Condensed-Matter Physics & Materials Science Seminar

"Imaging and Electric Control of Boundary Magnetization in Chromia and Chromia-based Exchange Bias Heterostructures"

Presented by Xi He, University of Nebraska

Tuesday, December 6, 2011, 11:00 am — Bldg. 480 conference room

Controlling magnetism and information encoded in magnetic bits has been playing a vital role in information technology. Controlling magnetism via voltage other than current is the key to reduce power consumption while enhancing processing speed, integration density and functionality in comparison with present-day complementary metal-oxide-semiconductor electronics technology. Promising spintronic device concepts utilize the electric control of interface and surface magnetization. Symmetry arguments require the magnetoelectric antiferromagnet Cr2O3 (0001) has a surface magnetization which is coupled with the bulk antiferromagnetic order parameter. Macroscopic evidences from integral methods include magneto optical Kerr and superconducting quantum device magnetometry, spin-polarized photoemission spectroscopy, and first-principles calculations [1]. Moreover, microscopic spatial resolved evidences of electrically controlled magnetization domains are observed by magnetic force microscopy and photoemission electron microscopy combined with X-ray magnetic circular dichroism contrast [2]. This unique surface magnetization is coupled to the bulk antiferromagnetic domain state. Therefor reversing the electric field while maintaining a permanent magnetic field switches the bulk antiferromagnetic domain state thus reverses the surface magnetization coupled to it. Using a perpendicular ferromagnetic Pd/Co multilayer deposited on the (0001) surface of a Cr2O3 single crystal to form a Cr2O3 based exchange bias heterostructure, this unique electrically controlled surface magnetization functions as the pinning layer. By electrically controlling the pinning layer, we achieve reversible, isothermal electrically switching of the exchange-bias field between positive and negative values at room temperature [1]. This approach offers a promising new route to voltage-controlled spintronic devices, such as non-volatile magnetoelectric memory, which may be viewed as an alternative to other a

Hosted by: Ivan Bozovic

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