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研究了低温下NdMnO3单晶的比热随温度和磁场的变化(2K≤T≤200K,0T≤H≤8T).对应于Mn磁矩亚晶格的A型反铁磁(AAF)相变,零场下的比热曲线在85K附近出现尖锐的λ形峰,随着磁场的增加,此λ峰降低展宽而且平滑变化,这与此温度附近磁化强度的变化规律一致.与磁有序相变相关的熵变约为理论值的26%,这可能是由于磁有序涨落延续在较大温区造成的.在20K以下,比热曲线出现了明显的肩膀形状的Schottky反常,其峰值随着磁场的增加而逐渐向高温移动.考虑了低温下比热的各种贡献,根据Nd3+位有效分子场(Hmf)引起的Nd3+基态双重态(GSD)劈裂对上述现象进行了解释.通过对2K≤T≤20K,0T≤H≤8T范围内比热数据的拟合,得到了样品的GSD劈裂,德拜温度和AAF自旋波劲度系数以及它们对磁场的依赖关系.发现GdFeO3型八面体旋转引起的AAF结构中Mn磁矩亚晶格的铁磁成分可能是Hmf的来源.
The specific heat of NdMnO3 single crystals with temperature and magnetic field (2K≤T≤200K, 0T≤H≤8T) was investigated at low temperature.The A-type antiferromagnetic (AAF) phase transitions corresponding to Mn magnetic sub-lattices, The specific heat curve at zero field shows a sharp λ-shaped peak near 85K, which decreases with the increase of magnetic field, and it is consistent with the change of magnetization near this temperature. The relative entropy change is about 26% of the theoretical value, which may be due to the magnetic orderly continuation in the larger temperature region. Under 20K, obvious shoulder shape Schottky anomaly appears in the specific heat curve, The magnetic field increases and gradually moves to high temperature.According to the various contributions of specific heat at low temperature, the above phenomenon is explained by Nd3 + ground state doublet (GSD) cleavage caused by the effective molecular field (Hmf) of Nd3 + 2K≤T≤20K, 0T≤H≤8T, the GSD splitting, Debye temperature and AAF spin wave stiffness coefficients of the samples and their dependence on the magnetic field were obtained.It was found that the GdFeO3 type The ferromagnetic composition of Mn magnetic subgrains in the AAF structure caused by octahedral rotation may be the source of Hmf.