Validity of the Néel-Arrhenius model for highly anisotropic CoxFe3−xO4 nanoparticles

• DOI: 10.1063/1.4935146
• Publication Date: 2015-11-12T18:00:24Z
• Authors: T. E. Torres; E. Lima; A. Mayoral; A. Ibarra; C. Marquina; M. R. Ibarra; G. F. Goya
• Keywords: Magnetocrystalline anisotropy; Exchange bias

We report a systematic study on the structural and magnetic properties of CoxFe3−xO4 nanoparticles with sizes between 5 25 nm, prepared by thermal decomposition Fe(acac)3 Co(acac)2. The large magneto-crystalline anisotropy synthesized particles resulted in high blocking temperatures (42 K < TB 345 for d 13 nm) coercive fields (HC ≈ 1600 kA/m T = K). smallest (⟨d⟩=5 revealed existence magnetically hard, spin-disordered surface. dependence static dynamic whole series samples could be explained within Neel–Arrhenius relaxation framework including magnetocrystalline constant K1(T), without need ad-hoc corrections. This approach, using empirical Brükhatov-Kirensky relation, provided K1(0) values very similar to bulk material from either or measurements, as well realistic response times (τ0 10−10s). Deviations found qualitatively based Zener's relation K1(T) M(T).