doi:10.1063/1.4935146engTorres, T. E.Lima Jr., E.Mayoral, A.Ibarra, A.Marquina, C.Ibarra, M. R.Goya, G. F.Validity of the Néel-Arrhenius model for highly anisotropic CoxFe3-xO4 nanoparticlesART-2015-92357We report a systematic study on the structural and magnetic properties of CoxFe3_xO4 magnetic nanoparticles with sizes between 5 and 25 nm, prepared by thermal decomposition of Fe(acac)3 and Co(acac)2. The large magneto-crystalline anisotropy of the synthesized particles resulted in high blocking temperatures (42 K < TB < 345 K for 5 < d < 13 nm) and large coercive ¿elds (HC ~ 1600 kA/m for T ¼ 5 K). The smallest particles (hdi¼5 nm) revealed the existence of a mag-netically 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 K1(T), without the need of ad-hoc corrections. This approach, using the empirical Br€ukhatov-Kirensky relation, provided K1(0) values very similar to the bulk material from either static or dynamic magnetic measurements, as well as realistic values for the response times (s0 ~ 10^-10s). Deviations from the bulk anisotropy values found for the smallest particles could be qualitativelyconstant explained based on Zener’s relation between K1(T) and M(T).2015http://zaguan.unizar.es/record/3245410.1063/1.4935146http://zaguan.unizar.es/record/32454oai:zaguan.unizar.es:32454info:eu-repo/grantAgreement/ES/MINECO/MAT2010-19326info:eu-repo/grantAgreement/ES/MINECO/MAT2013-42551Journal of Applied Physics 118 (2015), 183902 [11 pp]All rights reservedhttp://www.europeana.eu/rights/rr-f/info:eu-repo/semantics/openAccess