Specific heat of single-crystal NdMnO₃

The temperature and field dependences of the specific heat of single-crystal NdMn03 were investigated from 2K to 200K under different fields up to 8 T. Corresponding to the Type-A antiferromagnetic (A-AF) phase transition in the Mn sub-lattice, the specific heat under zero field exhibited a sharp λ-shaped peak at about 85 K, which was depressed and broadened and changed smoothly with the increase of magnetic field. But the entropy change due to the magnetic order is only 26% of the expected value, which might arise from the extension of the magnetic fluctuation in a larger temperature range. The specific heat curves exhibited a shoulder-shaped Schottky-like anomaly below 20K, whose maximum shifts gradually to higher temperatures with the magnetic field. By considering the contributions to the specific heat at low temperatures, the above phenomena can be interpreted in terms of the model of effective molecular field (H_mf) at Nd³⁺ site that causes the splitting of the ground state doublet (GSD) of Nd³⁺. The specific heat below 20K under different magnetic fields was successfully fitted, through which the meaningful parameters, including the splitting of the GSD of Nd³⁺, Debye temperature and the A-AF spin wave stiffness coefficients, as well as their field dependence were obtained. It was found that the ferromagnetic component of the Mn sub-lattice caused by the GdFeO₃-type octahedron rotation could be the origin of the H_mf.