Effects of Ni substitution on magnetism and thermal expansion of antiperovskite Mn₃Ga_1-xNi_xN (0 ≤ x ≤ 1.0)

Effects of Ni substitution on magnetic and thermal expansion properties in Mn₃Ga_1−xNi_xN (0 ≤ x ≤ 1.0) were investigated. The magnetic structure for Mn₃GaN is a typical noncollinear antiferromagnetic Γ^{5 g}. After Ni was introduced to the Ga site, the spin alignment was changed from antiferromagnetic to ferromagnetic. In addition, the magnetic transition temperature first decreased and then increased with increasing Ni content, which could be ascribed to the competition between the electron-type doping effect and the lattice effect. Near the magnetic transition, Mn₃Ga_1−xNi_xN showed an abrupt lattice contraction with increasing temperature and the magnitude of the lattice contraction gradually decreased from 0.38% (for x = 0) to 0.09% (for x = 1.0) with increasing Ni substitution. In particular, zero thermal expansion behavior below 150 K was observed in Mn₃Ga_.6Ni_.4N, and thermal expansion coefficient α was estimated to be 0.311 × 10⁻⁶ K⁻¹. The obtained zero thermal expansion is very useful for practical applications in precision devices. The zero thermal expansion behavior was assumed to be associated with the ferromagnetic characteristic induced by the Ni substitution, which stabilized the Γ^{5 g} antiferromagnetic structure.