bluuebunny/crossref_metadata_2025 huggingface dataset:
Growth-induced lowering of magnetoelastic symmetry
Authors: Muller M. W.
Published: February 2003

Growth-induced nonrandom ordering of ions on crystallographically equivalent sites of cubic magnetic garnets may reduce the symmetry of both the anisotropy and magnetoelastic tensors. The crystal tensors can be evaluated as weighted sums over all sites of the local ionic tensors. Such sums reflect both the site symmetries and the site occupation preferences. Unlike the anisotropy (whose growth-induced axial terms are of lower order in the spin components than the cubic terms) the growth-induced magnetoelastic tensor is of the same rank as the cubic component; it may, however, lack the symmetry between strain and spin components imposed by the cubic point group. We determine the symmetry and estimate the magnitude of the non-cubic magnetostriction associated with nonrandom rare earth site occupation, an effect that should be observable. We argue on plausible grounds that the non-cubicity associated with iron ions should be much smaller.
Effect of tensile stress on the magnetic domain structure of Fe and NiFe thin films
Authors: Darby T. P. , Parker K. L. , Tong H. C.
Published: February 2003

A systematic study was made on how tensile stress affects the magnetic domain structure of RF-sputtered Fe and NiFe films. These films have thicknesses of 100 to 500 Å and various orientations of the stress axis relative to the magnetization. Stressing was done in the plane of the film and the effect was observed in situ using Lorentz microscopy. When large rotations (i.e., 50° to 90°) of the magnetization are required in response to the applied stress and the domains are large (i.e., ≳10 μm), the magnetization rotates smoothly as the stress is increased. This realignment of the magnetization often creates head-on domain walls with a concomitant increase of the magnetostatic energy which is partially relieved by a faceting of the walls into a sawtooth geometry. For small domains similar wall faceting results and can extend entirely across a domain, splitting the domain into smaller sections which are then gradually eliminated. Thus, a region consisting of several domains can be transformed to a single domain. When only small rotations of the magnetization are required, the domain walls are more stable but eventually start to facet unless the applied stress is in a direction such that the magnetization is exactly parallel to the walls.
Grain-size effects on microwave ferrite magnetic properties
Authors: Inui T. , Ogasawara N.
Published: February 2003

A general review is given on effects and controls of grain size, so far documented, concerning both soft and microwave ferrites, while referring to the findings of ceramists as well as to the representative models available for initial permeability spectra and for microwave parameters, such as ΔHk and ΔHeff. As an illustrative example, a briefing is given on narrow linewidth CaV-garnet families, finding an ever-increasing usage, with reduced loss resulting from the grain size being intentionally increased.
a-c response of ideally soft magnetic metals
Authors: Arrott A. S. , Heinrich B.
Published: February 2003

The influences of intrinsic damping, eddy currents and exchange in determining the a-c response of magnetic metals without anisotropy or magnetostriction are studied using a model calculation for finite cylinders. The theory is compared to experimental results for iron whiskers just below the Curie temperature. It appears that the intrinsic damping coefficient is proportional to the square of the spontaneous magnetization.
Effect of composition and original orientation on secondary recrystallization of 3% silicon-iron single crystals
Authors: Littmann M. F. , Dahlstrom N. A.
Published: February 2003

Single crystals of 3% silicon-iron 2.2 mm thick were prepared with (a) virtually no second phase precipitates, (b) MnS particle inhibitors and (c) MnS plus AlN particle inhibitors. For each composition crystals having original orientations near the (110) [001], (111) [1̄1̄2], and (110) [011] were cold rolled to 0.26 mm using one and two stages of cold reduction. Compositions (b) and (c) included C in amounts used for commercial grain oriented and high permeability silicon-iron; these specimens were decarburized before the 1200 °C final anneal. For the (110) [001] crystals, complete secondary recrystallization took place with MnS+AlN and one stage cold reduction. Secondary recrystallization by a different mechanism took place in the pure single crystal with two stages of cold reduction. With MnS+AlN and two stages of cold reduction, the primary recrystallization structure remained stable and no secondary recrystallization took place. The effects of the inhibitors and original orientation on both primary and secondary recrystallization structures and textures are discussed.
Magnetic anisotropy in MnBi particles grown by directional solidification of the Mn-Bi eutectic
Authors: Notis M. R. , Shah Dilip , Graham C. D. , Trout Stanley R.
Published: February 2003

Directional solidification of the eutectic Mn-Bi alloy (2 at% Mn) produces an aligned array of ferromagnetic Mn-Bi needles, 0.1 to 1.5 μm in diameter, in a matrix of diamagnetic Bi. Samples grown at about 50 cm/hr and then annealed at 200 °C contain two magnetic phases. One phase is normal equilibrium MnBi, known in the recent literature as the low-temperature phase (LTP). The second phase is crystallographically similar to the high-temperature phase (HTP) Mn1.08Bi, but has a much lower Curie temperature of 240 K. Low-temperature hysteresis loops measured parallel and perpendicular to the axis of freezing are of unusual form. If the magnetization due to the normal MnBi phase is subtracted the resulting loop in the parallel direction has Hci≳100 kOe, suggesting single-domain behavior. The resulting loop in the perpendicular direction can be accounted for by the presence of a relatively large fourth-order anisotropy.
High coercivity, isotropic plasma sprayed samarium-cobalt magnets
Authors: Kumar K. , Das D. , Wettstein E.
Published: February 2003

A value of 67.5 kOe has been measured for the room temperature coercivity of an isotropic, heat treated, 1-5 samarium-cobalt plasma sprayed deposit. This value is believed to be the largest published, so far, for a permanent magnet. Sprayed magnets are generally found to be better than 93 percent dense with coercivities of 35 to 60 kOe. Deposits comprised of fine microstructures yield broad, unresolved x-ray diffraction peaks. Low temperature crystallization of these deposits yields diffraction patterns representative of the high temperature equilibrium structure. The emergence of peaks, ascribed to SmCo5, from a low temperature 700 °C heat treatment implies both formation and stability of the SmCo5 phase at this temperature. These results dispute the existence of the generally accepted eutectoid decomposition reaction for SmCo5 at 750–800 °C. If such a reaction were present the products of crystallization should have included Sm2Co7 and not SmCo5. High temperature investigations on sprayed magnets indicate that temperatures of 1100 °C result in low values of coercivity, possibly due to grain growth.
Dependence of oxygen diffusion in epitaxial YIG : Ca on defect concentration
Authors: Gyorgy E. M. , LeCraw R. C. , Blank S. L. , Pierce R. D. , Johnson D. W.
Published: February 2003

Measurements of oxygen diffusion in YIG : Ca at different oxygen partial pressures have shown that the diffusion rate strongly depends on oxygen vacancy concentration. At very high vacancy concentration this diffusion is quite rapid. For example, with approximately 0.1 vacancies per formula unit the oxygen diffused 0.9 mm in 24 h at 325 °C. It has also been shown that under many conditions the rate limiting process occurs at the surface of the YIG : Ca. An additional thin epitaxial layer having a much higher defect concentration greatly reduces the limitations imposed by the surface.
Small region magneto-optic measurements of Permalloy I bars
Authors: Huijer E. , Dove D. B. , Watson J. K.
Published: February 2003

We have developed a Kerr magneto-optic probe capable of examining regions of ∼3 μm diameter and have used it to measure the magnetization distributions within Permalloy I bars. The measurements were made so as to bring into evidence the location and movement of domain walls. By suitable adjustment of the polarizing elements, signals can be observed either from the longitudinal Kerr effect from domains or from the polar Kerr effect of the out-of-plane magnetization of the Bloch wall. This paper reports the use of the polar effect to make precise determinations of Bloch wall locations in Permalloy I bars of 100×12×0.3 μm. Two different domain configurations were studied and wall locations were mapped as a function of applied field for each. Wall curvature is evident from the results. Local saturation and wall nucleation fields were also observed. Both types of domain configuration were found to respond qualitatively as predicted by a series-based continuum calculation but with some notable differences.
Calculation and analysis of the forces on ferro-fluid particles on the surface of a Permalloy overlay bar
Authors: Khaiyer I.
Published: February 2003

The formation of the ferro-fluid particles on the domain walls of a Permalloy overlay bar is due to the forces exerted on each particle by the stray field of the bar. Domain wall observation by Interference Contrast Technique reveals that the ferro-fluid particles do not form at some parts of the 180° domain walls. A further investigation by normal illumination technique has shown in fact that the particles are repelled from these areas as they look brighter than the grayish background. By calculation of the magnetic force from magnetic stress tensor and employing the domain wall model for an overlay bar, it is shown that a magnetization reversal inside the 180° domain wall is responsible for repelling the ferro-fluid particles. Inside the volume of an overlay bar, the forces exerted on the magnetization inside a 90° domain wall is also calculated and it is shown that these walls rotate under the torques applied by these forces until the resultant torque becomes zero. The force lies along the wall at this stage.
1K bit bubble lattice storage device: Initial tests
Authors: Hu H. L. , Beaulieu T. J. , Chapman D. W. , Franich D. M. , Henry G. R. , Rosier L. L. , Shew L. F.
Published: February 2003

All elements required for writing, storing, and reading information in a bubble lattice device have been designed and fabricated in a single test chip. Design considerations and operating margins are given for the five major components of the device: (1) write station (nucleation and wall state control in an isolated-bubble region); (2) read station (wall state discrimination and bubble detection in an isolated-bubble region); (3) storage (confinement and translation of a close-packed hexagonal bubble lattice); (4) isolated-bubble to bubble lattice transition; and (5) bubble lattice to isolated-bubble transition. All functions have been demonstrated on a single test device operating in a data-in, data-out mode. Initial error rates and sources of errors are discussed.
Design and characterization of 3 μm bubble memory chips utilizing Y-Y patterns
Authors: Yoshimi K. , Yoshioka N. , Urai H. , Morimoto A. , Wada Y.
Published: February 2003

Major-minor organized bubble memory chips have been developed utilizing 14 μm period Y-Y propagation circuits. First type is a 75 kbit memory chip consisting of four major-minor units for high performance demands. Designed access time and data rate for 300 kHz drive are 0.3 nsec and 2×600 kbits/sec, respectively. Second type is a single unit major-minor 78 kbit memory chip for medium access time use. Main chip design features are as follows: (1) 14 μm Y shaped Permalloy circuits are used throughout the chip, except for the 18 μm chevron stretcher. (2) Y-Y transfer gates have been tailored in order to adapt to Y patterns. (3) A thin film Permalloy detector is used for the sake of large output (15 mV/2 mA) amd O-π phase detection. The 3 μm bubble chips are fabricated on (YSmTmCa)3(FeGe)5O12 garnet films. Wafers are processed through 3 evaporation steps and 5 masks. Total 20 Oe operating bias margin is obtained at 300 kHz for 50 Oe drive field.
A 300 kbit bubble memory chip with planar structure
Authors: Orihara S. , Kinoshita R. , Yanase T. , Segawa M. , Matsuyama S. , Yamagishi K.
Published: February 2003

A 300 kbit bubble memory chip has been designed based on 3 μm bubble technology. Nominal circuit period is 14 μm and chip size is 9.8 mm×9.6 mm. A gap-tolerant design is fully employed, such as, asymmetric half-disk propagation pattern, half-disk transfer gate, a novel asymmetric-chevron stretcher, etc. The chip is fabricated using a new planar process solving step-coverage problems to achieve good process yield. A typical bias field margin of 18 Oe is obtained at 55 Oe with a triangular wave drive.
Magnetic anisotropy in Gd-Tm alloys
Authors: Okamoto T. , Fujii H. , Hashimoto Y.
Published: February 2003

The magnetization of single crystal binary Gd-Tm alloys were measured at 4.2 K in applied field up to 52 kOe along the three principal crystallographic directions. The magnetocrystalline anisotropy constants K02 and K04 were determined from the analysis of the hard magnetization curve on the basis of the molecular field theory. The values of K02 and K04 are negative and positive, respectively, in all concentration ranges, and both values increase quadratically with increasing Tm concentration in magnitude. From these results we estimated the value of the single ion anisotropy constant K02(R)SIA and anisotropic exchange interaction constant K02(R)AEI of the Tm metal. The values of K02(R)SIA and K02(R)AEI are −73 cm−1 and −60 cm−1, respectively. It may be assumed that the AEI contribution to K04 is approximately the same as K02.
Origins of magnetic anisotropy in cubic RFe2 Laves phase compounds
Authors: Koon N. C. , Williams C. M.
Published: February 2003

Detailed studies of magnetic anisotropy and spin orientations in ternary and quaternary high magnetostriction compounds of the form HoxTbyDy1−x−yFe2 have clearly demonstrated the existence of both continuous and discontinuous rotation of the easy axis between principal crystallographic directions as a function of composition and temperature. While the usual single ion crystal field model successfully explains the qualitative features of the data, there still remain significant differences between the actual and predicted compositions at which the rotations occur. We show that these differences are largely due to changes in the magnetoelastic energy with spin orientation.
Reciprocal and nonreciprocal high TE-TM modes conversions in Tb,Al and Gd,Ga substituted garnet films
Authors: Torfeh M. , Desvignes J. M. , Courtois L. , Le Gall H.
Published: February 2003

Very large energy exchange (more than 97%) between TE and TM modes of YIG : Tb,Al guides have been obtained for short propagation lengths (less than 2 mm) in the near infrared (1.152 μm). These performances are better than those of YIG : Gd,Ga layers (97% in 4 mm). With such guides we can reduce M.O. device dimensions; they can be used in the integrated magneto-optics. Also high nonreciprocal conversions (9% conversion in one propagation direction and 93% in the opposite direction) have been obtained in YIG : Gd,Ga films. A nonreciprocity theory is discussed for monosection uniform waveguides. This theory shows that the guides in which we obtained the nonreciprocity cannot be monosection but multisections.
Anomalous attenuation of ultrasound in ferrofluids under the influence of a magnetic field
Authors: Isler William E. , Chung David Y.
Published: February 2003

Ultrasonic wave propagation has been studied in a water-base ferrofluid by pulse-echo methods. A commercial box-car integrator was used to measure the change in attenuation due to an external magnetic field applied at various angles relative to the ultrasonic propagation vector. Anomalous results were obtained when the attenuation was plotted as a function of the magnetic field strength. As the field increased, the attenuation reached a maximum and then decreased to a flat minimum before it approached saturation at a field of 2 kG. This variation of attenuation with magnetic field cannot be explained from the simple picture derivable from the work of McTague on the viscosity of ferrofluids. In no case was the viscosity seen to decrease with field, nor was the oscillatory behavior observed. The results of this study were compared with the theory developed by Parsons.
Relationship between coercive force and anisotropy field for oriented barium ferrite tapes and magnets
Authors: Fayling R. E.
Published: February 2003

The approximate anisotropy field (Han) has been determined for twelve experimental oriented barium ferrite recording tapes and magnets with coercive force (Hc) between 715 Oe and 5250 Oe, and squareness ratio greater than 0.80. The Han values were taken as the ratio of saturation magnetic moment (ms) to the initial hard-axis susceptibility (m/H). Han values were generally within the 12.6–19.8 kOe range predicted by the Stoner-Wohlfarth model, for barium ferrite particles with combined magnetocrystalline and shape anisotropy. The samples with Hc less than 1.7 kOe had an average Han of 12.35 kOe, and the samples with Hc greater than 5 kOe had an average Han of 18.2 kOe. The 6 samples with Hc in the more common 2–5 kOe range had an average Han of 14.5 kOe, but the variation of Han with Hc did not appear to indicate a relationship between Han and Hc.
Isotropic films for curved data tracks in a cross-tie memory
Authors: Torok E. J. , Paul M. C. , Lo D. S. , Cosimini G. J. , Johnson L. H. , Nelson G. F.
Published: February 2003

Use of a serrated NiFe strip as a data track for a cross-tie memory was introduced by Schwee et al. [AIP Conf. Proc. 29, 624 (1975)]. Use of an isotropic film instead of an anisotropic one in such a strip has two advantages: it confines the wall in the central portion of the strip, and it permits the use of curved data tracks. The isotropic film is deposited on a rotating substrate in the presence of a dc orienting field in order to eliminate angle of incidence effects. Serrated strips are etched from these films. The edges of the serration supply a local shape anisotropy. Cross-tie walls run parallel to the local easy axis. If the magneticaly induced easy axis of an isotropic film is skewed with respect to the edge of the strip, the wall eventually intersects the edge; this is avoided by the use of isotropic films. Equations for the magnitude of the anisotropy and the skew angle are presented. Curved isotropic film strips were fabricated; placement of a cross-tie wall all around the curve was achieved via a curved stripline deposited under the NiFe film. The cross-ties in an isotropic film are wider than in an anisotropic film, drive currents are lower, and the effective area for magneto-resistive sensing larger.
Cross-tie/Bloch line detection
Authors: Cosimini G. J. , Johnson L. H. , Lo D. S. , Nelson G. F. , Paul M. C. , Torok E. J.
Published: February 2003

Electronic detection of cross-tie/Bloch line pairs is essential for the use of these pairs as data bits in a serial access memory. The physical size of the cross-ties and Bloch lines is small and their associated magnetic flux is weak. Results obtained to data indicate that the detection of cross-tie/Bloch line pairs based on magnetoresistive principles is the most feasible and practical for memory array applications. Three detector designs, fabrication techniques and experimental results are presented. The detectors consist of two gold electrodes 1500 Å thick, separated by a small gap. Under the detector is an isotropic or anisotropic NiFe film serration 350 Å thick. The gap in the detector is placed on a cross-tie or Bloch line position and is shaped so as to maximize the resistance change in the magnetoresistive film for a ’’zero’’ and ’’one’’ state. The relationships between sensing current and magnetization distributions are described with the aid of Lorentz electron micrographs. Normal signal levels for the most promising design are in the range of 15–20 μV/mA. Sensing currents of 5–6 mA are used which produce safe current densities, thus typically yielding 100 μV signals.
Spherulitic growth of Fe3O4 film and its properties
Authors: Makino K. , Nakagawa T. , Kobayashi K. , Shinohara M.
Published: February 2003

Fe3O4 spherulites have been obtained for the first time by reducing α-Fe2O3 films to Fe3O4 using isopropyl alcohol. α-Fe2O3 films were prepared by reactively sputtering from an Fe target in mixed gases of Ar and O2 using an r.f. sputterer. Growth behavior of the spherulite was directly observed under a polarizing microscope equipped with a high temperature stage. It is observed that spherulites grow at a liner radial rate until they impinge on each other. Electron diffraction patterns show that the structure of the spherulite is spinel. The spherulite consists of radially oriented fine fiber-like crystallites, the diameter being less than 100 Å. Metallic conductivity of 103 (Ω cm)−1 are observed for the spherulite. Coercive force is 700 Oe, twice as large as that of the crystalline Fe3O4 films.
Measurement of stripe head velocity using magneto-resistance signal
Authors: Hannon David M.
Published: February 2003

Stripe head velocity has been measured by monitoring the signal from a straight magneto-resistive element as a stripe expands and contracts along the element. The MR element provides a path for the stripe as well as indicating its position versus time. This new measurement technique allows continuous monitoring of the stripe velocity as drive and in-plane field are varied. An ion-implanted garnet film of composition Y1.95Sm0.09Lu0.09Ca0.87Ge0.87Fe4.13O 12 with a thickness of 2.0 μm was measured using an MR element 0.04 μm thick, 4 μm wide, and 150 μm in length. The in-plane field H1 is approximately perpendicular to the stripe head velocity. Two types of velocity behavior are observed depending on the direction of H1×V. For H1×V pointing toward the implanted surface, the velocity versus drive depends on the H1 magnitude. For H1<50 Oe, the velocity versus drive is linear up to a velocity instability above which the velocity tends to saturate. The instability is assigned as a horizontal Bloch line motion. For H1≳100 Oe, the velocity increases to a much higher value which is in agreement with the terminal velocity formula, (π/2) γΔH1. For 50<H1<100 Oe, the velocity curve shows the horizontal Bloch line instability; but at higher drive the velocity suddenly increases up to the terminal velocity. For H1×V pointing toward the nonimplanted surface, the velocity curve has a weak instability at low drive followed by a concave shape.
Thermally induced substrate fracture in LPE garnet film growth
Authors: Stein B. F. , Chen T. F. , Greifer A. P.
Published: February 2003

The cracking of substrates which may arise during the withdrawal of garnet films from the baffled vertical furnaces conventionally used is shown to be the result of blocking of the convection currents by the substrate when it is level with the baffle. Temperature differences of over 200 °C have been measured through the substrate thickness. When differences of this magnitude occur at high temperatures (∼700 °C), the stresses generated are greater than the tensile strength of GGG causing fracture. Baffle placement is critical with respect to maintaining a uniform temperature directly above the melt and establishing a non-fracture gradient in the upper zone of the furnace. A baffle arrangement is described which eliminated substrate fracture. Suggestions for new furnace designs eliminating or minimizing the substrate blocking effect are made.
Microstructure and microsegregation in substrate garnet materials
Authors: Mishra Raja K. , Thomas G.
Published: February 2003

Electron microscopy is used to study the microstructure of gadolinium gallium garnet (GGG) and calcium gallium germanium garnet (CGGG), materials used as substrates for bubble garnet films. Isolated undissociated dislocations with Burgers vectors (1/2) 〈111〉 are characterized using dynamical contrast analysis. Microcracks (≲1 μ in size) bounded by groups of dislocations are observed in both GGG and CGGG. The occurrence of small inclusions (and voids) in CGGG are also investigated. A model is developed to explain the formation of these precipitates due to microsegregation of vacancy-atom clusters.
Magnetomechanical coupling and variable delay characteristics by means of a giant ΔE effect in iron-rich amorphous ribbon
Authors: Arai K. I. , Tsuya N.
Published: February 2003

The saturation magnetostriction constants λs of amorphous (Fe0.9Co0.1)xSiyBz and (Fe1−xCox)78Si8B14 ribbons were measured at room temperature by a three terminal capacitance method, and the largest constant λs was found to be 44×10−6 for the composition (Fe0.9Co0.1)0.83B0.14. The magnetomechanical coupling factor k and the giant ΔE effect of the amorphous Fe78Si10B12 ribbons were also observed. These values depended on the annealing of the ribbons in a magnetic field, and were larger than those previously reported. The largest coupling factor was found to be 0.75 for the ribbon annealed at 410 °C for 12 minutes and the largest ΔE effect to be 1.9 for a ribbon annealed at 410 °C for 10 minutes. The variable delay time, by using Fe78Si10B12 ribbons with 20, 15 and 5 μm thick was also measured from 150 kHz to 10 MHz as a function of the frequency.
Metglas 2826B—Transport, magnetic and thermal properties
Authors: Malmhäll R. , Bäckström G. , Rao K. V. , Bhagat S. M. , Meichle M. , Salamon M. B.
Published: February 2003

We report Hall resistivity, magnetization, heat capacity, and electrical resistivity studies on Metglas 2826B (Fe29Ni49P14B6Si2) spanning the temperature regime 77 to 800 K. The critical exponents for this system are found to be β=0.40±0.01, δ=5.25±0.10, and γ=1.7±0.1. The magnetic isotherms fit into universal scaling functions over a rather wide range of temperature both above and below Tc. The specific heat exhibits a sharp peak at Tc. The temperature derivative of the electrical resistivity has a marked change at Tc. Although Tc increases slightly on thermal cycling to higher temperatures, the critical exponents are not influenced by this.
Structure of agron sputtered Gd-Co and Gd-Co-Mo amorphous thin films
Authors: Graczyk J. F.
Published: February 2003

We have investigated the short range order structure, microstructure and compositional fluctuations in argon bias-sputtered very thin films of Gd-Co and Gd-Co-Mo alloys. Bright field microscopy results show compositional fluctuations in the form of rods and thin sheets of Gd-rich material nearly perpendicular to the surface. The size of these rods is approximately from 30 to 100 Å and is consistent with the observed low angle anisotropic halo which occurs in the vicinity of ‖s‖=0.19 (Å)−1. We also find the surface of these films to have thickness modulations and irregularities which are found to be dependent on the bias at which the films were deposited. Energy filtered low angle electron scattering data show one or two well defined haloes. From the annealing behavior of the low angle scattering we determined that small pores in the structure anneal out and coalesce into larger pores of approximately 30 Å in diameter at about 120 °C±50 °C. At this temperature the intensity of the first split halo at s1=2.0 (Å)−1 and s2=2.6–2.95 (Å)−1 sharpens up, which results from atomic redistribution of both Gd and Co in real space. This relaxation of the structure occurs prior to crystallization. We also observe the low angle scattering halo at ‖s‖=0.19 (Å)−1 to increase in intensity as the temperature is lowered below 300 °K. This increase we attribute to an increase in the net magnetization of the film.
Dipolar mechanisms for magnetic anisotropy in amorphous ferrimagnetic alloys
Authors: Cargill III G. S. , Mizoguchi T.
Published: February 2003

Classical magnetic dipolar interactions can make significant contributions to magnetic anisotropy in amorphous ferrimagnetic alloys with slight structural anisotropies on either atomic or microstructural scales. Simple expressions have been derived for this magnetic anisotropy in terms of structural anisotropy parameters, p, V, and Δx. For an alloy with atomic scale structural anisotropy (pair ordering), p is a measure of alignment of unlike nearest neighbor pairs. For an alloy with aligned, elongated composition inhomogeneities, V is the volume fraction of the inhomogeneities and Δx is the composition difference (atom fraction) between the inhomogeneities and their surroundings. Accounting for magnetic anisotropy observed experimentally in bias-sputtered GdCo-based alloy films solely in terms of pair ordering and classical dipolar interactions requires p∼0.015. Accounting for the anisotropy solely in terms of composition inhomogeneities requires V∼0.5 and Δx∼0.1. Although such atomic scale structural anisotropy will be very difficult to detect with currently available experimental techniques, composition inhomogeneities of this magnitude should be easily detectible in x-ray, electron, or neutron small-angle scattering experiments. No evidence for anisotropic composition inhomogeneities is seen in x-ray scattering experiments on micron-thick bias sputtered GdCo-based alloy films, although such inhomogeneities may be present in oxygen-doped, evaporated Gd-Co films and in some annealed Gd-Co films prepared by evaporation and by zero-bias sputtering. Magnetic anisotropy in GdCo-based films probably involves spin orbit interactions as well as classical magnetic dipolar interactions.
Magnetic properties of bias-sputtered Gd-Co-Fe amorphous films with uniaxial perpendicular anisotropy
Authors: Chen C. T. , Wilson W. L. , Roberts G. E.
Published: February 2003

The magnetic properties of amorphous bias-sputtered films of Gdx(FeyCo1−y)1−x are investigated. In particular, the effects of changing the relative amounts of Co and Fe are studied. Increasing the iron by 12% lowers the exchange between the rare earth and the transition metal by about 35%. There is no apparent change in the anisotropy constant with iron-cobalt ratio.
Magnetism and catalysis
Authors: Richardson James T.
Published: February 2003

Catalysts have been characterized through their magnetic properties for many years. Bulk phases, such as metals, oxides, carbides, etc., are easily identified by magnetic transitions and moments. Unique magnetic contributions to catalysis occur in catalyst dispersions and adsorption. Catalysts are prepared as small crystallites upon the surface of a refractory support. These crystallites are in the diameter range of 10 to 200 Å, which means they are superparamagnetic for ferromagnetic metals and superantiferromagnetic for antiferromagnetic oxides. Magnetization measurements lead to crystallite size distributions of dispersed nickel and these have been useful in the investigation of preparational methods, crystallite size effects in adsorption and catalysis and sintering phenomena. Similar results are possible for supported oxides, such as NiO, Fe2O3, etc., but reported applications are not extensive. Adsorption of gases on ferro- and paramagnetic catalysts may result in a transfer of electrons, detectable through magnetic changes. This effect has been applied to adsorption intermediates. Current trends in catalysis indicate the importance of molecular clusters of atoms, which will be a promising application for magnetism, both experimental and theoretical.
Magnetic potentiometer as an aid in testing and analyzing magnetic devices
Authors: McDonald D. , Steingroever E.
Published: February 2003

The steel portions of a properly designed, constant mmf magnetic device should be operated at the highest values of flux density consistent with the requirement that these steel portions consume a minimum of available mmf. The customary procedure to determine if the above criterion has been met is an indirect one. This procedure is to measure the flux density B in the several steel branches of the magnetic circuit and then calculate from B-H curves of this steel the mmf required to drive these levels of B through these branches. Although techniques for directly measuring the mmf consumed by any branch of a magnetic circuit have been available for many years, these mmf’s are usually obtained by the indirect procedure noted above. Both the instrumentation and the techniques for obtaining the desired mmf values by direct measurement are described.
Variable delay lines using magnetostrictive metallic-glass film overlays
Authors: Forester D. W. , Vittoria C. , Webb D. C. , Davis K. L.
Published: February 2003

A variable surface acoustic wave (SAW) delay line was fabricated using a thin (<1 μm) magnetostrictive film, metallic-glass overlay. It is well known that metallic-glasses can be prepared in ribbon form by rapid quenching from the melt. However, it is difficult to prepare thin film overlays of these materials for SAW and other devices with this technique. We have succeeded in preparing film overlays of Fe-B by co-evaporation. Our measured magnetostrictions and magnetizations of these films are virtually the same as in ribbon materials. Delay measurements were made using a vector voltmeter method with a bias magnetic field applied along the direction of SAW propagation and in the two perpendicular directions. The largest delay change is in the plane and perpendicular to the direction of propagation. Although the magnetostriction constants are approximately equal to that of Ni, the changes in delay time, Δτ, in the Fe-B coated SAW delay lines are larger than for Ni coated SAW devices. Also, much lower saturation bias magnetic fields, H, are required. A figure of merit, Δτ/τH, is about 250 times larger for some of the Fe-B films than for Ni.
Fabrication of thin film magnetic garnet structures for intra-cavity laser applications
Authors: Whitcomb E. C. , Henry R. D.
Published: February 2003

Garnet compositions similar to those used for bubble domain materials have been used to fabricate ferrimagnetic nonreciprocal devices for ring laser gyro biasing at 1.152 μm. Such devices are used inside an active laser cavity, therefore precise control of the optical and physical thickness of the films is required. Two concepts of Faraday elements have been demonstrated and new material and fabrication techniques have been developed to implement them. Operating Faraday elements with 0.5 percent insertion loss have been produced.
A calorimetric investigation of an yttrium-dysprosium spin glass
Authors: Wenger L. E.
Published: February 2003

In an effort to compare the spin glass characteristics of yttrium–rare earth alloys with those of the noble-metal spin glasses, the susceptibility and heat capacity of Y0.98Dy0.02 have been measured in the temperature range 2.5–40 K. The low-field ac susceptibility measurement shows the characteristic cusp-like peak at 7.64 K. The magnetic specific heat of the same sample shows a peak at 7.0 K and may be qualitatively described as a semi-cusp. The magnetic entropy change from absolute zero to 7 K is approximately 0.52 of cR ln(2J+1). These results are qualitatively different than previous calorimetric results on the archetypal spin glasses, AuFe and CuMn, where rounded maxima are observed at temperatures above the spin glass transition temperatures.
Magnetic and transport properties of amorphous NiY and FeY
Authors: Cochrane R. W. , Ström-Olsen J. , Williams Gwyn , Liènard A. , Rebouillat J. P.
Published: February 2003

We report resistivity and magnetoresistivity measurements on several samples of NiY and FeY over the temperature range 1.1 to 350 K and in magnetic fields up to 50 kOe. Although both systems are amorphous their transport and magnetic behavior is in strong contrast. NiY is extremely soft magnetically exhibiting characteristics of a weak itinerant ferromagnet. Its resistivity exhibits a minimum near 10 K with a logT region at lower temperatures and a relatively large positive ∂ρ/∂T at higher temperatures. The onset of magnetic order is seen in the transport data as a sharp step in ∂τ/∂T around Tc. On the other hand, FeY is very hard magnetically and has a resistivity characterized by a negative ∂ρ/∂T at all temperatures. The magnetoresistivity is positive and no effect is observed at the magnetic ordering temperature.
Magnetic properties of amorphous Y-Ni alloys
Authors: Liénard A. , Rebouillat J. P.
Published: February 2003

YxNi1−x amorphous alloys are shown to behave as weak itinerant ferromagnets. The model of Edwards and Wohlfarth allows for a satisfactory understanding of their major properties. However, discrepancies with this model lead us to analyse our results in the light of recent theories of itinerant ferromagnetism. Satisfying agreement is found.
Spin resonances in amorphous alloy films
Authors: Bhagat S. M. , Lloyd J. N. , Heiman N.
Published: February 2003

Spin resonance studies have been done on a series of amorphous thin films of Y-Co, Zr-Co, La-Fe, Zr-Fe and Lu-Fe alloys prepared by co-evaporation onto room temperature substrates. Y-Co alloys behave in accord with static magnetic measurements. In Y29Co71 and Y20Co80 the exchange stiffness has been determined to be 0.6×10−6 and 0.4×10−6 erg/cm, respectively. Zr-Co alloys, especially with high Co concentration show highly unexpected behavior by exhibiting several rather narrow resonances. The RE-Fe alloys are also anomalous in that they give ferromagnetic resonances at 300 K while static measurements fail to show any evidence for long range order.
Magnetic ordering in amorphous Nd-Co, Gd-Co and Er-Co alloys
Authors: Gerber J. A. , Miller D. J. , Sellmyer D. J.
Published: February 2003

Previous studies of magnetism in amorphous rare earth–transition metal alloys have emphasized alloys rich in transition metal. We report here results on three rare earth rich amorphous alloys: Nd64Co36, Gd65Co35, and Er65Co35. Low field susceptibility, χ, was measured for T in the range 4.2 K⩽T⩽300 K and magnetization was measured for 1.3⩽T⩽200 K and applied fields, H, of 0⩽H⩽80 kOe. Curie-Weiss fits were made to high temperature χ (T) data to determine average effective moments and Weiss temperatures. Hysteresis loops were used to determine the coercive force and the ordering temperatures, TC. The effective moments and saturation moments are compared with values calculated on the assumption of local moments on both the rare earth and Co ions. TC values for Nd, Gd, and Er alloys are 38 K, 170 K, and 12 K, respectively. The data are consistent with a ferrimagnetic structure in Gd65Co35. Local random anisotropy appears to play an important role in the Nd-Co and the Er-Co alloys.
Iron hyperfine fields in the Co-based Heusler alloys Co2TiSn, Co2ZrSn and Co2HfSn
Authors: Leiper W. , MacKay G. R. , Blaauw C.
Published: February 2003

We have measured iron impurity hyperfine fields H (Fe) in Heusler alloys Co2BSn (B=Ti, Zr, and Hf), by means of the Mössbauer effect. By using both Fe57- and Co57-doped alloys we have been able to obtain H (Fe) at all three sites in the alloys. We find similar results for all three alloys. The saturation iron hyperfine fields at the Co, B, and Sn sites are ‖H (FeCo) ‖≲20 kG, H (FeB) ?−350 kG and H (FeSn) ?−300 kG.
Interactions in rare earth trihalides
Authors: Skjeltorp A. T.
Published: February 2003

High frequency measurements have been made of the field dependence of the adiabatic differential susceptibility of CeCl3, CeBr3, and GdCl3. This has permitted the determination of the leading coefficients in the high temperature expansion CM/R=𝒥Cn/Tn for the magnetic specific heat and λ/χT= (T+𝒥Bn/Tn−1) for the inverse isothermal susceptibility. For CeCl3 and CeBr3, these coefficients have been combined with earlier EPR measurements allowing an unambiguous determination of the nondipolar interaction constants. The analysis shows that the interactions are quite similar for these two compounds and that the antiferromagnetic ordering is dominated by the antiferromagnetic nearest-neighbor coupling. However, there are a number of other terms both ferromagnetic and antiferromagnetic in sign and precise ordering is therefore determined by a subtle balance between these interactions. The results for GdCl3 have produced more accurate values for the nearest- and next-nearest-neighbor exchange interactions than earlier measurements. In addition, upper limits were also obtained for the third-nearest-neighbor exchange interactions.
Growth and characterization of LPE hexagonal ferrites
Authors: Glass H. L. , Liaw J. H. W.
Published: February 2003

Hexagonal ferrites are of interest for microwave and millimeter-wave devices. We have grown single crystal layers of hexagonal ferrites on non-magnetic spinel substrates using the isothermal dipping method of liquid phase epitaxy. Ferrimagnetic resonance spectra of M-type layers at 35 GHz exhibited half power linewidths as narrow as 26 Oe. Resonant absorption measurements at frequencies up to 60 GHz showed linear tuning characteristics. For W-type hexagonal ferrites, the narrowest linewidth observed was 42 Oe.
Ferromagnetic resonance in ion-implanted garnet bubble films
Authors: Soohoo R. F.
Published: February 2003

Ferromagnetic resonance spectra in garnet bubble films before and after implantation are reported. These results are in turn used to determine the samples’ anisotropy profile. Two sets of Gd0.9YTm1.1Ga0.44Fe4.56O12 samples of thicknesses 328 nm and 555 nm were used in these experiments. The six 328 nm samples were implanted with 2×1016 H ions/cm2 at 50 keV while the six 555 nm samples were implanted with 1014 Ne ions/cm2 at 200 keV. FMR spectra of all 12 samples before and after implantation were observed. In general, the unimplanted films show only one resonance peak each while the implanted ones show four such peaks in their spectra. After ion-milled to various thicknesses, the changes in mode intensity and position of these peaks were carefully measured. From the intensity An and resonance field Hon vs thickness h curves, it has been possible to ascertain the uniaxial anisotropy variation across the thickness of the film. Whereas the anisotropy profile obtained for Ne+-implanted films is in qualitative agreement with what would be expected from nuclear-stopping-power ion-damage LSS theory, that for H+-implanted ones do not. Possible causes for these discrepancies are discussed.
Magnetostatic modes of stripe domain structure
Authors: Charap S. H. , Artman J. O.
Published: February 2003

In connection with our study of ferromagnetic resonance in nonsaturated magnetic films or platelets, we have also considered the spectrum of magnetostatic modes for a stripe domain structure. For materials with large q (=HA/4πMs), the domain walls are very thin compared to the stripe width and the effective internal field, including anisotropy and demagnetizing fields, is relatively uniform within each domain. In a film of finite thickness the modes are essentially those given by Damon and van de Vaart for a disk uniformly magnetied normal to the plane. Only volume waves are permitted. If there is a nonzero component of the propagation vector in the direction of the intersection of the film plane and the domain wall, the magnetic potential must vanish at each wall. This condition requires that the propagation constant associated with the direction normal to the walls=integer×π/domain width. The domain walls are ’’transparent’’ for propagation normal to their planes and the corresponding magnetostatic modes are identical to those of a normally magnetized saturated film.
Spin glass and metallic antiferromagnetism in disordered (Ti1−xVx)2O3: High magnetic field and x-ray studies
Authors: Dumas J. , Schlenker C. , Chouteau G. , Eddine M. Nasr , Sayetat F.
Published: February 2003

(Ti1−xVx)2O3 has been shown to be a spin glass for 0.5%<x<10% and a micromagnet at higher V concentrations. For x≳0.4, magnetic susceptibility and electrical resistivity data give experimental evidence for a metallic antiferromagnetic phase, with Neel temperatures ranging from 60 K to 10 K, depending on x. Magnetization measurements have been performed for several V concentrations, at 4.2 K and 1.4 K in fields up to 150 kG. For 0.01<x<0.10, the approach to saturation can be discussed in terms of the Virial theory of Larkin et al.; the strength V0 of the RKKY interaction is found of the order of 0.5×10−36 erg cm3 and of the same order of magnitude as the value deduced from the initial reversible susceptibility extrapolated to T=0 K. For x=0.2% the large value of V0, compared with the transport properties, which are well described at low temperatures by a hopping process of the electrons, suggest that such a hopping mechanism might be responsible for efficient magnetic couplings between the V ions. For x=0.75, the absence of any saturation of the magnetization at 4.2 K up to 150 kG corroborates the antiferromagnetic nature of this compound. X-ray studies also show lattice parameter and volume anomalies (?0.2%) below the Neel temperature.
Pressure dependence of crystal field splitting in Pr pnictides and chalcogenides
Authors: Schirber J. E. , Weaver H. T. , Ginley D. S.
Published: February 2003

We have measured the pressure dependence of the Pr nuclear magnetic resonance shift in PrN, PrP, PrSb, PrAs, PrS and PrSe. The shifts in all the pnictides increase while in the chalcogenides the shifts decrease with pressure. The rare earth frequency shift is inversely proportional to the crystal field splitting in the context of the point charge model (PCM) so a decrease would be expected for all of these materials at a rate of 5/3 the volume compressibility. Our values for the pnictides tend to be considerably larger than the PCM value as well as the wrong sign. The chalcogenide values are much nearer in magnitude and are of the right sign for the PCM. Contrary to the report of Guertin et al. we see no anomaly in the pressure dependence of the susceptibility of PrS. The fact that PrN which is reported to be non-metallic also shows the wrong sign for the PCM presents difficulties for various conduction electron explanations for this unexpected behavior of the pnictides.
Magnetic properties of hydrides of the rare earths and rare earth intermetallics
Authors: Wallace W. E. , Malik S. K. , Takeshita T. , Sankar S. G. , Gualtieri D. M.
Published: February 2003

Rare earth elements (R) react with hydrogen at elevated temperatures to form hydrides with compositions approaching RH3. Intermetallic compounds involving the rare earths in chemical union with Mn, Fe, Co or Ni absorb copious quantities of hydrogen rapidly and dissociatively at room temperature. In all the hydrides RH3 and in many of the hydrogenated intermetallics the proton density exceeds that in condensed elemental hydrogen. The presence of such large amounts of hydrogen significantly modifies various physical properties of the host metal. In the elemental rare earths hydrogenation produces a loss in metallic conduction and greatly weakens exchange. Magnetic ordering is suppressed by as much as 250 degrees. In contrast hydrogenation of intermetallics may either strengthen or weaken exchange, the latter predominating numerically in the systems studied to date. Contrasting behavior is exhibited by the isostructural pair of compounds Y6Mn23 and Th6Mn23. Th6Mn23 exhibits Pauli paramagnetism whereas Y6Mn23 is ferromagnetic. Hydrided Th6Mn23 and Y6Mn23 are ferromagnetic and paramagnetic, respectively. The weakening of exchange in RH3 is a simple consequence of the depopulation of the conduction band to form anionic hydrogen. Elucidation of the magnetic behavior of the hydrided intermetallics requires detailed band structure information, which is non-existent at present.