4 research outputs found
Spin-current amplification by stimulated spin pumping
Stimulated emission is a process during which an atomic system gives away
energy to create a coherent photon. It is fundamental to the operation of the
optical amplifier. Here we propose two mechanisms for amplifying AC spin
currents in a solid-state magnetic medium by a stimulated spin pumping process.
The first is synchronous and consists of phase-locked pulses that perturb a
precessing magnetic moment. The second is asynchronous and is driven by DC spin
currents. The amplification relies on a non-adiabatic interaction taking place
in a ferromagnetic medium in which the magnetic moment emits spin angular
momentum in the form of spin current before equilibrating with the environment.
The pumped spin current amplifies or absorbs the injected AC spin current
mimicking the operation of the optical gain medium as readily seen from the
gain saturation profiles. The mechanisms we propose are a first step towards a
realistic spin current amplifier.Comment: 17 pages, 4 figure
The Ferris ferromagnetic resonance technique: principles and applications
Measurements of ferromagnetic resonance (FMR) are pivotal to modern magnetism
and spintronics. Recently, we reported on the Ferris FMR technique, which
relies on large-amplitude modulation of the externally applied magnetic field.
It was shown to benefit from high sensitivity while being broadband. The Ferris
FMR also expanded the resonance linewidth such that the sensitivity to spin
currents was enhanced as well. Eventually, the spin Hall angle ({\theta}_SH)
was measurable even in wafer-level measurements that require low current
densities to reduce the Joule heating. Despite the various advantages, analysis
of the Ferris FMR response is limited to numerical modeling where the linewidth
depends on multiple factors such as the field modulation profile and the
magnetization saturation. Here, we describe in detail the basic principles of
operation of the Ferris FMR and discuss its applicability and engineering
considerations. We demonstrated these principles in a measurement of the
orbital Hall effect taking place in Cu, using an Au layer as the orbital to
spin current converter. This illustrates the potential of the Ferris FMR for
the future development of spintronics technology
Efficient generation of spin currents by the Orbital Hall effect in pure Cu and Al and their measurement by a Ferris-wheel ferromagnetic resonance technique at the wafer level
We present a new ferromagnetic resonance (FMR) method that we term the Ferris
FMR. It is wideband, has significantly higher sensitivity as compared to
conventional FMR systems, and measures the absorption line rather than its
derivative. It is based on large-amplitude modulation of the externally applied
magnetic field that effectively magnifies signatures of the spin-transfer
torque making its measurement possible even at the wafer-level. Using the
Ferris FMR, we report on the generation of spin currents from the orbital Hall
effect taking place in pure Cu and Al. To this end, we use the spin-orbit
coupling of a thin Pt layer introduced at the interface that converts the
orbital current to a measurable spin current. While Cu reveals a large
effective spin Hall angle exceeding that of Pt, Al possesses an orbital Hall
effect of opposite polarity in agreement with the theoretical predictions. Our
results demonstrate additional spin- and orbit- functionality for two important
metals in the semiconductor industry beyond their primary use as interconnects
with all the advantages in power, scaling, and cost