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Title: Temperature dependence of magnetization and anisotropy in uniaxial NiFe₂O₄ nanomagnets: Deviation from the Callen-Callen power law

The thermal variation of magnetic anisotropy (K) and saturation magnetization (M{sub S}) for uniaxial nickel ferrite (NiFe₂O₄) nanomagnets are investigated. Major magnetic hysteresis loops are measured for the sample at temperatures over the range 5–280 K using a vibrating sample magnetometer. The high-field regimes of the hysteresis loops are modeled using the law of approach to saturation, based on the assumption that at sufficiently high field only direct rotation of spin-moment take place, with an additional forced magnetization term that is linear with applied field. The uniaxial anisotropy constant K is calculated from the fitting of the data to the theoretical equation. As temperature increases from 5 K to 280 K, a 49% reduction of K, accompanied by an 85% diminution of M{sub S} is observed. Remarkably, K is linearly proportional to M{sub S}₂.₆ in the whole temperature range violating the existing theoretical model by Callen and Callen. The unusual power-law behavior for the NiFe₂O₄ uniaxial nanomagnets is ascribed to the non-negligible contributions from inter-sublattice pair interactions, Neel surface anisotropy, and higher order anisotropies. A complete realization of the unusual anisotropy-magnetization scaling behavior for nanoscale two-sublattice magnetic materials require a major modification of the existing theory by considering the exact mechanism of eachmore » contributions to the effective anisotropy.« less
Authors:
;  [1] ;  [1] ;  [2]
  1. School of Materials Science and Nanotechnology, Jadavpur University, Jadavpur, Kolkata 700032 (India)
  2. (India)
Publication Date:
OSTI Identifier:
22305830
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 116; Journal Issue: 15; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Publisher:
American Institute of Physics (AIP)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; ANISOTROPY; EQUATIONS; FERRITES; HYSTERESIS; MAGNETIC MATERIALS; MAGNETIZATION; MODIFICATIONS; NANOMATERIALS; NANOSTRUCTURES; NICKEL COMPOUNDS; PAIRING INTERACTIONS; ROTATION; SATURATION; SCALING; SPIN; SURFACES; TEMPERATURE DEPENDENCE; VIBRATING SAMPLE MAGNETOMETERS