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

Journal Article · Sat Nov 14 04:00:00 EST 2015 · Journal of Applied Physics

DOI:https://doi.org/10.1063/1.4935146· OSTI ID:22492908

Torres, T. E.; Ibarra, M. R. ^[1]; Lima, E. ^[2]; Mayoral, A.; Ibarra, A. ^[1]; Marquina, C. ^[3]

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1. Instituto de Nanociencia de Aragón (INA), Universidad de Zaragoza, 50018 Zaragoza (Spain)
2. División Resonancias Magnéticas, Centro Atómico Bariloche/CONICET, S. C. Bariloche 8400 (Argentina)
3. Departamento de Física de la Materia Condensada, Facultad de Ciencias, Universidad de Zaragoza, 50009 Zaragoza (Spain)

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)

• OSTI ID: 22492908
• Journal Information: Journal of Applied Physics, Journal Name: Journal of Applied Physics Journal Issue: 18 Vol. 118; ISSN JAPIAU; ISSN 0021-8979
• Country of Publication: United States
• Language: English

Related Subjects

71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ANISOTROPY
CHANNELING
CORRECTIONS
MAGNETIC PROPERTIES
NANOPARTICLES
PYROLYSIS
RELAXATION
SPIN
SURFACES