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.

We report on a comparative study of spin Hall related effects and magnetoresistance in YIG|Pt and YIG|Ta bilayers. These combined measurements allow to estimate the characteristic transport parameters of both Pt and Ta layers juxtaposed to YIG: the spin mixing conductance G ↑↓ at the YIG|normal metal interface, the spin Hall angle ΘSH, and the spin diffusion length λ sd in the normal metal. The inverse spin Hall voltages generated in Pt and Ta by the pure spin current pumped from YIG excited at resonance confirm the opposite signs of spin Hall angles in these two materials. Moreover, from the dependence of the inverse spin Hall voltage on the Ta thickness, we extract the spin diffusion length in Ta, found to be λ Ta sd = 1.8 ± 0.7 nm. Both the YIG|Pt and YIG|Ta systems display a similar variation of resistance upon magnetic field orientation, which can be explained in the recently developed framework of spin Hall magnetoresistance.

Electronic and magnetic structure of Fe3O4/BiFeO3 multiferroic superlattices: First principles calculations J. Appl. Phys. 112, 063925 (2012) Platinum thickness dependence of the inverse spin-Hall voltage from spin pumping in a hybrid yttrium iron garnet/platinum system Appl. Phys. Lett. 101, 132414 (2012) Pulse voltage-induced dynamic magnetization switching in magnetic tunneling junctions with high resistancearea product Appl. Phys. Lett. 101, 102406 (2012) Spin transport and spin dephasing in zinc oxide Appl. Phys. Lett. 101, 082404 (2012) Spin and valley dependent electronic transport in strain engineered graphene

In recent years, spin–orbit effects have been widely used to produce and detect spin currents in spintronic devices. The peculiar symmetry of the spin Hall effect allows creation of a spin accumulation at the interface between a metal with strong spin–orbit interaction and a magnetic insulator, which can lead to a net pure spin current flowing from the metal into the insulator. This spin current applies a torque on the magnetization, which can eventually be driven into steady motion. Tailoring this experiment on extended films has proven to be elusive, probably due to mode competition. This requires the reduction of both the thickness and lateral size to reach full damping compensation. Here we show clear evidence of coherent spin–orbit torque-induced auto-oscillation in micron-sized yttrium iron garnet discs of thickness 20 nm. Our results emphasize the key role of quasi-degenerate spin-wave modes, which increase the threshold current.

Spin-Hall magnetoresistance in platinum on yttrium iron garnet Vlietstra, N.; Shan, J.; Castel, V.; van Wees, B. J.; Ben Youssef, J. Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the number of authors shown on this cover page is limited to 10 maximum. The occurrence of spin-Hall magnetoresistance (SMR) in platinum (Pt) on top of yttrium iron garnet (YIG) has been investigated, for both in-plane and out-of-plane applied magnetic fields and for different Pt thicknesses [3, 4, 8, and 35 nm]. Our experiments show that the SMR signal directly depends on the in-plane and out-of-plane magnetization directions of the YIG. This confirms the theoretical description, where the SMR occurs due to the interplay of the spin-orbit interaction in the Pt and the spin-mixing conductance at the YIG/Pt interface. Additionally, the sensitivity of the SMR and spin pumping signals on the YIG/Pt interface conditions is shown by comparing two different deposition techniques (e-beam evaporation and dc sputtering).

We report the observation of the spin Peltier effect (SPE) in the ferrimagnetic insulator yttrium iron garnet (YIG), i.e., a heat current generated by a spin current flowing through a platinum ðPtÞjYIG interface. The effect can be explained by the spin transfer torque that transforms the spin current in the Pt into a magnon current in the YIG. Via magnon-phonon interactions the magnetic fluctuations modulate the phonon temperature that is detected by a thermopile close to the interface. By finite-element modeling we verify the reciprocity between the spin Peltier and spin Seebeck effect. The observed strong coupling between thermal magnons and phonons in YIG is attractive for nanoscale cooling techniques. DOI: 10.1103/PhysRevLett.113.027601 PACS numbers: 72.20.Pa, 75.78.-n, 85.80.Fi The discovery of the spin Seebeck effect (SSE) in YIGjPt bilayers [1] opened up a new research direction in the field of spin caloritronics. Contrary to spin-dependent thermoelectric effects carried by the electron spin-up and spindown currents that are presumably dominant in metallic ferromagnets [2,3], only magnons can drive the SSE in magnetic insulators. In the SSE a temperature difference between the magnons in the magnetic insulator and the electrons in the metal contact leads to thermal pumping of a spin current [4][5][6]. In a suitable metal such as Pt, this spin current is transformed into an observable transverse voltage by the inverse spin Hall effect [7]. Numerical simulations of the phonon, magnon, and electron temperatures show good agreement with experiments [8]. In this Letter we report the observation of the spin Peltier effect (SPE), which is the Onsager reciprocal [9] of the SSE.The SPE is the generation of a magnon heat current in the magnetic insulator by a spin current through the interface with the metal contact. The latter can be generated by a charge current in the Pt film that by the spin Hall effect generates a transverse spin current normal to the interface. The spin Peltier heat current generates a temperature difference between magnons and phonons in the YIG that when relaxing leads to a change in the lattice temperature. We confirm this scenario experimentally by picking up such temperature changes via proximity thermocouples. According to our modeling the experimental results are consistent with Onsager reciprocity between the SPE and the SSE, which we measure separately (see Supplemental Material [10], Sec. IV). Our results confirm recent indications for a strong magnon-phonon interaction in YIG at room temperature [8,11,12].A charge current through a Pt strip generates a transverse spin current induced by the spin Hall effect that leads to a spin accumulation V s at the boundaries. At the interface to YIG the spin current is absorbed as a spin transfer torque proportional to the spin mixing conductance [13,14], as depicted in Fig. 1(a). When the magnetic moment of the spin accumulation (μ s ) at the YIGjPt interface is parallel (antiparallel) to the average magnetization direction, the spin torqu...

Spintronics is a field of electronics based on using the electron spin instead of its charge. The recent advance in the manipulation of pure spin currents, i.e. angular momentum transfer not associated to conventional charge currents, has opened new opportunities to build spin based devices with low energy consumption [1]. It has also allowed to integrate ferromagnetic insulators in spintronic devices, either as spin sources [2][3][4][5][6] or spin conductors [2, 7, 8] using their magnetic excitations to propagate a spin signal. Antiferromagnetic insulators belong to another class of materials that can also sustain magnetic excitations, even with a higher group velocity [9]. Hence, they have potential as angular momentum conductors, possibly making faster spin devices. At the opposite end, angular momentum insulators are also required in spintronic circuits. The present letter underlines some essential features relevant for spin current conduction, based on measurements of angular momentum transmission in antiferromagnetic NiO and in the non-magnetic light element insulator SiO 2 .

We studied the nonlocal transport behavior of both electrically and thermally excited magnons in yttrium iron garnet (YIG) as a function of its thickness. For electrically injected magnons, the nonlocal signals decrease monotonically as the YIG thickness increases. For the nonlocal behavior of the thermally generated magnons, or the nonlocal spin Seebeck effect (SSE), we observed a sign reversal which occurs at a certain heater-detector distance, and it is influenced by both the opacity of the YIG/heater interface and the YIG thickness. Our nonlocal SSE results can be qualitatively explained by the bulk-driven SSE mechanism together with the magnon diffusion model. Using a two-dimensional finite element model (2D-FEM), we estimated the bulk spin Seebeck coefficient of YIG at room temperature. The quantitative disagreement between the experimental and modeled results indicates more complex processes going on in addition to magnon diffusion and relaxation, especially close to the contacts.