An exotic kind of magnetic behavior, driven by the mere proximity of two materials, has been analyzed by a team of researchers at MIT and elsewhere using a technique called spin-polarized neutron reflectometry. They say the new finding could be used to probe a variety of exotic physical phenomena, and could ultimately be used to produce key components of future quantum computers.
The novel phenomenon occurs at the boundary between a ferromagnet and a type of material called a topological insulator, which blocks electricity from flowing through all of its bulk but whose surface is, by contrast, a very good electrical conductor.
Now, a layer of topological insulator material is bonded to a ferromagnetic layer. Where the two materials meet, an effect takes place called proximity-driven magnetic order, producing a localized and controllable magnetic pattern at the interface.
The research is described in a paper appearing this week in the journal Physical Review Letters.
This “proximity magnetism” effect could create an energy gap, a necessary feature for transistors, in a topological insulator, making it possible to turn a device off and on as a potential building block for spintronics. “However, the proximity effect is usually weak,” without the use of a magnetic topological insulator “to enhance it and lock new magnetic order near the interface.”
One of the new findings of this research is that the magnetism induced by the proximity of the two materials is not just at the surface, but actually extends into the interior of the topological insulator material.
Possible applications of the new findings include the creation of spintronics, transistors based on the spin of particles rather than their charge. These are expected to have low energy dissipation if based on topological insulators, and are a very active area of research.
Because the interface produces a channel with virtually no dissipation, it can act as “a perfect quantum wire”. “It cannot be better than that for a quantum conductance channel. So having this precise control of the magnetic structure could lead to novel quantum spintronics.”
