利用磁近邻效应进一步提高(Ga,Mn)As的居里温度

Ferromagnetic semiconductors combine the properties of both the ferromagnetic metals and semiconductors. Since the successful demonstration of ferromagnetism in (Ga,Mn)As, (Ga,Mn)As has served as a model material in which to explore new magnetic semiconducors as well as to test concepts for spintronic applications of the III-V group in the past decade. Up to now, the highest Curie temperature (Tc) is 200 K, still below the room temperature, which made this material limited to the laboratory use.Can we increase the Tc further? Both theoretical and experimental researchers are interested in this question and it needs to be answered immediately. The p-d Zener model predicted that Tc of (Ga,Mn)As can be raised to room temperature with increasing both magnetic dopant concentration and carrier density, so most laboratories in the world start from these two points to increase Tc. However, few considers how to increase the p-d exchange integral between the hole and localized Mn.In view of this point, in this project application, we want to further increase the Tc of (Ga,Mn)As in ferromagnetic metal/(Ga,Mn)As bilayers by proximity effect.The true nature of proximity effect is the d-d interaction between ferromanetic metal and Mn ions, which can keep the spin polarization of Mn in (Ga,Mn)As even above Tc.This project application is to utilize this effect to raise the Tc of (Ga,Mn)As above 200 K or even to room temperature.

磁性半导体同时兼具铁磁金属和半导体的性质，不论是在磁性半导体材料探索还是在半导体自旋电子器件研发中，(Ga,Mn)As已被当做磁性半导体家族中的样板材料。但是由于居里温度（Tc）还低于室温（目前最高纪录为200 K），所以严重限制了走向实际应用。是否能够继续提高Tc？不论对于理论还是实验研究者，这都是一个亟待回答的问题。由于Tc正比于有效Mn含量和空穴浓度，所以大多数实验室都从这两个方面入手，却很少考虑如何提高空穴与局域Mn离子的交换相互作用强度。有鉴于此，本申请项目旨在磁性金属/(Ga,Mn)As异质结构中，利用磁性金属与(Ga,Mn)As层的近邻效应，进一步提高(Ga,Mn)As的Tc。所谓磁近邻效应是指铁磁金属与局域Mn离子存在d-d相互作用，可以使(Ga,Mn)As中Mn离子自旋在Tc以上仍保持铁磁有序。本项目旨在利用该效应，将(Ga,Mn)As的Tc提高到200 K以上甚至室温。

磁性半导体(Ga,Mn)As结合了半导体和磁性材料的优势，阻碍(Ga,Mn)As走向实际应用的最大瓶颈在于其最高居里温度仍只有200K左右。本项目旨在利用铁磁金属/(Ga,Mn)As的磁近邻效应进一步提高(Ga,Mn)As的居里温度。我们利用了X射线磁圆二色谱（XMCD），直接磁性测量以及磁输运测量研究了Co2FeAl/(Ga,Mn)As和Fe/(Ga,Mn)As两种异质结构的磁近邻效应。XMCD 测量表明Co2FeAl/(Ga,Mn)As界面处(Ga,Mn)As在400 K时仍保持自旋极化；磁性及磁输运测量表明Fe/(Ga,Mn)As结构中，磁近邻效应使(Ga,Mn)As的居里温度升高。我们的研究表明，利用磁近邻效应可能继续提高基于(Ga,Mn)As的自旋电子器件的工作温度。