Anomalous Nernst effect in Co thin films under laser irradiation

TL;DR

This study demonstrates a laser irradiation method combined with finite-element analysis to quantify the anomalous Nernst effect in Co thin films, revealing larger localized temperature gradients and consistent ANE coefficients compared to traditional heating methods.

Contribution

The paper introduces a novel laser-based approach for measuring the ANE coefficient, enabling the creation of large, localized temperature gradients and improving quantification accuracy.

Findings

Laser irradiation produces ac temperature gradients up to 10^3 K/mm.

Estimated ANE coefficients align with previous reports and heater-based measurements.

Laser method offers advantages over conventional heating in localized thermoelectric studies.

Abstract

The anomalous Nernst effect (ANE) generates electromotive forces transverse to temperature gradients and has attracted much attention for potential applications into alternative thermoelectric power generators. ANE efficiency is generally characterized by uniform temperature gradients in a steady state prepared by heaters. However, although focusing laser beams on a magnetic film can form much larger temperature gradients, the laser-irradiation method has not been sufficiently considered for quantifying the ANE coefficient due to the difficulty in estimating the localized in-homogeneous temperature gradients. In this study, we present a quantitative study of ANE in Ru(5 nm)/Co($t_{\mathrm{Co}}$) ($t_{\mathrm{Co}}$ = 3, 5, 7, 10, 20, 40, and 60 nm) bilayers on sapphire (0001) substrates by combining a laser irradiation approach with finite-element analysis of temperature gradients under laser excitation. We find that the estimated ANE coefficients are consistent with previously reported values and one independently characterized using a heater. Our results also reveal the advantages of the laser irradiation method over the conventional method using heaters. Intensity-modulated laser beams can create ac temperature gradients as large as approximately 10$^3$ K/mm at a frequency of tens of kilohertz in a micrometer-scale region.