Superparamagnetism and spin-glass like state for the MnFe2O4 nano-particles synthesized by the thermal decomposition method

MnFe2O4 nano-particles with an average size of about 7 nm were synthesized by the thermal decomposition method. Based on the magnetic hysteresis loops measured at different temperatures the temperature-dependent saturation magnetization (MS) and coercivity (HC) are determined. It is shown that above 20 K the temperature-dependence of the MS and HC indicates the magnetic behaviors in the single-domain nano-particles, while below 20 K, the change of the MS and HC indicates the freezing of the spin-glass like state on the surfaces. By measuring the magnetization–temperature (M–T) curves under the zero-field-cooling (ZFC) and field-cooling procedures at different applied fields, superparamagnetism behavior is also studied. Even though in the ZFC M–T curves peaks can be observed below 160 K, superparamagnetism does not appear until the temperature goes above 300 K, which is related with the strong inter-particle interaction.

► MnFe2O4 nano-particles with size of 7 nm were prepared.
► The surface spin-glass like state is frozen below 20 K.
► The peaks in ZFC magnetization–temperature curves are observed below 160 K.
► The inter-particle interaction inhibits the superparamagnetism at room temperature.