Ricardo da Silva

Universidade Federal de Santa Maria · Department of Physics

Magnetic systems with competing anisotropies generally exhibit asymmetry between the maximum amplitudes of the right and left maxima in a magnetoimpedance curve. Small errors in positioning the samples at the experimental setup may also produce such asymmetry. In this work, we present a study on the sources of the asymmetry between magnetoimpedance...

The potential for technological applications of systems presenting perpendicular magnetic anisotropy is undeniable. With the advent of spintronics and the possibility to explore spin textures, such as skyrmions, in devices, it becomes fundamental to understand how to finely tune the magnetic properties of nanometric systems. In multilayered thin film...

Magnetization reversal processes occurring in amorphous CoFeB thin films of thicknesses 100 nm, 200 nm and 300 nm were experimentally investigated. Analysing hysteresis loops traced with a vectorial VSM and the angular behaviour of coercivity, we concluded that domain wall displacement is the leading reversal mechanism for films with 200 and 300 nm...

In this work, CoFe2O4/CoFe2 nanoparticles with core/shell structure were synthesized by carbothermic reduction using chitosan beads impregnated with Fe³⁺ and Co²⁺ ions. The samples were synthesized at 400, 550, 650 and 750 °C, during intervals of 30, 90 and 120 min and under air, N2 and H2 gases. To apply the carbothermic method, chitosan was therm...

We report a simple, efficient manner to assess magnetic interactions, more specifically the exchange interaction, in systems as blocked magnetic nanoparticles. Specifically, we investigate what is the theoretical limit for the external magnetic susceptibility in a system described by the plain old Stoner-Wohlfarth model. We go beyond and introduce...

We synthesize CoFe2O4@BiFeO3 core/shell nanoparticles by coprecipitation and systematically investigate the structural, morphological, and magnetic properties in such nanostructured system. Through structural and morphological characterization, we demonstrate the obtainment of core/shell nanostructure with pure phases. By performing a broad experim...

We investigate the magnetic nanoparticles (fluid) hyperthermia in non-adiabatic conditions through the calorimetric method. Specifically, we propose a theoretical approach to magnetic hyperthermia from a thermodynamic point of view. To test the robustness of the approach, we perform hyperthermia experiments and analyze the thermal behavior of magne...

We investigated magnesium ferrite MgFe2O4 nanoparticles synthesized by the sol-gel method followed by heat treatment at distinct temperatures. Specifically, we evaluated the influence of the heat treatment on the structural, magnetic, electrical, and dielectric properties of particles with dimensions of nm. Then, we brought a route, a synthesis met...

Bismuth layer-structured ferroelectric Bi3R2Ti3FeO15 (R = Bi, Nd, and Gd) ceramics were synthesized by conventional solid-state reaction. All the samples showed an orthorhombic structure with A21am space group. Bi3Nd2Ti3FeO15 and Bi3Gd2Ti3FeO15 presented a reduction in the orthorhombicity when compared to Bi5Ti3FeO15. The magnetic susceptibility of...

Magnetic skyrmions are non-trivial spin textures that resist external disturbances and are promising candidates for use in next generation spintronic devices. However, a major challenge in the realization of devices based on skyrmions is the stabilization of ordered arrangements of these spin textures under ambient temperature and zero applied fiel...

We investigate the structural, morphological, chemical, and magnetic properties of Ni–NiO nanocomposites synthesized through two distinct routes, sol–gel and coprecipitation, followed by calcination. By considering several techniques we show that the resulting nanocomposites, as well as their properties, are strongly dependent on both, synthesis me...

Devices based on spin rectification effects are of great interest for broadband communication applications, since they allow the rectification of radio frequency signals by simple ferromagnetic materials. The phenomenon is enhanced at ferromagnetic resonance condition, which may be attained when an external magnetic field is applied. The necessity...

A presente invenção descreve um dispositivo, processo e uma antena, para uma possível aplicação, formado por uma camada semente, uma camada antiferromagnética (AF) e ferromagnética (FM), que ao ser irradiado por uma micro-onda já pré-estabelecida consegue fazer com que a camada ferromagnética (FM) entre em ressonância ferromagnética (FMR) e com iss...

Materials presenting high spin-orbit coupling are able to convert spin currents in charge currents. The phenomenon, known as inverse spin Hall effect, promises to revolutionize spintronic technology enabling the electrical detection of spin currents. It has been observed in a variety of systems, usually non-magnetic metals. We study the voltage eme...

We investigate the magnetoimpedance effect in ferromagnetic multilayered biphase films. We verify that the films present asymmetric magnetoimpedance behavior and, by playing with the number of the repetitions of the base structure of the multilayer and the probe current frequency, we explore the possibility of tailoring the linear region around zer...

The magnetoimpedance effect is a versatile tool to investigate ferromagnetic materials, revealing aspects on the fundamental physics associated to magnetization dynamics, broadband magnetic properties, important issues for current and emerging technological applications for magnetic sensors, as well as insights on ferromagnetic resonance effect at...

We investigate the angular dependence of asymmetric magnetoimpedance of NiFe/IrMn multilayers and explore the possibility of tuning the linear region of the magnetoimpedance curves by modifying the angle between the applied external magnetic field and exchange bias field, and probe current frequency. We quantify the sensitivity by calculating the rat...

The magnetoimpedance (MI) effect was investigated in NiFe/Ag multilayered (ML) and ML/SiO2/Ag/SiO2/ML structured multilayered (SD) ferromagnetic films grown by magnetron sputtering. The MI measurements were performed with an impedance analyzer over a wide frequency range, from 10 MHz to 1.8 GHz. Sample geometries are mainly responsible for the diff...

In the framework of models that assume planar domain wall formed at the antiferromagnetic part of the interface of exchange-biased bilayers, one cannot distinguish between the cases of high or low ratios between the coupling and the antiferromagnet’s anisotropy fields by using hysteresis loop measurement, ferromagnetic resonance, anisotropic magnet...

Gigahertz magnetoimpedance (MI) curves obtained in an exchange biased Ni81Fe19/Fe50Mn50 multilayer are reported. Experimental MI curves are shifted by the exchange bias field (HEB), following the features presented by the hysteresis curves. Theoretical MI curves, calculated using the classical expression for the impedance of a planar magnetic condu...

Field-dependent transverse permeability characterization of amorphous thin films with nominal composition Fe _73.5 Cu ₁ Nb ₃ Si _13.5 B ₉ was performed for frequencies in the range of 100 kHz –1.8 GHz . Dynamic and static magnetic properties were investigated in films with thickness in the range...

In this work, very high magnetoimpedance measured at frequencies up to 1.8 GHz in nanostructured Fe _73.5 Cu ₁ Nb ₃ Si _13.5 B ₉/ Cu films is reported. Magnetoimpedance ratios of 280% and 50% were observed in multilayered and sandwiched samples, respectively. For the last one, the magnetoimpedanc...

High-frequency differential magnetic permeability and magnetoimpedance measurements were performed in Fe73.5Cu1Nb3Si13.5B9 as-made and annealed thin films at frequencies up to 1.8 GHz. The results show complex dynamical properties characterized by multiple ferromagnetic resonance modes at relatively low frequencies for the amorphous as-made sample....

In this work, we report a comparative study of the magnetoimpedance in sandwiched films with the structure FS/Cu/FS (SWS) and FM/Cu/FM (SWM) where FS=single-layer FeCuNbSiB and FM=multilayer FeCuNbSiB/Cu. Magnetoimpedance ratios of 250% were obtained for the real part of the impedance in the SWM sample, while variations of 100% were reached for the...

This work presents the dynamic and static magnetic properties of an 85nm-thick amorphous thin film precursor of the well-known Finemet material, deposited by RF sputtering. Hysteresis evidences in-plane isotropic properties that are distinguished as contributions of hard and soft axis simultaneously. High-frequency permeability measurements were pe...

Very high magnetoimpedance (MI) measured at frequencies up to 1.8 GHz in single and multilayered thin films with composition Fe73.5Cu1Nb3Si13.5B9 and (Fe73.5Cu1Nb3Si13.5B9+Cu) are reported. The magnetic properties of both systems are also compared. MI ratio as high as 300% for the multilayered samples were obtained.

Magnetoimpedance curves at frequencies up to 1.8GHz for (Ni81Fe19/Ag)n multilayers with n=15, 50 and 100, and thickness ratio tPy/tAg: 1007, 10025, 100100, 20014, 20050 and 200200Å are presented. Evidences of FMR are observed in most samples studied. Samples with 15, 50 and 100 bilayers exhibited a maximum MI ratio of about 100%, 175% and 250%, res...

The magnetic domain structure of the Co70.4Fe4.6Si10B15 glass-covered amorphous microwires Joule-heated of different annealing currents (temperatures) is studied. From the magnetization curves and ferromagnetic resonance features obtained from the impedance spectra measured at different magnetic fields, a domain structure is proposed for the as-pro...

Impedance spectra (100 kHz⩽f⩽1.8 GHz) were measured at different magnetic fields, and magnetoimpedance and magnetization measurements were performed in as-produced and Joule-heated Co70.4Fe4.6Si10B15 glass-covered amorphous microwires. From the magnetization curves and ferromagnetic resonance features obtained from the impedance spectra, it was pos...

In this work, results on the magnetoimpedance (MI) of magnetic amorphous wires with nominal compositions Fe77.5Si7.5B15, Co68.15Fe4.35Si12.5B15 and Co72.5Si12.5B15 are presented. The impedance Z=R+iX has been investigated as function of frequency (from 100kHz up to 1.8GHz) and magnetic field, using a HP4396B impedance analyzer and an appropriate co...

In this work, results on the giant magnetoimpedance (GMI) of a glass-covered amorphous microwires with nominal compositions Co70.4Fe4.6Si15B10 and Fe77.5Si7.5B15 are presented. The impedance /Z=R+iX has been investigated as function of frequency (up to 1.8GHz) and magnetic field (up to +/-400Oe), using a HP4396B impedance analyzer and an appropriat...

In this work, results on the giant magnetoimpedance of glass-covered amorphous microwires with nominal composition Co70.4Fe4.6Si15B10 are presented. The impedance Z=R+iX has been investigated as function of frequency (1 MHz–1.8 GHz) and magnetic field (up to ±400 Oe), using a HP4396B impedance analyzer and an appropriate coaxial microwave cavity. T...