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Title: Site occupancy and magnetic properties of Al-substituted M-type strontium hexaferrite

We use first-principles total-energy calculations based on density functional theory to study the site occupancy and magnetic properties of Al-substituted M-type strontium hexaferrite SrFe{sub 12−x}Al{sub x}O{sub 19} with x = 0.5 and x = 1.0. We find that the non-magnetic Al{sup 3+} ions preferentially replace Fe{sup 3+} ions at two of the majority spin sites, 2a and 12k, eliminating their positive contribution to the total magnetization causing the saturation magnetization M{sub s} to be reduced as Al concentration x is increased. Our formation probability analysis further provides the explanation for increased magnetic anisotropy field when the fraction of Al is increased. Although Al{sup 3+} ions preferentially occupy the 2a sites at a low temperature, the occupation probability of the 12k site increases with the rise of the temperature. At a typical annealing temperature (>700 °C) Al{sup 3+} ions are much more likely to occupy the 12k site than the 2a site. Although this causes the magnetocrystalline anisotropy K{sub 1} to be reduced slightly, the reduction in M{sub s} is much more significant. Their combined effect causes the anisotropy field H{sub a} to increase as the fraction of Al is increased, consistent with recent experimental measurements.
Authors:
; ;  [1] ;  [2] ;  [3] ; ;  [4] ;  [5] ;  [6]
  1. Department of Physics and Astronomy, Mississippi State University, Mississippi State, Mississippi 39762 (United States)
  2. (United States)
  3. Center for Computational Sciences, Mississippi State University, Mississippi State, Mississippi 39762 (United States)
  4. Department of Electrical and Computer Engineering and MINT Center, The University of Alabama, Tuscaloosa, Alabama 35487 (United States)
  5. Department of Physics, University of North Texas, Denton, Texas 76203 (United States)
  6. Thematic Unit of Excellence on Computational Materials Science, S.N. Bose National Centre for Basic Sciences, Sector-III, Block-JD, Salt Lake, Kolkata-700098 (India)
Publication Date:
OSTI Identifier:
22489444
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 117; Journal Issue: 24; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; ALUMINIUM IONS; ANISOTROPY; ANNEALING; CONCENTRATION RATIO; DENSITY FUNCTIONAL METHOD; FERRITES; IRON IONS; MAGNETIC PROPERTIES; MAGNETIZATION; PROBABILITY; SPIN; STRONTIUM