High efficiency spin-filtering with Ultra-thin epitaxial ferromagnetic g-Fe₂O₃layer

报告人：Xi-xiang Zhang   教授

Division of Physical Science and Engineering,

King Abdullah University of Science and Technology (KAUST),

Thuwal 23955, Kingdom of Saudi Arabia

E-mail: (xixiang.zhang@kaust.edu.sa)

邀请人：颜世申 教授

报告时间：2017年4月4日 上午9:30

报告地点：知新楼C1111

摘要:

The spin-filtering effect across a ferromagnetic insulating layer originates from an unequal tunneling barrier height, caused by exchange splitting Δ, for spin-up and spin-down electrons that has shown great promise for use in different ferromagnetic materials. However, spin filtering in some materials has proven to have relatively low efficiency, seriously hindering its application. Inadequacies may be ascribed to the difficulty in fabricating high-quality ferromagnetic insulating layers or/and reliably attaining high spin-filter efficiency. Here, we present the spin-filter effect across high-quality g-Fe₂O₃(a ferromagnetic insulator) layers in Nb:SrTiO₃/g-Fe₂O₃/Ti/Au heterostructures. Because it is very difficult to grow high quality g-Fe₂O₃layers using the existing deposition methods, we developed a new technique that involves transforming epitaxial Fe₃O₄ layers onto a g-Fe₂O₃layer through oxidation at elevated temperatures. We also propose a new model based on the Zeeman Effect to more easily and reliably determine spin-filtering efficiency. In optimized samples, we found that spin polarization of the tunneled current can be as high as -94.3%. Our work emphasizes that ferrimagnetic insulator spinel ferrites are very promising materials as candidates for spintronics, particularly for spin injection into semiconductors.