High-quality thulium iron garnet films with tunable perpendicular magnetic anisotropy by off-axis sputtering - correlation between magnetic properties and film strain.

Thulium iron garnet (TmIG) films with perpendicular magnetic anisotropy (PMA) were grown on gadolinium gallium garnet (GGG) (111) substrates by off-axis sputtering. High-resolution synchrotron radiation X-ray diffraction studies and spherical aberration-corrected scanning transmission electron microscope (Cs-corrected STEM) images showed the excellent crystallinity of the films and their sharp interface with GGG. Damping constant of TmIG thin film was determined to be 0.0133 by frequency-dependent ferromagnetic resonance (FMR) measurements. The saturation magnetization (Ms) and the coercive field (Hc) were obtained systematically as a function of the longitudinal distance (L) between the sputtering target and the substrate. A 170% enhancement of PMA field (H⊥) was achieved by tuning the film composition to increase the tensile strain. Moreover, current-induced magnetization switching on a Pt/TmIG structure was demonstrated with an ultra-low critical current density (jc) of 2.5 × 106 A/cm2, an order of magnitude smaller than the previously reported value. We were able to tune Ms, Hc and H⊥ to obtain an ultra-low jc of switching the magnetization, showing the great potential of sputtered TmIG films for spintronics.

Strongly exchange-coupled and surface-state-modulated magnetization dynamics in Bi2Se3/yttrium iron garnet heterostructures.

Harnessing the spin-momentum locking of topological surface states in conjunction with magnetic materials is the first step to realize novel topological insulator-based devices. Here, we report strong interfacial coupling in Bi2Se3/yttrium iron garnet (YIG) bilayers manifested as large interfacial in-plane magnetic anisotropy (IMA) and enhancement of damping probed by ferromagnetic resonance. The interfacial IMA and damping enhancement reaches a maximum when the Bi2Se3 film approaches its two-dimensional limit, indicating that topological surface states play an important role in the magnetization dynamics of YIG. Temperature-dependent ferromagnetic resonance of Bi2Se3/YIG reveals signatures of the magnetic proximity effect of TC as high as 180 K, an emerging low-temperature perpendicular magnetic anisotropy competing the high-temperature IMA, and an increasing exchange effective field of YIG steadily increasing toward low temperature. Our study sheds light on the effects of topological insulators on magnetization dynamics, essential for the development of topological insulator-based spintronic devices.

In-situ atomic layer deposition of tri-methylaluminum and water on pristine single-crystal (In)GaAs surfaces: electronic and electric structures.

The electronic structure of single-crystal (In)GaAs deposited with tri-methylaluminum (TMA) and water via atomic layer deposition (ALD) is presented with high-resolution synchrotron radiation core-level photoemission and capacitance-voltage (CV) characteristics. The interaction of the precursor atoms with (In)GaAs is confined at the topmost surface layer. The Ga-vacant site on the GaAs(111)A-2 × 2 surface is filled with Al, thereby effectively passivating the As dangling bonds. The As-As dimers on the GaAs(001)-2 × 4 surface are entirely passivated by one cycle of TMA and water. The presumed layerwise deposition fails to happen in GaAs(001)-4 × 6. In In0.20Ga0.80As(001)-2 × 4, the edge row As atoms are partially bonded with the Al, and one released methyl then bonds with the In. It is suggested that the unpassivated surface and subsurface atoms cause large frequency dispersions in CV characteristics under the gate bias. We also found that the (In)GaAs surface is immune to water in ALD. However, the momentary exposure of it to air (less than one minute) introduces significant signals of native oxides. This indicates the necessity of in situ works of high κ/(In)GaAs-related experiments in order to know the precise interfacial atomic bonding and thus know the electronic characteristics. The electric CV measurements of the ALD-Al2O3 on these (In)GaAs surfaces are correlated with their electronic properties.

Methyl transfer from methylcobalamin to diaquocobinamide.

The transfer of the methyl group from methylcobalamin to diaquocobinamide in aqueous solution has been demonstrated by proton, carbon-13, and phosphorus-31 nuclear magnetic resonance spectroscopy. The products of this reaction are aquocobalamin and the methylaquocobinamides. Dicyanocobinamide and the cyanoaquocobinamides do not serve as methyl acceptors, while ligands such as pyridine and histidine reduce the rate of the transfer reactions. The methyl transfer is not affected by oxidizing agents such as O2, N2O, and H2O2, suggesting that the reaction does not involve free Co(I) or Co(II) corrinoids. The pH dependence of the rate of the transfer reaction from methylcobalamin to diaquocobinamide demonstrates that methylcobalamin in the "base-on" form and diaquocobinamide are the most effective methyl donor and acceptor, respectively. The most plausible mechanism for the transfer reaction involves the one-electron oxidation of methylcobalamin by diaquocobinamide to a methylcobalamin radical cation and cob(II)inamide. The very unstable methylcobalamin radical cation releases a methyl radical, which reacts with cob(II)inamide to generate the methylaquocobinamides.