Thermomagnetization Curves and Atomic Short-Range Order for Ni_1-xMn_x (x=0.20, 0.21, 0.23, 0.25, 0.27) Alloys

Abstract

The thermomagnetization curves of rapidly quenched Ni_1-xMn_x (x=0.20, 0.21, 0.23, 0.25, 0.27) alloys and Ni_0.79Mn_0.21 alloy annealed at 693 K for 200 h and 1,000 h were investigated in the temperature range of 100-650 K. The change in saturation magnetization and Curie temperature with heat treatment and Mn concentration was studied on the basis of the atomic short-range order estimated by statistical and EXAFS methods. The magnetism of these alloys depends on the number of nearest-neighbor Mn atoms around an Mn atom. After annealing for 1,000 h, the thermomagnetization curve of Ni_0.79Mn_0.21 alloy shows a double stage, which consists of the ferromagnetic phase and a long tail above the Curie temperature. The latter was analyzed by using a superparamagnetic model as a random set of ferromagnetic clusters distributed in a nonmagnetic matrix.