Voltage Control of Magnetization and Its Chemical Properties

Magnetization control using an electric field [1] will be useful because of its expected ultra-low power consumption and coherent behavior. Several experimental approaches to realize it have been done using ferromagnetic semiconductors [2], materials with magnetostriction together with piezo-driver [3], multiferroic materials [4], ferromagnetic metal films sintered in a liquid electrolyte [5], and ultra-thin ferromagnetic layer in solid-state junctions[6-8].

One of the critical issues in the electric field switching is a realization of bi-stable switching. Since the electric field does not break time reversal symmetry, it does not remove degeneracy of two magnetic states with opposite magnetization. Therefore, a selection of an arbitral magnetic state is not straightforward [9]. Here, we demonstrate a realization of the bi-stable switching using a coherent precessional magnetization toggle switching in nanoscale magnetic cells with a few atomic FeCo (001) epitaxial layers adjacent to MgO barrier [10].

The control of the magnetization by voltage requires well controlled interface structure. We have investigated chemical states of the ferromagnetic atoms at interface with MgO using XAS and XMCD, and found several problems that may happen at the interfaces in voltage devices, i.e. segregation [11] and voltage controlled reversible oxidization/reduction [12]. We discuss the significance of those effects and the intrinsic effect.

 References:

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