High-Temperature Magnetic Behaviour of 10 % Aluminium-Substituted Cobalt Ferrite.

Magnetic studies on aluminum-substituted cobalt ferrite nanoparticles (CoFeAl O ) of average particle size ∼20 nm in the broad range of temperature varying from room temperature (300 K) to 900 K has been presented. The temperature dependence of DC magnetization curve exhibits paramagnetic to ferrimagnetic transition at ∼736 K. Zero field cooling and field cooling magnetization measurement shows that the blocking temperature is far above the room temperature. The presence of ferrimagnetic order in the sample has been analyzed by Arrott plot technique for M-H data measured over the temperature range 300-900 K in the magnetic field of ±9 T. The magnetocrystalline anisotropy constant was determined by employing the 'law of approach (LA) to saturation' theory. The saturation magnetization, magnetocrystalline anisotropy constant and coercivity are found to decrease with the increase in temperature. [ABSTRACT FROM AUTHOR]