Order-disorder phase transformations and magnetic structure of Ni1-xCoxMn alloys

Neutron diffraction was used to study structural and magnetic states in que nched and annealed Ni1-xCoxMn alloys. The order-disorder structural transit ion from the ordered tetragonal to the disordered cubic phase was found to occur at x approximate to 0.3 in quenched alloys and at x approximate to 0. 7 in annealed ones. The magnetic structure of theta -NiMn is shown to chang e upon substitution of Co for Ni in such a manner that the magnetic moments of manganese atoms reorient from the [110] direction in the tetragonal pha se toward the [111] direction in the cubic phase and the local moment at ma nganese atoms decreases from 3.8 to 1.4 mu (B). No magnetic moment is prese nt at nickel and cobalt atoms either in the tetragonal or cubic phases.