Effect of growth temperature on the magnetic, microwave, and cation inversion properties on NiFe2O4 thin films deposited by pulsed laser ablation deposition

Abstract

First principles band structure calculations suggest that the preferential occupation of Ni2+ ions on the tetrahedral sites in NiFe2O4 would lead to an enhancement of the exchange integral and subsequently the Néel temperature and magnetization. To this end, we have deposited NiFe2O4 films on MgO substrates by pulsed laser deposition. The substrate temperature was varied from 700to900°C at 5mTorr of O2 pressure. The films were annealed at 1000°C for different times prior to their characterization. X-ray diffraction spectra showed either (100) or (111) orientation with the spinel structure dependent on the substrate orientation. Magnetic studies showed a magnetization value of 2.7kG at 300K. The magnetic moment was increased to the bulk value as a result of postdeposition annealing at 1000°C. The as produced films show that the ferromagnetic resonance linewidth at 9.61GHz was 1.5kOe, and it was reduced to 0.34kOe after postannealing at 1000°C. This suggests that the annealing led to the redistribution of Ni2+ ions to their equilibrium octahedral sites. Further, it is shown that the magnetically preferred direction of Ha can be aligned perpendicular to the film plane when films are grown with a fixed oxygen pressure of 5mTorr for films deposited at 700 and 900°C.