Interfacial magneto-plasticity in partially oxidized magnetite inferred from linear and nonlinear dielectric response

Abstract

In partially oxidized polycrystalline magnetite, defects/dislocations are formed at the grain/interphase boundaries among the remaining magnetite and oxidized phases. Here, the studied sample is a pellet with the composition of Fe3O4 and α-Fe2O3(3:7), which is obtained by annealing partially air-oxidized polycrystalline Fe3O4. To probe the dislocation behavior in it under the magnetic field, linear and nonlinear dielectric spectroscopy has been utilized under three conditions: before applying the magnetic field, under a magnetic field after cooling at the same field, and after removing the magnetic field. An excessive qualitative and quantitative difference between the dielectric data—both linear and nonlinear harmonic components—taken in the first two protocols has been observed. The dielectric data feature remains like the field-cooled measurement after magnetic field withdrawal. In the field-cooled dielectric frequency spectrum, grain boundary relaxation shows a glass transition above 110 K. This phenomenon occurs mainly due to the plastic deformation through the dislocation movements at the boundaries by the magnetostrictive strain produced in the magnetite grains below the Verwey transition (TV). The dislocations freeze into a glassy phase below the TV of magnetite. The interaction among the dislocations and the boundaries are responsible for showing the nonlinear features.