Abstract

The ferromagnetic resonance (FMR) experiment is pivotal for detecting spin currents in
Spintronics technology. It occurs on Gigahertz timescales due the relatively slow relaxation time
of the spins in ferromagnets. In contrast, optical fields oscillate much faster, at ∼ 400 − 800 THz.
Therefore, it seems unlikely that such fast-oscillating fields may interact with magnetic
moments. However, by combining principles from quantum optics and quantum computation, we
have recently realized that the equations governing the FMR experiment are even relevant to
magnetic fields that oscillate at much faster optical frequencies. Namely, the interaction between
optical beams and the magnetization is made possible. We find that the strength of the interaction
is determined by an elementary efficiency parameter , where is the amplitude of the optical
magnetic field, is the dissipation rate of spin angular momentum to the lattice, and and are the
optical frequency and gyromagnetic ratio. Our results can explain a variety of highly debated
experimental observations on the interactions between optical fields and ferromagnets that have
been reported in the last 25 years.

Short Bio

Assistant Prof. Amir Capua heads the Spintronics Lab at the Institute of Electrical Engineering
and Applied Physics at the Hebrew University of Jerusalem, Israel. Amir received his Ph.D.
(2013) from the Electrical Engineering Department at the Technion, Israel where he worked in
the fields of semiconductor laser physics and quantum optics. In 2013 Amir joined the
Spintronics research group at the IBM Almaden Research Labs in California managed by Prof.
Stuart Parkin and in 2016 he joined the Max Planck Institute for Microstructure Physics,
Germany. Since 2017 Amir heads the Spintronics Lab at the Hebrew University. His team
explores spin transport and magnetization dynamics for novel sensing, processing, and memory
applications.