Voltage-controlled Exchange Bias: A Building Block for Ultra-low Power Memory and Logic Device Applications
Voltage-controlled exchange bias (VCEB) enables dissipationless control of interface magnetic states thus paving the way towards ultra-low power, non-volatile spintronics. We exploit quantum mechanical exchange between a ferromagnetic (FM) CoPd thin film and the electrically switchable boundary magnetization (BM) of the magnetoelectric (ME) antiferromagnet chromia to enable VCEB, i.e., electrically shifting the FM hysteresis along the magnetic field axis. The switchable remnant magnetization serves as non-volatile state variable in memory and logic devices. I report on the challenging realization of VCEB in all thin film geometry and the role of BM as a key element to overcome limitations due to the weak linear ME susceptibility of bulk chromia. I introduce voltage-switchable BM and VCEB, provide experimental evidence, present our latest results on VCEB in patterned thin films with reference to applications, and introduce a tabletop method to measure switching of the antiferromagnetic order parameter in chromia. The figure shows a cartoon of our magneto-optical method. It utilizes dispersion of the electric field-induced Faraday rotation in ME antiferromagnets to measure magnitude and sign of the order parameter and its coupling with BM.