Magnetic Phase Diagram of Three-Dimensional Diluted Ising Antiferromagnet Ni_0.8Mg_0.2(OH)₂

Abstract

H–T diagram of 3D diluted Ising antiferromagnet Ni_cMg_1−c(OH)₂ with c=0.8 has been determined from measurements of SQUID DC magnetization and AC magnetic susceptibility. At H=0, this compound undergoes two magnetic phase transitions: an antiferromagnetic (AF) transition at the Néel temperature T_N (=20.7 K) and a reentrant spin glass (RSG) transition at T_RSG (≈6 K). The H–T diagram consists of the RSG, spin glass (SG), and AF phases. These phases meet a multicritical point P_m (H_m=42 kOe, T_m=5.6 K). The irreversibility of susceptibility defined by δ (=χ_FC−χ_ZFC) shows a negative local minimum for 10≤H≤35 kOe, suggesting the existence of possible glassy phase in the AF phase. A broad peak in δ and χ″ at H≥20 kOe for T_N(c=0.8,H)≤T≤T_N(c=1,H=0) (=26.4 K) suggests the existence of the Griffiths phase.