Negative Magnetization and Spin-Phonon Coupling in Faceted Nd2FeCrO6 Double Perovskite

The magnetic feature of a faceted double perovskite Nd₂FeCrO_6, synthesized by the solid-state reaction method, is investigated. Nd₂FeCrO₆ exhibits an orthorhombic structure with Fe and Cr ions in 3⁺ oxidation states. These ions are shifted away from the centre of FeO₆/CrO₆ octahedral sublattice, indicating distortion. The Isomer shift in the Mössbauer spectrum correlates with the 3⁺ oxidation state of Fe, and the existence of magnetic fraction leading to magnetic frustration in Nd₂FeCrO₆ is established. The superexchange Fe³⁺ -O- Fe³⁺ and Cr³⁺ -O- Cr³⁺ interactions favour antiferromagnetic ordering, while Fe³⁺ -O- Cr³⁺ interactions promote weak ferromagnetic ordering. The low-temperature magnetic study traces negative magnetization in FC mode for the applied external fields of 100 Oe and 1000 Oe, attributed to the paramagnetic effect of Nd³⁺ ions aligning antiparallel to the ferromagnetic component of the |Fe+Cr| sublattice internal field. Also, the negative magnetization of FC mode is found to be field-dependent. The deviation of the B_2g phonon around the magnetic ordering temperature T_N~250 K provides evidence of spin-phonon coupling. This variation in the B_2g phonon is analysed in terms of the full width at half maximum (FWHM), peak position, intensity, and height.