Second-order spin reorientation reform in the two-sublattice ferromagnetic system

Based on a two-sublattice mean-field model, the temperature dependences of the spontaneous magnetization and its derivatives with respect to the temperature of the two-sublattice ferromagnetic system were exhaustively investigated. Second-order spin reorientation reforms (SOSRRs) were found in the system, depending on the variation of the competition among the exchange and the opposite anisotropies of the two sublattices with temperature evolution. When the SOSRR transition takes place, both the first derivative of the canting angle and those of the strengths of the sublattice moments possess discontinuous jumps, accompanied with the sudden alterations of the first derivatives of the exchange fields and the anisotropies. Meanwhile, sharp peaks could be observed in each second-derivative curve of these intrinsic magnetic properties. A new concept of exchange-anisotropy flow is proposed to make more straightforward description of the thermal behavior of the two-sublattice ferromagnetic system. Phase diagrams concerning the SOSRR transition are given by means of analyzing the exchange-anisotropy flow. (C) 2001 Elsevier Science B.V. All rights reserved.