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Investigating magnetic excitation-induced spin current in chromium trihalides

Investigating magnetic excitation-induced spin current in chromium trihalides
Credit: Tokyo Tech

A nifty little approach toward developing low-power, high-speed, and high-density memory devices is founded on spintronics, an emerging frontier in technology that harnesses a qualification of freedom of electrons referred to as spin. Quite simply, electrons, with their negative charge, have a very spin whose orientation could be controlled using magnetic fields. That is particularly relevant for magnetic insulators, where the electrons cannot maneuver around, however the spin remains controllable. In these materials, the magnetic excitations can provide rise to a spin current, which forms the foundation of spintronics.

Scientists have already been searching for efficient solutions to generate the spin current. The photogalvanic effect, a phenomenon seen as a the generation of DC current from light illumination, is specially useful in this regard. Studies have discovered a photogalvanic spin current could be generated similarly utilizing the magnetic fields in electromagnetic waves. However, we currently lack candidate materials and an over-all mathematical formulation for exploring this phenomenon.

Now, Associate Professor Hiroaki Ishizuka from Tokyo Institute of Technology (Tokyo Tech), together with his colleague, has addressed these issues. Within their recent study published in Physical Review Letters, they presented an over-all formula which you can use to calculate the photogalvanic spin current induced by transverse oscillating magnetic excitations. Then they used this formula to comprehend how photogalvanic spin currents arise in bilayer chromium (Cr) trihalide compounds, namely chromium triiodide (CrI3) and chromium tribromide (CrBr3).

“Unlike past studies that considered longitudinal oscillating magnetic fields for generating spin currents, our study targets transverse oscillating magnetic fields. Predicated on this, we discovered that processes involving one magnon (quantum of spin wave excitations) band in addition to two magnon bands donate to the spin current,” elaborates Dr. Ishizuka.

Utilizing their formula, the duo discovered that both CrI3 and CrBr3 showed a big photogalvanic spin current for magnetic excitations corresponding to at gigahertz and terahertz frequencies. However, the existing only appeared once the spins showed antiferromagnetic ordering, meaning successive spins were anti-parallel, instead of ferromagnetic ordering (where successive spins are parallel).

Moreover, the spin current direction was governed by the orientation of the antiferromagnetic ordering (if the spins on the initial and second layers were arranged up-down or down-up). Additionally, they remarked that, unlike previous findings that attributed the spin current to only the two-magnon process, their formula showed a large response was, generally, possible with the single magnon process.

These results claim that bilayer CrI3 and CrBr3 are strong candidates for investigating the mechanism connected with photogalvanic spin current generation.

“Our study not merely predicts unforeseen contributions to the but additionally offers a guideline for the look of novel materials driven by the photogalvanic aftereffect of ,” says Dr. Ishizuka.

More info: Hiroaki Ishizuka et al, Large Photogalvanic Spin Current by Magnetic Resonance in Bilayer Cr Trihalides, Physical Review Letters (2022). DOI: 10.1103/PhysRevLett.129.107201

Citation: Investigating magnetic excitation-induced spin current in chromium trihalides (2022, September 2) retrieved 3 September 2022 from

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