General Regularities and Differences in the Behavior of the Dynamic Magnetization Switching of Ferrimagnetic (CoFe 2 O 4
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General Regularities and Differences in the Behavior of the Dynamic Magnetization Switching of Ferrimagnetic (CoFe2O4) and Antiferromagnetic (NiO) Nanoparticles S. I. Popkova, b, *, A. A. Krasikova, S. V. Semenova, b, A. A. Dubrovskiia, S. S. Yakushkinc, V. L. Kirillovc, O. N. Mart’yanovc, and D. A. Balaeva, b a Kirensky
Institute of Physics, Krasnoyarsk Scientific Center, Siberian Branch, Russian Academy of Sciences, Krasnoyarsk, 660036 Russia b Siberian Federal University, Krasnoyarsk, 660041 Russia c Boreskov Institute of Catalisis, Siberian Branch, Russian Academy of Sciences, Novosibirsk, 630090 Russia *e-mail: [email protected] Received March 26, 2020; revised March 26, 2020; accepted April 2, 2020
Abstract—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: CoFe2O4 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 HC at the dynamic magnetization switching is markedly higher than HC at quasi-static conditions. HC increases as the pulse duration τP decreases and the maximum applied field H0 increases. The dependence of HC on field variation rate dH/dt = H0/2τP is a unambiguous function for CoFe2O4 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 H0 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. Keywords: CoFe2O4 nanoparticles, antiferromagnetic NiO nanoparticles, dynamic magnetization switching, coercive force DOI: 10.1134/S1063783420090255
1. INTRODUCTION Interest in magnetic nanoparticles is caused by an expansion of the area of their possible applying in practice and also by the fundamental problems related to the influence of surface and size effects on their magnetic characteristics. One of significant manifestations of surface and size effects is the formation of additional (besides the main) magnetic subsystems in nanoparticles. Here, first, we bear in mind the subsystem of surface spins [1–3] that can demon
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