Continued efforts toward both fundamental knowledge and application of spintronics rely on improved materials for converting spin to charge and vice-versa. We recently demonstrated that the longitudinal spin Seebeck effect (LSSE) 1 shows large spin-charge conversion and large spin Seebeck voltages of thermally-evaporated chromium thin films relative to sputtered platinum at room temperature. However, determining the exact nature and control of thermal gradients in LSSE experiments is imperative, especially at the interface 2,3. In this work, we adopt the Hall bar geometry and current-driven heating 4,5 for LSSE experiments in a vacuum cryostat for better manipulation of thermal gradients. In figure 1, we show the LSSE signal for a 10 nm thin film of chromium (Cr) and 10 nm sputtered platinum (Pt) thin film both grown on a polycrystalline yttrium iron garnet (YIG) substrate under the same experimental conditions using Peltier devices to establish a thermal gradient external to the sample. Figure 2 shows the local LSSE signal for a 10 nm Cr and 25 nm Pt Hall bar utilizing a local heating method via Joule heating in a controlled vacuum cryostat environment. The high resistance of the evaporated Cr leads to very large local LSSE voltages, indicating this easily prepared film holds promise for probing thermally generated spin current phenomena in a range of magnetic insulators.
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