Giant Electrically Controlled Spinterface in Organic Ferroelectric Copolymer-based Multiferroic Tunnel Junctions

Controlling spin of electron by purely electrical means at high temperature is challenging and a long sought device in spintronics. In this APL (110, 053302, 2018), we report electrically controlled interfacial spin polarization, or the magnetoelectric effect in multiferroic tunnel junctions (MTJs) by employing organic ferroelectric copolymers, poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)), as a tunneling barrier. First, we show that the spontaneous ferroelectric polarization of the P(VDF-TrFE) films can be formed in a thin interlayer. Next, the tunneling magnetoresistance in the unpolarized TMJ quenches from 21% at 20 K to 0.7% at 296 K. Remarkably, the interfacial spin polarization of the device, dubbed spinterface, can be gradually tuned by an applied electric field. Upon the electric polarization reversal, the tunneling electroresistance reaches about 30% at 200 K and the spinterface of the device significantly changes up to 1000%. The interface between P(VDF-TrFE) and Co electrode might act as an electric-field-dependent spin filter causing the large magnetoelectric effect. The resistance of the MTJs can be controlled by either electric field or magnetic field, and therefore can potentially be used as a high density information storage element with four states.