18 research outputs found
Exchange-enhanced Ultrastrong Magnon-Magnon Coupling in a Compensated Ferrimagnet
The ultrastrong coupling of (quasi-)particles has gained considerable
attention due to its application potential and richness of the underlying
physics. Coupling phenomena arising due to electromagnetic interactions are
well explored. In magnetically ordered systems, the quantum-mechanical
exchange-interaction should furthermore enable a fundamentally different
coupling mechanism. Here, we report the observation of ultrastrong intralayer
exchange-enhanced magnon-magnon coupling in a compensated ferrimagnet. We
experimentally study the spin dynamics in a gadolinium iron garnet single
crystal using broadband ferromagnetic resonance. Close to the ferrimagnetic
compensation temperature, we observe ultrastrong coupling of clockwise and
anticlockwise magnon modes. The magnon-magnon coupling strength reaches more
than 30% of the mode frequency and can be tuned by varying the direction of the
external magnetic field. We theoretically explain the observed phenomenon in
terms of an exchange-enhanced mode-coupling mediated by a weak cubic
anisotropy
Tunable Cooperativity in Coupled Spin--Cavity Systems
We experimentally study the tunability of the cooperativity in coupled
spin--cavity systems by changing the magnetic state of the spin system via an
external control parameter. As model system, we use the skyrmion host material
CuOSeO coupled to a microwave cavity resonator. In the different
magnetic phases we measure a dispersive coupling between the resonator and the
magnon modes and model our results by using the input--output formalism. Our
results show a strong tunability of the normalized coupling rate by magnetic
field, allowing us to change the magnon--photon cooperativity from 1 to 60 at
the phase boundaries of the skyrmion lattice state
High-Throughput Techniques for Measuring the Spin Hall Effect
The spin Hall effect in heavy-metal thin films is routinely used to convert charge currents into transverse spin currents and can be used to exert torque on adjacent ferromagnets. Conversely, the inverse spin Hall effect is frequently used to detect spin currents by charge currents in spintronic devices up to the terahertz frequency range. Numerous techniques to measure the spin Hall effect or its inverse have been introduced, most of which require extensive sample preparation by multistep lithography. To enable rapid screening of materials in terms of charge-to-spin conversion, suitable high-throughput methods for measuring the spin Hall angle are required. Here we compare two lithography-free techniques, terahertz emission spectroscopy and broadband ferromagnetic resonance, with standard harmonic Hall measurements and theoretical predictions using the binary-alloy series AuxPt1−x as a benchmark system. Despite their being highly complementary, we find that all three techniques yield a spin Hall angle with approximately the same x dependence, which is also consistent with first-principles calculations. Quantitative discrepancies are discussed in terms of magnetization orientation and interfacial spin-memory loss