Atomic order and magnetization distribution in the half metallic and nearly half metallic C1_bcompounds NiMnSb and PdMnSb

Abstract

Polarized neutron diffraction has been used to study the magnetization distribution in two isostructural inter-metallic compounds NiMnSb and PdMnSb. Band structure calculations have predicted that whereas the former should be a half metallic ferromagnet the latter should not. Measurements made at 5 K on different crystals show that disorder can occur between the A (Mn) and B (Sb) sites in both alloys and in the case of NiMnSb, by partial occupation of the void D sites by Ni. In all the crystals most of the moment was found on the Mn atoms in the A sites; in NiMnSb it is due to spin only but in PdMnSb there is evidence for a significant orbital contribution (g = 2.22). The magnitudes of the moments associated with each atom are in fair agreement with the theoretical values; however, the distribution of magnetization around the Mn atoms is found to have nearly spherical symmetry (40% e(g)) rather than the 50% e(g) character expected from the band structure.

Order–disorder transition of vacancies from the full- to the half-Heusler structure in Ni2−xMnSb alloys

“…According to their experimental results, the HH structure is basically stable over the whole composition range with the vacancies having a strong tendency to occupy the C site, even for compositions close to Ni 2 MnSb (x ¼ 0). On the other hand, it was also reported that even in the stoichiometric NiMnSb alloy, the degree of atomic order depends on the heat-treatment and that a large number of vacancies occupy not only the C site, but also the A site [4]. This observation suggests that the Ni 2Àx MnSb alloys may exhibit an order-disorder transition from the L2 1 to the C1 b structure due to ordering of vacancies, which at elevated temperatures are randomly dispersed between the A and C sites.…”

Spectral signatures of thermal spin disorder and excess Mn in half-metallic NiMnSb

“…While the energies of atom-pair swaps [30] are related to the formation energies of different defects, the concentration of each non-stoichiometric defect depends on the chemical potentials of the relevant elements and thus on the material synthesis protocol. A polarized neutron diffraction measurement [33] of a low-quality crystal found a large concentration of Mn Sb and Sb Mn defects. Since the Mn-Sb swap energy is rather high [30], the formation of these defects could be due to nonequilibrium growth conditions.…”

Coexistence of Ferromagnetism and Superconductivity in Rapidly Quenched Ni2NbSn Heusler Alloy

“…Analysis reveals single phase L2 1 characteristic for full Heusler alloys with the lattice parameter a = 6.1654 Å. The lattice constant is slightly lower than that observed for bulk materials (6.179 Å [3]). The absence of super lattice reflections (111) and (311) confirms structural disorder between Nb and Sn elements (which is called B2 disorder structure) [2,7].…”

“…In the last years, even the superconducting Heusler alloys attract attention [2]. One of the few disadvantages of the Heusler alloys is their complicated production process that contains high temperature (> 1100 K) processing for a long time (7-12 days [3][4][5]). Recently, rapid quenching method has been proved to be very efficient for cheap and easy production of large amount of the Heusler alloys [6].…”