School of Electrical and Computer Engineering, Purdue University, West Lafayette, IN 47907, USA.
J Phys Condens Matter. 2010 Jun 2;22(21):216002. doi: 10.1088/0953-8984/22/21/216002. Epub 2010 Apr 30.
It is well known that the Curie temperature, and hence the magnetization, in diluted magnetic semiconductors (DMS) like Ga(1-x)Mn(x)As can be controlled by changing the equilibrium density of holes in the material. Here, we propose that even with a constant hole density, large changes in the magnetization can be obtained with a relatively small imbalance in the quasi-Fermi levels for up-spin and down-spin electrons. We show, by coupling the mean field theory of diluted magnetic semiconductor ferromagnetism with master equations governing the Mn spin-dynamics, that a mere splitting of the up-spin and down-spin quasi-Fermi levels by 0.1 meV will produce the effect of an external magnetic field as large as 1 T as long as the alternative relaxation paths for Mn spins (i.e. spin-lattice relaxation) can be neglected. The physics is similar to the classic Overhauser effect, also called the dynamic nuclear polarization, with the Mn impurities playing the role of the nucleus. We propose that a lateral spin-valve structure in an anti-parallel configuration with a DMS as the channel can be used to demonstrate this effect, as quasi-Fermi level splitting of such magnitude, inside the channel of similar systems, has already been experimentally demonstrated to produce polarization of paramagnetic impurity spins.
众所周知，在像 Ga(1-x)Mn(x)As 这样的稀磁半导体 (DMS) 中，可以通过改变材料中的平衡空穴密度来控制居里温度和磁化强度。在这里，我们提出，即使空穴密度保持不变，通过 quasi-Fermi 能级对于上自旋和下自旋电子的微小不平衡，也可以获得较大的磁化强度变化。通过将稀磁半导体铁磁体的平均场理论与控制 Mn 自旋动力学的主方程耦合，我们表明，只要可以忽略 Mn 自旋的替代弛豫途径（即自旋晶格弛豫），仅仅通过将上自旋和下自旋 quasi-Fermi 能级分裂 0.1 meV，就可以产生与 1 T 相当大的外部磁场的效果。这种物理现象类似于经典的 Overhauser 效应，也称为动态核极化，其中 Mn 杂质扮演核的角色。我们提出，在反平行配置的横向自旋阀结构中，以 DMS 作为沟道，可以用来证明这种效应，因为在类似系统的沟道中已经实验证明了如此大的 quasi-Fermi 能级分裂会产生顺磁杂质自旋的极化。
