Interfacial Structure Dependent Spin Mixing Conductance in Cobalt Thin Films

Enhancement of Gilbert damping in polycrystalline cobalt thin-film multilayers of various thicknesses, overlayered with copper or iridium, was studied in order to understand the role of local interface structure in spin pumping. X-ray diffraction indicates that cobalt films less than 6 nm thick have strong fcc(111) texture while thicker films are dominated by hcp(0001) structure. The intrinsic damping for cobalt thicknesses above 6 nm is weakly dependent on cobalt thickness for both overlayer materials, and below 6 nm the iridium overlayers show higher damping enhancement compared to copper overlayers, as expected due to spin pumping. The interfacial spin mixing conductance is significantly enhanced in structures where both cobalt and iridium have fcc(111) structure in comparison to those where the cobalt layer has subtly different hcp(0001) texture at the interface

Overcoming the limits of vortex formation in magnetic nanodots by coupling to antidot matrix

Static magnetic configurations of thin circular soft (permalloy) magnetic nanodots, coupled to a hard antidot matrix with perpendicular magnetization, are studied by micromagnetic simulations. It is demonstrated, that dipolar fields of the antidot matrix promotes the formation of a magnetic vortex state in nanodots. The vortex is the dot ground state at zero external field in ultrathin nanodots with diameters as low as 60 nm, that is far beyond the vortex stability range in an isolated permalloy nanodot. Depending on the geometry and antidot matrix material it is possible to stabilize either radial vortex state or unconventional vortices with the angle between in-plane magnetization and radial direction ψ ≠ 0 , π / 2

Control of Structural and Magnetic Properties of Polycrystalline Co2FeGe Films via Deposition and Annealing Temperatures

: Thin polycrystalline Co2FeGe films with composition close to stoichiometry have been fabricated using magnetron co-sputtering technique. Effects of substrate temperature (TS) and postdeposition annealing (Ta) on structure, static and dynamic magnetic properties were systematically studied. It is shown that elevated TS (Ta) promote formation of ordered L21 crystal structure. Variation of TS (Ta) allow modification of magnetic properties in a broad range. Saturation magnetization ~920 emu/cm3 and low magnetization damping parameter α ~ 0.004 were achieved for TS = 573 K. This in combination with soft ferromagnetic properties (coercivity below 6 Oe) makes the films attractive candidates for spin-transfer torque and magnonic devices

Millimeter-Wave Surface Impedance Characterization of HTS Films and Single Crystals Using Quasi-Optical Sapphire Resonators

High-Q sapphire quasi-optical dielectric resonators (QDRs) excited on whispering-gallery modes are key techniques for accurate characterization in millimeter (mm) wavelength range of surface impedance of HTS large-area films and can be useful for impedance characterization of small HTS single crystals, including various unconventional superconductors. Hemispherical QDR-based technique for mm impedance characterization of HTS films is analysed theoretically and confirmed experimentally. Such an approach can be applied to QDR of modified forms. The temperature dependences of the YBaCuO films resistance properties using hemispherical resonator and the iron-pnictide single-crystal impedance properties using radially-slotted one are measured in Ka-band

Route to form skyrmions in soft magnetic films

Magnetic skyrmions which are topologically nontrivial magnetization configurations have attracted much attention recently due to their potential applications in information recording and signal processing. Conventionally, magnetic skyrmions are stabilized by chiral bulk or interfacial Dzyaloshinskii-Moriya interaction (DMI) in noncentrosymmetric B20 bulk crystals (at low temperatures) or ultrathin magnetic films with out-of-plane magnetic anisotropy (at room temperature), respectively. The skyrmion stability in the ultrathin films relies on a delicate balance of their material parameters that are hard to control experimentally. Here, we propose an alternate approach to stabilize a skyrmion in ferromagnetic media by modifying its surroundings in order to create strong dipolar fields of the radial symmetry. We demonstrate that artificial magnetic skyrmions can be stabilized even in a simple media such as a continuous soft ferromagnetic film, provided that it is coupled to a hard magnetic antidot matrix by exchange and dipolar interactions, without any DMI. Néel skyrmions, either isolated or arranged in a 2D array with a high packing density, can be stabilized using antidot as small as 40 nm in diameter for soft magnetic films made of Permalloy. When the antidot diameter is increased, the skyrmion configuration transforms into a curled one, becoming an intermediate between the Néel and Bloch skyrmions. In addition to skyrmions, the considered nanostructure supports the formation of nontopological magnetic solitons that may be regarded as skyrmions with a reversed core