arXiv subjects

Viktor Lauer

Publications and source records attributed to Viktor Lauer.

5 recordsLinked to original sources

arXiv2018

Spin Seebeck effect and ballistic transport of quasi-acoustic magnons in room-temperature yttrium iron garnet films

We studied the transient behavior of the spin current generated by the longitudinal spin Seebeck effect (LSSE) in a set of platinum-coated yttrium iron garnet (YIG) films of different thicknesses. The LSSE was induced by means of pulsed microwave heating of the Pt layer and the spin currents were measured electrically using the inverse spin Hall effect in the same layer. We demonstrate that the time evolution of the LSSE is determined by the evolution of the thermal gradient triggering the flux of thermal magnons in the vicinity of the YIG/Pt interface. These magnons move ballistically within the YIG film with a constant group velocity, while their number decays exponentially within an effective propagation length. The ballistic flight of the magnons with energies above 20K is a result of their almost linear dispersion law, similar to that of acoustic phonons. By fitting the time-dependent LSSE signal for different film thicknesses varying by almost an order of magnitude, we found that the effective propagation length is practically independent of the YIG film thickness. We consider this fact as strong support of a ballistic transport scenario - the ballistic propagation of quasi-acoustic magnons in room temperature YIG.

cond-mat.mes-hall↗

arXiv2016

Temporal evolution of auto-oscillations in a YIG/Pt microdisc driven by pulsed spin Hall effect-induced spin-transfer torque

The temporal evolution of pulsed Spin Hall Effect - Spin Transfer Torque (SHE-STT) driven auto-oscillations in a Yttrium Iron Garnet (YIG) / platinum (Pt) microdisc is studied experimentally using time-resolved Brillouin Light Scattering (BLS) spectroscopy. It is demonstrated that the frequency of the auto-oscillations is different in the center and at the edge of the investigated disc that is related to the simultaneous STT excitation of a bullet and a non-localized spin-wave mode. Furthermore, the magnetization precession intensity is found to saturate on a time scale of 20 ns or longer, depending on the current density. For this reason, our findings suggest that a proper ratio between the current and the pulse duration is of crucial importance for future STT-based devices.

cond-mat.mes-hall↗

arXiv2015

Sign of inverse spin Hall voltages generated by ferromagnetic resonance and temperature gradients in yttrium iron garnet|platinum bilayers

We carried out a concerted effort to determine the absolute sign of the inverse spin Hall effect voltage generated by spin currents injected into a normal metal. We focus on yttrium iron garnet (YIG)|platinum bilayers at room temperature, generating spin currents by microwaves and temperature gradients. We find consistent results for different samples and measurement setups that agree with theory. We suggest a right-hand-rule to define a positive spin Hall angle corresponding to with the voltage expected for the simple case of scattering of free electrons from repulsive Coulomb charges.

cond-mat.mtrl-sci↗

arXiv2014

Microwave-induced spin currents in ferromagnetic-insulator|normal-metal bilayer system

A microwave technique is employed to simultaneously examine the spin pumping and the spin Seebeck effect processes in a YIG|Pt bilayer system. The experimental results show that for these two processes, the spin current flows in opposite directions. The temporal dynamics of the longitudinal spin Seebeck effect exhibits that the effect depends on the diffusion of bulk thermal-magnons in the thermal gradient in the ferromagnetic-insulator|normal-metal system.

cond-mat.mes-hall↗

arXiv2013

Optimizing the spin-pumping induced inverse spin Hall voltage by crystal growth in Fe/Pt bilayers

We examine the influence of crystal growth on the spin-pumping induced inverse spin Hall effect in Fe/Pt bilayers. The morphology of the Fe/Pt interface influences the effective spin mixing conductance. The increase of growth temperature leads to smoother and larger grains at the interface that enhance the effective spin mixing conductance. The spin current injection efficiency into Pt, measured by the inverse spin Hall effect, is maximized by optimizing the epitaxy of Pt on Fe. In magnetic field dependent measurements, the presence of a strong magnetic anisotropy gives rise to two distinct inverse spin Hall effect voltage peaks.

cond-mat.mtrl-sci↗