Anomalous Magnetism in 3d-4f Double Perovskite Oxide Nd2FeCrO6 with Kramer’s Ion

The complex magnetic behavior of double-perovskite oxides (A2BB’O6) with rare-earth (RE) element A and transition metal (TM) elements B-B’ is determined by the interactions between intra- and interatomic magnetic moments. The peculiar magnetism in these systems stems from the interplay between spin, orbit, and lattice degrees of freedom. This study comprehensively investigates the role of spin-orbit entangled Jeff = 1/2 moments of the Kramers ion Nd3+ on the magnetic ground state of a B-site ordered ferrimagnetic (FiM) double-perovskite oxide, Nd2FeCrO6. Furthermore, employing microscopic techniques like μSR (muon spin rotation and relaxation) and neutron diffraction, we gained insight into the origin of low-temperature anomalies in the magnetic ground state of the system. The DC magnetization data encompass the first transition at critical temperature TN = 250 K, followed by a negative magnetization below 15 K. The temperature-dependent neutron diffraction shows a commensurate magnetic ordering below 250 K, forming a ferrimagnetic ground state, supported by theoretical calculations. In addition, a sharp drop in initial muon asymmetry confirms the transition from a disordered state to a long-range-ordered state at 250 K. Interestingly, the thermal evolution of the dynamic muon spin-relaxation rate (λL) reveals a transition at two temperatures, at 250 K and ≈ 11 K, suggesting a low-T ordering at the A site. The heat-capacity data show that Nd3+ hosts the ground-state doublet (pseudospin-1/2) at low temperatures. Our analysis of neutron diffraction, heat capacity, and μSR results suggests that the correlation between the Nd3+ doublet and the complex interaction between Nd-TM moments gives rise to the observed low-temperature anomaly.