Crystal distortion and magnetic structure of γ-MnPt alloys

We have made X-ray and neutron-diffraction experiments and magnetic susceptibility measurements for γ-MnPt alloys. The alloy containing 8 at. % Pt shows a face-centered orthorhombic structure with a=3.807, b=3.748 and c=3.685 A and a non-collinear antiferromagnetic structure with μa=0, μb=1.27 and μc=2.001 μB/Mn atom at 10 K. The crystal transition occurs from the orthorhombic structure to a tetragonal structure with c/a<1 at 450 K, and finally to a cubic structure at 510 K, which is nearly equal to the Neel temperature. Another alloy containing 12 at. % Pt shows a face-centered tetragonal structure with c/a>1 and μ=2.58 μB/Mn atom at 10 K, and transforms to a cubic structure at 325 K, which is lower than the Neel temperature (=500 K). We have determined a phase diagram for γ-MnPt alloys containing 7-20 at. % Pt. (orig.)