Evidence for weak ferromagnetism and metamagnetic phase transitions in frustrated antiferromagnetic systems with octahedral structure

Abstract

Possible source of the weak ferromagnetism and the metamagnetic phase transitions in the antiferromagnetic systems with octahedral structure, such as perovskites, is identified in the framework of the antiferromagnetic spin-1/2 Ising model on the octahedral recursive lattice. It is shown that the weak ferromagnetism of the studied antiferromagnetic model is directly related to the competition between two qualitatively different kinds of spin loops (frustrated and bipartite) realized within each elementary octahedron. The free energy of the model is found, the magnetization properties of the model are studied, and the phase diagram of the metamagnetic phase transitions in the external magnetic field is determined. The discrete system of the model ground states is found and discussed. The discontinuity of the susceptibility at the metamagnetic phase transitions is studied. The exact expression for the Néel temperature of the antiferromagnetic system is determined and compare to the Curie temperature of the ferromagnetic system.