Exchange bias effects were studied in the simple perovskite NdMnO3. Nd3+ ordering is induced by the Mn3+ ferromagnetic component, and they are antiferromagnetically coupled with each other. At 30 K, both negative and positive exchange bias effects are found, which are dependent on the cooling field. The exchange bias fields are around −2400 Oe and 1800 Oe, respectively. Positive and negative exchange bias effects were also observed at 8 K, but the exchange bias fields are only 130 Oe and −120 Oe. The coupling intensity between Nd3+ ordering and Mn3+ ordering, and their initial states determine the polarity of the exchange bias fields.
Perovskite DyMn0.33Fe0.67O3 experiences a paramagnetism-antiferromagnetism transition at 450K and spin reorientation at 290 K. Magnetodielectric properties were studied around the spin reorientation transition. Both giant positive and giant negative magnetodielectric coupling (MDC) were observed near room temperature. The MDC shows strong temperature and frequency dependence, and the sign changes from positive to negative when magnetic state transits from a canted antiferromagnetic state to a collinear antiferromagnetic state. Possible mechanisms are proposed based on the Maxwell-Wagner model, phase transition, the magnetoresistance effect, and spin-phonon coupling.
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