Exchange bias in epitaxial Fe/Ir0.2Mn0.8 bilayers grown on MgO (001)
Exchange bias in epitaxial Fe/Ir0.2Mn0.8 bilayers grown on MgO (001)
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DOI：
10.1088/0022-3727/42/22/225001
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发表时间：
2009-11-21
影响因子：
3.4
通讯作者：
Ward, R. C. C.
中科院分区：
文献类型：
--
作者：
Wang, S. G.;Kohn, A.;Ward, R. C. C.
研究了在MgO（0 0 1）衬底上用分子束外延生长的Fe/Ir 0.2 Mn 0.8（IrMn）双层膜的交换偏置。IrMn层具有化学无序的fcc结构，其外延关系为MgO（0 0 1）[1 1 0]//Fe（0 0 1）[1 0 0]//IrMn（0 0 1）[1 1 0]。在该系统中，通过沿着bcc Fe [1 0 0]易磁化轴施加小磁场H-A，在室温下生长过程中诱导交换偏置，而无需后退火。交换偏置场和沿Fe [1 0 0]易磁化轴的磁化率沿着的温度依赖性，测量到大约一半的Neel温度，显示出这些参数随温度的增加呈指数衰减。作为沿沿着Fe [1 0 0]易磁化轴施加的磁场的函数而测量的磁化导致负移位的磁滞回线，这对于交换偏置是典型的，而当磁场沿沿着Fe [0 1 0]易磁化轴（垂直于H-A）施加时，观察到对称的双移位回线。在这两种情况下，磁化反转通过两个连续的事件发生，涉及磁矩彼此垂直的畴的成核和传播。我们证明，由于IrMn层的外延生长，由交换偏置引起的单向各向异性与Fe易轴方向之一对齐，并且实际上，被添加到Fe层的四倍立方各向异性。
Exchange bias has been studied in epitaxial Fe/Ir0.2Mn0.8 (IrMn) bilayers grown by molecular beam epitaxy on MgO (0 0 1) substrates. The IrMn layer has a chemically disordered fcc structure with an epitaxial relationship of MgO(0 0 1)[1 1 0]//Fe(0 0 1)[1 0 0]//IrMn(0 0 1) [1 1 0]. In this system, exchange bias is induced during growth at room temperature without post-annealing, by applying a small magnetic field, H-A, along the bcc Fe [1 0 0] easy axis. The temperature dependence of the exchange bias field and the coercivity along the Fe [1 0 0] easy axis, measured up to approximately half the Neel temperature, shows an exponential decay of these parameters with increasing temperature. The magnetization measured as a function of applied field along the Fe [1 0 0] easy axis results in a negatively shifted hysteresis loop, typical for exchange bias, while when the magnetic field is applied along the Fe [0 1 0] easy axis (perpendicular to H-A), a symmetric double-shifted loop is observed. In both cases, the magnetization reversal occurs through two successive events involving nucleation and propagation of domains in which the magnetic moments are perpendicular to each other. We demonstrate that due to the epitaxial growth of the IrMn layer, the unidirectional anisotropy induced by exchange bias is aligned with one of the Fe easy axis directions and, in effect, is added to the four-fold cubic anisotropy of the Fe layer.