報告題目：Tunneling Magneto-Dielectric (TMD) effect: The discovery and recent advances
報告人： 曹洋 助理教授 (Tohoku University, Japan)
Single-phase and nanocomposite material with multifunctional properties, such as combining both electronic and magnetic properties that is magnetoelectric (ME) effect, holds potential for both fundamental science and device application. Our group recently discovered a new kind of ME effect in insulating granular nanocomposites, wherein superparamagnetic nanoparticles are homogeneously distributed in an insulating matrix. This dielectric enhancement is caused by the charge tunneling through the MgF barrier, whereby the tunneling rate depends on the relative orientation of the magnetic moments between two magnetic granules, i.e., the spin-dependent tunneling. By analogy with tunneling magnetoresistance (TMR) in granular films, we termed the tunneling MD (TMD) effect.
In this presentation, I will revisit the recent advances of this TMD effect. I first clarified how the granular content determined the frequency dependence of the TMD response. The frequency response of the TMD effect was artificially controlled by in-situ insertion of several insulator layers; this verified the important role of granular distribution played in the regulation of TMD response. Second, to improve the low-field TMD response, I fabricated a two-dimensional (2D) granular heterostructures, wherein a new mechanism based on a balanced control of ferromagnetic and super-paramagnetic components has been proposed. The discovery of TMD effect opens a new door for room temperature ME fields.