| Magnetic properties of two composites of γ-Fe2O3 (maghemite) nanoparticles covered by molecular magnets of Me3[Fe(CN)6]2·H2O (Me(II)=Co and Ni) have been studied. Temperature dependence of magnetic susceptibility in ZFC and FC modes has been obtained for different applied magnetic fields. Additionally, magnetic field dependence of the magnetization has been recorded at different temperatures. For sample with cobalt, no blocking temperature up to 350K was registered in an applied magnetic field of 100 Oe. On the other hand, in 500 Oe the blocking temperature was about 300K. For the system with nickel, the blocking temperature was much lower at high values of applied magnetic field. In both cases, the hysteresis loops have been recorded and the coexistence of ferromagnetic and antiferromagnetic phase has been observed. The antiferromagnetic interactions were stronger for the sample with nickel ions. The presence of stronger antiferromagnetic interaction influenced the coercive field, the remanence field and saturation magnetization. Especially interesting was its influence on the temperature dependences of these parameters. |
full paper (pdf, 416 Kb)