In the past decades, the damping constant α has been successfully described theoretically-in some cases even quantitatively-using various approaches such as the breathing Fermi-surface model 1,2 , the torque correlation model 3 , scattering theory 4,5 and the torquetorque correlation within a linear response model 6,7 . On the basis of these works, α is expected to scale as α ~ n(E F )ξ 2 τ −1 under certain circumstances, where n(E F ) is the density of states at the Fermi level E F , ξ is the strength of the spin-orbit interaction and τ is the electron momentum scattering time 8,9 . Indeed, the dependences on n(E F ) (refs 9-11 ), ξ (refs 12,13 ) and τ (ref.14 ) have been confirmed separately in a large variety of materials. In general, it is assumed that damping is isotropic. However, several theoretical works [15][16][17][18] have suggested that damping should be anisotropic in single-crystalline ferromagnetic metals, such as bulk Fe, Co and Ni. This prediction is based on the anisotropic electronic structure where the shape of the Fermi surface depends on the orientation of the magnetization direction due to the spin-orbit interaction. The anisotropic electronic structure and thus the anisotropic damping, however, can be dramatically reduced due to smearing of the energy bands in the presence of electron scattering, which makes the experimental observation of the anisotropic damping in bulk materials difficult. So far, only a few experiments [19][20][21][22] have tried to prove the existence of anisotropic damping in bulk magnets but convincing experimental evidence is still lacking.Here, we report the observation of anisotropic Gilbert damping in a quasi-two-dimensional Fe/GaAs(001) system. The idea behind this is to explore the interfacial spin-orbit interaction of a singlecrystalline ferromagnetic metal/semiconductor interface. Our findings differ distinctly from the theoretical predictions made for bulk magnets. The Fe/GaAs heterostructure was intensively studied in the past two decades for semiconductor spintronics, and has been utilized, for example, to realize spin injection at room temperature 23 . Recently, interest in this system has been revived in view of spin-orbit electronics, because of the existence of robust spin-orbit fields at the Fe/GaAs interface, which can cause a mutual conversion between spin and charge currents at room temperature 24 . The spinorbit fields, including both Bychkov-Rashba-and Dresselhaus-like terms, result from the C 2v symmetry of the interface 25 . Specifically, at the Fe/GaAs(001) interface, Fe Bloch states near E F penetrate into GaAs. Therefore, electrons of Fe 'feel' both Bychkov-Rashba and Dresselhaus spin-orbit interaction at the interface, causing a rich variety of interfacial spin-orbit-related phenomena. It has been found, for example, that the symmetry of anisotropic magnetoresistance 26 and the polar magneto-optic Kerr effect 27 of Fe is governed by the twofold interfacial C 2v symmetry rather than its bulk fourfold C 4v symmetry when the thickne...

We report the experimental observation of Snell's law for magneto-static spin waves in thin ferromagnetic Permalloy films by imaging incident, refracted and reflected waves. We use a thickness step as the interface between two media with different dispersion relation. Since the dispersion relation for magneto-static waves in thin ferromagnetic films is anisotropic, deviations from the isotropic Snell's law known in optics are observed for incidence angles larger than 25°with respect to the interface normal between the two magnetic media. Furthermore, we can show that the thickness step modifies the wavelength and the amplitude of the incident waves. Our findings open up a new way of spin wave steering for magnonic applications.

Terahertz emission spectroscopy (TES) of ultrathin multilayers of magnetic and heavy metals has recently attracted much interest. This method not only provides fundamental insights into photoinduced spin transport and spin-orbit interaction at highest frequencies, but has also paved the way for applications such as e±cient and ultrabroadband emitters of terahertz (THz) electromagnetic radiation. So far, predominantly standard ferromagnetic materials have been exploited. Here, by introducing a suitable¯gure of merit, we systematically compare the strength of THz emission from X/Pt bilayers with X being a complex ferro-, ferri-and antiferromagnetic metal, that is, dysprosium cobalt (DyCo 5 ), gadolinium iron (Gd 24 Fe 76 ), magnetite (Fe 3 O 4 ) and iron rhodium (FeRh). We¯nd that the performance in terms of spin-current generation not only depends on the spin polarization of the magnet's conduction electrons, but also on the speci¯c interface conditions, thereby suggesting TES to be a highly interface-sensitive technique. In general, our results are relevant for all applications that rely on the optical generation of ultrafast spin currents in spintronic metallic multilayers.

We report the experimental observation of spin-orbit torque induced switching of perpendicularly magnetized Pt/Co elements in a time resolved stroboscopic experiment based on high resolution Kerr microscopy. Magnetization dynamics is induced by injecting sub-nanosecond current pulses into the bilayer while simultaneously applying static in-plane magnetic bias fields. Highly reproducible homogeneous switching on time scales of several tens of nanoseconds is observed. Our findings can be corroborated using micromagnetic modelling only when including a field-like torque term as well as the Dzyaloshinskii-Moriya interaction mediated by finite temperature.Magnetization switching induced by spin-orbit torques (SOTs) generated by in plane (ip) current pulses in ferromagnet (FM)/heavy metal (HM) bilayers has attracted great attention in recent years [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]. A typical structure comprises a FM element with perpendicular magnetization structured on top of a HM conductor carrying the current. Technologically such a device has the advantage that the write current causing magnetization switching does not have to pass through a potential memory element itself thus avoiding its degradation [18]. Studying magnetization dynamics in such elements is of interest since the exact mechanisms enabling deterministic magnetization reversal remain to be disentangled. SOT driven magnetization reversal in HM/FM bilayers originates from a combination of effects which manifest themselves as field and damping like torques. These torques arise from bulk and interface effects such as the bulk spin Hall effect (SHE) or the interfacial inverse spin Galvanic effect (iSGE). Recent efforts have been dedicated to the understanding of the switching process induced by static or quasi-static currents [1,2,4,5,10,15,19]. However, the nature of the switching process itself is still under debate. Two possible scenarios exist: coherent rotation [4] or domain nucleation and propagation [2]. The critical current densities required for these distinct processes differ by orders of magnitude since for domain driven reversal a much smaller energy barrier needs to be overcome. It is believed that for devices much larger than one domain wall width, the quasi-static switching process is domain driven [2,5,9,15]. However, when reducing the size, it has been demonstrated recently that the switching process can be described by uniform motion [14]. By studying switching probabilities using short current pulses of variable width [3,6,7,14] reliable switching for applied pulse widths as short as 180 ps [6] has been demonstrated. In these experiments, switching dynamics is investigated indirectly by examining the final state long after the current pulse has been applied. To understand the speed and type of the SOT induced switching process in detail, temporal and spatial resolution is required which is met in this Letter using time resolved scanning magneto-optical Kerr micoscopy (TRMOKE).Here we measure the trajectory of...

We investigate the interplay between the governing magnetic energy terms in patterned La 0.7 Sr 0.3 MnO 3 (LSMO) elements by direct high-resolution x-ray magnetic microscopy as a function of temperature and geometrical parameters. We show that the magnetic configurations evolve from multidomain to flux-closure states (favored by the shape anisotropy) with decreasing element size, with a thickness-dependent crossover at the micrometer scale. The flux-closure states are stable against thermal excitations up to near the Curie temperature. Our results demonstrate control of the spin state in LSMO elements by judicious choice of the geometry, which is key for spintronics applications requiring high spin-polarizations and robust magnetic states.