Magnetic properties of nanoparticles of cobalt ferrite at high magnetic field

In this paper we report high magnetic field (-140 <= H <= 140 kOe) magnetization data for cobalt ferrites (crystallites size similar to 42 nm) for temperatures (T) varying from 5 to 340 K. The T-dependence for the cubic magnetocrystalline anisotropy constant K-1 was determined by using the "law of approach" (LA) to saturation. The values of K-1 were found to be substantially different from previously reported values obtained using the same procedure but with H up to 50 kOe. By properly choosing the quantum parameters we found a very good agreement between the values calculated by using the model proposed by Tachiki [Prog. Theor. Phys. 23, 1055 (1960)] and the K-1 versus T data. For instance, the values of K-1 measured (calculated) for 5 K and 340 K were 28.3 x 10(6) erg/cm(3) (27.7 x 10(6) erg/cm(3)) and 7.4 x 10(6) erg/cm(3) (6.8 x 10(6) erg/cm(3)), respectively. The values of the parameters used to fit the data in both magnetic field regimes were chosen based on cation distribution over the A and B-sites on the spinel structure of the nanoparticles. (C) 2011 American Institute of Physics. [doi:10.1063/1.3626931]