Abstract

The nature of the training effect in exchange-biased compounds is studied. This effect consists in a decrease in the exchange bias field (H_EB) during a cyclic change in the magnetic field. The electrical resistivity training effects in the GdBaCo₂O_{5 + δ} (δ ≈ 0.5) cobaltite, namely, the changes in the electrical resistivity during a cyclic change in the magnetic field (ρ_cycl(N), N is the cycle number) and during sample rotation (ρ_rot(N)), are shown to be analogs of the H_EB training effect. Like H_EB, the electrical resistivity changes sharply after the first cycle (N > 1(2)) and slowly during the next cycles, which is related to a decrease in the magnetization of ferromagnetic particles. These results are explained by the influence of two mechanisms: the magnetization decreases fast in the first mechanism and slowly in the second. The nonequilibrium state and the training effect are assumed to be interrelated and caused by the existence of single-domain ferromagnetic particles of different volumes V and by the dependence of the magnetization relaxation time of the particles on the single-domain (superparamagnetic) particle volume, τ ∝ exp(K_anV/kT), where K_an is the magnetic anisotropy energy density. The nature of the sharp changes in H_EB and the electrical resistivity after the first cycles is caused by the closeness of the small single-domain particle energy (K_anV) to heat energy kT. In this model, the exchange bias disappears (H_EB = 0) during infinite cyclic magnetization reversal.

中文翻译：

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交换偏压的GdBaCo 2 O 5.5钴中的电阻率训练效果

摘要

研究了交换偏置化合物中训练效果的性质。这种影响在于在磁场的周期性变化过程中交换偏置场（H _EB）的减小。GdBaCo ₂ O _{5 +δ}（δ≈0.5）钴矿中的电阻率训练效果，即磁场周期变化中电阻率的变化（_ρCycl（N），N是循环数），以及样品旋转（ρ期间_腐烂（ñ）），被示为的类似物ħ _EB训练效果。像H _EB，电阻率在第一个周期后急剧变化（N > 1（2）），而在下一个周期中变化缓慢，这与铁磁颗粒的磁化强度降低有关。这些结果由两种机理的影响来解释：第一种机理中的磁化强度快速降低，第二种机理中的磁化速率缓慢。假设非平衡状态和训练效果是相互关联的，并且是由于存在不同体积V的单畴铁磁颗粒以及颗粒的磁化弛豫时间对单畴（超顺磁）颗粒体积的依赖性而引起的， τ∝ exp（K _an V / kT），其中K _an是磁各向异性能量密度。在第一周期之后，H _EB和电阻率急剧变化的性质是由小的单畴粒子能量（K _an V）与热能kT的接近引起的。在此模型中，在无限循环磁化反转期间，交换偏置消失（H _EB = 0）。