Synthetic route to low damping in ferromagnetic thin-films

Previous theory indicated that the individual monolayers within transition metal ferromagnet thin-films contribute different magnitudes to the total ferromagnetic damping. Here, the aim was to investigate if the thin-film damping could be reduced by electronic engineering of the higher damping regions via localized doping. We present new theoretical analysis and experimental results for sputtered Co thin-films in which the upper and lower surface regions were locally doped with Cr. Theory indicates that local doping does reduce the damping and the experiments show a comparable reduction of the damping with increasing local doping up to 30% Cr, while the measured damping falls further with higher local doping, which may be attributed to changes in the film structure. This work opens a route to create low-damping magnetic thin-films

Magnetic properties of permalloy antidot arrayfabricated by interference lithography

The interference laser lithography and ion-beam sputtering have been reported. Magneto-optical Kerr effect magnetometry indicated that the sample exhibits four-fold anisotropic behaviour, i.e. different magnetization loops were observed when the external magnetic field was applied along either x-or y-axis, or along the array diagonal. Broadband ferromagnetic resonance measurements revealed a rich variety of different magnetization configurations in the unsaturated state that can be controlled by the orientation of the external magnetic field. Micromagnetic simulations have been performed to explain the observed results. On the contrary, in the saturated regime the system demonstrated almost isotropic magnetic behaviour that improves with external field increase. The obtained results show the potential of interference lithography for the fabrication of large area antidot arrays. (C) 2019 Author(s).The Portuguese team acknowledges the Network of Extreme Conditions Laboratories-NECL and Portuguese Foundation of Science and Technology (FCT) support through the projects NORTE-01-0145-FEDER-022096, MIT-EXPL/IRA/0012/2017, POCI-01-0145-FEDER-031302, EXPL/IF/01191/2013 (D.N.), EXPL/IF/00541/2015 (S.A.B.), EXPL/IF/00981/2013 (G.N.K). D.N., G.N.K., C.R and R.M. acknowledge the support by the European Union Horizon 2020 Research and Innovation Programme under Marie Sklodowska-Curie Grant Agreement EU H2020-MSCA-RISE-2016 (No 734801). The Spanish team acknowledges the support from Spanish MINECO through the grant FIS2016-76058 (AEI/FEDER, UE). A.H.-R. acknowledges the support from European Union's Horizon 2020 research and innovation program under the Marie Sklodowska-Curie Action (reference H2020-MSCA-IF-2016-746958). G.N.K. and O.V.D. acknowledge the support from European Cooperation in Science and Technology (COST) project CA16218 "NANOCOHYBRI.

Spin-wave eigenmodes in direct-write 3D nanovolcanoes

Extending nanostructures into the third dimension has become a major research avenue in modern magnetism, superconductivity, and spintronics, because of geometry-, curvature-, and topology-induced phenomena. Here, we introduce Co-Fe nanovolcanoes-nanodisks overlaid by nanorings-as purpose-engineered 3D architectures for nanomagnonics, fabricated by focused electron beam-induced deposition. We use both perpendicular spin-wave resonance measurements and micromagnetic simulations to demonstrate that the rings encircling the volcano craters harbor the highest-frequency eigenmodes, while the lower-frequency eigenmodes are concentrated within the volcano crater, due to the non-uniformity of the internal magnetic field. By varying the crater diameter, we demonstrate the deliberate tuning of higher-frequency eigenmodes without affecting the lowest-frequency mode. Thereby, the extension of 2D nanodisks into the third dimension allows one to engineer their lowest eigenfrequency by using 3D nanovolcanoes with 30% smaller footprints. The presented nanovolcanoes can be viewed as multi-mode microwave resonators and 3D building blocks for nanomagnonics.O.V.D. and S.L.C. acknowledge the Austrian Science Fund (FWF) for support through Grant No. I 4889 (CurviMag). The Portuguese team acknowledges the Network of Extreme Conditions Laboratories-NECL and the Portuguese Foundation of Science and Technology (FCT) support through Project Nos. NORTE-01-0145-FEDER-022096, PTDC/FIS-MAC/31302/2017, POCI-0145-FEDER-030085 (NOVAMAG), and EXPL/IF/00541/2015. N. Z. and A. V. C. acknowledge the Austrian Science Fund (FWF) for support through Grant No. I 4917. S. B. acknowledges funding by the) Deutsche Forschungsgemeinschaft (DFG through Grant Nos. BA 6595/2-1 and BA 6595/1-1. K. G. acknowledges support from IKERBASQUE (the Basque Foundation for Science). The work of K. G. was supported by the Spanish Ministry of Science and Innovation through Grant No. PID2019-108075RB-C33/AEI/10.13039/501100011033. M.H. acknowledges the DFG for support through Grant No. HU 752/16-1. Support through the Frankfurt Center of Electron Microscopy (FCEM) is gratefully acknowledged. Further, support of the European Cooperation in Science and Technology via COST Action No. CA16218 (NANOCOHYBRI) is acknowledged

Engineered magnetization and exchange stiffness in direct-write Co-Fe nanoelements

Media with engineered magnetization are essential building blocks in superconductivity, magnetism and magnon spintronics. However, the established thin-film and lithographic techniques insufficiently suit the realization of planar components with on-demand-tailored magnetization in the lateral dimension. Here, we demonstrate the engineering of the magnetic properties of CoFe-based nanodisks fabricated by the mask-less technique of focused electron beam induced deposition (FEBID). The material composition in the nanodisks is tuned \emph{in-situ} via the e-beam waiting time in the FEBID process and their post-growth irradiation with Ga ions. The magnetization $M_s$ and exchange stiffness $A$ of the disks are deduced from perpendicular ferromagnetic resonance measurements. The achieved $M_s$ variation in the broad range from $720$ emu/cm$^3$ to $1430$ emu/cm$^3$ continuously bridges the gap between the $M_s$ values of such widely used magnonic materials as permalloy and CoFeB. The presented approach paves a way towards nanoscale 2D and 3D systems with controllable and space-varied magnetic properties.Comment: 5 pages, 4 figure

Measurement of Millimeter-Wave Surface Resistance and Temperature Dependence of Reactance of Thin HTS Films Using Quasi-Optical Dielectric Resonator

The technique proposed by authors earlier for accurate measurement of large-area HTS thin film surface resistance (R-s) is developed further. It is based on application of quasioptical dielectric resonators (QDR). Data on R-s of individual Y-123 films obtained at 77 K by using "round robin" procedure are presented. The main attention is paid to developing technique of temperature dependence measurement of thin film surface reactance variation (Delta X-s). The dependence obtained by experiment is analyzed by means of fitting procedure that allows one to determine the validity of theoretical models for the temperature dependence of field penetration depth. Particularly, the 3D XY critical regime, Ginzburg-Landau behavior and two-fluid model are compared near T-c. Our data show that the former approach best follows the observed dependence

Quasioptical Sapphire resonators in the form of a truncated cone

This paper reports on a detailed experimental study of quasioptical dielectric resonators (QDRs) designed in the form of a truncated cone and excited on whispering-gallery modes. One aim of this paper is to study of the eigenfrequency spectrum and quality factors of single-crystal sapphire resonators. A second aim is to show the applicability of the resonator technique not only in optical but also in the millimeter-wave range, in particular, for studying the surface resistance (R-s) of high-temperature superconducting films. The measured frequencies of QDR as a function of the wedge angle of the cone resonator are in a good agreement with those frequencies simulated using the CST Microwave Studio 2006 program. Additionally, electrodynamic characteristics of the cone resonator and hemispherical dielectric resonator with conducting endplate are compared