University of Groningen physicists have developed a method to control the direction of electron spins in devices. By being able to conrol the spin, they open the way to produce efficient and low-cost spintronic electrodes, with potential applications to magnetic random access memories under industrial development. The results were published on 29 August 2018 in the journal Nano Letters.
Spin currents are the basis of spintronics, a field that promises faster and energy-efficient electronics. A method to electrically inject spin current is the spin Hall effect, but this has so far relied on expensive heavy metals like platinum. Moreover, the direction of the spins generated via the spin Hall effect is fixed, generally pointing in-the-plane on the material. Last year, researchers at the University of Groningen and at the University of Manchester have discovered an efficient way of electrical spin injection and detection, which they call the anomalous spin Hall effect.
Kumar Sourav Das, the first author of both the 2017 and the new Nano Letters paper says: "This anomaous spin Hall effect refers to the spin current generated within a ferromagnet, with the spins aligned along the direction of its magnetization. Therefore, this effect has a distinct advantage over the spin Hall effect since the direction of the spins can be controlled by manipulating the magnetization of the ferromagnet." Using this technique, the researchers have achieved the electrical injection and detection of spins oriented in the out-of-plane direction, flowing perpendicular to the direction of the charge current, which is highly significant spin-torque based devices.
The discovery was realised by using nanowires of a common ferromagnetic metal (permalloy) as the spin injector and detector electrodes, and an insulating magnetic material (yttrium iron garnet) for transport via 'spin waves' with minimum energy losses. "The anomalous spin Hall effect in permalloy leads to a high spin injection efficiency, comparable to that of platinum. This work enables future spin logic operations and opens up the possibility to utilize a variety of ferromagnets as efficient and low-cost spintronic electrodes, with potential applications to magnetic random access memories under industrial development", says Kumar.
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