Effects of Random Fields on the Phase Diagram
in the Field-Temperature Plane of the Diluted
Antiferromagnet Mn_xMg_1-xTiO₃

Abstract

The diluted antiferromagnet Mn_xMg_1-xTiO₃ with x ≥ 0.64 has been studied by magnetization measurements, and the magnetic phase diagrams in the field-temperature (H-T) plane have been determined for the samples with different x including pure MnTiO₃. It is demonstrated that the existence of random fields gives large effects on the phase transitions. The most noticeable result is that the H-T phase diagram of the samples except MnTiO₃ consists of four phases: well known three phases of a paramagnetic, an antiferromagnetic (AF) and a spin-flop (SF) phase, and a new type of phase. The shape of the phase diagram changes systematically as the Mn concentration, x, decreases. It is considered that in this ``new phase'' an AF like short range order and a SF like short range order coexist and that appearance of the ``new phase'' is caused by random fields. In this paper, we discuss the effects of random fields on the phase diagram of Mn_xMg_1-xTiO₃ and the x dependence of phase diagram.