Magnetization Dynamics in Proximity-Coupled Superconductor-Ferromagnet-Superconductor Multilayers:II. Thickness Dependence of the Superconducting Torque

In this work, we study magnetization dynamics in superconductor-ferromagnet-superconductor thin-film structures. Results of the broad-band ferromagnetic resonance spectroscopy are reported for a large set of samples with varied thickness of both superconducting and ferromagnetic layers in a wide frequency, field, and temperature ranges. Experimentally the one-dimensional anisotropic action of superconducting torque on magnetization dynamics is established; its dependence on thickness of layers is revealed. It is demonstrated that experimental findings support the recently proposed mechanism of the superconducting torque formation via the interplay between the superconducting imaginary conductance and magnetization precession at superconductor-ferromagnet interfaces. Microwave spectroscopy studies in this work are supplemented by investigations of the crystal structure and the microstructure of studied multilayers.</p

Interplay of magnetization dynamics with a microwave waveguide at cryogenic temperatures

In this work, magnetization dynamics is studied at low temperatures in a hybrid system that consists of a thin epitaxial magnetic film coupled with a superconducting planar microwave waveguide. The resonance spectrum was observed over a wide magnetic field range, including low fields below the saturation magnetization and both polarities. Analysis of the spectrum via a fitting routine we develop allows the derivation of all magnetic parameters of the film at cryogenic temperatures, the detection of waveguide-induced uniaxial magnetic anisotropies of the first and the second order, and the uncovering of a minor misalignment of the magnetic field. A substantial influence of the superconducting critical state on the resonance spectrum is observed and discussed

Nonlinear spin waves in ferromagnetic/superconductor hybrids

© 2020 Author(s). This work is focused on the numerical investigation of spin waves that propagate in nonlinear ferromagnet/superconductor bilayered films and periodic structures. The nonlinearity in these hybrid structures emerges due to the non-monotonous dependence of magnetization of a superconducting subsystem on the magnetic field, which is characterized by the superconducting critical field. It is shown that at relatively high amplitudes of spin waves in comparison to the superconducting critical field, the spin-wave spectrum changes drastically: the spin-wave spectral line can either bifurcate or stretch continuously depending on the type of considered superconductor. In addition, in the case of propagation of spin waves with relatively high amplitude in periodic magnonic metamaterials, additional zero-group-velocity modes appear that are known as flatbands. Overall, these findings suggest a versatile way for tunability of the spin-wave spectrum in nonlinear ferromagnet/superconductor structures by changing the excitation signal in respect to the superconducting critical field

Ferromagnetic resonance with long Josephson junction

In this work we propose a hybrid device based on a long Josephson junction (JJ) coupled inductively to an external ferromagnetic (FM) layer. The long JJ in a zero-field operation mode induces a localized AC magnetic field in the FM layer and enables a synchronized magnetostatic standing wave. The magnetostatic wave induces additional dissipation for soliton propagation in the junction and also enables a phase locking (resonant soliton synchronization) at a frequency of natural ferromagnetic resonance. The later manifests itself as an additional constant voltage step on the current-voltage characteristics at the corresponding voltage. The proposed device allows to study magnetization dynamics of individual micro-scaled FM samples using just DC technique, and also it provides additional phase locking frequency in the junction, determined exclusively by characteristics of the ferromagnet

Bubble-to-void transition promoted by oxide nanoparticles in ODS-EUROFER steel ion implanted to high He content

International audienceThe paper deals with a detailed study of He-filled cavity ensemble development in ODS-EUROFER steel implanted with 10 keV helium ions to a high peak concentration of 8.5 × 10 3 appm both with and without simultaneous irradiation with 4 MeV gold ions, which allowed us to strongly vary the ratios of dpa/He introduction. The subsequent transmission electron microscopy examination reveals excellent radiation stability of He-implanted sample in the single-beam implantation mode. In contrast, after the simultaneous dual-beam irradiation a bubble-to-void transition was observed for bubbles that were associated with yttria nanoparticles. The relative importance of different He bubble families observed in the He-implanted samples for the swelling accumulation is quantitatively assessed, emphasizing the potential risks of abrupt swelling acceleration in the case of bubble-to-void transition launched by nanoparticles. A model of bubble-to-void transition for gas bubbles associated with spherical second-phase particles is developed and used to rationalize experimental observations

Magnetization Dynamics in Proximity-Coupled Superconductor-Ferromagnet-Superconductor Multilayers

© 2020 American Physical Society. In this work, magnetization dynamics is studied in superconductor-ferromagnet-superconductor three-layered films in a wide frequency, field, and temperature ranges using the broad-band ferromagnetic resonance measurement technique. It is shown that in the presence of both superconducting layers and of superconducting proximity at both superconductor-ferromagnet interfaces a massive shift of the ferromagnetic resonance to higher frequencies emerges. The phenomenon is robust and essentially long-range: It has been observed for a set of samples with the thickness of ferromagnetic layer in the range from tens up to hundreds of nanometers. The resonance frequency shift is characterized by proximity-induced magnetic anisotropies: By the positive in-plane uniaxial anisotropy and by the drop of magnetization. The shift and the corresponding uniaxial anisotropy grow with the thickness of the ferromagnetic layer. For instance, the anisotropy reaches 0.27 T in experiment for a sample with a 350-nm-thick ferromagnetic layer, and about 0.4 T in predictions, which makes it a ferromagnetic film structure with the highest anisotropy and the highest natural resonance frequency ever reported. Various scenarios for the superconductivity-induced magnetic anisotropy are discussed. As a result, the origin of the phenomenon remains unclear. Application of the proximity-induced anisotropies in superconducting magnonics is proposed as a way for manipulations with a spin-wave spectrum

Magnetization Dynamics in Proximity-Coupled Superconductor-Ferromagnet-Superconductor Multilayers

In this work, magnetization dynamics is studied in superconductor-ferromagnet-superconductor three-layered films in a wide frequency, field, and temperature ranges using the broad-band ferromagnetic resonance measurement technique. It is shown that in the presence of both superconducting layers and of superconducting proximity at both superconductor-ferromagnet interfaces a massive shift of the ferromagnetic resonance to higher frequencies emerges. The phenomenon is robust and essentially long-range: it has been observed for a set of samples with the thickness of ferromagnetic layer in the range from tens up to hundreds of nanometers. The resonance frequency shift is characterized by proximity-induced magnetic anisotropies: by the positive in-plane uniaxial anisotropy and by the drop of magnetization. The shift and the corresponding uniaxial anisotropy grow with the thickness of the ferromagnetic layer. For instance, the anisotropy reaches 0.27 T in experiment for a sample with a 350-nm-thick ferromagnetic layer, and about 0.4 T in predictions, which makes it a ferromagnetic film structure with the highest anisotropy and the highest natural resonance frequency ever reported. Various scenarios for the superconductivity-induced magnetic anisotropy are discussed. As a result, the origin of the phenomenon remains unclear. Application of the proximity-induced anisotropies in superconducting magnonics is proposed as a way for manipulations with a spin-wave spectrum.peerReviewe

Micromagnetic modeling of critical current oscillations in magnetic Josephson junctions

In this work we propose and explore an effective numerical approach for investigation of critical current dependence on applied magnetic field for magnetic Josephson junctions with in-plane magnetization orientation. This approach is based on micromagnetic simulation of the magnetization reversal process in the ferromagnetic layer with introduced internal magnetic stiffness and subsequent reconstruction of the critical current value using total flux or reconstructed actual phase difference distribution. The approach is flexible and shows good agreement with experimental data obtained on Josephson junctions with ferromagnetic barriers. Based on this approach we have obtained a critical current dependence on applied magnetic field for rectangular magnetic Josephson junctions with high size aspect ratio. We have shown that the rectangular magnetic Josephson junctions can be considered for application as an effective Josephson magnetic memory element with the value of critical current defined by the orientation of magnetic moment at zero magnetic field. An impact of shape magnetic anisotropy on critical current is revealed and discussed. Finally, we have considered a curling magnetic state in the ferromagnetic layer and demonstrated its impact on critical current

Visualization of the magnetic flux structure in phosphorus-doped EuFe2As2 single crystals

Magnetic flux structure on the surface of EuFe2(As1-xPx)2 single crystals with nearly optimal phosphorus doping levels x = 0.20 and x = 0.21 is studied by low-temperature magnetic force microscopy and decoration with ferromagnetic nanoparticles. The studies are performed in a broad temperature range. It is shown that the single crystal with x = 0.21 in the temperature range between the critical temperatures TSC= 22 K and TC = (18 ± 0.3) K of the superconducting and ferromagnetic phase transitions, respectively, has the vortex structure of a frozen magnetic flux, typical for type-II superconductors. The magnetic domain structure is observed in the superconducting state below TC. The nature of this structure is discussed