NER: Spin Injector for Nanomagnetics and Spintronics Research

AbstractThis建议是在响应纳米科学和工程倡议，计划征求NSF 01-157，在NER类别。 该提案侧重于一类独特的金属-半导体异质结构的开发和表征，这可能会导致自旋注入器的生产。 具体而言，问题在于表征纳米磁性和自旋电子材料界面的自旋输运和散射的性质。 随着人们对各种潜在的混合结构的研究，需要能够探测半导体、铁磁体、非磁性金属和绝缘体之间的界面的自旋相关的传输特性是至关重要的。我们的目标是制造和表征一种结构，通过提供一种易于控制的自旋极化电子源，使人们能够询问自旋相关的传输特性。 该器件使用圆偏振光激发GaAs中的自旋相关载流子，并采用Ag薄膜量子阱自旋过滤器来选择热电子的能量。 然后，这种可选择的自旋极化电子的能量源形成了随后磁性结构生长的衬底。 我们将利用在这种自旋注入器上生长的Co薄膜的空少数态作为分析器来表征自旋极化的程度。 当改变GaAs的掺杂提供了一个粗略的能量选择时，明智地选择Ag的厚度提供了一个通过相关Ag量子阱态的能量微调这些电子的能量。我们的计划是演示，改进和校准这个设备，包括在解理的GaAs（110）和GaAs（100）晶片上生长量子稳定的Ag膜。 我们已经表明，这些银膜表现出量子阱态，它们将被用来进一步的自旋极化电子的能量过滤。 要分析这些电子的自旋极化，我们willepitaxially生长Co的Ag/GaAs结构和校准自旋相关的运输到空的少数状态带，无论是作为一个函数的电子从GaAs的极化，以及themagnetization的Co。未来的扩展包括纳入一个Al 2 O3绝缘屏障，以测试在实际的自旋隧道设备的操作。 在整个研究计划中，重点将放在nanophaseheterostructures的原子/形态和电子特性与随之而来的自旋依赖电导的相关性上。 这种结构提供了一种廉价的工具来询问自旋输运性质，并提供了一种替代自旋极化光电发射和逆光电发射。 一旦校准，它可以用来快速评估先进材料，如半金属薄膜的自旋相关的输运性质。 此外，它可以直接用于提供有价值的数据，自旋相关的散射过程，发生在自旋电子结构的界面。

AbstractThis proposal was received in response to the Nanoscale Science andEngineering Initiative, Program Solicitation NSF 01-157, in the NERcategory. The proposal focuses on the development and characterization ofone unique class of metal-semiconductor heterostructures, which potentiallywill result in production of a spin injector. Specifically, problems existin characterizing the nature of spin transport and scattering through theinterfaces of nanomagnetic and spintronic materials. As one considersvarious potential hybrid structures, the need to be able to probe thespin-dependent transmission properties of the interfaces betweensemiconductors, ferromagnets, non-magnetic metals, and insulators becomescritical.Our objective is to fabricate and characterize a structure that will allowone to interrogate the spin-dependent transmission properties by providingan easily-controlled source of spin-polarized electrons. The device usescircularly-polarized light to excite spin-dependent carriers within GaAs,and incorporates a Ag thin-film quantum-well spin-filter to energy selectthe hot electrons. This source of energy-selectable spin-polarizedelectrons then forms the substrate for the subsequent growth of magneticstructures. We will characterize the degree of spin-polarization by usingthe empty minority states of a Co film grown on this spin injector as ananalyzer. While changing the doping of the GaAs provides a coarse energyselection, judicious choice of the Ag thickness provides a fine-tuning ofthe energy of these electrons via the energetics of the relevant Agquantum-well state.Our plan to demonstrate, refine, and calibrate this device involves thegrowth of quantum-stabilized Ag films on cleaved GaAs(110) and on GaAs(100)wafers. We have already shown that these Ag films exhibit quantum-wellstates and they will be used to further energy-filter the spin-polarizedelectrons. To analyze the spin-polarization of these electrons, we willepitaxially grow Co on the Ag/GaAs structure and calibrate thespin-dependent transport into the empty minority-state bands, both as afunction of the polarization of the electrons from GaAs as well as themagnetization of the Co. Future extensions include the incorporation of anAl2O3 insulating barrier to test the operation in practical spin-tunnelingdevices. Throughout the research plan, emphasis will be placed oncorrelating atomic/morphological and electronic properties of nanophaseheterostructures with ensuing spin-dependent conductance.This project impacts the field of magnetics in several ways. Thisstructure provides an inexpensive tool to interrogate spin transportproperties and provides an alternative to spin-polarized photoemission andinverse photoemission. Once calibrated, it can be used to quickly evaluatethe spin-dependent transport properties of advanced materials such ashalf-metallic thin-films. Furthermore, it can be used in a direct mannerto provide valuable data on the spin-dependent scattering processes thatoccur at the interfaces of spintronic structures.