Vanadium-containing silicate MCM-41 (V-MCM-41) zeolite and aluminophosphate AFI (VAPO-5) zeolite were synthesized and characterized by spectroscopic techniques. In as-synthesized form, the vanadyl ions (VIVO)2+ were found to be the major vanadium species in the form of atomic dispersion on AFI by EPR and to exist simultaneously with tetrahedral (T d) V5+ in MCM-41 by UV−vis. 29Si MAS NMR investigations suggested that the vanadium ions might attach to MCM-41 through interaction with the silanol groups on the internal wall of hexagonal tubes. The V5+ (in T d) ions are incorporated into the lattice of MCM-41 during synthesis, while the VO2+ (in T d) is the loosely bound V species. The results of Raman spectroscopy indicated that the rodlike aggregation of cationic surfactant (cetyltrimethylammonium bromide, CTAB) was encapsulated in the intrachannel space of synthetic MCM-41 as in an aqueous solution. After calcination and hydration, the V4+ species in as-synthesized V-MCM-41 was totally oxidized to +5 as shown by UV−vis and EPR spectroscopies, and they further aggregated as two-dimensional vanadate chain species that were nonuniformly deposited on the wall of MCM-41 channels as verified by Raman and HREM with EDS spectroscopies, while the V5+ species of synthetic V-MCM-41 remains stable in a tetrahedral coordination. Comparatively, two types of VO2+ ions were observed in as-synthesized VAPO-5 by EPR and they could be oxidized by calcination treatment. The presence of water vapor facilitates the oxidation of (VIVO)2+ and the formation of V2O5 cluster instead of isolated (VVO)3+ species.

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.

High-quality single-crystal thulium iron garnet (TmIG) films of 10-30 nm thick were grown by off-axis sputtering at room temperature (RT) followed by post-annealing. X-ray photoelectron spectroscopy (XPS) was employed to determine the TmIG film composition to optimize the growth conditions, along with the aid of x-ray diffraction (XRD) structural analysis and atomic force microscope (AFM) for surface morphology. The optimized films exhibited perpendicular magnetic anisotropy (PMA) and the saturation magnetization at RT was ∼99 emu/cm3, close to the RT bulk value ∼110 emu/cm3 with a very low coercive field of ∼2.4 Oe. We extracted the H⊥ of 1734 Oe and the peak-to-peak linewidth ΔH of ferromagnetic resonance are only about 99 Oe, significantly lower than that of PLD grown TmIG film and bulk single crystals. The high-quality sputtered single-crystal TmIG films show great potential to be integrated with topological insulators or heavy metals with strong spin-orbit coupling for spintronic applications.

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.

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