Low-damping magnetic materials have been widely used in microwave and spintronic applications because of their low energy loss and high sensitivity. While the Gilbert damping constant can reach 10−4 to 10−5 in some insulating ferromagnets, metallic ferromagnets generally have larger damping due to magnon scattering by conduction electrons. Meanwhile, low-damping metallic ferromagnets are desired for charge-based spintronic devices. Here, we report the growth of Co25Fe75 epitaxial films with excellent crystalline quality evident by the clear Laue oscillations and exceptionally narrow rocking curve in the X-ray diffraction scans as well as from scanning transmission electron microscopy. Remarkably, the Co25Fe75 epitaxial films exhibit a damping constant <1.4 × 10−3, which is comparable to the values for some high-quality Y3Fe5O12 films. This record low damping for metallic ferromagnets offers new opportunities for charge-based applications such as spin-transfer-torque-induced switching and magnetic oscillations.

Metallic ferromagnets with ultra-low damping are highly desirable for charge-based spintronic applications. Here, we systematically investigate the magnetic dynamics of Co25Fe75 epitaxial films with a Gilbert damping constant as low as 7.1 × 10−4. The in-plane angular dependence of ferromagnetic resonance (FMR) was measured on various thicknesses of Co25Fe75 films grown on MgO and MgAl2O4, from which the mechanisms for FMR linewidth broadening can be distinguished and quantified. The thickness dependencies of the magnetic anisotropy and inhomogeneous broadening of the linewidth are good indicators of crystal quality and magnetic uniformity. Additionally, it is shown that anisotropic two-magnon scattering is induced by defects at the surfaces.

We measure the spin Hall angle in Au layers of 5 to 100 nm thicknesses by spin pumping from Y 3 Fe 5 O 12 epitaxial films grown by ultrahigh vacuum, off-axis sputtering. We observe a striking increase in the spin Hall angle for Au layers thinner than the measured spin diffusion length of 12.6 nm. In particular, the 5 nm Au layer shows a large spin Hall angle of 0.087, compared to those of 0.016 and 0.017 for the 50 and 100 nm Au layers, respectively, suggesting that the top surface plays a dominant role in spin Hall physics when the spin current is able to reach it. Other spin pumping related parameters, including Gilbert damping enhancement, interfacial spin mixing conductance, and spin current are also determined for Au layers of various thicknesses.Given the pervasive role ultrathin films in electrical and spin transport applications, this result emphasizes the importance of considering the impact of the top surface and reveals the possibility of tuning critical spin parameters by film thickness. PACS: 72.25.Ba, 76.50.+g, 72.25.Mk, 75.70.Ak 2The spin Hall effect (SHE) and its reciprocal process, the inverse spin Hall effect (ISHE), have generated intense interest in recent years as a means of producing, manipulating, and detecting spin currents in nonmagnetic materials, opening new routes to spin-based electronic applications.1-13 The ability to convert an unpolarized electrical current into a spin current can be quantitatively described by the spin Hall angle (θ SH ).14,15 θ SH is a material-specific quantity that arises from spin-orbit coupling (SOC). Its magnitude and sign are primarily determined by atomic number, and for transition metals, by the d-orbital filling. [16][17][18][19] Au is a transition metal with a large atomic number of 79, which should lead to strong SOC and hence a large θ SH . As a result, both SHE and ISHE in Au have been extensively studied by various techniques. 20-28These studies have reported values of θ SH for Au between 0.25% (0.0025) and 11% (0.11 during film growth and the substrate rotates at 10 degrees/sec to achieve optimal film uniformity.A radio-frequency power of 60 W is used for YIG sputtering, which gives a deposition rate of 0.51 nm/min. The Au is grown in-situ on the YIG film at room temperature by off-axis DC sputtering at a deposition rate of 2.24 nm/min. The crystalline quality of the YIG films and YIG/Au bilayers are examined by X-ray diffraction (XRD) and X-ray reflectivity (XRR) using a 3 Bruker D8 Discover high-resolution triple-axis X-ray diffractometer, and scanning transmission electron microscopy (STEM) using an FEI probe-corrected Titan 3 80-300 S/TEM. where e is the electron charge, σ Au is the Au conductivity, λ SD is the spin diffusion length in Au, is the effective interfacial spin mixing conductance, L is the sample length, P = 1.21 is a factor due to the ellipticity of magnetization precession, 5 γ is the gyromagnetic ratio, h rf = 0.25Oe is the rf magnetic field in the EPR cavity at P rf = 200 mW, and α is the Gilbert damping constant of ...

The saturation magnetization of Y3Fe5O12 (YIG) epitaxial films 4 to 250 nm in thickness has been determined by complementary measurements including the angular and frequency dependencies of the ferromagnetic resonance fields as well as magnetometry measurements. The YIG films exhibit state-of-the-art crystalline quality, proper stoichiometry, and pure Fe3+ valence state. The values of YIG magnetization obtained from all the techniques significantly exceed previously reported values for single crystal YIG and the theoretical maximum. This enhancement of magnetization, not attributable to off-stoichiometry or other defects in YIG, opens opportunities for tuning magnetic properties in epitaxial films of magnetic insulators.

Auto-oscillation of a ferromagnet due to spin-orbit torques in response to a dc current is of wide interest as a flexible mechanism for generating controllable high frequency magnetic dynamics. However, spin wave mode degeneracies and nonlinear magnon-magnon scattering impede coherent precession. Discretization of the spin wave modes can reduce this scattering. Spatial localization of the spin wave modes by the strongly inhomogeneous dipole magnetic field of a nearby spherical micromagnet provides variable spatial confinement, thus offering the option of systematic tunability of magnon spectrum for studying multi-mode interactions. Here we demonstrate that field localization generates a discrete spin wave mode spectrum observable as a series of well-resolved localized modes in the presence of imposed spin currents arising from the spin Hall effect (SHE) in a permalloy/platinum (Py/Pt) microstrip. The observation of linewidth reduction through damping control in this micromagnetically engineered spectrum demonstrates that localized modes can be controlled efficiently, an important step toward continuously tunable SHE driven auto-oscillators.