Exchange interactions, anisotropy, and low-temperature magnetization reversal in NdFeO₃

We have gained a microscopic insight into the phenomenon of double magnetization reversal observed in the NdFeO₃ perovskite compound at compensation temperatures of 6.3 K (T_comp1) and 4.3 K (T_comp2) through analysis of the evolutions of magnetic moments, magnetic anisotropies, and exchange interactions of Nd and Fe sublattices. This understanding stems from studies involving dc magnetization, neutron depolarization, neutron diffraction, and inelastic neutron scattering (INS) on powder and single-crystal samples. Below 8.6 K, additional (magnetic) Bragg peaks are detected in neutron diffraction patterns, corresponding to the C_xF_z-type Nd sublattice ordering, which entails C-type antiferromagnetic (AFM) ordering along the a axis and a ferromagnetic (FM) component along the c axis. The FM components (F_z) of the Nd³⁺ and Fe³⁺ moments are too diminutive to be quantified accurately via powder neutron diffraction; as single-crystal dc magnetization study estimates the FM component (along the c axis) to be approximately 0.09 μ_B at 2 K. Our INS investigations on single-crystal NdFeO₃ sample have unveiled the relative orientations of the F_z components of the Nd and Fe sublattice moments. The INS spectra are found to be consistent with AFM exchange couplings between the Nd-Nd and Nd-Fe sublattices as well as for a planar anisotropy of Nd spins. At 6.3 K, a complete cancellation of the F_z components of the Nd³⁺ and Fe³⁺ moments results in T_comp1, whereas a reversal in the sign of the total magnetic moment below 5 K leads to T_comp2 at 4.3 K. The present comprehensive single-crystal INS investigation thus shed light on the microscopic mechanism for magnetization reversal phenomenon. This microscopic understanding of such a distinctive phenomenon has practical implications for design of magnetic memory and spin-resolving devices.