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 SrTiO
3 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.
We have demonstrated spin pumping from a paramagnetic state of an insulator La2NiMnO6 into a Pt film. Single-crystalline films of La2NiMnO6 which exhibit a ferromagnetic order at TC ~ 270 K were grown by pulsed laser deposition. The inverse spin Hall
voltage induced by spin-current injection has been observed in the Pt layer not only in the ferromagnetic phase of La2NiMnO6 but also in a wide temperature range above TC. The efficient spin pumping in the paramagnetic phase is ascribable to ferromagnetic correlation, not to ferromagnetic order.
We have studied magnetoresistance and Hall effects for 1.8-nm-thick Pt films grown on a ferrimagnetic insulator Y3Fe5O12 in a wide temperature (0.46-300 K) and magnetic-field (-15-15 T) region. In the low-temperature regime where quantum corrections
to conductivity are observed, weak antilocalization behavior observed in Pt films is critically suppressed when the film is attached to Y3Fe5O12. Hall resistance in the Pt film is also affected by Y3Fe5O12, and it exhibits logarithmic temperature dependence in a broad temperature range. The magnetotransport properties in the high-field range are significantly influenced by the interface between Pt and Y3Fe5O12.
Detection and manipulation of electrons spins are key prerequisites for spin-based electronics or spintronics. This is usually achieved by contacting ferromagnets with metals or semiconductors, in which the relaxation of spins due to spin-orbit coupl
ing limits both the efficiency and the length scale. In topological insulator materials, on the contrary, the spin-orbit coupling is so strong that the spin direction uniquely determines the current direction, which allows us to conceive a whole new scheme for spin detection and manipulation. Nevertheless, even the most basic process, the spin injection into a topological insulator from a ferromagnet, has not yet been demonstrated. Here we report successful spin injection into the surface states of topological insulators by using a spin pumping technique. By measuring the voltage that shows up across the samples as a result of spin pumping, we demonstrate that a spin-electricity conversion effect takes place in the surface states of bulk-insulating topological insulators Bi1.5Sb0.5Te1.7Se1.3 and Sn-doped Bi2Te2Se. In this process, due to the two-dimensional nature of the surface state, there is no spin current along the perpendicular direction. Hence, the mechanism of this phenomenon is different from the inverse spin Hall effect and even predicts perfect conversion between spin and electricity at room temperature. The present results reveal a great advantage of topological insulators as inborn spintronics devices.
We report on a topological Hall effect possibly induced by scalar spin chirality in a quasi-two- dimensional helimagnet Fe$_{1+x}$Sb. In the low-temperature region where the spins on interstitial- Fe (concentration $x=0.3$) intervening the $120^circ$
spin-ordered triangular planes tend to freeze, a non-trivial component of Hall resistivity with opposite sign of the conventional anomalous Hall term is observed under magnetic field applied perpendicular to the triangular-lattice plane. The observed unconventional Hall effect is ascribed to the scalar spin chirality arising from the heptamer spin-clusters around the interstitial-Fe sites, which can be induced by the spin modulation by the Dzyaloshinsky-Moriya interaction.
