When energy is introduced into a region of matter, it heats up and the local temperature increases. This energy spontaneously diffuses away from the heated region. In general, heat should flow from warmer to cooler regions and it is not possible to externally change the direction of heat conduction. Here we show a magnetically controllable heat flow caused by a spin-wave current. The direction of the flow can be switched by applying a magnetic field. When microwave energy is applied to a region of ferrimagnetic Y3Fe5O12, an end of the magnet far from this region is found to be heated in a controlled manner and a negative temperature gradient towards it is formed. This is due to unidirectional energy transfer by the excitation of spin-wave modes without time-reversal symmetry and to the conversion of spin waves into heat. When a Y3Fe5O12 film with low damping coefficients is used, spin waves are observed to emit heat at the sample end up to 10 mm away from the excitation source. The magnetically controlled remote heating we observe is directly applicable to the fabrication of a heat-flow controller.

We present temporal evolution of the spin Seebeck effect in a YIG|Pt bilayer system. Our findings reveal that this effect is a sub-microseconds fast phenomenon governed by the temperature gradient and the thermal magnons diffusion in the magnetic materials. A comparison of experimental results with the thermal-driven magnon-diffusion model shows that the temporal behavior of this effect depends on the time development of the temperature gradient in the vicinity of the YIG|Pt interface. The effective thermal-magnon diffusion length for YIG|Pt systems is estimated to be around 700 nm.The spin Seebeck effect (SSE) [2-9] is one of the most fascinating phenomena in the contemporary era of spincaloritronics [10]. Analogous to the classical Seebeck effect, the SSE is a phenomenon where a spin current is generated in spin-polarized materials like metals [2], semiconductors [4,5], and insulators [6-9] on the application of a thermal gradient. Generally, the generated spin current is measured by the inverse spin Hall effect (ISHE) [11] in a normal metal like Pt, placed in contact with the spin-polarized material. Currently, this phenomenon has attracted much attention due to its potential applications, for example, recent progresses show that based on this effect thin-film structures can be fabricated to generate electricity from waste-heat sources [12]. Further advancements in industrial applications like temperature sensors, temperature gradient sensors, and thermal spincurrent generators require an in-depth understanding of this effect.Although there have been numerous experimental and theoretical studies about this effect, the underlying physics is yet not well understood. The most accepted theory predicts that the SSE is driven by the difference in the local temperatures of magnon-, phonon-, and electron baths [13,14] of the system. However, no clear evidences of such differences have been observed experimentally [15]. So, the origin of this effect is still under discussion. Some experimental studies show that the interface proximity effect in the YIG|Pt system could exhibit similar behavior as observed for the SSE [16]. However, very recent measurements claim no such proximity effects [17]. Moreover, the question whether the SSE is an interface or bulk effect, is still open [18,19].To shed light on this controversial physics, we developed an entirely new experimental approach where we studied the temporal evolution of the SSE in YIG|Pt bilayer structures. The observations were realized in the longitudinal configuration of the SSE [7,8]. In the longitudinal spin Seebeck effect (LSSE), a thermal gradient is created perpendicular to the film plane, and the spin current generated by thermal excitations of magnetiza-

The dependence of the spin pumping efficiency and the spin mixing conductance on the surface processing of yttrium iron garnet (YIG) before the platinum (Pt) deposition has been investigated quantitatively. The ferromagnetic resonance driven spin pumping injects a spin polarized current into the Pt layer, which is transformed into an electromotive force by the inverse spin Hall effect. Our experiments show that the spin pumping effect indeed strongly depends on the YIG/Pt interface condition. We measure an enhancement of the inverse spin Hall voltage and the spin mixing conductance by more than two orders of magnitude with improved sample preparation.

It is demonstrated that upon pulsed microwave excitation, the temporal behavior of a spin-wave induced inverse spin Hall voltage in a magnetic insulator-nonmagnetic metal structure is distinctly different from the temporal evolution of the directly excited spin-wave mode from which it originates. The difference in temporal behavior is attributed to the excitation of long-lived secondary spin-wave modes localized at the insulator-metal interface.

Brillouin light scattering spectroscopy is a powerful technique for the study of fast magnetization dynamics with both frequency and wavevector resolutions. Here, we report on a distinct improvement of this spectroscopic technique toward two-dimensional wide-range wavevector selectivity in a backward scattering geometry. Spin-wave wavevectors oriented perpendicularly to the bias magnetic field are investigated by tilting the sample within the magnet gap. Wavevectors which are oriented parallel to the applied magnetic field are analyzed by turning the entire setup, including the magnet system. The setup features a wide selectivity of wavevectors up to 2.04x10(5) rad/cm for both orientations, and allows selecting and measuring wavevectors of dipole- and exchange-dominated spin waves of any orientation to the magnetization simultaneously.