Effect of thermal treatment on magnetic and dielectric response of SrM hexaferrites obtained by hydrothermal synthesis

Abstract

Electric, dielectric and magnetic properties of SrFe₁₂O₁₉ hexaferrite ceramics obtained from hydrothermally synthesized single-phase nanopowders were studied in wide temperature range. The effect of space charge polarization, related to highly conducting grains with poor conducting grain boundaries, was found to be apparent at high temperatures and at low frequencies. The activation energy of relaxation of the (Fe³⁺–Fe²⁺) dipoles in low conducting grain boundary regions was found to amount to 0.20 eV for non-annealed ceramics and to increase to 0.32 eV after thermal treatment. The temperature and frequency dependences of the dielectric permittivity for non-annealed and annealed SrFe₁₂O₁₉ ceramics were found to be correlated with respective dependences of the electric conductivity. We relate the observed increase in the saturation magnetization after annealing to an increase in coherent spin rotation in greater grains, which are however still below the critical single-domain size.

Keywords:

• strontium M-type hexaferrite ceramics
• hydrothermal synthesis
• electric heterogeneity
• dielectric and electric response
• magnetic properties

Acknowledgments

The authors would like to acknowledge the support from the COST Action MP 0904 ‘Single- and multiphase ferroics and multiferroics with restricted geometries (SIMUFER)’.