Spin pumping at interfaces with ferro- and paramagnetic Fe60Al40films acting as spin source and spin sink

We present a study of spin pumping efficiency and determine the spin mixing conductance and spin diffusion length in thin bilayer films based on 3d transition metal alloy Fe60Al40. Due to its magnetostructural phase transition, Fe60Al40 can be utilized as a ferromagnetic (FM) or paramagnetic (PM) material at the same temperature depending on its structural order; thus a thin Fe60Al40 film can act as a spin source or a spin sink when interfaced with a paramagnet or a ferromagnet, respectively. Ferromagnetic resonance measurements were performed in a frequency range of 5-35 GHz on bilayer films composed of FM-Fe60Al40/Pd and PM-Fe60Al40/Ni80Fe20 (permalloy). The increase in damping with the thickness of the paramagnetic layer was interpreted as a result of spin pumping into the paramagnet. We determine the spin mixing conductance g P d ↑↓ = (3.8 ± 0.5) × 10 18 m - 2 at the FM-Fe60Al40/Pd interface and the spin diffusion length λ P d = 9.1 ± 2.0 nm in Pd. For the PM-Fe60Al40/permalloy interface, we find a spin mixing conductance g F e A l ↑↓ = (2.1 ± 0.2) × 10 18 m - 2 and a spin diffusion length λ F e A l = 11.9 ± 0.2 nm for PM-Fe60Al40. The demonstrated bi-functionality of the Fe60Al40 alloy in spin pumping structures may be promising for spintronic applications

Controlling the Oxidation of Magnetic and Electrically Conductive Solid-Solution Iron-Rhodium Nanoparticles Synthesized by Laser Ablation in Liquids

This study focuses on the synthesis of FeRh nanoparticles via pulsed laser ablation in liquid and on controlling the oxidation of the synthesized nanoparticles. Formation of monomodal γ-FeRh nanoparticles was confirmed by transmission electron microscopy (TEM) and their composition confirmed by atom probe tomography (APT). For these particles, three major contributors to oxidation were analysed: (1) dissolved oxygen in the organic solvents, (2) the bound oxygen in the solvent and (3) oxygen in the atmosphere above the solvent. The decrease of oxidation for optimized ablation conditions was confirmed through energy-dispersive X-ray (EDX) and Mössbauer spectroscopy. Furthermore, the time dependence of oxidation was monitored for dried FeRh nanoparticles powders using ferromagnetic resonance spectroscopy (FMR). By magnetophoretic separation, B2-FeRh nanoparticles could be extracted from the solution and characteristic differences of nanostrand formation between γ-FeRh and B2-FeRh nanoparticles were observed

Coherent Excitation of Heterosymmetric Spin Waves with Ultrashort Wavelengths

In the emerging field of magnonics, spin waves are foreseen as signal carriers for future spintronic information processing and communication devices, owing to both the very low power losses and a high device miniaturization potential predicted for short-wavelength spin waves. Yet, the efficient excitation and controlled propagation of nanoscale spin waves remains a severe challenge. Here, we report the observation of high-amplitude, ultrashort dipole-exchange spin waves (down to 80 nm wavelength at 10 GHz frequency) in a ferromagnetic single layer system, coherently excited by the driven dynamics of a spin vortex core. We used time-resolved x-ray microscopy to directly image such propagating spin waves and their excitation over a wide range of frequencies. By further analysis, we found that these waves exhibit a heterosymmetric mode profile, involving regions with anti-Larmor precession sense and purely linear magnetic oscillation. In particular, this mode profile consists of dynamic vortices with laterally alternating helicity, leading to a partial magnetic flux closure over the film thickness, which is explained by a strong and unexpected mode hybridization. This spin-wave phenomenon observed is a general effect inherent to the dynamics of sufficiently thick ferromagnetic single layer films, independent of the specific excitation method employed

Thick permalloy films for the imaging of spin texture dynamics in perpendicularly magnetized systems

We demonstrate that thick permalloy films exhibiting a weak growth-induced perpendicular magnetic anisotropy can be employed as an ideal test system for the investigation of gyration dynamics in topologically trivial and nontrivial magnetic states ranging from an isolated magnetic skyrmion to more complex nπ spin configurations

Oriented arrays of iron nanowires: synthesis, structural and magnetic aspects

Iron nanowires with the diameter of ca. 40 nm and a length up to few dozens of microns are fabricated via templated electrodeposition using anodic aluminum oxide (AAO) film as porous matrix. Despite polycrystalline structure of wires the technique allows fabrication of dense deposits with micrometer-sized single crystalline grains within AAO templates and high chemical stability towards oxidation. Nanowire arrays exhibit strong magnetization anisotropy with saturation magnetization of 180 emu/g and coercive field of 815 Oe in direction parallel to the long axis of nanowires and 230 Oe in perpendicular direction. The effective hyperfine fields on iron atoms as extracted from Mossbauer and Nuclear Forward Scattering of sample in demagnetized state indicates slight deviation of magnetization vector (~ 6°) from nanowire long axis appearing probably due to curling of magnetic moments by antisymmetric exchange interactions at the surface of nanowires

Свойства магнитореологических эластомеров в скрещенных переменном и постоянном магнитных полях

Dynamic properties of magnetorheological elastomers (MREs) with barium ferrite particles in the presence of crossed AC and DC magnetic fields were investigated. Calculations of the magnetic permeability were made based on the fact, that the inductance of the coil changes when the coil is filled with the elastomer. Measurements of inductances of an empty coil and the coil with elastomeric core were carried out. The core was smaller than the space inside the coil, so it was able to move within the coil. The dependencies of real and imaginary parts of magnetic permeability on AC field frequency had resonance peaks at different values of DC magnetic field strength. The sample vibration was considered in frame of the elastic rod oscillations model. The change of dielectric permittivity of the elastomer with conductive particles under magnetic field (so-called magnetodielectric effect) was also investigated. These effects are the examples of transformation of the magnetic field energy into the electrical or mechanical energy of the MREработе были исследованы динамические свойства магнитореологических эластомеров (МРЭ) с частицами феррита бария в скрещенных переменном и постоянном магнитных полях. Маг- нитная проницаемость МРЭ была измерена индуктивным методом. При этом эластомерный сердечник измерительной катушки не полностью заполнял пространство внутри катушки и имел возможность двигаться. На зависимостях действительной и мнимой частей магнитной проницаемости от частоты переменного поля присутствуют резонансные пики. Этот эффект рассматривался в рамках модели продольных колебаний упругого стержня. В работе также представлены результаты измерения диэлектрической проницаемости МРЭ с проводящими частицами в магнитном поле (так называемый магнитодиэлектрический эф- фект

Свойства магнитореологических эластомеров в скрещенных переменном и постоянном магнитных полях

Dynamic properties of magnetorheological elastomers (MREs) with barium ferrite particles in the presence of crossed AC and DC magnetic fields were investigated. Calculations of the magnetic permeability were made based on the fact, that the inductance of the coil changes when the coil is filled with the elastomer. Measurements of inductances of an empty coil and the coil with elastomeric core were carried out. The core was smaller than the space inside the coil, so it was able to move within the coil. The dependencies of real and imaginary parts of magnetic permeability on AC field frequency had resonance peaks at different values of DC magnetic field strength. The sample vibration was considered in frame of the elastic rod oscillations model. The change of dielectric permittivity of the elastomer with conductive particles under magnetic field (so-called magnetodielectric effect) was also investigated. These effects are the examples of transformation of the magnetic field energy into the electrical or mechanical energy of the MREработе были исследованы динамические свойства магнитореологических эластомеров (МРЭ) с частицами феррита бария в скрещенных переменном и постоянном магнитных полях. Маг- нитная проницаемость МРЭ была измерена индуктивным методом. При этом эластомерный сердечник измерительной катушки не полностью заполнял пространство внутри катушки и имел возможность двигаться. На зависимостях действительной и мнимой частей магнитной проницаемости от частоты переменного поля присутствуют резонансные пики. Этот эффект рассматривался в рамках модели продольных колебаний упругого стержня. В работе также представлены результаты измерения диэлектрической проницаемости МРЭ с проводящими частицами в магнитном поле (так называемый магнитодиэлектрический эф- фект