Dynamic study of the internal magnetic order of Mn3O4 nanoparticles

The dynamic magnetic properties of Mn3O4 nanoparticles with mean diameter aOE (c) I center dot aOE(a) = 15 nm have been investigated by frequency and dc-field (H (DC)) dependence of the in phase (chi') and out of phase (chi aEuro(3)) ac-susceptibility. The studies were performed in non-interacting and interacting systems of Mn3O4 nanoparticles diluted in a polymer with concentrations 1.5 and 17.6%. The ac-susceptibility of the non-interacting system, measured with H (DC) = 0 Oe, presents only one maximum located at T (C) = 42 K associated to the paramagnetic (PM)-ferrimagnetic (FiM) transition. In contrast, the susceptibility of the interacting system shows two anomalies. One frequency independent peak associated to T (C) and a second low temperature maximum was observed in chi aEuro(3), located at T (P). The position of the T (P) maximum shifts to higher temperature when the frequency increases. The relation between the relaxation time and T (P) was well described by the Vogel-Fulcher law. When the susceptibility was measured with H (DC) = 20 kOe, the PM-FiM transition was observed in both systems. Remarkably, in the non-interacting system, the low temperature anomaly is evidenced by the magnetic field. This anomaly is present as a well-defined maximum, which shifts to higher temperature when the frequency increases.