Magnetic phase diagram of GdAg1− xZnx

Abstract

The magnetic phase diagram of GdAg 1− x Zn x , an intermetallic solid solution of an antiferromagnet ( GdAg: T N = 136 K) and a ferromagnet ( GdZn: T C = 269 K), has been elaborated from magnetization measurements. The antiferromagnetic phase boundary T N( x) first passes a broad maximum meeting the ferromagnetic phase boundary T C( x) at x 1 = 0.575 and T 1 = 72 K, where four phases coexist. On approaching ( x 1, T 1) along T N( x) the magnetization phenomena vanish. At x 1 the phase transition still has ferromagnetic appearance but proceeds into a state without spontaneous magnetic moment. Two different ferromagnetic phases (F 1, F 2) and one ferrimagnetic phase (F 3) occur in the composition intervals 0.69 < x 1 <1, and 0.61 < x 2 < 0.69 and 0.51 < x 3 < 0.61. All phase transitions seem to be of second order except th e F 1− F 2 one at x = 0.69 which is of first order. This phase line meets the paramagnetic to ferromagnetic phase boundary T C( x) in a multicritical point with the coordinates x m = 0.69, T m = 123 K. Six further mixed magnetic phases, M 1, 2, ..., 6, are observed between x = 0.33 and 0.6 below the antiferromagnetic branch and exhibit irreversible thermodynamic properties, such as hysteresis, below about 40 K. Assuming local magnetic interactions only between nearest and next-nearest Gd neighbours, the T N( x) and T C( x) phase boundaries can be described fairly well by a simple model calculation using different exchange parameters for a few relevant distributions of Ag and Zn atoms.