Magnetoelectric transport properties of quenched polycrystalline magnetite

Abstract

Ultrafine Fe 3O 4 particles were prepared through chemical co-precipitation. Powder compact was sintered and quenched in a controlled CO 2/CO atmosphere to obtain bulk specimen. X-ray diffraction and Mössbauer spectroscopy showed homogeneous polycrystalline Fe 3O 4 phase. The electrical resistance was measured in applied magnetic fields up to 5 T over the temperature range of 55–155 K. The temperature dependence of resistivity showed a semiconductor behavior without discontinuity at Verwey point, while the magnetoresistance (MR) exhibited an extremum in its temperature dependence and correspondingly the magnetization manifested a discontinuous decrease, with temperature decreasing through Verwey point. Meanwhile X-ray diffraction showed no observable structural transition in the range from 77 to 300 K. The results different from those of well-annealed samples are suggested to be attributed to quench related stress and defects. It is proposed that near Verwey point the MR behavior in Fe 3O 4 is not completely determined by the `structural–electronic’ mechanism. Below Verwey temperature T v, MR value increased sharply when temperature decreased. The transport behavior is modeled as an activated mechanism above T v and a variable range hopping mechanism below T v.