Competing Exchange Interactions and Temperature-Dependent Exchange Bias Sign Reversal in Nanocrystalline Nd2NiCrO6 Double Perovskite

Double perovskite Nd2NiCrO6 (NNCO) is synthesized via Sol-gel technique. XRD with Rietveld refinement unveiled two structural phases, with monoclinic (P21/n space group) as primary phase with ∼88%, while orthorhombic (Pbnm space group) as secondary phase with ∼12%. A crystallite size of ∼55 nm signified a nanocrystalline nature, while a strain of 7.61 × 10−3 was observed, owing to NiO6/CrO6 octahedral distortions. X-ray photoelectron spectroscopy identified mixed Ni2+/Ni3+ and Cr2+/Cr3+ oxidation states. Magnetic field-dependent magnetization (M-H loops) in low-temperature range (1.8–30 K) suggested ferrimagnetic (FiM) ordering with noticeable coercivity and remnant magnetization. The loops remained unsaturated even at high field, suggesting competing exchange interactions. Antisite disorder-induced antiferromagnetic (AFM) interactions competed with Ni3+-O2−-Cr3+ ferromagnetic (FM) superexchange interactions, leading to antiparallel unequal magnetic sublattices with FiM behavior with a net magnetization. Maximum magnetization of 17.82 emu/g is attained at 1.8 K, which increased to 19.01 emu/g at 5 K, and afterwards gradually decreased to 9.83 emu/g at 30 K. Temperature-dependent magnetization (M-T) from 5 to 300 K at 100 Oe revealed sharp deviation of field-cooled (FC) and zero field-cooled (ZFC) at transition temperature of 91 K. Curie-Weiss (CW) fitting suggested a negative CW temperature (−74 K) suggesting dominance of AFM interactions. The behavior of temperature-dependent inverse susceptibility suggested the occurrence of a strong Griffiths phase. A rare double sign reversal of exchange bias is observed in 1.8–10 K, where positive exchange bias (+HEB) occurred at 1.8 K, which turned to negative exchange bias (-HEB) at 5 K, which again shifted to +HEB at 10 K. Such a phenomenon in Nd2NiCrO6 can be a useful property for spintronics and magnetic storage applications.