[5a-C18-1~12] 10.1 Emerging materials in spintronics and magnetics (including fabrication and charactrization methodologies)

▲ [5a-C18-12] Anomalous Nernst Effect in Co_x(MgO)_1-x Composite Films

〇Peng Sheng^1,2, Masaki Mizuguchi^1,2,3 (1.Institute for Materials Research, Tohoku University, 2.CREST, Japan Science and Technology Agency, 3.Center for Spintronics Research Network, Tohoku University)

Keywords:anomalous Nernst effect, granular thin film

Many researches in spin caloritronics have been reported, since the discovery of the spin Seebeck
effect. Important roles of anomalous Nernst effect (ANE) in spin caloritronics regarding not only
physical aspect but also application to thermoelectric devices are now recognized [1-3]. ANE is the
thermal analogue of anomalous Hall effect (AHE). So far ANE in metallic multilayers attracts a lot
of interest due to the enhancement of ANE. On the other hand, giant AHE is observed in
ferromagnetic-insulator (FM-I) granular films, such as Fe_1−x(SiO₂)_x and (Co₂FeSi)_x(Al₂O₃)_1-x. In
strongly disordered systems such as granular films, the mechanisms of longitudinal and anomalous
Hall transports are not simple. To understand ANE in nano-systems further, it is interesting to
investigate ANE in FM-I nano-composite films. Here we systematically study the electrical and
thermal transport properties in Co_x(MgO)_1-x composite films with Co volume fractions (x) changes.
The films with different x were fabricated by co-sputtering method on MgO substrates at RT by
changing the sputtering powers for Co and MgO targets. Thickness of all the films is 100 nm. In the
electrical measurement, the longitudinal (R_xx) and transverse resistance (R_xy) decrease with
increasing x. In addition, the AHE angle (ρ_xy/ρ_xx) increases with x increases, it shows maximum
value for pure Co film. On the other hand, for the thermal measurement, the longitudinal (Seebeck)
voltage and transverse (ANE) voltage increase with increasing x. Interestingly, ANE angle (S_xy/S_xx)
nonmonotonically changes with x increases. It shows maximum value when large amount of Co is
included in MgO matrix, which is 1.9 times larger than that of pure Co. It manifests that ANE angle
can be significant enhanced in Co_x(MgO)_1-x films compared with pure Co.
Acknowledgements
This work was supported by JST CREST Grant Number JPMJCR1524, Japan. We would like to
thank H. Sharma, T. Seki, and K. Takanashi for their help in experiments.
References
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Express 5, 093002 (2012).
[2] Y. Sakuraba, K. Hasegawa, M. Mizuguchi1, T. Kubota, S. Mizukami, T. Miyazaki, and K.
Takanashi, Appl. Phys. Express 6, 033003 (2013).
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Miyazaki, and K. Takanashi, Appl. Phys. Lett. 106, 252405 (2015).