The field and temperature dependence of the magnetic and structural properties of the shape memory compound Ni(1.84)Mn(1.64)In(0.52).

Magnetization and high resolution neutron powder diffraction measurements have been made on the magnetic shape memory alloy Ni(1.84)Mn(1.64)In(0.52). The compound undergoes a broad structural phase transition, which on heating starts at ∼150 K and finishes at ∼215 K. On cooling there is a ∼20 K hysteresis. The high temperature parent phase is cubic (a = 5.988 Å) with the L2(1) structure in which the excess Mn atoms occupy the vacancies on the Ni and In sites. The magnetic moment is located mainly on the Mn atoms with the same magnitude on both the 4a (Mn) and 4b (In) sites. The low temperature martensite is monoclinic with parameters a = 4.405(2), b = 5.553(2), c = 12.950(2) Å, ß = 86.47(10)° and space group P2/m. The magnetic properties of the martensitic phase are complex and indicate metamagnetic behaviour.

Magnetic and structural properties of the magnetic shape memory compound Ni(2)Mn(1.48)Sb(0.52).

Magnetization and high resolution neutron powder diffraction measurements on the magnetic shape memory compound Ni(2)Mn(1.48)Sb(0.52) have confirmed that it is ferromagnetic below 350 K and undergoes a structural phase transition at T(M)≈310 K. The high temperature phase has the cubic L2(1) structure with a = 5.958 Å, with the excess manganese atoms occupying the 4(b) Sb sites. In the cubic phase above ≈310 K the manganese moments are ferromagnetically aligned. The magnetic moment at the 4(a) site is 1.57(12) µ(B) and it is almost zero (0.15(9) µ(B)) at the 4(b) site. The low temperature orthorhombic phase which is only fully established below 50 K has the space group Pmma with a cell related to the cubic one by a Bain transformation a(orth) = (a(cub) + b(cub))/2; b(orth) = c(cub) and c(orth) = (a(cub) - b(cub)). The change in cell volume is ≈2.5%. The spontaneous magnetization of samples cooled in fields less than 0.5 T decreases at temperatures below T(M) and at 2 K the magnetic moment per formula unit in fields up to 5.5 T is 2.01(5) µ(B). Neutron diffraction patterns obtained below ≈132 K gave evidence for a weak incommensurate magnetic modulation with propagation vector (2/3, 1/3, 0).

Atomic order and magnetization distribution in the half metallic and nearly half metallic C1(b) compounds NiMnSb and PdMnSb.

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.