Ferrimagnetic Resonance Linewidth Research Articles

Ferrimagnetic resonance linewidths of thick barium hexaferrite films on MgO [111

C-axis oriented barium hexaferrite films having thickness from 3-30 /spl mu/m were deposited onto 0.5 mm magnesium oxide (MgO) [111] substrates by pulsed laser ablation deposition, and were characterized by magnetometry and ferrimagnetic resonance (FMR) measurements. The FMR linewidth for as-produced 30 /spl mu/m films was 0.65-0.70 kOe, while those of thinner (3 /spl mu/m) films was near 0.50 kOe. The narrowest linewidth of /spl sim/0.06 kOe was obtained for a 3 /spl mu/m film after annealing for two hours. However, increased annealing time beyond two hours caused an increase in FMR linewidth. The FMR linewidth of 30 /spl mu/m films where from 55-77% of the MgO substrate was removed decreased by 0.15-0.20 kOe compared to as-produced films. Further improvement in the FMR linewidth to 0.20 kOe was obtained by a two hour annealing. These FMR results are discussed in terms of the homogeneity, planar stress, and stoichiometry of these thick pulsed laser deposited films.

Microwave envelope solitons in YIG film under oblique magnetisation

A detailed study of the output pulse profiles and envelope soliton characteristics are studied in a YIG film under oblique magnetisation for different input pulse widths, operating frequencies and ferrimagnetic resonance line widths. Dispersion characteristics and nonlinear characteristics of the YIG film are predicted by the first order multiple scale method. The analysis of the soliton in the YIG film is carried out using a split step Fourier method for arbitrary orientation of magnetisation. The conditions for the bright and dark soliton are established using the Lighthill criterion. A switchable bright to dark soliton is theoretically predicted by varying the angle of DC magnetisation. Pulse compression is also estimated for different magnetisation angles.

Temperature dependence of spin-lattice relaxation in rare-earth iron garnets

The spin-lattice relaxation rate in iron garnets containing ions of the rare-earth series features a peak in the temperature range from 30 to 100 K that is consistent throughout the group. This effect is important in microwave applications at liquid nitrogen temperatures because magnetic losses increase directly with the intrinsic ferrimagnetic resonance linewidth ΔH, which in turn is proportional to the relaxation rate τ−1. The decrease in X-band linewidth with lowering temperatures is accounted for by the Orbach exponential relation for τ−1 of individual paramagnetic rare-earth ions. To explain the decrease in ΔH above the peak, the Orbach function is multiplied by the magnetic exchange energy between the iron and rare-earth spins. Computations of the linewidth as a function of temperature for Dy3+, Ho3+, Er3+, and Yb3+ are made by utilizing the multiple sublattice molecular-field theory. By fitting theory to data, values are extracted for excited state energy splitting D that enters the exponent (−D/kT) of the Orbach function. Measurement data from high purity yttrium iron garnet also confirm that iron relaxation rates decrease monotonically with reducing temperatures, indicating that microwave magnetic loss at cryogenic temperatures can be reduced below room temperature values if offending rare-earth impurities are removed.

Microwave properties of pulsed laser deposited Sc-doped barium hexaferrite films

The properties of thick BaScxFe12−xO19 (0.3<x<0.6) scandium hexaferrite films were measured by static and microwave field techniques. Films were deposited by pulsed laser ablation onto c-plane sapphire at oxygen pressures of 20 and 50 mTorr. Vibrating sample magnetometer measurements as corroborated by x-ray data showed that the films below 3 μm had easy axis of magnetization (c-axis) normal to the film plane with saturation magnetization values of 3.0–3.8 kG. From the ferrimagnetic resonance frequency versus external magnetic field, we deduced a g value of 1.96±0.03 and uniaxial anisotropy field of ∼10 kOe. The ferrimagnetic resonance linewidth for the film thicker than 5 μm was maximum at 32 GHz and decreased with increasing frequency, indicating evidence for nonuniform magnetic field scattering internally. However, the linewidths were lower for films having thickness below 3 μm.

LPE-like growth of YIG ferrimagnetic thin films by pulsed laser ablation with molten droplets

Yttrium iron garnet (YIG) films were grown by pulsed laser ablation (PLA) on (111) Gadolinium Gallium Garnet (GGG) substrates. The second harmonic of YAG laser (532 nm) with a high laser fluence was employed to produce YIG droplets efficiently. It was found that YIG films prepared at RT substrates have a large number of solidified droplets of various sizes. Highly oriented YIG crystals were grown on the (111) GGG substrate heated at 860 °C by PLA using a large number of molten droplets, suggesting an LPE-like growth. This YIG film shows a small ferrimagnetic resonance linewidth of 7.5 Oe. This value is quite small for films prepared by vapor-phase epitaxy techniques.

Two-magnon processes and ferrimagnetic linewidth calculation in manganese ferrite

A procedure has been developed to obtain the two-magnon linewidth contributions in single and polycrystalline ferrites in which, working with ferrimagnetic resonance experiments, the applied field was only slightly larger than the value required to saturate the sample. This theory has been shown to work in manganese ferrites. Single-crystal ${\mathrm{MnFe}}_{2}{\mathrm{O}}_{4}$ has been prepared by the floating-zone technique and polycrystalline ferrite by the ceramic method. The spinel structure and composition have been confirmed by x-ray and inductively coupled plasma spectrometry, respectively. Fitting of the experimental ferrimagnetic resonance linewidth obtained by means of the Bloch-Bloembergern formalism show errors less than 4%. The fit gave the following parameters: averaged radius of the sample surface pits, porosity in polycrystalline sample, activation energy, and values of the conductivity. The values of the activation energy imply the existence of ${\mathrm{Fe}}^{2+}$ cations in the sample. Additional measurements on magnetization in manganese ferrites are presented.

Dependence of the ferrimagnetic resonance linewidth on sintering conditions in manganese ferrite

Ferrimagnetic resonance linewidth of manganese ferrites, Mn1.0Fe2.0O4 has been measured at 8.9 GHz from 77 to 320 K. Single crystal was prepared by floating zone technique and their composition confirmed by inductively coupled plasma spectrometry. Polycrystalline samples were sintered under different conditions of temperature, time, and atmosphere. Eddy current and valence exchange contributions according to Sparks’ theory and a new procedure for evaluating superficial and porosity mechanisms are taken into account to analyze the ferrimagnetic resonance linewidth. Different contributions are present depending on sintering conditions: valence exchange mechanism appears only in samples sintered under low temperatures and high pressures; conductivity decreases for samples sintered at high pressures; porosity is highly raised up when sintering time decreases. Resonance fields, obtained from experimental data, are used to calculate anisotropy fields for polycrystalline samples.

Oriented barium hexaferrite films grown on amorphous substrates

Pulsed laser deposition has been investigated as a means to obtain c-axis oriented barium hexaferrite films on amorphous substrates. Three film growth approaches were used: (1) deposition from a bulk polycrystalline barium hexaferrite target directly onto fused quartz substrates; (2) post-annealing of the as-deposited films; and (3) deposition onto a zinc oxide (ZnO) buffer layer on fused quartz, which was also grown using PLD. The first approach yielded four phases: amorphous, Fe 3O 4 (magnetite), α-Fe 2O 3 (hematite), and BaFe 12O 19 (barium hexaferrite). Films grown at temperatures greater than about 750°C and 100 mTorr were single-phase barium hexaferrite with texture, but exhibited no significant c-axis orientation. However, annealing the amorphous films at 700°C for 6 h produced a c-axis oriented barium hexaferrite film. From approach (2), X-ray diffraction revealed that the films of ZnO deposited on fused quartz at 600°C and 200 mTorr were c-axis oriented, and that subsequent deposition from the barium hexaferrite target at 750-800°C and 300 mTorr led to the growth of a c-axis oriented barium hexaferrite film. The saturation magnetization, magnetic anisotropy field and ferrimagnetic resonance linewidths of these films are in agreement with bulk values found in the literature.

Oriented barium hexaferrite thick films grown on c-plane and m-plane sapphire substrates

The magnetic and structural properties of thick pulsed laser deposited (PLD) barium hexaferrite (BaM) films grown on c-plane and m-plane sapphire substrates were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), Rutherford backscattering spectroscopy (RBS), vibrating sample magnetometry (VSM), and ferrimagnetic resonance (FMR). Previously, BaM thin films (-0.5 /spl mu/m) grown on c-plane (0001) sapphire substrates exhibited magnetic properties closely approaching those of single crystal spheres. These films are potentially useful for thin film millimeter-wave devices such as circulators, isolators, and phase shifters, provided that thick films (e.g., 20 to 100 /spl mu/m) with suitable magnetic and dielectric properties can be grown. In general, it was found that an increase in film thickness leads to the growth of either textured polycrystalline BaM, which can be loosely adherent, or delamination of the films. However, well oriented thick BaM films were grown up to 15 and 20 /spl mu/m on the c-plane and m-plane sapphire substrates, respectively, before delamination occurred. The FMR linewidth, /spl Delta/H, was 200 Oe at 85 GHz for an annealed 15 /spl mu/m thick PLD BaM film on c-plane sapphire with 4/spl pi/M=4200 G, H/sub A/=16000 Oe and an XRD /spl omega/-scan of 0.51/spl deg/ FWHM about the (008) BaM plane. The FMR linewidth of PLD BaM films grown on m-plane (11_00) sapphire substrates were greater than 450 Oe with 4/spl pi/M-4000 G H/sub A/=16000 Oe. the m-plane films were magnetically well oriented in the film plane with M/sub r//M/sub s/ along the easy axis greater than 90% for all PLD m-plane BaM films. >

The magnetic and structural properties of ferrite plated NiZn-ferrite films

Magnetization, magnetic anisotropy and ferrimagnetic resonance linewidth measurements have been made on a series of NiZn-ferrite films synthesized using a low temperature (T<100/spl deg/C) ferrite plating technique developed by one of the authors. Films made by this technique are of considerable interest because of their potential use in the fabrication of non-reciprocal components for high frequency device applications. Our results show the films are textured and have a large magnetic anisotropy perpendicular to the plane of the film and a much smaller in-plane anisotropy. The magnetization, magnetic anisotropy and resonance linewidth scaled with ferrous ion concentration. The magnetic anisotropy is explained in terms of a single ion anisotropy directed along a [111] texture.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Effect of slowly relaxing impurities on ferrimagnetic resonance linewidths of single crystal nickel ferrites

Ferrimagnetic resonance (FMR) linewidths have been measured at X-band frequencies (11 GHz) from 77 K to 400 K in single crystal nickel ferrites with composition Ni/sub x/Fe/sub 3-x/O/sub 4/ with x=0.9, 1.0, 1.2. Measurements have been carried out by means of an automatic technique based on a modified short-circuit SMA transmission line. Linewidths ranged from 40 Oe to 80 Oe in all the temperature range. The dependence of the FMR linewidth with temperature leads to a contribution of the valence-exchange mechanism for x 1. The collection of data obtained by the automatic system allows the authors to achieve the values for the relaxation times and activation energies of these mechanisms. >

Magnetic properties of aerosol synthesized Co-substituted spinel ferrites

An aerosol technique and pyrolysis of a mixture of cobalt-nickel-zinc-magnesium and iron nitrates with a fixed stoichiometric composition are used to prepare submicron spherical particles of Co substituted ferrite powders with a spinel-type structure. The magnetic properties are studied using vibrating sample magnetometry (VSM) and ferrimagnetic resonance (FMR). Important parameters such as saturation magnetization, FMR linewidth, and spectroscopic splitting factor are taken into analysis. >

Ferrimagnetic resonance linewidths of nickel ferrites from 26.5 to 60 GHz

A systematic study of the frequency dependence, from 26.5 to 60 GHz, of the ferromagnetic resonance linewidth for technologically useful nickel ferrites is presented in a wide range of compositions for both single-crystal and polycrystalline samples. The FMR linewidth of the polycrystalline samples appears to be virtually independent of the frequency. Theoretical approaches are applied in our range of frequencies providing a justification of our experimental results.

Intrinsic ferrimagnetic resonance linewidth of barium ferrite due to spin-wave scattering by trigonal site single-particle excitations

Time-dependent two-magnon scattering was previously proposed as a mechanism to explain the large magnitude of the ferrimagnetic resonance (FMR) linewidth of barium ferrite as a function of frequency. In the present work, it is shown that a quantum mechanical mechanism like the Kasuya–Le Craw process (KL)1 but with the phonon excitation replaced by a single-particle excitation of a trigonal site iron ion, which moves in an anharmonic potential well, gives a linewidth contribution of less than a tenth of an Oersted and proportional to the frequency, as in the KL mechanism. We conclude, based on this work and our previous work on the KL mechanism, that neither of these mechanisms can explain the observed FMR linewidths in barium ferrite at any frequency.

Ferrimagnetic resonance linewidth in single-crystal Mn-doped Ba2Zn2Fe12O22

The ferrimagnetic resonance linewidths in single crystals of Mn-doped Ba2Zn2Fe12O22 were measured as a function of frequency (0.01–40 GHz) and temperature (4–300 K). In addition, the saturation magnetization, g factor, and planar anistropy fields were measured. The field linewidth ΔH appears to scale with frequency; however, the field linewidth as a function of temperature for the hexaferrite exhibits maxima. The temperature-dependent resonant field values were used to calculate the anisotropy field as a function of temperature. These measurements were performed in a frequency-swept slot-coplanar device at a fixed value of applied magnetic field and in a traditional ferrimagnetic resonance system.

Spin-wave spectrum for barium ferrite (abstract)

In order to determine whether barium ferrite will be suitable for microwave and millimeter wave device applications, it is essential to calculate the intrinsic ferrimagnetic resonance linewidth for perfect single crystals of this compound. The two mechanisms believed to be responsible for the intrinsic linewidth of barium ferrite, the Kasuya–LeCraw1 two-magnon one-phonon process and the two-magnon scattering caused by the time fluctuations of 2b site (trigonal symmetry site) ions,2 require knowledge of the magnon dispersion relations throughout the Brillouin zone, and not just near the zone center. We describe the calculations of the spin-wave spectrum for barium ferrite, which is a highly complex exchange-coupled hexagonal ferrimagnetic compound, using a method similar to that used by Harris for YIG.3 The exchange integrals are calculated by fitting the Weiss molecular field approximation to the sublattice magnetizations while including single-ion anisotropy. The value for the space-averaged stiffness constant as calculated from the acoustic mode of the spin-wave spectrum is 2.5×10−9 Oe cm4.

Studies of the ferrimagnetic resonance relaxation for hexagonal ferrites

The Kasuya-LeCraw two-magnon-one-phonon process, which is generally considered to be the primary mechanism responsible for the intrinsic ferrimagnetic resonance linewidth of perfect single crystal ferrites, is studied, taking into account the effects of the local magnetic ion symmetry on the magnon-phonon interaction coupling strength. It is shown that octahedral symmetry sites will not contribute to the coupling, but the tetrahedral and trigonal sites will. The results are used to estimate the FMR linewidth for both YIG and barium ferrite. >

The anisotropy paradox of Co2+ ions in lithium ferrite

Microwave power absorption and hysteresis loops were studied on a series of ferrite materials prepared from a standard LiTi spinel host with Co2+ additions in amounts up to 0.05 ions per formula unit. Experimental results over this concentration range indicate that the rapid relaxation of Co2+ causes X-band spin wave linewidths to increase by more than an order of magnitude. The usual strong effects of Co2+ positive magnetic anisotropy, however, were not found in either ferrimagnetic resonance linewidths or hysteresis loop parameters. To account for the absence of anisotropy effects in the presence of strong relaxation effects, Co2+ is considered to act as a paramagnetic ion through decoupling from the exchange fields of the iron sublattices. This new theory of exchange isolation is based on selective clustering of dilutant ions that results from minimization of magnetic exchange, lattice electrostatic, and crystal field stabilization energies.

Surface contribution to the ferrimagnetic resonance linewidth of single-crystal YIG versus frequency and temperature

The knowledge of microwave intrinsic losses of ferrimagnetic single crystals is often obscured by the scattering process induced by surface defects. The existing data and the corresponding model dealing with this effect are far from sufficient to understand the phenomenon; in the millimetric range, the importance of the surface imperfection linewidth ΔHs is a major difficulty for obtaining the single-crystal intrinsic linewidth ΔHi from ΔH measurements. We have investigated on a pure YIG single crystal the full dependence of the surface effect as a function of the surface pit size, the frequency, and the temperature. An automatic linewidth spectrometer is used, which allows measurements in the frequency range 1–18 GHz and the temperature range −100 to 270 °C. The dc magnetic field is aligned with the 111] easy axis of the crystal. Three main conclusions are obtained: (1) For a constant sample diameter, the variation of the surface contribution ΔHs is found to be a nonlinear function of the pit size. (2) Whatever the surface roughness, ΔHs is a minimum when passing the top of the spin-wave manifold. This is similar to the behavior of the volume porosity line-broadening contribution observed in polycrystalline materials. (3) For a constant reduced internal field Ω (Ω=Hi/4πMs), the temperature dependence of ΔHs follows the temperature dependence of the saturation magnetization.

Anisotropy fields and FMR linewidth in single-crystal Al, Ga and Sc substituted hexagonal ferrites with M structure

Single crystals of nominally pure and of Al, Ga and Sc substituted BaFe 12O 19 ferrites have been grown from different solvents by the top seeding and bottom growth method. Ferrimagnetic resonance (FMR) measurements were made at room temperature on polished spheres of about 0.3 mm size at frequencies between 3 GHz and 90 GHz. From these measurements values of the anisotropy field from nearly zero up to 29 KOe were found for Sc-substitution levels x ≤ 1.65 and for Al levels x ≤ 2, respectively. The observed FMR linewidth ΔH can be described by a frequency independent two-magnon scattering contribution ranging between 5 Oe and 10 Oe, and an assumed intrinsic linewidth rising linearly with frequency and being for the substitutions studied proportional to the reciprocal of the Curie temperature. A relation predicting the dependence of ΔH on frequency and substitution level is proposed. The suppression of possible ferrous iron content by addition of Mn 3+ reduces the linewidth by several Oersteds.