LAUSR

Mapping out the magneto-Seebeck coefficient In the Seebeck effect, a temperature difference across a device generates voltage. If the thermal gradient is imposed across a magnetic tunnel junction—with two magnetized layers separated by an insulating tunnel barrier—the magnitude of the generated voltage depends on the relative orientation of the magnetization in the two layers. Transport measurements of this so-called magneto-Seebeck tunneling typically reveal only the signal averaged over the device. Friesen et al. created an atomic-scale version of this experiment by using a scanning tunneling microscope with a spin-polarized tip that they scanned across the surface of a magnetic sample. By heating the tip, they were able to map out the spatial dependence of the spin-resolved Seebeck coefficient. Science, this issue p. 1065 A heated, spin-polarized tip of a scanning tunneling microscope is used to map out the spin-resolved Seebeck coefficient. The tunneling of spin-polarized electrons across a magnetic tunnel junction driven by a temperature gradient is a fundamental process for the thermal control of electron spin transport. We experimentally investigated the atomic-scale details of this magneto-Seebeck tunneling by placing a magnetic probe tip in close proximity to a magnetic sample at cryogenic temperature, with a vacuum as the tunneling barrier. Heating the tip and measuring the thermopower of the junction while scanning across the spin texture of the sample lead to spin-resolved Seebeck coefficients that can be mapped at atomic-scale lateral resolution. We propose a spin detector for spintronics applications that is driven solely by waste heat, using magneto-Seebeck tunneling to convert spin information into a voltage that can be used for further data processing.