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Temperature dependence of the EPR spectra for the Ni<inf>1-x</inf>Co <inf>x</inf>Fe<inf>2</inf>O<inf>4</inf> nanoparticles

Abstract:

Electron Paramagnetic Resonance (EPR) was used to study, the temperature dependence, of the magnetic behavior of Ni1-xCoxFe 2O4 with 0.0 < x < 0.5, in the temperature range 80 < T < 700 K. Nanoparticles of sizes between 30 and 40 nm were obtained using the sol-gel method. The results show that the resonance field (H R) decrease while the linewidth (AHPP) increase, in the temperature range studied, when x is increased. The HR values for x 0 are in agreement with a superparamagnetic phase in the temperature range studied, while for x 0.2, HR and ΔHPP are in accordance with a ferri to superparamagnetic transition at T∼350 K, where T is related to the EPR blocking temperature of these samples. For sample with x 0.5 this temperature is T∼470 K. These results are in good agreement with the magnetization and MOKE results. MOKE measurements as a function of temperature were made to corroborate EPR results. © 2010 IOP Publishing Ltd.