Spin-Heat Coupling: Spin Caloritronics

Spatial- and time-resolved magnon spin transport in YIG

Thermal gradients cause heat flow. When the heat is localized in a magnetic solid, it will generate magnetic excitations that carry spin, called magnons, or spin-waves. These hot magnons will then diffuse in the material a characteristic distance before decaying. Magnon spins can be measured using a thin platinum strip in which the magnon spin generates a spin polarization in the metal leading to a voltage due to the inverse spin Hall effect. We can map out the spatial decay of the magnons by measuring the voltage on the platinum strip as a function of distance to the magnon injection site. Using a focused laser magnons are generated due to the local heat pulse and the laser focal point is scanned away from the spin detector. We found very long range magnon spin transport in YIG. The magnon dynamics can also be probed in the time-domain using an oscilloscope and a pulsed laser. Combining knowledge of the thermal transport using finite-element modeling, the complex waveform shape on the oscilloscope can be fitted to extract the magnon spin lifetime. These measurements (non-local and time-resolved spin transport) are therefore useful in probing fundamental transport properties in new magnetic systems. We are probing such measurements in magnetic materials that may host topologically protected magnons and other exotic exchange coupled systems.