Positive and negative exchange bias effects in the simple perovskite manganite NdMnO3

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.