FMR Linewidth Research Articles

Effect of Gd3+ on dielectric and magnetic properties of Y3Fe5O12

The Gd3+ doped Y3−xGdxFe5O12 (x=0.0, 0.05, 0.15, and 0.25) nanopowders were prepared using modified sol–gel route. The structural characterizations such as X-ray diffraction, transmission electron microscopy has been carried out. The nanopowders were sintered at 700°C/3h. The lattice parameters and density of the samples were increased with an increase of Gd3+ concentration. The microstructure was analyzed using atomic force microscopy. The room temperature dielectric (ε′ and ε″) and magnetic (μ′ and μ″) properties were measured in the frequency range 5–50GHz. with Gd3+ the dielectric properties were enhanced, but there is a decrease in the magnetic properties. The room temperature magnetization studies were carried out up to 1.5T. the saturation and remnant magnetization were decreased with an increase of gadolinium concentration. These garnets have low permeability, low losses and a broad distribution of FMR line width which makes them a promising material for microwave devices can be used in the high frequency range i.e. up to 50GHz.

Magnetocrystalline Anisotropy and FMR Linewidth of Zr and Zn-Doped Ba-Hexaferrite Films Grown on MgO (111)

Ba M-type ferrite films of composition BaFe11Zn0.5Zr0.5O19 were grown on MgO (111) substrates by pulsed laser deposition. Both Zn and Zr divalent ions were introduced to reduce the magnetic anisotropy field to ~7.5 kOe, or 46% lower than the parent Ba M-type compound. Temperature dependence of magnetization over 25 to 350°C was investigated, indicating a Curie temperature of 320°C. Ferromagnetic resonance linewidth, as the peak-to-peak power absorption derivative at 9.55 GHz, was 120 Oe. The substituted sample had a K1 of ~0.920 × 106 erg/cm3. Such sample properties provide an attractive option for self-biased microwave devices applications operating at X (8-12 GHz) and Ku bands (12-18 GHz) as circulators and isolators.

Co2FeAl thin films grown on MgO substrates: Correlation between static, dynamic, and structural properties

Co2FeAl (CFA) thin films with thickness varying from 10 nm to 115 nm have been deposited on MgO(001) substrates by magnetron sputtering and then capped by Ta or Cr layer. X-rays diffraction (XRD) revealed that the cubic $[001]$ CFA axis is normal to the substrate and that all the CFA films exhibit full epitaxial growth. The chemical order varies from the $B2$ phase to the $A2$ phase when decreasing the thickness. Magneto-optical Kerr effect (MOKE) and vibrating sample magnetometer measurements show that, depending on the field orientation, one or two-step switchings occur. Moreover, the films present a quadratic MOKE signal increasing with the CFA thickness, due to the increasing chemical order. Ferromagnetic resonance, MOKE transverse bias initial inverse susceptibility and torque (TBIIST) measurements reveal that the in-plane anisotropy results from the superposition of a uniaxial and of a fourfold symmetry term. The fourfold anisotropy is in accord with the crystal structure of the samples and is correlated to the biaxial strain and to the chemical order present in the films. In addition, a large negative perpendicular uniaxial anisotropy is observed. Frequency and angular dependences of the FMR linewidth show two magnon scattering and mosaicity contributions, which depend on the CFA thickness. A Gilbert damping coefficient as low as 0.0011 is found.

Magnetic-stress-assisted damping of magnetization precession in multilayered metallic films

Micromagnetic dynamics of spin relaxation in multilayered metallic films of stacked microelectronic devices is modeled by a modified Landau–Lifshitz–Gilbert equation with a newly introduced form of damping torque owing its origin to coupling between precessing magnetization-vector and stress-tensor of combined intrinsic and extrinsic magnetic anisotropy. Based on the magnetization energy loss equation, the exponential relaxation time as a function of precession frequency and angle of applied rf-field is obtained, depending upon two parameters of intrinsic and extrinsic damping torques acting on precessing magnetization. It is shown that theoretically obtained from the Gabor uncertainty relation the FMR linewidth, originating from the above magnetic-stress-assisted damping of magnetization precession, provides proper account for the empirical non-linear linewidth-vs-frequency curves deduced from recent in-plane FMR measurements on multilayered ultrathin films of ferromagnetic metals.

Ferromagnetic resonance, transverse bias initial inverse susceptibility and torque studies of magnetic properties of Co2MnSi thin films

Magnetic properties of Co2MnSi thin films of 20 nm and 50 nm in thickness grown by radio frequency sputtering on a-plane sapphire substrates have been studied. X-ray diffraction (XRD) revealed that the cubic Co2MnSi axis is normal to the substrate and that well defined preferential in-plane orientations are present. The static magnetic properties were studied at room temperature by conventional magneto-optical Kerr effect (MOKE), transverse bias initial inverse susceptibility and torque (TBIIST) MOKE. The dynamic magnetic properties were investigated by micro-strip ferromagnetic resonance (MS-FMR) at room temperature. The resonance and TBIIST measurements versus the direction of the in-plane applied magnetic field reveal that the in-plane anisotropy results from the superposition of a two-fold and a four-fold symmetry. The directions of the principal axes of the twofold anisotropy are sample dependent. The angular dependence of remanent normalized magnetizations and coercive fields, studied by MOKE are analyzed within the frame of a coherent rotation model. A good agreement is observed between the field anisotropy values obtained from MS- FMR and from TBIIST data. Frequency and angular dependence of FMR linewidth has been studied. Apparent damping coefficient of 0.0112 has been measured for 50 nm thick sample.

Preparation and characterization of barium hexagonal ferrite thin films on a Pt template

M-type barium hexagonal ferrite films with the crystallographic c axis out of plane were successfully deposited onto a Pt template using a metallo-organic decomposition technique. For the best film, x-ray diffraction patterns revealed strong (00l) reflections and a texture fraction of 0.953, confirming the out of plane c axis orientation. Atomic force microscopy images confirm hexagonal grains in this film with an average lateral size of ∼500 nm. Hysteresis loops revealed a high effective out of plane anisotropy field, high perpendicular remanent magnetization Mr=0.93 Ms, and out of plane coercivity of 4.5 kOe. Out of plane Ferromagnetic Resonance measurements determined the values of γ=2.79 GHz/kOe and effective anisotropy field. The full width at half maximum FMR linewidth was 338 Oe at 60 GHz. These properties are suitable for possible use in on-wafer millimeter wave devices.

Relaxation mechanism for ordered magnetic materials

We have formulated a relaxation mechanism for ferrites and ferromagnetic metals whereby the coupling between the magnetic motion and lattice is based purely on continuum arguments concerning magnetostriction. This theoretical approach contrasts with previous mechanisms based on microscopic formulations of spin-phonon interactions employing a discrete lattice. Our model explains for the first time the scaling of the intrinsic FMR linewidth with frequency, and 1/M temperature dependence and the anisotropic nature of magnetic relaxation in ordered magnetic materials, where M is the magnetization. Without introducing adjustable parameters our model is in reasonable quantitative agreement with experimental measurements of the intrinsic magnetic resonance linewidths of important class of ordered magnetic materials, insulator or metals.

Surface roughness and magnetic properties of Co/SiO2/Si(100) polycrystalline films deposited via DC magnetron sputtering

For polycrystalline films of cobalt that have the thickness t ≈ 1.3-133 nm and that are deposited via DC magnetron sputtering on SiO 2 (0.1 µ m)/Si(100) substrates, surface-roughness root-mean-square amplitude σ and surface correlation length ξ , which characterize the roughness of film surfaces, as well as saturation mag- netization 4 π M 0 , width of ferromagnetic-resonance line ∆ H , coercitivity H C , and saturation fields H S , are stud- ied as functions of film thickness t . It is shown that the behavior of dependences H C ( t ) and H S ( t ) coincides with the behavior of dependence σ ( t )/ t , whereas the behavior of 4 π M 0 ( t ) depends on ratio t / σ ( t ) . The dependence of the FMR line width on the film thickness, ∆ H ( t ) , is characterized by a minimum of ∆ H ≈ 60 Oe present in the region of thicknesses of 30 to 60 nm. The behavior of dependence ∆ H ( t ) is determined by ratio σ ( t )/ t at small thicknesses t ≤ 5 nm and by the behavior of σ ( t ) at t ≥ 5 nm.

Magnetic and Relaxation Properties of (CO<sub>45</sub>Fe<sub>45</sub>Zr<sub>10</sub>)x(Al2O3)<sub>1-x</sub> Thin Films

The work is devoted to the research of the magnetic resonance properties of composite (metal-dielectric) films and revealing their relationship with the nanostructure characteristics and degree of crystallinity. The FMR line width and resonance position for two series of composite films have been investigated. First films series has a small metal crystal phase content. The second one contains metal oxide and amorphous. The results of work shows that oxidation of a metal phase displaces percolation bound to area of the big metal concentration. Strong changes of FMR properties of the films are observed below the percolation bound. The significant changes of FМR properties are connected to nanostructural transformations in the ferromagnetic granules topology and presence of metal phase oxide.

Synthesis and study of the magnetic characteristics of nanocrystalline cobalt films

The effect of various technological factors on the main magnetic characteristics of nanocrystalline cobalt films obtained by chemical deposition is studied. The effective saturation magnetization, uniaxial anisotropy, coercive force, and other characteristics of local spots of films were measured using a scanning FMR spectrometer over the decimeter wavelength range. A technique for preparing substrates is developed, and the optimum technological conditions of thin-film synthesis are found making it possible to significantly decrease magnetic inhomogeneities across the area and thickness of samples. It is shown that one can significantly decrease the FMR linewidth and increase the magnetic permeability of films in a given microwave frequency range.

Ferromagnetic resonance spectra in patterned and unpatterned NiFe/Pt films

AbstractThe ferromagnetic resonance in nanostructured Ni81Fe19 films comprising flim parts and wire parts covered with Pt has been investigated. In contrast to the systematic variation of the FMR linewidth for the film parts, the linewidth for the nanostructured wire parts shows an irregular change with changing the thickness of Pt. This irregular change indicates that the spin current absorption in the Pt layer cannot fully account for the linewidth change in the wire parts. This FMR‐linewidth variation can be argued in terms of the competition between the spin pumping and the roughness effect. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Chemical and structural characterization of barium hexaferrite films deposited on 6H-SiC with and without MgO/BaM interwoven layers

High quality epitaxial barium hexaferrite (BaM) films with saturation magnetization of 4.3 kG, coercivity of 389 Oe, and FMR linewidth of 500 Oe, have been deposited by pulsed laser deposition on 6H-silicon carbide (SiC) single crystal substrates using an interwoven layer of magnesium oxide (MgO) and BaM of approximately 16 nm thick. This paper presents a chemical and structural study of the intermediate stages of BaM film growth on the interwoven layers compared to intermediate stages of BaM film growth directly on a SiC substrate. The purpose of these experiments is to understand the role of the interwoven layers and thus further improve the magnetic properties of BaM integrated with SiC substrates. X-ray photoelectron spectroscopy surface analysis and depth profiling shows that the interwoven layers effectively eliminate silicon diffusion into the bulk BaM film, and prevent the Fe diffusion which reduces Fe/Ba ratios in films deposited without the interwoven layers. By comparing the initial stages of film growth on the MgO/BaM interwoven layers with film deposited with the same number of BaM shots on a bare SiC substrate, scanning electron microscopy and atomic force microscopy results suggest that the MgO/BaM interwoven layers promote two-dimensional growth and improve the crystallographic texture of the BaM films, likely through relief of the lattice mismatch.

A ferromagnetic resonance study of NiFe alloy thin films

NiFe alloy films with thicknesses in the range from 60 to 150 Å were sputtered onto Si (0 0 1) wafers by DC magnetron sputtering, and then characterized by in-plane ferromagnetic resonance technique (FMR) at x-band. The FMR field ( H R) and linewidth (Δ H) were studied as a function of the in-plane angle, ϕ H, film thickness, t, and temperature, T. The main effects of temperature on the magnetic properties of these films is to increase the in-plane uniaxial anisotropy and to induce a surface anisotropy that pushes the magnetization out-of-plane. These anisotropies were found to vary with thickness and temperature. The main processes that determine the line broadening are the intrinsic conduction mechanism and the in-plane uniaxial dispersions.

Magnetic properties and structure of thin Ni–Mn–Sn films and alloys

We report structural and magnetic properties of Ni–Mn–Sn films and compare them with those of the bulk Ni–Mn–Sn alloys. Bulk Ni 50Mn 50− x Sn x ( x≈13–14) Heusler alloys show that at room temperature L2 1 (or B2) ordering for x=14 and modulated martensitic structure for x=13, and exhibit martensitic transformations typical of this system. The flash-evaporated films (200 nm in thickness) deposited from the powders obtained from the same alloys show a X-ray diffraction (XRD) of almost the same lattice spacing but completely different peak intensities with the most intense (1 1 1) reflection, resulting either from a high (1 1 1) texture or the L1 0 ordering. Magnetic properties of the films are typical of soft magnetic films with M s(0 K)≈650 Gs (4 πM eff=8000 Gs) with no sign of the martensitic transformation except for some anomalies in the FMR linewidth.

Spin dynamics at low microwave frequencies in crystalline Fe ultrathin film double layers using co-planar transmission lines

Magnetic damping has been studied in magnetic double layers using a network analyzer (NA) with a coplanar transmission line. The magnetic films consisted of ultrathin crystalline films of Fe separated by an Au spacer. The films were deposited on GaAs(0 0 1) substrates using the molecular beam epitaxy (MBE) technique. NA-ferromagnetic resonance (NA-FMR) measurements were carried out along the magnetic hard axis, allowing one to follow the frequency FMR linewidth down to the 1 GHz range of frequencies. It will be shown that the FMR linewidth in the NA-FMR measurements is not entirely described by Gilbert damping. The additional contribution in the frequency linewidth increases with decreasing frequency, and is most likely caused by dipolar fields associated with an inhomogeneous RF field around the coplanar transmission line.

Effects of SiO2 Addition on Microstructure and Magnetic Properties of Yttrium Iron Garnet

Pore free Yttrium Iron Garnet (YIG) ceramics with high density and low magnetic loss were manufactured by conventional ceramic processing. By small additions of SiO2, pores captured inside grains were effectively eliminated, and the number of pores in grain boundaries was markedly reduced. The density of specimens was 99.6% of the theoretical density. The FMR linewidth of a specimen was 47 Oe, which is comparable to that of other YIG specimens produced by more expensive and elaborate process such as hot pressing. However, adding more than 1 mol% SiO2 deteriorated the sintering characteristics of the YIG specimen. The added SiO2 may segregate at grain boundaries and inhibit the grain growth. As a result, the average grain size and sintered density were reduced in the case of SiO2 addition more than 1 mol%.

Magnetic properties of YIG (Y3Fe5O12) thin films prepared by the post annealing of amorphous films deposited by rf-magnetron sputtering

We report magnetic properties of Y3Fe5O12 (YIG) films on thermally oxidized Si (100) and (Gd3Ga5O12) GGG (111) substrates. Amorphous YIG films with the cation ratio Y:Fe=3.04:4.96, deposited by rf-magnetron sputtering at room temperature in pure argon atmosphere, were crystallized by postannealing (600–900 °C) of amorphous films in air and in 500 ppm oxygen. While postannealed YIG films on GGG substrates were well textured, those on Si (100) were randomly oriented. High-quality YIG films could be better obtained in the reduced (500 ppm O2) oxygen atmosphere than air since more effective YIG growth during annealing process and lower FMR linewidth (ΔH) of films could be achieved.

Ｃｕ／Ｎｉ８０Ｆｅ２０／Ｎ（Ｎ＝Ｃｕ，Ｃｕ／Ｐｔ）薄膜におけるＦＭＲ線幅とスピン拡散長

We have investigated the magnetic damping in two types of multilayer films, Cu(10 nm)/Ni80Fe20(3 nm)/Cu (dCu) and Cu(10 nm)/Ni80Fe20(3 nm)/Cu(dCu)/Pt(2 nm). Temperature dependence of the damping parameter and FMR linewidth with various Cu thickness dCu were measured. Spin diffusion length increased with decreasing temperature. We also measured the temperature dependence of FMR linewidth for the Cu/Ni80Fe20/Cu(dCu)/Pt films with dCu=400 nm, 800 nm. The increase of FMR linewidth with decreasing temperature suggested that the damping increased by spin diffusion in Cu layer.

Ferromagnetic Resonance in Bulk and Microparticle Samples of Mn1.3Fe1.7O4

Ferromagnetic resonance experiments on polycrystalline manganese ferrites Mn 1.3 Fe 1.7 O 4 are presented in a systematic way. The temperature dependence of the linewidth has been studied on samples with different sizes (0.025 mm 0.15 mm. Classical contributions to the FMR linewidth according to Sparks' outline are considered in the whole range of temperature. Contributions of porosity, surface pits, anisotropy, slowly and rapidly relaxing impurities, valence-exchange and eddy-current mechanisms are analyzed. The FMR linewidth increases with decreasing sample size. This observed dependence is attributed to the decrease of the surface contribution with increasing sample size.

Ferromagnetic resonance in nanocrystalline Fe 73.5CuNb 3Si 13.5B 9 (Finemet)

The ferromagnetic resonance linewidth of Fe 73.5CuNb 3Si 13.5B 9 melt-spun ribbons has been investigated as a function of annealing temperature. Fe 73.5CuNb 3Si 13.5B 9 possesses an ultrafine grain structure which can be altered by suitable annealing to exhibit a combination of excellent soft magnetic characteristics and high saturation induction. It is a ferromagnetic metal consisting of crystallites whose anisotropy axes are randomly oriented and which may interact with each other via exchange or dipolar fields. When annealed at moderate temperatures, Fe 73.5CuNb 3Si 13.5B 9 is characterized by an extremely low coercive field, and is useful in magnetic cores and memories. At a critical temperature (∼600°C), the grain size rapidly increases with annealing temperature. This onset of crystallization is accompanied by a relatively abrupt increase in the FMR linewidth, the magnetic anisotropy field, and the coercive field. We extend the scaling arguments of Herzer to explain these obviously related phenomena.