[16p-D61-1~13] 10.2 Fundamental and exploratory device technologies for spin

4:00 PM - 4:15 PM JST(7:00 AM - 7:15 AM UTC)Presentation by Applicant for JSAP Young Scientists Presentation AwardEnglish Presentation

[16p-D61-11] Thickness dependence of the anomalous Nernst effect in Co thin films studied by local laser heating

〇Soichiro Mochizuki¹, Itaru Sugiura², Tetsuya Narushima¹, Teruo Ono², Takuya Satoh¹, Kihiro Yamada¹ (1.Tokyo Tech, 2.Kyoto Univ.)

Keywords:

spintronics,spincaloritronics,anomalous Nernst effect

The anomalous Nernst effect (ANE) generates electromotive forces orthogonal to thermal gradients and magnetizations. Whereas the ANE is quantitatively studied using homogeneous thermal gradients prepared by heaters, local heating by laser irradiations is mainly used to visualize local magnetizations through the ANE. In this research, we would like to demonstrate the usefulness and limitations of local heating by laser irradiations for the quantitative study of the ANE. Here, we report the thickness dependence of ANE induced by laser irradiation in Co thin films with various thicknesses. Because the laser intensity exponentially decays within tens of nanometers, the thickness dependence is suitable for testing the method’s effectiveness. We fabricated magnetic bilayers with structures of Ru(5 nm)/ Co(t) (t = 3, 5, 7, 10, 20, 40, 60 nm) on sapphire (0001) substrates at room temperature by dc sputtering. These magnetic thin films were processed to Hall devices with a size of 0.4 mm × 0.4 mm by a standard photolithography technique. A green continuous wave laser beam was focused with a radius of 15 μm on the center of the Hall cross to create the thermal gradient in the thickness direction. The laser intensity was set at 70 mW and modulated at 85 kHz. We measured laser-induced electric voltages orthogonal to an in-plane magnetic field of ±800 Oe. Furthermore, thermal gradients were simulated using a finite element method with COMSOL Multiphysics equipped with the wave optics module. The peak amplitude of the calculated anomalous Nernst coefficient (Q_ANE) is 0.015 μV/(K・T). The calculated values of Q_ANE are of the same order of magnitude as those in a quantitative previous study using homogeneous thermal gradients. In this presentation, we would like to show more experimental details and discuss the results.