报告题目：Spin Polarized Tunneling, Spin Filtering and Interface Effects

报 告 人：Jagadeesh S. Moodera，Physics Department and Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology

报告时间：2014年6月4日11:00

报告地点：物理系三楼报告厅

报告摘要：Spin polarized tunneling (SPT) discovered by Robert Meservey and Paul Tedrow, is a powerful method to investigate high field properties of superconductors, spin polarization of tunneling electrons from ferromagnetic metals, ferromagnetic onset etc., has subsequently led to the discovery of tunnel magnetoresistance (TMR) in magnetic tunnel junctions. SPT has been widely explored in recent spintronic studies, whereas the spin filter (SF) tunneling is one of the later developments. SF occurs due to the high selectivity of either spin-up or -down electrons in quantum tunneling through a magnetic barrier, and is a unique way to generate highly spin-polarized tunnel currents using nonmagnetic electrodes. Another important feature of magnetic insulators is to provide a large effective internal exchange field locally confined to an interface, making them especially powerful in modifying adjacent one or two-dimensional electronic structures. For example, in one of our recent studies this phenomenon can be dramatically seen in verifying de Gennes’ decades old theoretical prediction of manipulating superconducting state in FI/S/FI (FI-ferromagnetic insulator; S-superconductor) trilayer structure by the magnetization direction of the two FI layers, thus creating a nonvolatile two-level memory state.

Spin transport in organic semiconductors (OS) has the potential in realizing the goal of information storage and computing at the molecular level in a straightforward way. The charge and spin transport at OS and ferromagnetic metal interface, although complex is one of the richest areas, which has the needed capabilities and potential for achieving molecular level spintronics. Our spin tunneling studies through layers of OS molecules show unexpected exchange coupling induced ferromagnetic and spin filter behavior at the ferromagnet/OS interfaces, showing the future possibility for information storage and manipulation in individual molecules.

In the talk we shall give an overview of these phenomena.