Effects of random fields on the phase diagram in the field-temperature plane of the diluted antiferromagnet MnxMg1-xTiO3

The diluted antiferromagnet MnxMg1-xTiO3 with x greater than or equal to 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-hop (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 MnxMg1-xTiO3 and the x dependence of phase diagram.