Dynamic study of the internal magnetic order of Mn3O4 nanoparticles

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

JOURNAL OF NANOPARTICLE RESEARCH

SPRINGER

Año: 2011 vol. 13 p. 5653 - 5659

1388-0764

The dynamic magnetic properties of Mn3O4 nanoparticles with mean diameter FI = 15 nm havebeen investigated by frequency and dc-field (HDC) dependence of the in phase (X´) and out of phase (X") ac-susceptibility. The studies were performed in noninteracting 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 HDC = 0 Oe, presents only onemaximum located at TC = 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 TC and a second low temperature maximum was observed in v00, located at TP. The position of the TP maximum shifts to higher temperaturewhen the frequency increases. The relation between the relaxation time and TP was well describedby the Vogel–Fulcher law. When the susceptibility was measured withHDC = 20 kOe, the PM–FiM transition was observed in both systems. Remarkably, in the noninteracting 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.