We investigated the structure and magnetic properties of the multiferroic hexagonal manganite Y1−xTbxMnO3 (x = 0, 0.1, 0.2) single crystals. At 23 K, a Mn spin reorientation transition, which is not reported in the parent compound YMnO3, is observed in Y0.8Tb0.2MnO3. At a lower temperature, another new transition is observed in the doping system, which is attributed to the formation of long range antiferromagntic order of the doped Tb3+ moments. Based on the experimental results, we suggest that the effect of Tb doping is to bring about the increase of the Mn-O-Mn bond angle and the relief of the magnetic frustration. With increasing the doping level, for x = 0.2, when a magnetic field is applied parallel to the c axis, the field induced spin-flop transition is appeared, which indicates the reorientation of the Mn3+ moments along with the field-induced ferromagnetic ordering of the Tb3+ moments. These results suggest that the possibility of the Tb doping can change the magnetic structure and ferroelectricity properties of YMnO3.
Measurements of isothermal magnetization and electrical transport on Pr0.5Ca0.5Mn0.97Ga0.03O3 have been performed in a magnetic field up to 15 T. Two distinct metamagnetic transitions, which may relate to the collapse of the pseudo-CE-type and CE-type antiferromagnetic phases (CE, a composite antiferromagnetic structure composed of a chequeboard of alternating C and E type), have been observed in the temperature region of 2.5–140 K. Different from the traditional magnetization steps, the two metamagnetic transitions are not dependent on the field sweep rate. These peculiar features are sensitive to the microstructure of the sample. A temperature-field phase diagram has been constructed and found to exhibit a minimum critical field, similar to other phase-separated systems.
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