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Title: Validity of the Néel-Arrhenius model for highly anisotropic Co{sub x}Fe{sub 3−x}O{sub 4} nanoparticles

We report a systematic study on the structural and magnetic properties of Co{sub x}Fe{sub 3−x}O{sub 4} magnetic nanoparticles with sizes between 5 and 25 nm, prepared by thermal decomposition of Fe(acac){sub 3} and Co(acac){sub 2}. The large magneto-crystalline anisotropy of the synthesized particles resulted in high blocking temperatures (42 K < T{sub B} < 345 K for 5 < d < 13 nm) and large coercive fields (H{sub C} ≈ 1600 kA/m for T = 5 K). The smallest particles (〈d〉=5 nm) revealed the existence of a magnetically hard, spin-disordered surface. The thermal dependence of static and dynamic magnetic properties of the whole series of samples could be explained within the Neel–Arrhenius relaxation framework by including the thermal dependence of the magnetocrystalline anisotropy constant K{sub 1}(T), without the need of ad-hoc corrections. This approach, using the empirical Brükhatov-Kirensky relation, provided K{sub 1}(0) values very similar to the bulk material from either static or dynamic magnetic measurements, as well as realistic values for the response times (τ{sub 0} ≈ 10{sup −10}s). Deviations from the bulk anisotropy values found for the smallest particles could be qualitatively explained based on Zener's relation between K{sub 1}(T) and M(T)
Authors:
;  [1] ;  [2] ;  [3] ;  [4] ; ;  [1] ;  [3] ;  [5] ;  [6] ;  [1] ;  [2]
  1. Instituto de Nanociencia de Aragón (INA), Universidad de Zaragoza, 50018 Zaragoza (Spain)
  2. (Spain)
  3. (LMA), Universidad de Zaragoza, 50018 Zaragoza (Spain)
  4. División Resonancias Magnéticas, Centro Atómico Bariloche/CONICET, S. C. Bariloche 8400 (Argentina)
  5. Departamento de Física de la Materia Condensada, Facultad de Ciencias, Universidad de Zaragoza, 50009 Zaragoza (Spain)
  6. (ICMA), CSIC—Universidad de Zaragoza, 50009 Zaragoza (Spain)
Publication Date:
OSTI Identifier:
22492908
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 118; Journal Issue: 18; 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; ANISOTROPY; CHANNELING; CORRECTIONS; MAGNETIC PROPERTIES; NANOPARTICLES; PYROLYSIS; RELAXATION; SPIN; SURFACES