Search NASA⌕ Search

Engineering topics

Roschewsky, Niklas

Publications and source records attributed to Roschewsky, Niklas.

5 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Spin-orbit torque and Nernst effect in Bi-Sb/Co heterostructures

Here, harmonic measurements of the longitudinal and transverse voltages in Bi-Sb/Co bilayers are presented. A large second harmonic voltage signal due to the ordinary Nernst effect is observed. In experiments where a magnetic field is rotated in the film plane, the ordinary Nernst effect shows the same angular dependence in the transverse voltage as the damping-like spin-orbit torque and in the longitudinal voltage as the unidirectional spin-Hall magnetoresistance, respectively. Therefore, the ordinary Nernst effect can be a spurious signal in spin-orbit torque measurements, leading to an overestimation of the spin-Hall angle and spin-Hall conductivity in topological insulators.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Perpendicular magnetic tunnel junction performance under mechanical strain

We investigate effect of the mechanical stress on the performance of magnetic tunnel junctions with perpendicular magnetic anisotropy. We developed a 4-point bending setup that allows us to apply a constant stress over a large substrate area with access to electrical measurements and an external magnetic field. This setup enables us to measure key device performance parameters, such as tunnel magnetoresistance, switching current ( I c 50 % ), and thermal stability (Δ), as a function of applied stress. Finally, we find that variations in these parameters are negligible: less than 2% over the entire measured range between the zero stress condition and the maximum stress at the point of wafer breakage.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Spin-orbit torques in ferrimagnetic GdFeCo alloys

In this work, the spin-orbit torque switching of ferrimagnetic Gd x (Fe 90 Co 10 ) 100-x films was studied for both transition metal (TM)-rich and rare earth (RE)-rich configurations. The spin-orbit torque driven magnetization switching follows the same sense in TM-rich and RE-rich samples with respect to the total magnetization, but the sense of the switching is reversed with respect to the TM magnetization. This indicates that the sign of the spin-orbit-torque-driven magnetic switching follows the total magnetization, although transport based techniques such as anomalous Hall effect are only sensitive to the transition metal magnetization. Finally, these results provide important insight into the physics of spin angular momentum transfer in materials with antiferromagnetically coupled sublattices.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Time resolved spin Seebeck effect experiments

In this Letter, we present the results of transient thermopower experiments, performed at room temperature on yttrium iron garnet/platinum bilayers. Upon application of a time-varying thermal gradient, we observe a characteristic low-pass frequency response of the ensuing thermopower voltage with cutoff frequencies of up to 37 MHz. We interpret our results in terms of the spin Seebeck effect, and argue that small wavevector magnons are of minor importance for the spin Seebeck effect in our thin film hybrid structures.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗