Magnetic properties of nanoparticles of cobalt ferrite at high magnetic field

摘要

In this paper we report high magnetic field (- 140 ≤ H ≤ 140 kOe) magnetization data for cobalt ferrites (crystallites size ~ 42 nm) for temperatures (7) varying from 5 to 340 K. The T-dependence for the cubic magnetocrystalline anisotropy constant K1 was determined by using the "law of approach" (LA) to saturation. The values of K1 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 K1 versus T data. For instance, the values of K1 measured (calculated) for 5 K and 340 K were 28.3 × 10~6 erg/cm~3 (27.7 × 10~6 erg/cm~3) and 7.4 × 10~6 erg/cm~3 (6.8 × 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.