EuS/SrS、EuS/PbSe和EuS/PbTe磁性半导体超晶格中的层间耦合
Interlayer coupling in EuS/SrS, EuS/PbSe and EuS/PbTe magnetic semiconductor superlatices
摘要：
对EuS/SrS、EuS/PbSe和EuS/PbTe全半导体超晶格进行了中子反射率研究，以寻找交换层间耦合。在EuS/SrS和EuS/PbSe体系中发现了较弱的反铁磁耦合，而在EuS/PbTe超晶格中没有发现层间耦合。在EuS/SrS中，其中SrS间隔物是绝缘体（$E_g\approx 4$ eV），非常弱且短程的层间耦合与早期的理论预测一致，即在EuS基磁性半导体超晶格中的层间耦合强度强烈地取决于掺杂层的能隙，并且应该随着间隔物材料的能隙的增加而减小。EuS/PbSe中的弱耦合和EuS/PbTe中的无耦合，其中PbSe和PbTe都是窄隙半导体（$E_g\approx 0.3$ eV），不仅与理论预期不一致，而且与另一个窄隙间隔物系统EuS/PbS的早期结果形成鲜明对比，其中即使在PbS层厚度高达200 μ m的样品中也存在明显的反铁磁耦合。EuS和间隔物材料之间的晶格失配（PbS、SrS、PbSe和PbTe分别为0.5%、0.8%、2.5%和8.2%）的增加对EuS层的磁面内有序性以及因此对层间耦合的可能影响通过极化中子反射法在EuS/PbTe的情况下进行了研究。
英文摘要：
Neutron reflectivity studies of EuS/SrS, EuS/PbSe, and EuS/PbTe all-semiconductor superlattices were carried out in search for exchange interlayer coupling. A relatively weak antiferromagnetic coupling was found in EuS/SrS and in EuS/PbSe systems but no interlayer coupling was detected in EuS/PbTe superlattices. In EuS/SrS, where the SrS spacer is an insulator ($E_g\approx 4$ eV), a very weak and short range interlayer coupling is in agreement with the earlier theoretical predictions that the interlayer coupling strength in EuS-based magnetic semiconductor superlattices depends strongly on the energy gap of the nonmagnetic layer and should decrease with an increase of the energy gap of the spacer material. A weak coupling in EuS/PbSe and no coupling in EuS/PbTe, where both PbSe and PbTe are narrow-gap semiconductors ($E_g\approx 0.3$ eV), is in disagreement not only with the theoretical expectations but also in a stark contrast with earlier results for another narrow-gap spacer system -- EuS/PbS, where pronounced antiferromagnetic coupling persists even in samples with PbS layer thickness as large as 200 Å. A possible influence of the increasing lattice mismatch between EuS and the spacer materials (0.5%, 0.8%, 2.5%, and 8.2% for PbS, SrS, PbSe, and PbTe, respectively) on the magnetic in-plane ordering of EuS layer and, consequently, on the interlayer coupling was investigated by polarized neutron reflectometry in the case of EuS/PbTe.
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