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Register a new userInfluence of interface condition on spin-Seebeck effects
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The longitudinal spin-Seebeck effect (LSSE) has been investigated for Pt/yttrium iron garnet (YIG) bilayer systems. The magnitude of the voltage induced by the LSSE is found to be sensitive to the Pt/YIG interface condition. We observed large LSSE voltage in a Pt/YIG system with a better crystalline interface, while the voltage decays steeply when an amorphous layer is introduced at the interface artificially.
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We performed temperature-dependent optical pump - THz emission measurements in Y3Fe5O12 (YIG)|Pt from 5 K to room temperature in the presence of an externally applied magnetic field. We study the temperature dependence of the spin Seebeck effect and observe a continuous increase as temperature is decreased, opposite to what is observed in electrical measurements where the spin Seebeck effect is suppressed as 0K is approached. By quantitatively analysing the different contributions we isolate the temperature dependence of the spin-mixing conductance and observe features that are correlated to the bands of magnon spectrum in YIG.
We report the observation of longitudinal spin Seebeck effects (LSSE) in an all-oxide bilayer system comprising an IrO$_2$ film and an Y$_3$Fe$_5$O$_{12}$ film. Spin currents generated by a temperature gradient across the IrO$_2$/Y$_3$Fe$_5$O$_{12}$ interface were detected as electric voltage via the inverse spin Hall effect in the conductive IrO$_2$ layer. This electric voltage is proportional to the magnitude of the temperature gradient and its magnetic field dependence is well consistent with the characteristic of the LSSE. This demonstration may lead to the realization of low-cost, stable, and transparent spin-current-driven thermoelectric devices.
We study the spin transport theoretically in heterostructures consisting of a ferromagnetic metallic thin film sandwiched between heavy-metal and oxide layers. The spin current in the heavy metal layer is generated via the spin Hall effect, while the oxide layer induces at the interface with the ferromagnetic layer a spin-orbital coupling of the Rashba type. Impact of the spin Hall effect and Rashba spin-orbit coupling on the spin Seebeck current is explored with a particular emphasis on nonlinear effects. Technically, we employ the Fokker-Planck approach and contrast the analytical expressions with full numerical micromagnetic simulations. We show that when an external magnetic field is aligned parallel (antiparallel) to the Rashba field, the spin-orbit coupling enhances (reduces) the spin pumping current. In turn, the spin Hall effect and the Dzyaloshinskii-Moriya interaction are shown to increase the spin pumping current.
Thermoelectric generation is an essential function of future energy-saving technologies. However, this generation has been an exclusive feature of electric conductors, a situation which inflicts a heavy toll on its application; a conduction electron often becomes a nuisance in thermal design of devices. Here we report electric-voltage generation from heat flowing in an insulator. We reveal that, despite the absence of conduction electrons, a magnetic insulator LaY2Fe5O12 converts a heat flow into spin voltage. Attached Pt films transform this spin voltage into electric voltage by the inverse spin Hall effect. The experimental results require us to introduce thermally activated interface spin exchange between LaY2Fe5O12 and Pt. Our findings extend the range of potential materials for thermoelectric applications and provide a crucial piece of information for understanding the physics of the spin Seebeck effect.
Thermoelectric effects have been applied to power generators and temperature sensors that convert waste heat into electricity. The effects, however, have been limited to electrons to occur, and inevitably disappear at low temperatures due to electronic entropy quenching. Here, we report thermoelectric generation caused by nuclear spins in a solid: nuclear-spin Seebeck effect. The sample is a magnetically ordered material MnCO$_{3}$ having a large nuclear spin ($I = 5/2$) of $^{55}$Mn nuclei and strong hyperfine coupling, with a Pt contact. In the system, we observe low-temperature thermoelectric signals down to 100 mK due to nuclear-spin excitation. Our theoretical calculation in which interfacial Korringa process is taken into consideration quantitatively reproduces the results. The nuclear thermoelectric effect demonstrated here offers a way for exploring thermoelectric science and technologies at ultralow temperatures.
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