Long-distance transport of magnon spin information in a magnetic insulator at room temperature

Abstract

The transport of spin information has been studied in various materials, such as metals 1 , semiconductors 2 and graphene 3 . In these materials, spin is transported by diffusion of conduction electrons 4 . Here we study the diffusion and relaxation of spin in a magnetic insulator, where the large bandgap prohibits the motion of electrons. Spin can still be transported, however, through the diffusion of non-equilibrium magnons, the quanta of spin wave excitations in magnetically ordered materials. Here we show experimentally that these magnons can be excited and detected fully electrically 5,6 in linear response, and can transport spin angular momentum through the magnetic insulator yttrium iron garnet (YIG) over distances as large as 40 μm. We identify two transport regimes: the diffusion limited regime for distances shorter than the magnon relaxation length, and the relaxation limited regime for larger distances. With a model similar to the diffusion-relaxation model for electron spin transport in (semi)conducting materials, we extract the magnon relaxation length = . ± . μm in a 200 nm thin YIG film at room temperature.

Long-range pure magnon spin diffusion observed in a nonlocal spin-Seebeck geometry

“…Conversely, Tx at high temperature exhibits a much larger magnitude than at low temperature due to the decrease in thermal conductivity of Pt and YIG at high temperature, however no VNL is observed at these conditions. The lack of VNL at high temperature is attributable to the reduction of the magnon spin diffusion length, which agrees with a recent report of room temperature measurement of magnon spin diffusion in YIG of 9 m [19], which is smaller than the spatial resolution of our current experiment.…”

“…This allows for an experimental determination of the magnon spin diffusion length in YIG. A similar non-local magnon spin measurement in YIG was very recently reported by Cornelissen et al [19], where they utilized the spin Hall effect to inject a spin current into YIG and measured a spin diffusion length of 9 m at room temperature. In the current experiment, we extend those measurements to 23 K and find a remarkable increase in the spin diffusion length up to 47 m upon cooling the sample.…”

Spin injection and detection via the anomalous spin Hall effect of a ferromagnetic metal

“…This type of spin current generation perpendicular to a charge current has a significant technological relevance for spin transfer torque devices [3,4] and also for the electrical injection of magnons (quantized spin waves) in magnetic insulators [5][6][7]. The electrical injection and detection of magnons offer a distinct technological advantage for the integration of magnon spintronics into solid state devices, over other magnon generation mechanisms such as spin pumping by radiofrequency fields [8] or the spin Seebeck effect due to a temperature gradient [9].…”

“…3(a) and 3(b), respectively. The thermally generated magnons due to Joule heating at the Py injector produce the R 2f NL signal at the detector, via the spin Seebeck effect [6].…”

“…Electron beam lithography was used to pattern the devices, which consist of two Py strips and one reference Pt strip, as shown in the optical image in Fig. 1 The linear signal corresponding to the electrical injection and detection is measured as the first harmonic (1f ) response of the non-local voltage [6], while the thermally generated magnons due to Joule heating at the injector are detected as a Spin Seebeck signal, measured as the second harmonic (2f ) response. For all our experiments, we normalize the detected non-local voltage (V 1(2)f ) by the injection current (I) for the first harmonic response (R 1f NL = V 1f /I) and by I 2 for the second harmonic response (R 2f NL = V 2f /I 2 ).…”