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“Optical Detection of Transverse Spin-Seebeck Effect in Permalloy Films using Sagnac Interferometer Microscopy”

The field of spintronics, which involves the design of novel electronic devices that utilize the spin of electrons, requires researchers to develop a robust source of spin-polarized currents to fuel future technology. One promising avenue for a reliable spin-current source is the spin Seebeck effect, where a thermal gradient is used to drive a spin-current in a ferromagnet. We used the magneto-optical Kerr effect (the rotation of polarized light by a magnetic medium) to gain an unprecedented look into the microscopic physics of the spin-Seebeck effect in a permalloy ferromagnet film. The breakthrough required the ultra-high sensitivity of our homebuilt fiber optic Sagnac interferometer, which we adapted into a diffraction-limited confocal microscope in order to spatially map the magnetization change of magnetic thin films with 20 nano-radian angular resolution.