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Voltage Controlled Magnetism: Towards an Ultralow-Power Switch for New Magnetic Devices

G. Beach and H. Tuller

Figure: Left. Magneto-ionic device containing a nanometer-thick magnetic cobalt (Co) layer and a gadolinium-oxide (GdOx) layer. Voltage applied to the top gold (Au) gate electrode pushes oxygen ions (O2-) in the oxide layer either towards or away from the Co layer depending on the voltage polarity. The magnetic properties of the Co layer are controlled by the amount of oxygen at the interface. Right. Cross-sectional TEM image of gated structure, with inset showing in-situ electrical probe attached to top gate. This experiment allowed (for the first time) direct in-situ observation of ion migration across the layered structure.

MIT MRSEC researchers have discovered a new class of materials in which magnetism can be controlled electrically by using a small gate voltage. The poles of a ferromagnet tend to align along a preferred axis, a fact exploited in all magnetic memory devices. In a nanometer-thick ferromagnet/oxide sandwich structure, this axis depends sensitively on the degree to which the magnetic atoms at the interface are oxidized. This work shows that in cobalt/gadolinium-oxide bilayers, an applied voltage can move oxygen at the interface, controlling not just the magnet’s orientation, but the very existence of magnetism itself. This discovery amounts to an ultralow-power switch for magnetic bits, and gives fundamental insight into material properties at interfaces. More broadly, since many electrical, optical, and thermal properties derive from interface chemistry and structure, this work provides a path towards designing “voltage-programmable materials” in which these properties can be toggled in solid-state devices.

U. Bauer, et al., Nature Mater. 14, 174 (2015)

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