Canted surface spins driven exchange anisotropy in erbium substituted nickel ferrite nanoparticles

Abstract

Single-phase nickel ferrite nanoparticles doped with rare earth Er3+ ions have been prepared using conventional chemical co-precipitation technique. Existence of pure spinel cubic structure of all samples was confirmed by the X-ray diffraction profiles and Raman modes. Average crystallite sizes ranged from 4 nm to 15 nm were estimated using Williamson-Hall plot. The crystallite size was found to decrease with increasing Er dopants in nanosized nickel ferrites. Compressive microstrain was detected for all the synthesized nanoferrites. Lattice constant increased with the increase of Er concentration due to its large ionic diameter. The crystal symmetry of octahedral sublattices was lowered for higher Er content nanoferrites as detected by the Raman spectra. Indirect optical band gaps increased with Er doping as observed in Tauc plots. Existence of exchange anisotropy in Er content nickel nanoferrites was seen by field cooled (7 T) M(H) plots recorded at 5 K. Both the exchange bias and coercivity were observed to increase at 5 K with the increment of Er percentage. Saturation magnetization also decreased with the increase of Er content. The highest Er content nanoferrites exhibited superparamagnetic nature at room temperature as seen from M(T) plots. The irreversibility temperature as well as blocking temperature was reduced because of mean size reduction of nanoparticles with increasing Er percentage.