Local charge and spin currents in magnetothermal landscapes

Abstract: A scannable laser beam is used to generate local thermal gradients in metallic (Co2FeAl) or insulating (Y3Fe5O12) ferromagnetic thin films. We study the resulting local charge and spin currents that arise due to the anomalous Nernst effect (ANE) and the spin Seebeck effect (SSE), respectively. In the local ANE experiments, we detect the voltage in the Co2FeAl thin film plane as a function of the laser spot position and external magnetic field magnitude and orientation. The local SSE effect is detected in a similar fashion by exploiting the inverse spin Hall effect in a Pt layer deposited on top of the Y3Fe5O12. Our findings establish local thermal spin and charge current generation as well as spin caloritronic domain imaging.

Local Charge and Spin Currents in Magnetothermal Landscapes

The study conducted by Weiler et al., centers on the utilization of a laser-based approach to generate local thermal gradients in ferromagnetic thin films, specifically metallic Co$_2$FeAl and insulating Y$_3$Fe$_5$O$_{12}$ (YIG), to probe spin caloritronic effects. The findings of this research hold significance in the fields of spintronics and thermoelectrics, offering insights into the spatial resolution of charge and spin current phenomena.

Methodology

The experimental procedure involves using a laser beam to create localized thermal gradients by heating the sample surface. This controllable thermal landscape enables the study of the anomalous Nernst effect (ANE) in conductive ferromagnets and the spin Seebeck effect (SSE) in ferromagnetic insulators. The Co$_2$FeAl thin films exhibited the ANE, resulting in measurable voltages due to the cross product of magnetization and the temperature gradient. In contrast, spin currents induced by the SSE in YIG were detected as electric fields in an adjacent platinum layer via the inverse spin Hall effect (ISHE).

Results

One significant discovery is that both the anomalous Nernst effect and the spin Seebeck effect display identical symmetry properties with respect to magnetization and thermal gradient vectors, an observation validated through spatially resolved electric field measurements. In the Co$_2$FeAl samples, the researchers demonstrated domain imaging enabled by the detection of ANE-induced voltages, which correspond to specific magnetization patterns. The investigation of YIG/Pt samples further confirmed the presence of spin currents, which were detected by the ISHE in the platinum layer.

The experiments notably revealed that the thermal gradients in ferromagnetic thin films are capable of generating localized electric fields or pure spin currents. This demonstration underlines the potential for these effects to be utilized together with electric readouts to image magnetic microstructures spatially.

Implications and Future Directions

The implications of this study are profound for both applied and theoretical spintronics. The capacity to generate and detect local charge and spin currents lays a foundation for future devices that leverage such phenomena for enhanced data storage, magnetic sensing, and energy conversion. The spatial control and detection of spin currents provide a powerful tool for probing magnetic textures and could potentially lead to advancements in memory devices with resolutions reaching the micro and nanoscale.

Given the parallels drawn between the ANE and SSE in their symmetry and behavior, future research could expand these findings into a broader range of materials, enhancing understanding and capability in spin caloritronics. Additionally, further quantification of coefficients such as the Nernst and spin Seebeck coefficients in various materials will provide deeper insight into the efficiency and technological applicability of these effects.

In conclusion, Weiler et al.'s study offers a rigorous and detailed exploration into the fundamentals of spin caloritronics through the application of local thermal gradients. By establishing a direct relationship between thermal manipulations and observable electric and spin phenomena, this work deepens our understanding of the interplay between spin, charge, and thermal properties in chalcogenide and oxide systems.