Temperature Dependence of Magnetic Anisotropy Constant in Manganese Ferrite Nanoparticles at Low Temperature

The temperature dependence of the effective magnetic anisotropy constant, K ( T ), of MnFe 2 O 4 nanoparticles is obtained based on superconducting quantum interference device magnetometry measurements. The variation of the blocking temperature, T B , as a function of particle radius, r , is first determined by associating the particle size distribution and the anisotropy energy barrier distribution deduced from the hysteresis curve and magnetization decay curve, respectively. Finally, the magnetic anisotropy constant at each temperature is calculated from the relation between r and T B . The resultant effective magnetic anisotropy constant K ( T ) decreases markedly with increasing temperature from 8.5 × 10 4 J/m 3 at 5 K to 0.35 × 10 4 J/m 3 at 125 K.