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 H_C at the dynamic magnetization switching is markedly higher than H_C at quasi-static conditions. H_C increases as the pulse duration τ_P decreases and the maximum applied field H₀ increases. The dependence of H_C on field variation rate dH/dt = H₀/2τ_P 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.

中文翻译：

---

亚铁磁性（CoFe 2 O 4）和反铁磁性（NiO）纳米粒子的动态磁化转换行为的一般规律和差异

摘要

在反铁磁（AFM）纳米粒子中，会形成额外的铁磁相，并导致AFM纳米粒子中出现未补偿的磁矩和常见FM纳米粒子典型的磁性。在这项工作中，为了揭示FM和AFM纳米粒子中动态磁化转换的规律和差异，研究了此类材料的典型代表：CoFe ₂ O ₄和平均尺寸分​​别为6和8 nm的NiO纳米颗粒。这些样品的磁化强度不可逆行为的高磁场决定了在研究动态磁滞现象时必须使用强脉冲场（振幅至130 kOe）来消除部分磁滞回线的影响。对于这两种类型的样品，动态磁化切换时的矫顽力H _C明显高于准静态条件下的H _C。ħ _Ç随着脉冲持续时间τ _P减小，并且最大施加场ħ ₀增加。H _C对场变化率dH的依赖性/ DT = ħ ₀ /2τ _P是由CoFe一个明确的函数₂ ø _4个纳米颗粒，并且它是从单域FM纳米颗粒的系统精确地这样的行为的预期。同时，对于AFM NiO纳米粒子，矫顽力不再是dH / dt的明确函数，而施加场的值H ₀影响更大。FM和AFM纳米粒子行为上的这种差异是由于FM子系统与AFM纳米粒子内部的AFM“核心”的相互作用引起的。在开发AFM纳米粒子的动态磁滞理论时，应考虑这种情况，并考虑其实际应用。