Особенности импульсного перемагничивания высококоэрцитивного материала на основе наночастиц ε-Fe-=SUB=-2-=/SUB=-O-=SUB=-3-=/SUB=-

Abstract

The magnetic structure of the polymorphic modification of iron oxide ε-Fe2O3 is collinear ferrimagnetic in the range from room temperature to ~ 150 K. Further, with decreasing a temperature in ε-Fe2O3, a magnetic transition occurs, accompanied by a significant decrease in the coercive force HC, and in the low temperature range ε-Fe2O3 is characterized by a complex incommensurate magnetic structure. In this work, we experimentally investigated the processes of dynamic magnetization reversal of ε-Fe2O3 nanoparticles of an average size of 8 nm in the temperature range of 80–300 K, comprising various types of magnetic structure of this iron oxide. A bulk material was studied - xerogel SiO2 with ε Fe2O3 nanoparticles embedded in pores. To measure the magnetic hysteresis loops under dynamic magnetization reversal, a pulsed magnetic field technique of Hmax up to 130 kOe was used, using the method of discharging a capacitor bank through a solenoid. The coercive force of HC during dynamic magnetization reversal noticeably exceeds HC for quasi-static conditions. This is caused by processes of superparamagnetic relaxation of the magnetic moments of particles during pulsed magnetization reversal. In the range from room temperature to ~ 150 K, the rate of change of the external field dH / dt is the main parameter determining the behavior of the coercive force under the conditions of dynamic magnetization reversal. This behavior is expected for a system of single-domain ferro- and ferrimagnetic particles. Under external conditions (at a temperature of 80 K), when the magnetic structure of ε Fe2O3 is incommensurate, the coercive force during pulsed magnetization reversal already depends on the parameter dH / dt, and is largely determined by the maximum applied field Hmax. Such a behavior, atypical for systems of ferrimagnetic particles, is already caused by dynamic spin processes inside ε-Fe2O3 particles during fast magnetization reversal.