Spin reorientation in MnBi

High purity MnBi was prepared by arc-melting under He gas. The prepared sam ples have the property of being hard to oxidize in air and progress of oxid ation was not observed by X-ray diffraction 1 year later. It is easy to pul verize a good quality sample into powder even in air. We confirmed that coe rcive force at room temperature depends on the powder size and takes a valu e of S kOe for less than 400 mesh. The permeability has a hysteresis in a t emperature range between 77 and 300 K and exhibits a maximum at 100 It corr esponding to the spin reorientation temperature T,. The pressure (P) depend ence of I; was examined by measuring the permeability at various pressures. The value of dT(t)/dP was obtained to be 9.6 K/kbar. The results of therma l expansion revealed that both the lattice parameters a and c increase abru ptly near 250 K. (C) 2001 Elsevier Science B.V. All rights reserved.