Voltage-controlled Switching of Boundary Magnetization: A Fundamental Phenomenon with Potential Application in Ultra-low Power Spintronics
Voltage-controlled magnetization switching at surfaces, interfaces or boundaries in layered heterostructures enables dissipationless control of remnant magnetic states. It paves the way towards scalable, ultra-low power, and non-volatile spintronics. We exploit electrically switchable boundary magnetization (BM) of the magnetoelectric (ME) antiferromagnet chromia and its Boron doped high-TN counterpart. Quantum mechanical exchange at the interface between a ferromagnetic (FM) CoPd thin film of perpendicular anisotropy and BM at the (0001) surface of chromia enables voltage-controlled exchange bias (VCEB), i.e., electrically shifting of the FM hysteresis along the magnetic field axis [1,2,3]. Similarly, we investigate VC switching of induced magnetization in nonmagnetic metals (NM) with high Stoner susceptibility . Polar Kerr and anomalous Hall effect are employed to measure magnetization induced by the exchange field of the BM exerted on NMs. VC switching of induced magnetization can overcome problems associated with the energy-delay constraints accompanying reversal of magnetization in ferromagnets . In both chromia/FM and chromia/NM hetero-layers, different forms of switchable magnetization serve as non-volatile state variable enabling ultra-low power 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, and present our latest results on VCEB and VCBM in patterned thin films with reference to applications. In addition, I introduce a tabletop magneto-optical method to measure electric field induced Faraday rotation in ME antiferromagnets, switching of the antiferromagnetic order parameter and the accompanying BM .
We acknowledge support by NERC, a wholly-owned subsidiary of SRC, through CNFD, an SRC-NRI Center under Task IDs 2398.001 and 2587.001, by C-SPIN, one of six centers of STARnet, a SRC program, sponsored by MARCO and DARPA, and by NSF through MRSEC DMR-1420645. Research was performed in part in the NNF supported by the NSF under Award NNCI: 1542182.
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