General regularities and differences in the behavior of the dynamic magnetization switching of ferrimagnetic (CoFe$_2$O$_4$) and antiferromagnetic (NiO) nanoparticles

In antiferromagnetic (AFM) nanoparticles, an additional ferromagnetic phase forms and leads to the appearance in AFM nanoparticles of a noncompensated magnetic moment and the magnetic properties typical of common FM nanoparticles. In this work, to reveal the regularities and differences of the dynamic magnetization switching in FM and AFM nanoparticles, the typical representatives of such materials are studied: CoFe$_2$O$_4$ and NiO nanoparticles with average sizes 6 and 8 nm, respectively. The high fields of the irreversible behavior of the magnetizations of these samples determine the necessity of using strong pulsed fields (amplitude to 130 kOe) to eliminate the effect of the partial hysteresis loop when studying the dynamic magnetic hysteresis. For both types of the samples, coercive force $H_C$ at the dynamic magnetization switching is markedly higher than $H_C$ at quasi-static conditions. $H_C$ increases as the pulse duration $\tau_P$ decreases and the maximum applied field $H_0$ increases. The dependence of $H_C$ on field variation rate $dH/dt=H_{0}/2\tau_{P}$ is a unambiguous function for CoFe$_2$O$_4$ nanoparticles, and it is precisely such a behavior is expected from a system of single-domain FM nanoparticles. At the same time, for AFM NiO nanoparticles, the coercive force is no longer an unambiguous function of $dH/dt$, and the value of applied field $H_0$ influences more substantially. Such a difference in the behaviors of FM and AFM nanoparticles is caused by the interaction of the FM subsystem and the AFM “core” inside AFM nanoparticles. This circumstance should be taken into account when developing the theory of dynamic hysteresis of the AFM nanoparticles and also to take into account their practical application.