Energy harvesting technologies, which generate electricity from environmental energy, have been attracting great interest because of their potential to power ubiquitously deployed sensor networks and mobile electronics. Of these technologies, thermoelectric (TE) conversion is a particularly promising candidate, because it can directly generate electricity from the thermal energy that is available in various places. Here we show a novel TE concept based on the spin Seebeck effect, called 'spin-thermoelectric (STE) coating', which is characterized by a simple film structure, convenient scaling capability, and easy fabrication. The STE coating, with a 60-nm-thick bismuth-substituted yttrium iron garnet (Bi:YIG) film, is applied by means of a highly efficient process on a non-magnetic substrate. Notably, spin-current-driven TE conversion is successfully demonstrated under a temperature gradient perpendicular to such an ultrathin STE-coating layer (amounting to only 0.01% of the total sample thickness). We also show that the STE coating is applicable even on glass surfaces with amorphous structures. Such a versatile implementation of the TE function may pave the way for novel applications making full use of omnipresent heat.
Epitaxial thin films of Sr2FeMoO6, that are ordered double perovskite with half-metallic nature, have been successfully prepared on SrTiO3 (001) and (111) substrates by pulsed laser deposition in a narrow window of the temperature and oxygen pressure. From the surface morphology analysis for the atomic scale step-and-terrace structures, the film growth is concluded to take place with the chemical formula as the growth unit when the ordering direction is normal to the surface. The films showed metallic conduction with ferromagnetic transition temperature above 400 K and intergrain tunneling type magnetoresistance even at room temperature.
Spectra of the third-order nonlinear susceptibility chi((3)) have been investigated for one-dimensional Mott insulators, Sr(2)CuO(3) and Ca(2)CuO(3), by applying the third-harmonic generation (THG) spectroscopy on their single-crystalline thin films. The three-photon resonance to the lowest charge-transfer (CT) state with odd parity strongly enhances chi((3)), which is of the order of 10(-9) esu. The two-photon resonant structure unravels the even-CT state, located close to the odd-CT state. Two types of chi((3)) spectra obtained from THG and the electroreflectance measurements are explained based on the concept of spin-charge separation.
Magnetic tunneling junctions are fabricated from epitaxially grown La0.8Sr0.2MnO3/SrTiO3/La0.8Sr0.2MnO3 trilayers. A large tunneling magnetoresistance of 150% is observed for a junction with a thin barrier layer (1.6 nm) under a low switching field (<10 Oe) at 5 K. A small tunneling magnetoresistance is observed even at 270 K, which is close to the ferromagnetic Curie temperature (290 K) of the La0.8Sr0.2MnO3 film. The large magnetoresistance and high operating temperature are attributed to the sufficiently thin and uniform barrier layer of SrTiO3.
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