Characterization, specific heat and magnetization measurements on Ni2YZ Heusler alloys

In this report we describe the synthesis and characterization of several members of the Ni(2)YZ (Y = V, Cr; Z = Ga, Ge) family. While the Heusler alloy Ni2VGa was prepared phase pure, the Ni2CrGa sample consisted of a slightly Cr-deficient alloy and elemental Cr inclusions. The Ge analogues, Ni2VGe and Ni2CrGe, were also prepared as primarily Y-element deficient alloys, with minor secondary phases to balance the starting composition. Despite the minor secondary phases, all Ni2VGa, Ni2CrGa, and Ni2CrGe have diffraction patterns consistent with the cubic Heusler structure (a = 5.814(5), 5.765(3), and 5.788(8) angstrom, respectively). Ni2VGe was concluded to consist of at least two highly off-stoichiometric phases and was excluded from further study. Specific heat and magnetization measurements on the prepared samples demonstrated they are non-magnetic or only weakly paramagnetic down to lowest temperature. No measurable magnetic moment was found in phase pure Ni2VGa down to 2 K, while only low moments (mu(2K)(7T) = 0.027(1)mu(B) and 0.170(2) mu(B)) were observed in Ni2CrGa and Ni2CrGe. Low values of magnetic moments were discussed from the viewpoint of magnetic Cr impurities in a non-magnetic lattice. Such interpretation was well supported by the specific heat data revealing a strong lowest-temperature contribution ascribed to ferromagnetic Cr clusters in the material. The impact of atomic disorder is discussed, particularly with respect to previous theoretical studies and the predicted properties.