Abstract
A major barrier to the development of spin-based electronics is the transition from current-driven spin torque, or magnetic-field-driven magnetization reversal, to a more scalable voltage-driven magnetization reversal. To achieve this, multiferroic materials appear attractive, however the effects in current materials occur at very large voltages or at low temperatures. Here the potential of a new class of hybrid multiferroic materials is described, consisting of a topological insulator adjacent to a magnetic insulator, for which an applied electric field reorients the magnetization. As these materials lack conducting states at the chemical potential in their bulk, no dissipative charge currents flow in the bulk. Surface states at the interface, if present, produce effects similar to surface recombination currents in bipolar devices, but can be passivated using magnetic doping. Even without conducting states at the chemical potential, for a topological insulator there is a finite spin Hall conductivity provided by filled bands below the chemical potential. Spin accumulation at the interface with the magnetic insulator provides a torque on the magnetization. Properly timed voltage pulses can thus reorient the magnetic moment with only the flow of charge current required in the leads to establish the voltage. If the topological insulator is sufficiently thick the resulting low capacitance requires little charge current.
Highlights
Topological insulators[1,2] exhibit peculiar bulk transport properties, which can be harnessed to produce unique spin-accumulation properties when a voltage is applied to the material
The focus of recent research has been mostly on the surface states that exist at the interface between a topological insulator and a trivial insulator, the bulk transport properties exist independently of that surface, and correspond to coherent transport of spin across the material, in response to a voltage, due to the evolution properties of the entire full band under the effect of an electric field.[3]
In analogy to a multiferroic material, in which an applied electric field can generate a reorientation of the bulk magnetization, for these hybrid topological insulator/magnetic insulator structures an electric field applied to the topological insulator generates a reorientation of the magnetic insulator’s magnetization
Summary
Topological insulators[1,2] exhibit peculiar bulk transport properties, which can be harnessed to produce unique spin-accumulation properties when a voltage is applied to the material. In analogy to a multiferroic material, in which an applied electric field can generate a reorientation of the bulk magnetization, for these hybrid topological insulator/magnetic insulator structures an electric field applied to the topological insulator generates a reorientation of the magnetic insulator’s magnetization. This hybrid material can be described as a special type of hybrid multiferroic. 100 GHz can be achieved for currently-known material properties
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