Magnetic resonance studies of the fundamental spin-wave modes in individual submicron Cu/NiFe/Cu perpendicularly magnetized disks

Spin wave spectra of perpendicularly magnetized disks with trilayers consisting of a 100 nm permalloy (Py) layer sandwiched by two Cu layers of 30 nm, are measured individually with a Magnetic Resonance Force Microscope (MRFM). It is demonstrated by 3D micromagnetic simulations that in disks having sub-micron size diameters, the lowest energy spin wave mode of the saturated state is not spatially uniform but rather is localized at the center of the Py/Cu interface in the region of a minimum demagnetizing field

Magnetic resonance spectroscopy of perpendicularly magnetized permalloy multilayer disks

Using a Magnetic Resonance Force Microscope, we compare the ferromagnetic resonance spectra of individual micron-size disks with identical diameter, 1 $m$m, but different layer structures. For a disk composed of a single 43.3 nm thick permalloy (Py) layer, the lowest energy mode in the perpendicular configuration is the uniform precession. The higher energy modes are standing spin-waves confined along the diameter of the disk. For a Cu(30)/Py(100)/Cu(30) nm multilayer structure, it has been interpreted that the lowest energy mode becomes a precession localized at the Cu/Py interfaces. When the multilayer is changed to Py(100)/Cu(10)/Py(10) nm, this localized mode of the thick layer is coupled to the precession of the thin layer

Bistability of vortex core dynamics in a single perpendicularly magnetized nano-disk

Microwave spectroscopy of individual vortex-state magnetic nano-disks in a perpendicular bias magnetic field, $H$, is performed using a magnetic resonance force microscope (MRFM). It reveals the splitting induced by $H$ on the gyrotropic frequency of the vortex core rotation related to the existence of the two stable polarities of the core. This splitting enables spectroscopic detection of the core polarity. The bistability extends up to a large negative (antiparallel to the core) value of the bias magnetic field $H_r$, at which the core polarity is reversed. The difference between the frequencies of the two stable rotational modes corresponding to each core polarity is proportional to $H$ and to the ratio of the disk thickness to its radius. Simple analytic theory in combination with micromagnetic simulations give quantitative description of the observed bistable dynamics.Comment: 4 pages, 3 figures, 1 table, 16 references. Submitted to Physical Review Letters on December 19th, 200

Smart Antennas and Front-End Modules in Q-band for Backhaul Networks

[EN] As mobile operators face increasing density of base stations as well as growing bandwidth requirements, mobile backhaul has become the new challenge. This article defines the architecture for future mobile backhaul networks as proposed in the framework of the FP7 EU SARABAND project. This solution exploits a new and wider frequency spectrum band, the Q-band (40.5 43.5 GHz), to provide massive amounts of capacity. However, for the full deployment of such backhaul networks, new technology development in the Q-band must be addressed. In particular, this article gives an overview of the disruptive technology on antennas and front-end modules developed within this project.Vilar Mateo, R.; Martí Sendra, J.; Czarny, R.; Sypek, M.; Makowski, M.; Martel, C.; Crepin, T.... (2014). Smart Antennas and Front-End Modules in Q-band for Backhaul Networks. Microwave Journal. S:28-34. http://hdl.handle.net/10251/52765S2834

Growth, structural, and magnetic characterization of epitaxial Co2MnSi films deposited on MgO and Cr seed layers

We report detailed structural characterization and magneto-optical Kerr magnetometry measurements at room temperature in epitaxial Co2MnSi thin films grown on MgO(001) and Cr(001) buffered MgO single crystals prepared by sputtering. While Co2MnSi/Cr//MgO(001) films display the expected cubic anisotropy, the magnetization curves obtained for Co2MnSi// MgO(001) samples exhibit a superimposed in-plane uniaxial magnetic anisotropy. The evolution of magnetization with film thickness points to a relevant interfacial Co2MnSi-buffer layer (Cr or MgO) contribution which competes with magnetic properties of bulk Co2MnSi, resulting in a drastic change in the magnetism of the whole sample. The origin of this interfacial magnetic anisotropy is discussed and correlated with our structural studies. © 2013 American Institute of Physics.A. García-García would like to acknowledge the Fundaçao para a Ciencia e Tecnologia (FCT) for his postdoctoral grant (Grant No. SFRH/BPD/817102011).Peer Reviewe

Experimental Study of Microwave Susceptibility in Ferrite Composite Materials

The microwave susceptibility of NiFe2O4 and Co2Z was measured between 100 and 10000 MHz. The samples were either samples with different porosities or composites with different volume fractions, in the case of NiFe2O4, or composites with different granulometry, in the case of Co2Z. The measured susceptibility undergoes substantial changes at the crossover from a ceramic state to a composite of isolated particles and for different granulometries of Co2Z in the range 10 to 600 µm. We show that a model in which the susceptibility is uniform inside the particles cannot account for these results. We suggest that in order to compute the susceptibility of composites, a microscopic approach is required

Study of the Gyromagnetic Resonance Damping in Relaxing Rare Earth Substituted YGd2Fe5O12 Garnets

The influence of magnetic state (saturated or unsaturated states) on the gyromagnetic resonance damping in relaxing rare earth substituted Y1-xDyxGd2Fe5O12 garnets (with x=0;0.15;0.3;0.6) has been studied. The damping parameter α, as defined by Landau-Lifshitz equation, has been determined either by FMR at 10GHz (saturated state) or by measurement of the frequency dependence of the complex initial permeability in the 0.1GHz-10GHz band (unsaturated state). On the one hand, the damping parameter αsat has been calculated by fitting the FMR spectra of single crystals with the theoretical lorentzian shape. On the other hand, the damping parameter αunsat of polycrystals has been calculated using models which take into account the interaction between magnetic domains. In the fully magnetized state the introduction of relaxing rare earth (Dy) is found to increase significantly αsat values (from 0.02 to 0.3 when x varies from 0 to 0.6). On the contrary, the introduction of Dy hardly increases αunsat values. It appears that the difference between αsat and αunsat values stems not only from the interaction between magnetic domains but also from the modification of the damping in each magnetic domain owing to the presence of magnetic domain walls