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

C. N. Chinnasamy
S. D. Yoon
Aria Yang
Ashish Baraskar
C. Vittoria, Northeastern University
V. G. Harris, Northeastern University

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Originally published in Journal of Applied Physics 101, 09M517 (2007). DOI:10.1063/1.2714204 (http://dx.doi.org/10.1063/1.2714204).

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 NiFe₂O₄films on MgO substrates by pulsed laser deposition. The substrate temperature was varied from 700 to 900°C at 5 mTorr 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 2.7 kG at 300 K. 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 9.61 GHz was 1.5 kOe, and it was reduced to 0.34 kOe 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 H_a can be aligned perpendicular to the film plane when films are grown with a fixed oxygen pressure of 5 mTorr for films deposited at 700 and 900°C.