Ferromagnetic Resonance Study of Fe/Cu Multilayer Thin Film

Fe/Cu/Fe multilayer thin film was grown on Si (100) substrate by using magnetron sputtering technique at room temperature. Dynamic and static magnetisations of the film have been investigated using ferromagnetic resonance (FMR) and vibrating sample magnetometer (VSM) techniques in the temperature range of 10–300 K. From the room-temperature in-plane FMR measurements, a growth-induced uniaxial magnetic anisotropy was observed. Out-of-plane FMR measurements exhibited a large magnetic anisotropy due to a large saturation magnetisation of Fe. A computer code was written to simulate the experimental FMR data and to obtain the magnetic parameters of the Fe/Cu/Fe multilayer thin film. g value, effective magnetisation, uniaxial anisotropy field and perpendicular anisotropy constant from the fitting of the angular dependence of the resonance field at both the in-plane and out-of plane geometries were determined. The exchange bias effect was observed from the low-temperature VSM measurements. The saturation magnetisation and coercive field decrease with increasing temperature due to the increase of the thermal fluctuations.     

Annealing Effect on Structural and Magnetic Properties of Cu2MnAl Heusler Alloy Films

Cu₂MnAl Heusler alloy films were grown on MgO (001) substrates by using the ion beam sputtering technique. The films were post-annealed at varying temperatures in order to investigate the influence of annealing on crystal structure and magnetic properties. The structural properties of Cu₂MnAl films have been investigated by using x-ray diffraction (XRD) and magnetic properties have been investigated by both vibrating sample magnetometer (VSM) and ferromagnetic resonance (FMR) techniques. The experimental data indicates that the crystal structure of the films strongly depends on the annealing temperature. When the films were annealed at 200?°C, the saturation magnetization (M _s =250?emu/cm³) achieved its maximum and the coercive field (H _c ??7?Oe) reached its minimum with B2 ordered structure. In addition, FMR results have revealed that the Cu₂MnAl film annealed 200?°C has the highest effective magnetization. The combination of structural and magnetic characterization indicates that the optimum growth temperature is 200?°C for the Cu₂MnAl Heusler alloy films on MgO substrates.     

Ferromagnetic and spin wave resonances in thin layer of expanded austenite phase

Four samples of austenite coatings deposited by reactive magnetron sputtering on silicon substrate at four different temperatures and pressures were investigated by ferromagnetic resonance (FMR) method at room temperature. The expanded austenite phase S (γ _N ) layers with thickness in the 160–273 nm range and concentration of magnetic atoms: 72 % Fe, 18 % Cr and 10 % Ni, were obtained. The coatings with nanometric size grains were strongly textured and grown mostly in [100] direction, perpendicular to the sample surface. Intense FMR spectra were recorded at various angles between the static magnetic field direction and the sample surface. A strong magnetic anisotropy of the main uniform FMR mode was observed and the effective magnetization 4πM _eff determined. Spin wave resonance (SWR) modes were observed in all investigated samples in out-of-plane geometry of the magnetic field. The resonance fields of SWR modes in our samples varied linearly with the spin wave mode number. The value of the effective magnon stiffness constant was determined assuming a parabolic shape of the magnetization variation across the sample thickness.     

Thickness and Temperature Dependence of Exchange Bias in Co/CoO Bilayers

The effects of the ferromagnetic (FM) Co layer thickness on magnetic anisotropies and exchange bias (EB) properties of Co/CoO bilayers have been investigated by using ferromagnetic resonance (FMR) and vibrating sample magnetometer (VSM) techniques. The temperature and thickness dependence of EB were studied in temperature range of 4?C320?K. FMR and VSM measurements show that Co/CoO bilayers exhibit negative exchange bias just below the blocking temperature (T _B). Room-temperature in-plane FMR measurements reveal that the Co layer was epitaxially grown on MgO substrate with four-fold magneto-crystalline symmetry. The data also show that the easy axis of magnetization is in the film plane and parallel to the ??110?? crystallographic directions of MgO substrate in all samples.     

Induced in-plane magnetic anisotropy in YIG films

We have studied the symmetry properties of the in-plane induced magnetic anisotropy in {100} and {110} disks of single crystal YIG epitaxially grown on gadolinium gallium garnet (GGG) substrates. The ferromagnetic resonance (FMR) technique was used to determine the values of the cubic and induced magnetic anisotropies. The induced anisotropy is interpreted in terms of a magnetostrictive magnetic potential energy. We find that the effective field induced in the plane of the film is isotropic for {100} disks but for {110} disks the induced anisotropy is uniaxial within the plane.     

Exchange Bias Effect and Ferromagnetic Resonance Study of NiO/NiFe/NiO Trilayers with Different Thicknesses of NiO Layers

Antiferromagnetic (AFM₁)-ferromagnetic (FM)-antiferromagnetic (AFM₂) multilayer films are fabricated using a magnetron sputtering technique. The AFM₁, FM, and AFM₂ layers are NiO, NiFe, and NiO films, respectively, where AFM₁ and AFM₂ are of the same thickness ranging from 10 to 60 nm. The exchange bias effect and ferromagnetic resonance of NiO/NiFe (50 nm)/NiO have been investigated using the vibrating sample magnetometer (VSM) and ferromagnetic resonance (FMR) meter. Both saturation magnetization (M _s) and coercivity (H _c) increase first and then decrease with the increasing thickness of NiO layers. The maximum values (M _s = 457 kA/m, H _c = 1.86 kA/m) are achieved when the NiO thickness is 30 nm. The in-plane resonance field (H _r∥) and ferromagnetic resonance linewidth (ΔH _∥) show the lowest values (H _r = 77.4 kA/m, ΔH _∥ = 7.2 kA/m) which occur when the thickness of NiO layers is 30 nm. The dependence between exchange bias and NiO film thickness in NiO/NiFe/NiO trilayers has also been discussed.     

Enhanced Ferromagnetic Properties of Co-doped ZnO DMS Nanoparticles

A systematic investigation was done to determine the structural, morphological and magnetic properties of Zn_0.8Co_0.2O nanoparticles synthesized by a simple autocombustion technique. XRD, FE-SEM and EDX measurements were implemented for the structural, morphological and compositional investigation of the product. Additionally VSM was used for the magnetic property investigations of the sample. The average particle size of the nanoparticles was estimated using Debye–Scherrer’s equation and found to be 20.8 nm. Magnetization measurements have shown that the particles have room-temperature ferromagnetic behavior with relatively high coercive fields. Magnetization and the coercive field of the sample increase by decreasing the temperature, as expected. FMR signal confirms the room-temperature enhanced ferromagnetic behavior without Co precipitates.     

Composes ferrimagnetiques fluores de structure Na2SiF6

The magnetic properties of NaMnCrF₆ and of its antitype LiMnCrF₆, both related to trigonal Na₂SiF₆ structure, have been investigated. They are ferrimagnetic with respective Curie temperatures T_C of 21 and 23° K. The values of their asymptotic Curie temperatures θ_P involve ferromagnetic interactions. The observed difference between their respective saturation magnetization (6 and 4 μB/molecule) is discussed and related to the different types of cationic order, using an approached magnetic model with spins oriented along [001] axis. Magnetic properties of some substituted phases are also described.     

Magnetic resonance study of γ-Fe2O3 nanoparticles dressed in oxygen based free radicals

Two composites consisting of γ-Fe₂O₃ (maghemite) nanoparticles covered by two different oxygen-based free radicals derived from a 4-(methylamino)phenol sulphate and 8-hydroxy-1,3,6-trisulfonic trisodium salt acid were prepared and investigated by the magnetic resonance method in the 4–300 K range. Both composites displayed broad and very intense ferromagnetic resonance (FMR) lines originating from γ-Fe₂O₃ agglomerated nanoparticles. The FMR spectrum was fitted satisfactorily at each temperature by two Landau-Lifshitz functions reflecting the existence of magnetic anisotropy in the investigated system. The temperature dependence of the obtained FMR parameters (resonance field, linewidth, integrated intensity) was studied and the results were interpreted in terms of magnetic interactions between free radicals and nanoparticle agglomerates. A comparison with previously studied similar systems containing maghemite nanoparticles was made and conclusions about the role of free radicals were drawn.     

AC Potential-Dependent Concentration Variation and Domain Wall Pinning in Co1−x Zn x (x=0.4−0.5) Nanorods

The Co_1?x Zn _x (x=0.4?0.5) nanorods were synthesized via an AC electrochemical deposition method into anodized aluminum oxide (AAO) templates at different voltages ranging from 10 to 18 V, and nanorods of varying concentrations of Co and Zn were obtained. The characterization tools were used to examine different aspects of nanorods, e.g., shape, size, morphology, chemical composition, and magnetic behavior. Scanning electron microscope (SEM) images show that CoZn nanorods have length L=1μm and diameter d=50 nm. The grain size was calculated to be 25.4 nm using an X-ray diffraction (XRD) technique. The XRD also shows some other phases of ZnCoO. The M?H loops measured by a vibrating sample magnetometer (VSM) at room temperature show pure ferromagnetic behavior at all AC potentials. The nanorods show magnetic isotropic behavior due to strong magnetic interactions and presence of random nanorods. The potential-dependent coercivity H _c and saturation magnetization M _s show a non-linear curve which is explained on the basis of magnetic islands and domain wall pinning. This study is useful to tune the magnetic properties of nanorods by a simple and low-cost technique.     

Effect of annealing on the magnetic properties of Y3Fe5O12 and Y2.95La0.05Fe4.7Ga0.3O12 films

We have studied the effect of high-temperature (1273–1673 K) and low-temperature (523–873 K) anneals in air, O₂, and N₂ on the magnetic properties of Y₃Fe₅O₁₂ and Y_2.95La_0.05Fe_4.7Ga_0.3O₁₂ garnet ferrite films. The films, 5–15 μm in thickness, were grown on (111)-oriented gadolinium gallium garnet (Gd₃Ga₅O₁₂) substrates by liquid phase epitaxy. High-temperature annealing was shown to change the saturation magnetization and increase the ferromagnetic resonance linewidth ΔH of the films. Low-temperature annealing at 723 K in flowing dry oxygen for 20 h reduces the ΔH of the ferromagnetic resonance by 18–25% and makes it insensitive to changes in temperature and ambient humidity.     

Ferromagnetic Resonance Studies of Exchange Biased CoO/Fe Bilayer Grown on MgO Substrate

Dynamic and static magnetizations of an exchange biased bilayer system which is constructed as a proximity of a CoO layer on an Fe-layer grown on the (100) oriented MgO substrate by ion beam sputtering technique have been investigated by ferromagnetic resonance (FMR) and vibrating sample magnetometry (VSM) techniques. The room-temperature FMR measurements reveal that the Fe layer is epitaxially grown on MgO substrate with four-fold magnetocrystalline anisotropy and the hard magnetization axis of the sample is the [100] crystallographic directions of MgO substrate. We have determined the g-value, effective magnetization, magnetocrystalline anisotropy constants and contributions to FMR linewidth due to the intrinsic Gilbert damping and inhomogeneity of magnetization by using Landau–Lifshitz–Gilbert (LLG) equation. We observed an unusual FMR line shape attributed to impedance switching of resonance cavity and complex component of conductivity of sample system. The low-temperature FMR measurement shows asymmetric hysteretic behavior of resonance field related to magnetic coupling of ferromagnetic and antiferromagnetic layers. From both FMR and VSM measurements between 10–300 K, the magnetocrystalline anisotropy is observed to dominate above blocking temperature, while unidirectional anisotropy is observed to dominate below blocking temperature over internal magnetic anisotropy. FMR spectra have a comparatively small linewidth between 40–100 Oe, which indicates to a high crystallinity of the Fe film. Gilbert constant was calculated as 0.007 from the linewidth fitting of FMR spectra. This small value is a suitable for reducing the critical switching current used in magnetic tunneling junction. Detailed exchange bias studies were carried out for hard and easy axis of the sample in the temperature range of 10–300 K. From both low-temperature FMR and VSM measurements, the blocking temperature of the system was determined as ～60 K.     

Penetrative ferroconvection in a porous layer

Penetrative convection in a horizontal ferrofluid-saturated porous layer in the presence of a uniform applied vertical magnetic field has been investigated via the internal heating model using the Brinkman-extended Darcy equation. The rigid-isothermal boundaries of the porous layer are considered to be either paramagnetic or ferromagnetic. The eigenvalue problem is solved numerically using the Galerkin method with either thermal or magnetic Rayleigh number as the eigenvalue. The stability of the system is significantly affected by the internal heating in the porous layer. It is noted that the paramagnetic boundaries with large magnetic susceptibility delay the onset of penetrative ferroconvection the most when compared to very low magnetic susceptibility as well as ferromagnetic boundaries. An increase in the value of magnetic Rayleigh number (R _m ), heat source strength (N _S ) and non-linearity of magnetization (M ₃) is to hasten the onset of ferroconvection. In addition, the stability of the system when heated from above and also in the absence of thermal buoyancy has been discussed in detail.     

The magnetic anisotropy of thin epitaxial CrO<Subscript>2</Subscript> films studied by ferromagnetic resonance

The magnetic anisotropy of thin epitaxial films of chromium dioxide (CrO₂) has been studied as a function of the film thickness by the ferromagnetic resonance (FMR) technique. CrO₂ films with various thicknesses in the range from 27 to 535 nm have been grown on (100)-oriented TiO₂ substrates by chemical vapor deposition using CrO₃ as a solid precursor. In a series of CrO₂ films grown on the substrates cleaned by etching in a hydrofluoric acid solution, the FMR signal exhibits anisotropy and is strongly dependent on the film thickness. The magnetic properties of CrO₂ films are determined by a competition between the magnetocrystalline and magnetoelastic anisotropy energies, the latter being related to elastic tensile stresses caused by the lattice mismatch between the film and the substrate. In the films of minimum thickness (27 nm), this strain-induced anisotropy is predominant and the easy magnetization axis switches from the [ 001] crystallographic direction (characteristic of the bulk magnet) to the [ 010] direction.     

Preparation and characterization of bamboo charcoal/Ni0.5Zn0.5Fe2O4 composite with core-shell structure

Bamboo charcoal particles coated with Ni_0.5Zn_0.5Fe₂O₄, forming a core-shell structure, were synthesized by hydrothermal method. A structural characterization by FTIR, XRD and TEM proved that nanometer-sized Ni_0.5Zn_0.5Fe₂O₄ in the composite was responsible for the ferromagnetic behavior of the composite. Effects of the bamboo charcoal and temperature on the magnetic properties of bamboo charcoal/Ni_0.5Zn_0.5Fe₂O₄ composite have been studied by ferromagnetic resonance (FMR) technique. The measuring temperature was varied from 220 to 460 K. A clear evolution from ferromagnetic resonance to paramagnetic resonance (EPR) was observed as a function of temperature, which is related with the passage through the Curie point (∼ 380 K).     

Tuning the permeability spectra with a half-free ferromagnetic underlayer in (NiFe/IrMn)n exchange-biased multilayers

The influence of a half-free ferromagnetic underlayer on the static and microwave magnetic properties in [NiFe/IrMn]_n exchange bias multilayer thin film system has been systematically investigated. By changing the thickness of the half-free ferromagnetic underlayer, the linewidth of the ferromagnetic resonance (FMR) in this system can be tuned from 0.9 to 2.4 GHz. Theoretical fitting of the FMR frequencies based on the Landau-Lifshitz-Gilbert equation is also carried out to quantitatively identify the effective anisotropy fields and Gilbert damping parameters. The results provide an effective and flexible way to tailor the microwave permeability spectra and broaden the frequency linewidth toward the low frequency range in [ferromagnetic/antiferromagnetic]_n exchange bias multilayer films system. This approach has potential application for tunable wideband high frequency noise filters.     

Fe<Subscript>73.5</Subscript>Cu<Subscript>1</Subscript>Nb<Subscript>3</Subscript>Si<Subscript>15.5</Subscript>B<Subscript>7</Subscript> Thin Films Deposited by HiPIMS: Magnetic and Magnetostrictive Behavior

Results concerning the magnetic, magnetostrictive, structural, morphological, and topological properties of amorphous and nanocrystalline Fe _73.5Cu ₁Nb ₃Si _15.5 B ₇ thin films deposited using the high power impulse magnetron sputtering (HiPIMS) technique are reported. In as-deposited state, the samples are amorphous, the nanocrystalline state being achieved for samples isothermally annealed at adequate temperatures, in an electric furnace. For the optimum annealing temperature (475 ^°C), a decrease by about 70 % for the coercive magnetic field (50 A/m) and up to 1 order of magnitude for the saturation magnetostriction (~1×10^?6), compared to the as-deposited state, was obtained. The X-ray diffractometry (XRD) and scanning electron microscopy (SEM) results for samples thermally treated at 475 ^°C revealed a 53.6 % crystalline volume fraction of α-Fe(Si) nanograins with an average size of about 15 nm and a Si content of 10.78 %, uniformly dispersed in a residual amorphous matrix. Using the saturation magnetostriction values determined using the cantilever deflection method and the crystalline volume fraction of α-Fe(Si) nanograins, the contribution of crystalline phase to the saturation magnetostriction was also determined.     

Preparation of magnetic coatings from strontium hexaferrite on tin and cardboard by cold rolling

A finely dispersed powder of strontium hexaferrite doped with aluminum of the composition SrFe_12?x Al _x O₁₉ with an aluminum content x = 0.6 ± 0.1 is prepared through crystallization of oxide glasses. The powder is characterized by a saturation magnetization of 60.2 A m²/kg and a coercive force of 550 kA/m. The hexaferrite particles predominantly have the shape of thick hexagonal platelets with a diameter ranging from 300 to 500 nm and a thickness-to-diameter ratio varying from 0.3 to 0.5. Magnetic coatings on tin and cardboard substrates are produced by cold rolling of strontium hexaferrite powders. It is shown that hexaferrite particles in the magnetic coatings have the preferred orientation of the well-developed facets along the rolling plane, which manifests itself in anisotropy of the magnetic properties of the coatings. The degree of texturing in the strontium hexaferrite coatings on cardboard and tin substrates is equal to 44 and 66%, respectively.     

Magnetism of Nano-Graphene with Defects: A Monte Carlo Study

The effect of the defects on magnetic properties of a bilayer Ising ferromagnetic antiferromagnetic model is studied by Monte Carlo simulations, for a nano-graphene lattice with spins that can take the values σ=3/2 and S=5/2. We consider two ferromagnetic and antiferromagnetic bilayers with N=42 spins, with a random number of defects. We only consider the nearest-neighbor interactions between the site i and j on each layer. The effects of the defects on magnetization are investigated for fixed temperature, crystal field, and magnetic field values. The thermal dependency of each layer magnetization is calculated for fixed defect rate values K ₃ and K ₅, the crystal field, and external magnetic field. The magnetization hysteresis loops for several rate defects are also investigated as a function of the external magnetic field.     

Evolution of Phononic Band Gaps in One-Dimensional Phononic Crystals that Incorporate High-<Emphasis Type="Italic">T</Emphasis><Subscript>c</Subscript> Superconductor and Magnetostrictive Materials

In this work, we calculate the reflectance of one-dimensional phononic crystals (1D PnCs) using the transfer matrix method. We present numerical results for two different PnC structures, the first one, PnCs1, contains high- T _c superconducting compound (Bi-2223) and the second, PnCs2, contains a giant magnetostrictive material (Terfenol-D). Magnetostriction is a property of ferromagnetic materials that causes them to change their shape/dimensions when subjected to external magnetic field. PnC studies that dealt with such materials are few. In this study, we focus on discussing the effects of the temperature and the magnetic field on the phononic gaps of these PnCs. For PnCs1, numerical results show that local resonant modes of elastic waves with brilliant sharpness can be realized. In addition, increasing the temperature leads to a decrease in the gap width which can be controlled by the magnetic field due to the effect of the magnetic field on the velocity of waves in the high- T _c superconducting compound, the magnetic field effectively can widen the gap. For PnCs2, numerical results show that the gap width increases by increasing the magnetic field because the magnetostrictive material directly expanded in the presence of the magnetic field.