Dynamic study of the internal magnetic order of Mn3O4 nanoparticles

E. WINKLER; R.D. ZYSLER; J.P. SINNECKER; M. NOVAK

Roma

Congreso; X International Conference on Nanostructured Materials – NANO2010; 2010

The dynamic magnetic properties of Mn3O4 nanoparticles with mean diameter <d> = 15 nm have been investigated by frequency and dc-field (HDC) dependence of the in phase (X´) and out of phase (X") ac-susceptibility. The studies were preformed in non-interacting and interacting systems formed by 1.5 % and 17 % Mn3O4 nanoparticles diluted in a polymer. The ac-susceptibility of the noninteracting system, measured with HDC =0, presents only one maximum located at TC = 42 K associated to the paramagnetic (PM)-ferrimagnetic (FiM) transition. Instead, the susceptibility of the interacting system shows two anomalies. One frequency independent peak associated to TC and a second, low temperature maximum, was observed in X", located at TP. The position of the TP –peak shifts to higher temperature when the frequency increases. The relation between the relaxation time and TP was well described by the Vogel-Fulcher law. When the susceptibility was measured with HDC = 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 peak, which shifts to higher temperature when the frequency increases.