Rearrangement of crystallographic domains driven by magnetic field in Fe₃Pt and CoO and new phase appearance in Ni₂MnGa

Abstract
We have investigated the rearrangement of crystallographic domains driven by magnetic field in a ferromagnetic shape memory alloy of Fe₃Pt and an antiferromagnetic oxide of CoO. Also, we have determined the equilibrium stress-temperature phase diagram in a ferromagnetic shape memory alloy of Ni₂MnGa. Following results are obtained ; (i) We confirm that magnetic field promotes the rearrangement of crystallographic domains in Fe₃Pt and CoO and the condition of the rearrangement in the present two systems is the same, that is, the magnetic shear stress, which corresponds to the magnetic anisotropy energy divided by the twinning shear, is equal to or larger than the twinning stress. (ii) We construct the equilibrium stress-temperature phase diagram of Ni₂MnGa by compressive tests and magnetic susceptibility measurements, and show the existence of the new phase of X-phase. Moreover, we evaluate the triple point at which the I-, P- and X-phases coexist and suggest the existence of a critical point of the successive P → X → I transformation.

Note to the reader:
On pages 04008-p1, 04008-p2, 04008-p3 and 04008-p6 several mistakes have been corrected on October 19, 2009.