Invited Paper MI+MG-TuA3
Voltage-controlled Exchange Bias and Exchange Bias Training

Tuesday, November 11, 2014, 3:00 pm, Room 311

Voltage-controlled exchange bias (EB) is a seminal achievement in nanomagnetism. It enables dissipationless electric control of interface magnetic states with major implications for room temperature spintronic applications. Numerous prototypical solid-state spintronic devices rely on switchable interface magnetism, enabling spin-selective transmission or scattering of electrons. Controlling magnetism at thin-film interfaces, preferably by purely electrical means, i.e. in the absence of electric currents, is a key challenge to better spintronics. Currently, most attempts to voltage-control magnetism focus on potentially large magnetoelectric (ME) effects of multiferroics.

Here, we report on the use of antiferromagnetic (AF) ME Cr₂O₃ (chromia) for voltage-controlled magnetism [1,2]. Electrically switchable boundary magnetization (BM) can overcome the weak linear ME susceptibility of room temperature bulk ME antiferromagnets. BM is a roughness insensitive equilibrium property of ME antiferromagnets which is in sharp contrast to the surface magnetic properties of conventional antiferromagnets. Voltage-controlled BM is the key property enabling isothermal voltage-controlled switching of exchange bias (EB) which emerges at the interface of adjacent ferromagnetic (FM) and the ME antiferromagnetic (AF) thin film. The inter-layer exchange alters the magnetization reversal shifting the FM hysteresis loop along the magnetic field axis. In this presentation I introduce voltage-control of EB and EB training [2]. Electric switching between stable EB fields is investigated in heterostructures based on single crystal Cr₂O₃(0001)/PdCo heterostructures and compared with recent results in MBE grown all thin film EB heterostructures. In addition to voltage-switching of EB we electrically and isothermally tune chromia into distinct AF multi-domain states. As a result, EB training, which originates from triggered rearrangements of the AF interface magnetization during consecutively cycled hysteresis loops, is tuned between zero and sizable effects. We quantify and interpret the peculiar voltage-controlled training effect in Cr₂O₃(0001)/PdCo by adapting our recently developed theory which is based on a discretized Landau-Khalatnikov dynamic equation [3].

We acknowledge the Center for NanoFerroic Devices, C-SPIN, part of STARnet, a SRC program sponsored by MARCO and DARPA for partial funding of this work.

[1] Xi He, Yi Wang, N. Wu, A. N. Caruso, E. Vescovo., K. D. Belashchenko, P. A. Dowben, and Ch. Binek, Nature Mater. 9, 579 (2010).

[2] W. Echtenkmap, Ch. Binek, Phys. Rev. Lett. 111, 187204 (2013).

[3] Ch. Binek, et al., Phys. Rev. Lett. 96, 067201 (2006).