title: Atomic and magnetic order in the shape memory alloy Mn2NiGa.
abstract: Magnetization and high resolution neutron powder diffraction measurements on the magnetic shape memory alloy Mn(2)NiGa have confirmed that it is ferromagnetic with a Curie temperature above 500 K. The compound undergoes a broad structural phase transformation ΔT ∼ 90 K with a mean transition temperature T(M) ∼ 270 K. The high temperature parent phase is cubic (a = 5.937 Å) and has a modified L 2(1) structure. At 500 K the ordered magnetic moment essentially all on the 4a site is 1.35 μ(B)/Mn. The low temperature martensite has space group I4/mmm and is related to the cubic phase through a Bain transformation a(tet) = (a(cub) + b(cub))/2, b(tet) = (a(cub) - b(cub)) and c(tet) = c(cub) in which the change in cell volume is < 2.6%. In this structure at 5 K the ordered moment of ≈2.3 μ(B) is again found to be confined to the sites with full Mn occupation and is aligned parallel to c. Neutron diffraction patterns obtained at 5 K suggested the presence of a weak incommensurate antiferromagnetic phase characterized by either a ((1/3)0(1/3)) or (00(1/3)) propagation vector.
authors.affiliation: Department of Physics, Loughborough University, UK.
authors.forename: P J
authors.initials: PJ
authors.lastname: Brown
authors.forename: T
authors.initials: T
authors.lastname: Kanomata
authors.forename: K
authors.initials: K
authors.lastname: Neumann
authors.forename: K U
authors.initials: KU
authors.lastname: Neumann
authors.forename: B
authors.initials: B
authors.lastname: Ouladdiaf
authors.forename: A
authors.initials: A
authors.lastname: Sheikh
authors.forename: K R A
authors.initials: KR
authors.lastname: Ziebeck