arXiv subjects

Satoshi Sumi

Publications and source records attributed to Satoshi Sumi.

4 recordsLinked to original sources

arXiv2024

Maximizing bipolar sensitivity for anomalous Nernst thermopiles in heat flux sensing in amorphous GdCo alloys

A Heat Flux Sensor (HFS) facilitates the visualization of heat flow, unlike a temperature sensor, and is anticipated to be a key technology in managing waste heat. Recently, an HFS utilizing the Anomalous Nernst Effect (ANE) has been proposed garnering significant interest in enhancing the transverse Seebeck coefficient. However, ideal materials for HFS not only require a large transverse Seebeck coefficient but also meet several criteria including low thermal conductivity and a bipolar nature of the transverse Seebeck coefficient, especially a negative coefficient. In this study, we have investigated ANE in amorphous ferrimagnetic GdCo alloys, revealing their numerous advantages as HFS materials. These include a large transverse Seebeck coefficient, extremely low thermal conductivity, large negative sensitivity, unparalleled bipolar sensitivity, versatility for deposition on various substrates, and a small longitudinal Seebeck coefficient. These qualities position GdCo films as promising candidates for the advancement of HFS technology.

cond-mat.mtrl-sci↗

arXiv2024

Coexistence of large anomalous Nernst effect and large coercive force in amorphous ferrimagnetic TbCo alloy films

The Anomalous Nernst Effect (ANE) has garnered significant interest for practical applications, particularly in energy harvesting and heat flux sensing. For these applications, it is crucial for the module to operate without an external magnetic field, necessitating a combination of a large ANE and a substantial coercive force. However, most materials exhibiting a large ANE typically have a relatively small coercive force. In our research, we have explored the ANE in amorphous ferrimagnetic TbCo alloy films, noting that the coercive force peaks at the magnetization compensation point (MCP). We observed that transverse Seebeck coefficients are amplified with Tb doping, reaching more than 1.0 uV/K over a wide composition range near the MCP, which is three times greater than that of pure Co. Our findings indicate that this enhancement is primarily due to direct conversion, a product of the transverse thermoelectric component and electrical resistivity. TbCo films present several significant advantages for practical use: a large ANE, the capability to exhibit both positive and negative ANE, the flexibility to be deposited on any substrate due to their amorphous nature, a low thermal conductivity, and a large coercive force. These attributes make TbCo films a promising material for advancing ANE-based technologies.

cond-mat.mes-hall↗

arXiv2023

Observation of anisotropic magneto-inductance effect

We have discovered a new phenomenon that inductance oscillates as a function of the angle between an in-plane magnetic field and an electric current direction in permalloy films, which we have named "the anisotropic magneto-inductance (AML) effect". We have investigated the dependences of the AML effect on the size and voltage. The length, frequency, and amplitude dependences suggest that the AML effect should be evaluated in terms of "inductivity". Inductors based on this AML effect have the potential to be variable, on-chip, and one billion times smaller than the small commercial inductor.

cond-mat.mes-hall↗

arXiv2018

Interference induced enhancement of magneto-optical Kerr effect in ultrathin magnetic films

We have studied the magneto-optical spectra of ultrathin magnetic films deposited on Si substrates coated with an oxide layer (SiOx). We find that the Kerr rotation angle and the ellipticity of ~1 nm thick CoFeB thin films, almost transparent to visible light, show a strong dependence on the thickness of the SiOx layer. The Kerr signal from the 1 nm CoFeB thin film can be larger than that of ~100 nm thick CoFeB films for a given SiOx thickness and light wavelength. The enhancement of the Kerr signal occurs when optical interference takes place within the SiOx layer. Interestingly, under such resonance condition, the measured Kerr signal is in some cases larger than the estimation despite the good agreement of the measured and calculated reflection amplitude. We infer the discrepancy originates from interface states that are distinct from the bulk characteristics. These results show that optical interference effect can be utilized to study the magneto-optical properties of ultrathin films.

cond-mat.mes-hall↗