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Register a new userTransverse thermoelectric effect in La0.67Sr0.33MnO3|SrRuO3 superlattices
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Transverse thermoelectric effects in response to an out-of-plane heat current have been studied in an external magnetic field for ferromagnetic superlattices consisting of La0.67Sr0.33MnO3 and SrRuO3 layers. The superlattices were fabricated on SrTiO3 substrates by pulsed laser deposition. We found that the sign of the transverse thermoelectric voltage for the superlattices is opposite to that for La0.67Sr0.33MnO3 and SrRuO3 single layers at 200 K, implying an important role of spin Seebeck effects inside the superlattices. At 10 K, the magnetothermoelectric curves shift from the zero field due to an antiferromagnetic coupling between layers in the superlattices.
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Magnetic properties of a series of (La0.7Sr0.3MnO3/SrRuO3) superlattices, where the SrRuO3 layer thickness is varying, are examined. A room-temperature magnetocaloric effect is obtained owing to the finite size effect which reduces the TC of La0.7Sr0.3MnO3 layers. While the working temperature ranges are enlarged,, -DeltaSmax values remains similar to the values in polycrystalline La0.7Sr0.3MnO3. Consequently, the relative cooling powers are significantly improved, the microscopic mechanism of which is related to the effect of the interfaces at La0.7Sr0.3MnO3/SrRuO3 and higher nanostructural disorder. This study indicates that artificial oxide superlattices/multilayers might provide an alternative pathway in searching for efficient room-temperature magnetic refrigerators for (nano)microscale systems.
Exchange bias (EB) and the training effects (TE) in an antiferromagnetically coupled La0.7Sr0.3MnO3 / SrRuO3 superlattices were studied in the temperature range 1.8 - 150 K. Strong antiferromagnetic (AFM) interlayer coupling is evidenced from AC - susceptibility measurements. Below 100 K, vertical magnetization shifts are present due to the two remanent states corresponding to the two ferromagnetic (FM) layers at FM and AFM coupling condition. After field cooling (FC), significant decrease in the exchange bias field (HEB) is observed when cycling the system through several consecutive hysteresis loops. Quantitative analysis for the variation of HEB vs. number of field cycles (n) indicates an excellent agreement between the theory, based on triggered relaxation phenomena, and our experimental observations. Nevertheless, the crucial fitting parameter K indicates smooth training effect upon repeated field cycling, in accordance with our observation.
The electronic properties of SrRuO3/LaAlO3 (SRO/LAO) superlattices with different interlayer thicknesses of SRO layers were studied. As the thickness of SRO layers is reduced, the superlattices exhibit a metal-insulator transition implying transformation into a more localized state from its original bulk metallic state. The strain effect on the metal-insulator transition was also examined. The origin of the metal-insulator transition in ultrathin SRO film is discussed. All the superlattices, even those with SRO layers as thin as 2 unit cells, are ferromagnetic at low temperatures. Moreover, we demonstrate field effect devices based on such multilayer superlattice structures.
Thermoelectric effects in magnetic nanostructures and the so-called spin caloritronics are attracting much interest. Indeed it provides a new way to control and manipulate spin currents which are key elements of spin-based electronics. Here we report on giant magnetothermoelectric effect in Al2O3 magnetic tunnel junctions. The thermovoltage in this geometry can reach 1 mV. Moreover a magneto-thermovoltage effect could be measured with ratio similar to the tunnel magnetoresistance ratio. The Seebeck coefficient can then be tuned by changing the relative magnetization orientation of the two magnetic layers in the tunnel junction. Therefore our experiments extend the range of spintronic devices application to thermoelectricity and provide a crucial piece of information for understanding the physics of thermal spin transport.
Investigating the effects of the complex magnetic interactions on the formation of nontrivial magnetic phases enables a better understanding of magnetic materials. Moreover, an effective method to systematically control those interactions and phases could be extensively utilized in spintronic devices. SrRuO3 heterostructures function as a suitable material system to investigate the complex magnetic interactions and the resultant formation of topological magnetic phases, as the heterostructuring approach provides an accessible controllability to modulate the magnetic interactions. In this study, we have observed that the Hall effect of SrRuO3/SrTiO3 superlattices varies nonmonotonically with the repetition number (z). Using Monte Carlo simulations, we identify a possible origin of this experimental observation: the interplay between the Dzyaloshinskii-Moriya interaction and dipole-dipole interaction, which have differing z-dependence, might result in a z-dependent modulation of topological magnetic phases. This approach provides not only a collective understanding of the magnetic interactions in artificial heterostructures but also a facile control over the skyrmion phases.
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