Enhancement of anomalous Nernst effects in metallic multilayers free from proximity-induced magnetism

Ken-ichi Uchida, Takashi Kikkawa, Takeshi Seki, Takafumi Oyake, Junichiro Shiomi, Zhiyong Qiu, Koki Takanashi, and Eiji Saitoh

Phys. Rev. B 92, 094414 – Published 10 September 2015

Abstract

The anomalous Nernst effect (ANE) has been investigated in alternately stacked multilayer films comprising paramagnetic and ferromagnetic metals. We found that the ANE is enhanced by increasing the number of the paramagnet/ferromagnet interfaces and keeping the total thickness of the films constant, and that the enhancement appears even in the absence of magnetic proximity effects; similar behavior was observed not only in Pt/Fe multilayers but also in Au/Fe and Cu/Fe multilayers free from proximity ferromagnetism. This universal enhancement of the ANE in metallic multilayers suggests the presence of unconventional interface-induced thermoelectric conversion in the Fe films attached to the paramagnets.

Received 26 May 2015
Revised 19 July 2015

DOI:https://doi.org/10.1103/PhysRevB.92.094414

Authors & Affiliations

Ken-ichi Uchida^1,2,*, Takashi Kikkawa^1,3, Takeshi Seki¹, Takafumi Oyake⁴, Junichiro Shiomi⁴, Zhiyong Qiu^3,5, Koki Takanashi¹, and Eiji Saitoh^1,3,5,6

¹Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
²PRESTO, Japan Science and Technology Agency, Saitama 332-0012, Japan
³WPI Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
⁴Department of Mechanical Engineering, The University of Tokyo, Tokyo 113-8656, Japan
⁵Spin Quantum Rectification Project, ERATO, Japan Science and Technology Agency, Sendai 980-8577, Japan
⁶Advanced Science Research Center, Japan Atomic Energy Agency, Tokai 319-1195, Japan

^*kuchida@imr.tohoku.ac.jp

Article Text (Subscription Required)

Click to Expand

References (Subscription Required)

Click to Expand

Issue

Vol. 92, Iss. 9 — 1 September 2015

Reuse & Permissions

Access Options

Author publication services for translation and copyediting assistance advertisement

Images

Figure 1
Schematic illustrations of the LSSE in the Pt/YIG junction (a) and the ANE in the IM configuration in the Pt/Fe multilayer sample formed on the GGG substrate (b). $\nabla T, M, J_{s}, E_{ISHE}$ , and $E_{ANE}$ denote the temperature gradient, magnetization vector, spatial direction of the thermally generated spin current, electric field induced by the ISHE, and electric field induced by the ANE, respectively. Red areas in the Pt layers schematically illustrate proximity-induced ferromagnetic regions.
Reuse & Permissions
Figure 2
(a), (b) Schematic illustrations of the Pt/Fe multilayer sample in the (a) IM and (b) PM configurations. $H$ denotes the magnetic field vector with the magnitude of $H$ . During the measurements of the ANE, a uniform external magnetic field was applied by using a superconducting solenoid magnet. (c) The in-plane magnetization curve and the $H$ dependence of the transverse thermopower $S$ for the Pt/Fe multilayer samples for various values of $N$ in the IM configuration. $M$ and $N$ denote the total magnetization (in units of ${kemu / cm}^{3})$ of the Pt/Fe multilayer samples, measured with a vibrating sample magnetometer, and the number of the Pt/Fe interfaces, respectively. The $M$ data were measured by using Pt/Fe multilayer films formed on thermally oxidized silicon substrates since the large paramagnetism of GGG is an obstacle to detect $M$ of the thin films. In the $M − H$ curves, the contributions from the silicon substrates are subtracted. $S_{0}$ is the anomalous component of $S$ , obtained by extrapolating the $S − H$ curve in the high $H$ field range to zero field. (d) The perpendicular magnetization curve and the $H$ dependence of $S$ for the Pt/Fe multilayer samples for various values of $N$ in the PM configuration. (e) $N$ dependence of the total thickness of the Pt/Fe multilayer samples, measured with a surface profiler. (f) $N$ dependence of $M$ . (g) $N$ dependence of the sheet resistance $R_{s}$ of the Pt/Fe multilayer samples in the $y$ direction, measured by a four-probe method.
Reuse & Permissions
Figure 3
(a), (b) $N$ dependence of $S_{0}$ in the Pt/Fe, Au/Fe, and Cu/Fe multilayer samples in the (a) IM and (b) PM configurations. The total thickness of these multilayers is 10 nm. The $S_{0}$ signals in a 10-nm-thick Fe film on the GGG substrate and in 10-nm-thick Pt films on the GGG and YIG substrates are plotted at $N = 0$ . The Cu/Fe multilayer samples are covered with 1-nm-thick Pt films to avoid the oxidation of the top Cu layers. (c), (d) $N$ dependence of $S_{0} / R_{s}$ in the Pt/Fe multilayer, Au/Fe multilayer, Cu/Fe multilayer, Fe/GGG, Pt/GGG, and Pt/YIG samples in the (c) IM and (d) PM configurations.
Reuse & Permissions

Physical Review B

covering condensed matter and materials physics