H. J. Van Hook

Linewidth Reduction through Indium Substitution in Calcium‐Vanadium Garnets

On the garnets Y3−2xCa2xFe5−x−yVxInyO12, with x ≤ 1.5 and y ≤ 0.5, we have measured the polycrystalline linewidth ΔHpoly at X‐band and room temperature and have determined from single crystals the first‐order anisotropy constant, K1. Since the single‐crystal linewidth of these materials is but a few oersteds and the polycrystalline samples had less than 1% porosity and second phase, the observed ΔHpoly is attributed to anisotropy broadening, according to Schlomann. The introduction of indium reduces both | K1 | and ΔHpoly, for example: x = 0.63y = 0TC = 280°C4πMs = 650 GΔHpoly = 98 Oex = 0.80y = 0.50TC = 155°C4πMs = 750 GΔHpoly = 8 Oe. That last value is the lowest yet reported in the range of T ≈ 23 TC.

Near theoretical microwave loss in hot isostatic pressed (hipped) polycrystalline yttrium iron garnet

The ferromagnetic resonance (FMR) linewidth, the field dependent effective linewidth, and the parallel pump spin wave linewidth were measured for spheres and disks prepared from a block of hot isostatic pressed (hipped) polycrystalline yttrium iron garnet (YIG). All linewidths as well as static magnetization data indicate close to 100% density. Vibrating sample magnetometer measurements give an average saturation induction 4πMs of 1825 G. The FMR half-power linewidths for the spheres at 9.5 GHz were 13 Oe. Linewidths measured over the 9.5–18 GHz frequency range show a small but distinct drop and agree with Schlomann’s theory of anisotropy-dominated two-magnon scattering for polycrystalline ferrites. The effective linewidth versus field data at 10 GHz show a region of strong absorption that corresponds to the width of the spin wave manifold for low wave numbers and a high field value of about 2 Oe. Parallel pumping measurements give minimum spin wave linewidths of 1.2 and 0.6 Oe at 9 and 16.7 GHz, respecti...

In‐plane magnetized YIG substrates self‐biased by SmCo based sputtered film coatings

Highly anisotropic SmCo based films with the TbCu7‐type structure have been sputter deposited directly onto YIG substrates. The SmCo crystallites have the c axes approximately randomly splayed about the substrate plane such that the easy direction of magnetization of the SmCo film is in the film plane. The in‐plane static energy product of the SmCo film layers was about 16 MG Oe. In‐plane vibrating sample magnetometer hysteresis loops of the SmCo film and YIG substrate exhibit a composite form with the YIG field reversal shifted into the first quadrant by the looping field from the SmCo film layer. Approximately 4×4 mm2 pieces of YIG substrate have been measured to determine the YIG bias field and field required for reverse saturation of the YIG as a function of the SmCo based film layer thickness to YIG substrate thickness. It is observed that for SmCo to YIG thickness ratios greater than 0.22, the looping field from the SmCo film layer is sufficient to saturate the YIG magnetization in the reverse direc...

Magnetic resonance experiments on ion beam sputtered {100} Fe films

Ferromagnetic resonance (FMR) measurements have been performed on single‐crystal Fe films, produced by ion beam sputtering techniques on GaAs substrates. In‐plane FMR results over the frequency range 0.1–20.0 GHz were obtained by a slot line technique. The magnetic parameters deduced from these measurements are comparable to bulk Fe. In‐plane angular variation reveals a negligible uniaxial anisotropy contribution to the magnetic anisotropy energy. Spin‐wave excitations were observed in 9.5‐GHz cavity measurements, and are found to obey the n2 law. The exchange stiffness constant is found to be somewhat larger than seen in other epitaxial Fe films. These results show that epitaxial Fe/GaAs films possessing good magnetic properties may be produced by ion beam sputtering techniques.

Anisotropy Linebroadening in Polycrystalline V–In Substituted YIG

Polycrystalline linewidth and magnetization have been measured between 77° and 300°K at 9.2 GHz on V–In substituted YIG in the composition range 0[equal to or less-than]x[equal to or less-than]1.50 and 0[equal to or less-than]y[equal to or less-than]0.50 for Y3−2xCa2xFe5−x−y VxInyO12. The linewidths were compared with theoretical values inferred from measurements of K1 (K2 negligible) and Ms on single crystals for 0[equal to or less-than]x[equal to or less-than]0.90 and 0[equal to or less-than]y[equal to or less-than]0.35 between 4° and 300°K on the basis of a recent theory by Schlomann. Data on dense, single‐phase polycrystals are in good quantitative agreement with Schlomanns theory for samples with weak anisotropy (Ha≪4πMs, where Ha = 2 | K1 | / M). For high anisotropy materials (Ha[equal to or greater-than]4πMs), linewidth derived from area fitting of the normalized curves follows ΔH = 0.5Ha. Moderately small (<3%) amounts of porosity yield additive linebroadening effects.

Hysteresis loop properties of Li‐ferrite doped with Mn and Co

Measurements of coercive force Hc and remanent magnetization 4πMr have been made as a function of temperature (−195?T?150°C) on dense polycrystalline Li ferrite substituted with Mn (0?y?⋅.20) and Co (0?z?.02). We report an abrupt degradation in loop squareness (decreased 4πMr, increased Hc) at a characteristic temperature Tϑ, which increases with z but is independent of y. Single‐crystal data on anisotropy K1 show a correlation between Tϑ and the temperature at which sign reversal in K1 is found with Co substitution. The absence of a dependence on Mn content is in accord with the fact that K1 is relatively insensitive to Mn substitutions, which have been shown to control magnetostriction effects. The deterioration in the hysteresis loop is discussed in terms of the nucleation of reverse domains as K1 passes through zero.Measurements of coercive force Hc and remanent magnetization 4πMr have been made as a function of temperature (−195?T?150°C) on dense polycrystalline Li ferrite substituted with Mn (0?y?⋅.20) and Co (0?z?.02). We report an abrupt degradation in loop squareness (decreased 4πMr, increased Hc) at a characteristic temperature Tϑ, which increases with z but is independent of y. Single‐crystal data on anisotropy K1 show a correlation between Tϑ and the temperature at which sign reversal in K1 is found with Co substitution. The absence of a dependence on Mn content is in accord with the fact that K1 is relatively insensitive to Mn substitutions, which have been shown to control magnetostriction effects. The deterioration in the hysteresis loop is discussed in terms of the nucleation of reverse domains as K1 passes through zero.

Origin of the Microwave Loss in Ultra‐Low Linewidth Substituted Garnets

Linewidth measurements from 77–300°K and room temperature off‐resonance effective linewidth data at 9 GHz show that the microwave losses in ultra‐low‐loss Ca–V–In substituted YIG and Ca‐Ge‐In‐YIG are completely resolvable in terms of known processes and that only a small part of the loss is due to anisotropy broadening. For the lowest linewidth of 2 Oe observed to date (Ca‐Ge‐In‐YG), about 0. 5 Oe is due to rare earth impurities 0. 9 Oe is from porosity broadening, and 0. 2 Oe is from anisotropy. The remaining 0.4 Oe contribution is comparable to expected “intrinsic” single crystal linewidths.

Pulsed-laser deposition of oxides over large areas

Due to its short wavelength and high peak power the excimer laser has become the de facto choice for Pulsed Laser Deposition (PLD) of ceramic superconductors as well as other complex chemical compounds. This paper will describe a unique excimer-based laser deposition system which is capable of producing thin films of a variety of oxide compounds or other materials over large areas (up to 46 cm2). Well over a dozen chemical compounds have been deposited with this system for a wide variety of electronic applications. Also the PLD technique has been adapted to grow thin films on the internal surface of cored cylindrical substrates in order to form resonant microwave cavity structures. The uniformity morphology and electrical properties of films grown on both planar and cylindrical substrates will be discussed.

Microwave loss in low-magnetization polycrystalline garnets: A comparison of Ga and CA-V-In-substituted YIG

From available single-crystal data on YIG:Ga and YIG :Ca-V-In, a comparison has been made of anisotropy line broadening in each series for compositions with equivalent 4\piM_{s} and T c . The results indicate the latter materials have smaller anisotropies and should therefore have inherently lower magnetic loss when comparing ceramics with near perfect microstructures, i.e., where porosity line broadening is negligible.

Anisotropy and Magnetostriction Measurements on (Ca+V+In)‐Substituted YIG

Garnet crystals of the general composition {Ca2xY3−2x} [InvFe2−v] (VxFe3−x)O12 were obtained by flux growth in the ranges 0[equal to or less than]x[equal to or less than]1 and 0[equal to or less than]y[equal to or less than]0.35. The individual compositions of the crystals were determined by electron microprobe and confirmed by lattice parameter, magnetization Ms and Curie point Tc measurements. By microwave resonance techniques, magnetostriction constants λ100, λ111 (at room temperature) and magnetic anisotropy constants K1, K2 (with 4K[equal to or less than]T[equal to or less than]300K) were determined. The function |K1(x)| at T = 4K is nonlinear and exhibits a maximum at x≈0.20, as the well known Tc(x) does.1 The magnetostriction constants are both negative and vary between −1.5×10−6 and −4.3×10−6 with composition. These single‐crystal data are supplemented by polycrystalline resonance lineshape studies on compositions with 0.8[equal to or less than]x[equal to or less than]1.3, at 4K