Ultraviolet Raman spectroscopy reveals NiO spin-phonon coupling

Spintronic devices encode information through electrons’ spin instead of their charge. Without the need for electrons to generate current, spintronic devices can be much faster and dissipate less energy than today’s microelectronic devices, fostering considerable interest in this field.

Electron spins in nickel oxide, NiO, are not easily perturbed by an external magnetic field. This and other intrinsic properties of NiO make it an ideal antiferromagnetic material for spintronics. But optimizing the use of this material demands an understanding of its spin-phonon coupling dynamics, which determines how well spin propagates through the material.

In Applied Physics Letters, researchers report the first measurement of NiO spin-phonon coupling using ultraviolet Raman spectroscopy. Conventional Raman is an effective spectroscopic tool for most materials, but doesn’t work with NiO because of optical selection rules. Using an UV laser instead of a visible laser, however, allowed the authors to see how spins interact with NiO’s longitudinal and transverse phonons for the first time. They found that spins affect the two different types of optical phonons oppositely: Spin-phonon coupling decreases the energy of transverse optical phonons and increases energy of longitudinal optical phonons.

Alexander Balandin, one of the work’s authors, said that these results will help to better understand spin properties, as well as design spintronic devices based on NiO that minimize energy dissipation. Knowing how strongly spins affect different types of phonons could also allow tuning of a material so that spins interact more or less with longitudinal or transverse phonons.

Source: “Spin-phonon coupling in antiferromagnetic nickel oxide,” by E. Aytan, B. Debnath, F. Kargar, Y. Barlas, M. M. Lacerda, J. X. Li, R. K. Lake, J. Shi, and A. A. Balandin, Applied Physics Letters (2017). The article can be accessed at https://doi.org/10.1063/1.5009598 .