Benassi Andrea, Marioni Miguel A, Passerone Daniele, Hug Hans J
Empa, Swiss Federal Laboratories for Materials Science and Technology, CH-8600 Dübendorf, Switzerland.
1] Empa, Swiss Federal Laboratories for Materials Science and Technology, CH-8600 Dübendorf, Switzerland [2] Department of Physics, Universität Basel, CH-4056 Basel, Switzerland.
Sci Rep. 2014 Mar 28;4:4508. doi: 10.1038/srep04508.
Models of exchange-bias in thin films have been able to describe various aspects of this technologically relevant effect. Through appropriate choices of free parameters the modelled hysteresis loops adequately match experiment, and typical domain structures can be simulated. However, the use of these parameters, notably the coupling strength between the systems' ferromagnetic (F) and antiferromagnetic (AF) layers, obscures conclusions about their influence on the magnetization reversal processes. Here we develop a 2D phase-field model of the magnetization process in exchange-biased CoO/(Co/Pt)×n that incorporates the 10 nm-resolved measured local biasing characteristics of the antiferromagnet. Just three interrelated parameters set to measured physical quantities of the ferromagnet and the measured density of uncompensated spins thus suffice to match the experiment in microscopic and macroscopic detail. We use the model to study changes in bias and coercivity caused by different distributions of pinned uncompensated spins of the antiferromagnet, in application-relevant situations where domain wall motion dominates the ferromagnetic reversal. We show the excess coercivity can arise solely from inhomogeneity in the density of biasing- and anti-biasing pinned uncompensated spins in the antiferromagnet. Counter to conventional wisdom, irreversible processes in the latter are not essential.
薄膜中的交换偏置模型已经能够描述这种与技术相关效应的各个方面。通过对自由参数的适当选择，所模拟的磁滞回线能很好地与实验匹配，并且可以模拟典型的磁畴结构。然而，这些参数的使用，特别是系统中铁磁（F）层和反铁磁（AF）层之间的耦合强度，模糊了关于它们对磁化反转过程影响的结论。在此，我们开发了一种用于交换偏置的CoO/(Co/Pt)×n磁化过程的二维相场模型，该模型纳入了反铁磁体10纳米分辨率的测量局部偏置特性。仅将三个相互关联的参数设置为铁磁体的测量物理量和测量的未补偿自旋密度，就足以在微观和宏观细节上与实验匹配。我们使用该模型研究在与应用相关的情况下，即畴壁运动主导铁磁反转时，反铁磁体中固定未补偿自旋的不同分布所引起的偏置和矫顽力变化。我们表明，额外的矫顽力可能仅源于反铁磁体中偏置和反偏置固定未补偿自旋密度的不均匀性。与传统观点相反，后者中的不可逆过程并非必不可少。
