumed for phase boundary motion is 13.14 J/mol, only a small part of the latent heat of martensitic transformation. Furthermore, the results of transformation loops measured by ac magnetic susceptibility proved that the thermal hysteresis of martensitic transformation is in direct proportion to the volume fraction of martensite. It was also indicated that the thermal hysteresis of martensitic transformation originates from the friction of phase boundary motion.