bluuebunny/crossref_metadata_2025 huggingface dataset:
Forced Magnetostriction of Nickel, Cobalt, and Iron at 4.2°K
Authors: Fawcett E. , White G. K.
Published: January 2005

The longitudinal magnetostriction in single-crystal samples of nickel and cobalt and a polycrystal of iron was measured at 4.2°K in applied magnetic fields H up to 37 kOe. The forced magnetostriction in nickel was found to change sign for different crystal orientations. This probably explains the apparently contradictory results of previous attempts to measure the forced magnetostriction, either indirectly by the change of magnetization with hydrostatic pressure, or directly by measurements of the volume magnetostriction. A single crystal of cobalt magnetized along its easy c axis has a forced magnetostriction linear in H above 17 kOe, corresponding to ∂ε3/∂H = +2.4×10−10 Oe−1, where ε3 is the strain along the c axis. The magnetostriction in a single crystal of cobalt having its axis at an angle of 72° to the c axis is still not linear at H = 37 kOe, but appears to be approaching the same value of ∂ε/∂H. If ∂ε/∂H and the saturation magnetization σ0 of cobalt are assumed to be isotropic, this value of ∂ε/∂H and the elastic constants yield a value, ∂lnσ0/∂p = −3.4±0.4×10−4 kbar−1. for the pressure derivative of σ0, which is to be compared with the value −2.18×10−4 kbar−1 obtained by Kouvel and Hartelius by direct pressure measurements at room temperature. The forced magnetostriction of the polycrystalline iron sample is linear in H above H = 20 kOe, corresponding to ∂ε/∂H = 1.43±0.03×10−10 Oe−1. This value agrees with other measurements made at room temperature and at liquid-helium temperature, within their experimental accuracy.
Galvanomagnetic Properties of Single-Crystal Iron Films and Whiskers
Authors: Christopher J. E. , Isin Acar , Coleman R. V.
Published: January 2005

Galvanomagnetic effects have been measured and compared in single-crystal iron films 0.1 to 5 μ in thickness and in iron whiskers 10 to 500 μ in thickness. Measurements have been made in a temperature range 1° to 300°K and in magnetic fields to 80 kOe, although in this paper we discuss primarily the low-field negative magnetoresistance observed at helium temperatures. The negative magnetoresistance develops when the mean free path of the electron becomes long. In the case of whiskers with RRR≈1000 the effect can represent a 90% reduction in resistance at 4.2°K, while with films having RRR≈10–50 the effect is reduced to 1%. The negative magnetoresistance in 〈100〉 axial whiskers is very sensitive to measuring current, while the negative magnetoresistance in 〈111〉 axial whiskers is not as sensitive, although both cases show substantial deviations from Ohm's law. Analysis of the longitudinal and transverse data on the films indicates that the reverse galvanomagnetic effect is making a substantial contribution. Hall-effect measurements have also been made but do not show any anomalous behavior in low fields.
Magnetostriction of Nickel Single Crystals
Authors: Benninger G. N. , Pavlovic A. S.
Published: January 2005

The magnetostriction of single crystals of nickel has been determined within the temperature range 77°K to the Curie point in a magnetic field of 8 kOe. The data were fitted to a five-constant expression using a least-squares computer program. The absolute values of the constants decrease monotonically to zero from 77°K to the Curie point, with the exception of A1 which exhibits a broad maximum below 300°K. These constants have been found to be in fair agreement with the Callen-Callen theory of magnetostriction. It is shown that at low temperatures an expression involving more than five constants is necessary to describe the magnetostriction, although impractical because of the experimental errors.
Magnetoelastic Interaction of Dislocations and Ferromagnetic Domain Walls and Torsional Microcreep Experiments on Iron and Nickel Tubes
Authors: Allen C. W. , Donovan J. A.
Published: January 2005

Torsional microcreep experiments were carried out around room temperature in both iron and nickel tubing under a variety of magnetic conditions. The application of an alternating magnetic field caused an increase in the microcreep rate for nickel but not for decarburized iron in the temperature range 15°–70°C. The experimental value for the decrease in activation energy due to the application of an ac field in nickel was 0.04 eV, about half the theoretical value for the magnetoelastic interaction energy of a domain wall and a single dislocation. It is suggested that the absence of an effect in iron may be related to the Peierls-Nabarro stress and that an effect might be observed at much lower temperatures. There was no effect in either iron or nickel with the application of a dc field.
Energy Dependence of Magnetic Changes Induced by Electron Irradiation
Authors: Gordon D. I. , Sery R. S.
Published: January 2005

Ten-mil thick Supermalloy rings were irradiated at 110°C with electrons at energies of 0.5, 0.75, 1.0, 1.5 and 2 MeV. For each energy, doses ranged from 0.2 to 1.0×1017 electrons/cm2. The data show that the energy threshold for producing magnetic changes is <0.5 MeV and extrapolation indicates it is ∼0.4 MeV. Energy dependence of magnetic property changes above the threshold is steepest in the 0.5 to 1.0 MeV range, after which the slope of magnetic changes vs energy generally falls off. The particular pattern, however, is a function of dose, and the presence or absence of magnetic field during irradiation. With no applied field, magnetization curves and remanence are depressed. The amount of depression increases with energy, beginning with a small change at 0.5 MeV, exhibiting large changes at 0.75 and 1.0 MeV, and tending to saturate at higher energies. Increases in coercive force show a similar energy dependence. However, with an applied orienting field during irradiation (``radiomagnetic'' treatment) magnetization curves and remanence are elevated, rather than depressed. The elevation of Br increases with energy up to about 1.0 MeV, above which this effect tends to saturate. Up to this energy, coercive force changes are relatively small. Above 1.0 MeV, large increases in coercive force result. Directional ordering through radiation-enhanced vacancy diffusion is used in interpreting these data.
Solid-State Equilibria in the Iron-Nickel System
Authors: Ananthanarayanan N. I.
Published: January 2005

Critical examination of the literature on the iron-nickel system indicates that the available phase diagram for the solid-state region is inadequate. The reason for this is that solid-state transformations in this system are mostly sluggish (particularly below 500°C) and classical equilibration-anneal methods using specimens from massive alloys are laborious and generally fall short of yielding equilibrium. Equilibria can, however, be readily achieved by preparing the alloys in the form of fine-particle powders by the decomposition-reduction of mixed-crystal iron-nickel formates and/or by distilling off the mercury from mixed iron and nickel amalgams. Room-temperature and high-temperature x-ray diffraction studies of such alloy powders were made to obtain equilibrium data in compositions containing up to ∼65 at. % Ni, at temperatures between 1000° and 120°C. The γ/γ+α boundary as relocated from the results exhibits the following new features: (1) The boundary is concave downwards instead of upwards as in the older diagrams; (2) Three discontinuities are found at (a) ∼3 at. % Ni and ∼760°C, (b) ∼35–43 at.% Ni and 525°C, and (c) ∼330°C and ∼50 at. % Ni. These discontinuities have been interpreted to be indicative of three isobaric isothermal three-phase equilibria hithertofore unsuspected to exist in the Fe–Ni system. The boundary data below 300°C are being reported for the first time for this system. The need for a closer reexamination of the iron-nickel system is strongly indicated from the present results.
Magnetoresistance of Nickel-Copper Single-Crystal Thin Films
Authors: Walden R. H. , Cotellessa R. F.
Published: January 2005

Single-crystal nickel-copper thin films are obtained by utilizing a simultaneous dual-deposition technique. It is observed that the transverse magnetoresistance of the films is anisotropic with respect to magnetic field orientation for a given direction of current flow. The behavior of this anisotropy is examined at the temperatures of 77°, 173°, and 298°K, for a magnetic field strength of 10 kOe, and for film compositions ranging from pure nickel to 40% Cu-60% Ni. Data are recorded under the above-mentioned conditions with the current parallel to a [100] direction and with the magnetic field oriented in the corresponding (100) plane. The following observations are made: (1) The gross amplitude of the anisotropy passes through a maximum for a copper content of approximately 10%; (2) the gross amplitude of the magnetoresistance anisotropy decreases with decreasing temperature for a pure nickel single-crystal film and increases for most of the nickel-copper alloy single-crystal films; and finally, (3) it is noted that, as the total impurity content (materials other than nickel and copper) in the films increases, the gross amplitude of the magnetoresistance anisotropy decreases.
Ferromagnetism and Superconductivity in TiFexCo1−x
Authors: DeSavage B. F. , Goff J. F.
Published: January 2005

The magnetization and transport properties have been studied in the intermetallic system TiFexCo1−x, where 0≤x≤1. The composition x=0.5 is superconducting while all other alloys within the composition range 0.3<x<0.7 are ferromagnetic. Below the ferromagnetic transition temperature, alloys with 0.5<x<0.7 exhibit conventional field dependences, saturating at 2 kOe with a moment of the order of 10 emu/gm. Alloys with 0.3<x<0.5 do not saturate in fields of less than 25 kOe. The magnetization of the alloy with x=0.5 is nearly linear in field and no Curie temperature is observed. The magnitude of the magnetization is lower than neighboring compositions by a factor of four. The composition range of this behavior is very narrow, as alloys with x=0.55 and x=0.45 are ferromagnetic. Compositions with x<0.3 and x>0.7 are not ferromagnetic but exhibit paramagnetism presumably due to conduction electrons. The residual electrical resistivity appears to follow Nordheim's rule, suggesting disordered alloys, including the x=0.5 composition. The alloy x=0.5 has a superconducting transition temperature of 3.3°K, all other compositions within 0.3<x<0.7 not being superconductors. The low-temperature ideal resistivity is found to vary as T2, but near the composition x=0.5 the temperature dependence differs from T2. This is taken to be a result of multiband deviations from Matthiessen's rule. The implication is that the superconductivity is associated with only a portion of the Fermi surface.
Average Ripple-Angle Magnitude, Wall Pinning, and Susceptibility in Thin Permalloy Films
Authors: Comstock C. S. , Sharp A. C. , Frantsvog D. J. , Pohm A. V.
Published: January 2005

A modified bias-susceptibility apparatus and other instrumentations were used to examine the average ripple-angle magnitude 〈δφ〉av, the ``strip-domain wall pinning'', and the real and imaginary parts of the incremental susceptibility for several 1000-Å 80−20 Permalloy films with various dispersion angles. The measurements were performed under various field conditions and with various field histories.

The results of the experiments show that, as suggested by Harte et al., the average ripple-angle magnitude 〈δφ〉av depends primarily on a micromagnetic equilibrium between local perturbing torques and the average field aligning the magnetization. The angles typically ranged from 1° to 15°. Similar average ripple-angle magnitudes were obtained when the Stoner-Wohlfarth field threshold was approached with the magnetization at angles of 0°, 45°, and 90° from the rest direction. However, as discussed by Hoffman, second-order effects produced significant differences in the measurements.

Considerable pinning of the walls separating ``strip domains'' occurred. The wall pinning made the measurements sensitive to the magnetic history of a sample and displaced the peaks of the bias permeability loss curves to higher bias field values. Direct measurements indicated that internal demagnetizing fields from pinned walls reduced the real and imaginary parts of the incremental susceptibility in a direction perpendicular to the average magnetization by a factor from 2 to 10.
Spin-Wave Locking of the Uniform Rotational Switching Mode in Magnetic Films
Authors: Harte K. J.
Published: January 2005

The threshold field for high-speed, uniform rotational switching in magnetic films is experimentally found to be higher than predicted by single-domain theory.1,2 This discrepancy, which leads to the appearance of an intermediate-speed switching process, can be explained by a spin-wave locking model, which is here reviewed and extended. The underlying physical mechanism is the conversion of longitudinal spin-wave modes to transverse modes via the rotation of the uniform mode. A transient state of high magnetostatic energy is thereby created, and if the resultant spin-wave reaction torque becomes greater than the uniform torque, the uniform mode locks.

Two limiting cases are discussed. In the first, the spin-wave relaxation time is assumed to be greater than the uniform-mode switching time.3 It is the initial spin-wave state which acquires a transverse component, and locking can occur at any time up to the minimum in the uniform torque. In the second case, the relaxation time is assumed to be much less than the switching time.4 The initial spin-wave modes remain in equilibrium with respect to the uniform mode and grow in amplitude until they are prevented from reorienting by local instabilities induced by the component of the longitudinal magnetostatic force antiparallel to the magnetization,5 which becomes large near the minimum of the uniform torque. Then. conversion to transverse modes occurs as before, with locking of the uniform mode taking place near the torque minimum.

From calculations based on an initial dispersion-induced ripple state, the ``universal'' relation Tu (0) = 0.122 Kuα is derived for both cases and over a wide range of experimental situtions, where Tu (0) is the threshold starting torque for uniform rotation, Ku is the uniaxial anisotropy energy, and α is the rms hard-axis fallback angle6,7 (in degrees). Experimental results of Telesnin et al.8 appear to verify the above law.

Finally, an experiment is proposed to distinguish between the slow- and fast-relaxation models.
Origin of Stripe Domains in Ni–Fe Films
Authors: Lo D. S. , Hanson M. M.
Published: January 2005

Stripe domains have been observed in Ni–Fe films having positive, zero, or negative magnetostriction and with either tensile or compressive stress. By using the model of Saito et al. and assuming their anisotropy constant K is attributed to both the shape anisotropy K0 and the magnetostrictively induced anisotropy Ks, we can explain our experimental results quantitatively. Here K0 and Ks are determined from the stress, the magnetostriction and the geometry of a columnar grain structure (defined by Iwata et al.). From a critical thickness (the minimum thickness above which the stripe domains will be formed) vs film composition curve, it has been found that K0 is about an order of magnitude larger than Ks at a composition of 85% Ni. Therefore, the shape anisotropy, especially in the neighborhood of 81.7% Ni, is determined as the predominant factor in the perpendicular anisotropy which causes formation of stripe domains. Dependence of stripe domains on annealing, film thickness, substrate temperature, and vacuum pressure during film deposition further supports our conclusion.
Calculations of the Structure of Néel, Bloch, and Intermediate Walls and the Influence of Their Stray Fields on Bitter Powder Patterns
Authors: Olson A. L. , Oredson H. N. , Torok E. J. , Spurrier R. A.
Published: January 2005

A comprehensive computer investigation of Néel, Bloch, and intermediate walls in films 200 Å to 2000 Å thick was made by letting the computer adjust the magnetization direction in small segments of the wall until the sum of the torques on the magnetization in each segment was minimal. Many parallel walls lying parallel to the easy axis were assumed to exist as in a real film during hard axis remagnetization. The Néel wall width was found to be approximately proportional to φf−1, where φf is the angle between the magnetization in the center of the domain and the hard axis. Intermediate walls were found to exist for 90° > φf > φc, where φc is a critical angle dependent on thickness. For φf ≤ φc pure Néel walls exist and only for φf = 90° can pure Bloch walls exist. Once the magnetization distribution was known, the stray field from the wall was calculated. For Néel walls, the magnitude of the stray field was found to increase slightly as the film thickness increased (500 < T < 2000 Å) for a fixed-angle wall and to increase linearly as the wall angle increases for a fixed film thickness. For intermediate walls, the magnitude of the Bloch component of the stray field was found to be much less than the magnitude of the Néel component. This is due to differences in the Néel and Bloch wall magnetization tails, i.e., that portion of the wall where the magnetization angle changes slowly as opposed to the central portion of the wall where the magnetization angle changes rapidly. The binding energy of the Bitter powder colloid at the wall is proportional to the stray field; Néel walls are experimentally observed to have greater visibility.
Parallel Oblique-Incidence Anisotropy in NiFe Films
Authors: Crowther T. S. , Cohen M. S.
Published: January 2005

Magnetic films exhibiting an easy axis normal to the incidence plane (perpendicular anisotropy) when deposited at oblique incidence are well known. Anisotropic crystallite chains created by self-shadowing were postulated to explain this effect. One of the physical measurements supporting this model was the observation of optical dichroism. In the present work, an easy axis parallel to the incidence plane (parallel anisotropy) has been found in nonmagnetostrictive films deposited at low (<45°) incidence angles for certain substrate temperatures and film thicknesses. The value of Hk and direction of the easy axis in oblique incidence films was very sensitive to changes in incidence angle, substrate temperature, film thickness, and deposition rate. The magnitude of the magnetic anisotropy Hk was found to be linearly related to the magnitude of the dichroism Δγ by the same constant, dHk/dΔγ = 5.5 × 105 Å·Oe, for oblique incidence films having either parallel or perpendicular anisotropy. This result furnishes strong support for the view that parallel, like perpendicular oblique incidence anisotropy, originates in anisotropic microstructure, e.g., columnar growth. The resultant anisotropy is thus the result of a delicate balance between the crystallite chains and the columns.
Relaxation Processes for Ferromagnetic Resonance in Thin Films
Authors: Patton Carl E. , Wilts Charles H. , Humphrey Floyd B.
Published: January 2005

Ferromagnetic-resonance linewidth measurements have been made for two hundred Ni–Fe alloy films (77% Ni) 150–3200 Å thick at frequencies from 1–9 Gc/sec with the static field in the film plane. To avoid dispersion effects samples with the smallest linewidth (ΔHmin) were selected for each thickness. For film thickness less than a frequency-dependent critical thickness Dω, ΔHmin is independent of film thickness. For thicker films where D > Dω, ΔHmin increases linearly with film thickness. The observed Dω values (about 1000 Å) are in good agreement with predictions based on magnon scattering involving spin waves degenerate with the uniform mode. Because of the magnetostatic mode modification of the spin-wave dispersion relation for thin films there are no spin-wave states degenerate with the uniform mode for D < Dω and magnon scattering is not allowed. The applicability of two different magnon processes, s-d exchange and two-magnon scattering, is discussed. Neither mechanism provides a completely satisfactory explanation of the data. The present data indicate: (1) For D > Dω, the linewidth is a linear function of film thickness and a magnon process is important. (2) For D < Dω, a magnon process is not important. (3) The anisotropy dispersion makes a contribution to ΔH, which is significant and may mask the above effects if the dispersion is large.
Magnetoresistive Magnetostriction Monitor
Authors: Tolman C. H. , Rubens S. M. , Oberg P. E.
Published: January 2005

A monitor which is suitable for automatic control of magnetostriction of ferromagnetic alloy films is described. In operation, a glass substrate, upon which the monitor film is being deposited, is subjected to a low-frequency periodic torsional stress. The film also is subjected to a high-frequency alternating magnetic field which induces anisotropy in the film and also switches the state of magnetization. The periodic reversal of the applied stress and the related change of the strain induced anisotropy alters the magnetic switching characteristics of the film. Inductive sensing (pickup coil) and magnetoresistive sensing methods of the stress-modulated switching characteristics are reported. A modified monitoring technique, utilizing a dc magnetic field transverse to the ac field mentioned above, is also described. This method allows the deposition of a magnetostrictive film at an elevated substrate temperature which results in a near zero magnetostrictive value at room temperature, while employing a null output for magnetostriction control. Control of magnetostriction is achieved through regulation of source composition.
Anomalous Hysteresis Loops in Permalloy Thin Films near 4.2°K
Authors: Hagedorn F. B.
Published: January 2005

Mitchell and Briscoe have reported that the uniaxial anisotropy, Hk, in thin Permalloy films is 2 to 3 times larger at 4.2°K than it is at 300°K and that an additional doubling in Hk occurs in going from 4.2° to 1.46°K. Several new and interesting characteristics and a tentative explanation of this phenomenon are given in the present paper. The explanation is based on the formation of an antiferromagnetic oxide on the film surface. By oxidation in O2 and subsequent reduction in H2 (each for several hours at 120°C), the anomalous susceptibility at low temperatures has been introduced and removed repeatedly in the same sample. While in the low susceptibility state, measurement of the uniaxial anisotropy at 4.2°K by means of a rotating field magnetometer demonstrates that only the susceptibility, not the uniaxial anisotropy, is anomalous. A unidirectional anisotropy, arising from the exchange coupling between the ferromagnetic and antiferromagnetic materials, is thus proposed to explain the susceptibility. Several aspects of the hysteresis loops observed at 4.2°K support this explanation, and additional evidence is obtained from the temperature dependence of the anomalous loop behavior.
Magnetization Ripple in Multilayer Films
Authors: Iwata Takao , Prosen Richard J. , Gran Burton E.
Published: January 2005

Several types of multilayer films, Permalloy (81%Ni)-Cu-Ni or Permalloy (81% Ni or 74% Ni)-Cu with or without a periodic variation in the thickness of the copper layer, were prepared. It was found that the magnetization ripple depended on the nature of the copper layer. Ripple structure attributable to stray fields due to the island characteristics of a very thin copper layer was observed. Mean wavelength of the ripple is roughly ten times larger than that of the island structure. In the films with periodic roughness of the copper layer, the ripple pattern is enhanced and follows the periodicity. It was observed that the ripple generally increased the coercive force of films (by about 1 Oe).
Magnetic Properties of Compounds and Solid Solutions of Rare-Earth Metals
Authors: Bozorth R. M.
Published: January 2005

Studies of compounds and solid solutions of rare-earth elements (R) have already unearthed some generalizations regarding the behavior of this series of elements. In compounds with elements of the iron group (X) there is usually antiferromagnetic coupling between R and X when R is heavier than Gd, ferromagnetic coupling when R is lighter than Gd. This has been interpreted as interaction between spins only. The varying Curie temperatures of compounds of Eu and Gd with S, Se, and Te, especially in their solid solutions with each other, agree qualitatively with the theory of exchange through conduction electrons. In solid solutions R-R, when both R's are heavier than Gd, the Néel points (TN, transition temperature from spiral to paramagnetic phase), are proportional to Ḡ2/3, where Ḡ is the average of the deGennes factors (g−1)2J(J+1) of the R's. The Curie points of these solid solutions, however, are distinctly characteristic of the elements and seem to be closely related to their Stevens factors, the principal one of which changes from + to − in the middle of the heavy rare-earth series, between Ho and Er. Results for HoEr, DyEr, and DyEr3 crystals are interpreted in terms of the Kitano-Nagamiya theory of the mechanism of magnetization of the rare earths. Crystal anisotropy constants are derived for HoEr. Published and unpublished magnetic data illustrating these and other points will be shown and discussed.
NMR Studies of Magnetic Properties of Light Rare-Earth Hydrides
Authors: Kopp J. P. , Schreiber D. S.
Published: January 2005

Measurements of the 1H NMR line width and Knight shift have been made as functions of temperature and hydrogen concentration for CeHx (2≤x<3). Knight shifts of the order of +2.0% occur for x=2.45 at T=6°K for which the line width is 160 G. The shifts and widths decrease as the concentration is decreased or increased to 2.0 or 2.85, respectively. Calculations of the shifts are performed using the RKKY theory with the assumption of Weiss constants obtained from a linear fit to the reciprocal shift data. What appears to be a magnetic ordering occurs for the intermediate concentrations (TN=5.4°K for x=2.45), as observed by the disappearance of the line. A simple overlapping, rigid-band model is proposed to explain the results.
Basal-Plane Anisotropy of Gadolinium
Authors: Graham C. D.
Published: January 2005

The magnetocrystalline anisotropy in the basal plane of gadolinium (constant K4 in the usual notation) has been determined from torque measurements on a single-crystal disk in the temperature range 4.2° to 150°K. The easy direction in the basal plane is 〈112̄0〉, corresponding to K4<0. The use of anisotropy per unit mass instead of the customary anisotropy per unit volume is suggested for measurements which extend over a range of temperature, and the symbol Kn is suggested for anisotropy-per-unit mass. The value of K4 for Gd at 4.2°K is [minus]800 erg/g, and K4 approaches zero at about 170°K. The temperature dependence of K4 follows approximately the 21st power of the magnetization as predicted by theory.
Magnetic Moment Measurements in Single-Crystal Dy, Ho, Er, and Gd in dc Fields up to 170 kG
Authors: Foner S. , McNiff E. J.
Published: January 2005

Magnetic-moment measurements are presented for single-crystal1 Dy, Ho, Er and Gd with applied fields up to 170 kG. These results, obtained for various crystallographic orientations with a low frequency VSM developed for use in the NML dc solenoids, extend and augment a number of earlier measurements, including the recent pulsed field data of Flippen.2 The magnetic data are complex as is expected from the known magnetic structures at low fields. Briefly, at 4.2°K and with B0 ‖ C we find: (a) Dy-M increases slowly up to 170 kG; (b) Ho-M increases rapidly up to 12 kG, then more slowly, and there is a further rapid increase (transition) at about 130 kG; (c) Er-M increases rapidly up to 30 kG then approaches saturation more slowly; (d) Gd-M increases rapidly up to 25 kG and then is almost constant. For B0⊥C we find: (a) Dy-M increases rapidly at low fields and approaches saturation at high fields; (b) Ho-M increases rapidly at low fields and approaches saturation at high fields; (c) Er—broad transitions occur at about 16 and 120 kG; (d) Gd—the results are similar to those for B0 ‖ C. Except for Gd, the magnetic moments generally show an appreciable increase up to our maximum fields. Magnetic-moment measurements have also been completed for these materials at 77°K. The results will be published elsewhere.
Magnetocrystalline Anisotropy of Two Yttrium-Cobalt Compounds
Authors: Hoffer G. , Strnat K.
Published: January 2005

The magnetocrystalline constants of two ferromagnetic rare-earth-cobalt intermetallic compounds, YCo5 and Y2Co17, have been measured in the approximate temperature range 20°–300°K. The anisotropy constants were obtained from magnetization vs applied-field curves measured on single-crystal spheres in the principal crystallographic directions of the hexagonal structure. YCo5 has a magnetically easy c axis and no anisotropy in the hard basal plane. K1 increases from 7.03×106 erg/g at 300°K to 10.03×106 erg/g at 24°K. Y2Co17 has an easy basal plane with no anisotropy in the plane. At 307°K, K1=−3.61×105 erg/g, and K2=0.22×105 erg/g while at 21°K, K1=−6.99×105 erg/g and K2=−0.69×105 erg/g.
Magnetic Anisotropy of Terbium and Dysprosium
Authors: Rhyne J. J. , Clark A. E.
Published: January 2005

The enormous magnetic anisotropy of Tb and Dy has been studied in the temperature range from 11°K to near the Néel points. In order to directly determine the large axial anisotropy (>108 erg/cm3), a unique torque pendulum was used in which the difference between the specimen torque and that of a fixed-coil dipole was determined as a function of applied field. Torque data on single crystals of Tb and Dy in fields up to 140 kOe yielded values of the uniaxial anisotropy constant K2 of 5.5×108 erg/cm3 at 11°K to 1.7×108 erg/cm3 at 205°K for Tb, and 5×108 erg/cm3 at 22°K to 1.7×108 erg/cm3 at 152°K for Dy. The temperature dependence of the data agrees with that calculated from the single-ion interaction theory: K2(T)=K2(0)Î5/2[L−1(m)] where Î is a normalized hyperbolic Bessel function and L−1 is the inverse Langevin function of the reduced moment. The sixfold basal-plane anisotropy of Dy and Tb were obtained from an analysis of the angular dependence of the basal plane magnetostriction. Values of the basal-plane anisotropy constant K66 for Tb ranged from 2.4×106 erg/cm3 at 4°K to 2×105 erg/cm3 at 140°K, and for Dy from 7.5×106 erg/cm3 at 4°K to 2×105 erg/cm3 at 120°K. As in the case of K2, the strong monotonic temperature dependence can be adequately represented by the single-ion expression. Here K66(T)=K66(0)Î13/2[L−1(m)]. High-field facilities of the Naval Research Laboratory and the National Magnet Laboratory were utilized.
The Paramagnetic Form Factor of Gadolinium
Authors: Child H. R. , Moon R. M. , Raubenheimer L. J. , Koehler W. C.
Published: January 2005

A sample of Gd2O3 enriched to about 98% in the low absorbing isotope 160Gd was examined by neutron diffraction at temperatures from room temperature to 1.3°K. Measurements of the diffuse background scattering in the high and intermediate temperature patterns have been used to obtain the paramagnetic form factor as a function of sinθ/λ. The observed scattering cross section was converted to f2 values by assuming the full theoretical paramagnetic moment of g[J(J+1)]1/2 for Gd+3 and using this value to correct for the isotropic nonmagnetic part of the scattering. The form factor obtained in this manner is near the calculated Hartree-Fock free-atom form factor but appears to be slightly higher over most of the region out to sinθ/λ≅0.3 Å−1. Beyond this value, overlapping nuclear reflections in the powder pattern make it impossible to obtain usable values of the background intensity. Magnetic ordering of a complex antiferromagnetic nature appears at about 1.6°K but a large diffuse hump in the pattern remains to a few degrees above liquid-helium temperature. This hump never completely disappears at the lowest temperatures reached indicating the magnetic structure is by no means fully developed at 1.3°K.
Magnetic Structure of Er2O3 and Yb2O3
Authors: Moon R. M. , Child H. R. , Koehler W. C. , Raubenheimer L. J.
Published: January 2005

Neutron-diffraction measurements on single crystals and powders of Er2O3 and Yb2O3 have been used to establish the magnetic structures of these materials. Crystallographic structure parameters were determined by single-crystal measurements at 4.2°K and the magnetic intensities were measured at 1.3°K. The Néel temperatures are 3.36°K for Er2O3 and 2.25°K for Yb2O3. A noncollinear antiferromagnetic model is proposed for Er2O3 which gives good agreement with the observed magnetic intensities. In this model the eight rare earth sites with point symmetry C3i have moments along the local 〈111〉 symmetry axis. The remaining 24 Er ions, with point symmetry C2, have moments along the local 〈100〉 symmetry axis. Sites related by the body-center translation have moments in the same direction. This model is identical to that proposed by Bertaut and Chevalier,1 except they conclude that the two sites have equal moments, while we find 6.1±0.1 μB on the C3i sites and 5.4±0.1 μB on the C2 sites. This configuration is consistent with g-factor measurements which indicate highly anisotropic g tensors for both sites with the major axis for each site along the local symmetry axis. The dipole field produced by this array is self-consistent in that the resultant field at each site, due to dipoles at all the other sites, is in the direction of the dipole moment at that site. The dipole-dipole energy for the C3i sites is 4.0°K but is only 0.4°K for the C2 sites, so that superexchange coupling must be invoked to explain the observed transition temperature. A calculation of the expected moment for the C2 sites, based on the ground-state wavefunction given by Gruber, Krupke, and Poindexter,2 gives a value of 2.1 μB, in definite disagreement with the neutron diffraction result.

For Yb2O3 a structure is proposed in which moments of 1.06±0.06 μB at the C3i sites are oriented along 〈111〉 directions but not along the particular 〈111〉 local symmetry axis. The C2 sites have moments of 1.88±0.06 μB, oriented along 〈110〉 directions perpendicular to the local symmetry axis. Sites related by the body-center translation have their moments directed oppositely. This configuration is not consistent with a coupling scheme based on dipole-dipole interactions.
Magnetic Properties of Some Alloys of Thorium with Holmium and Erbium
Authors: Koehler W. C. , Child H. R. , Cable J. W. , Moon R. M.
Published: January 2005

Neutron diffraction studies have been carried out on a number of alloys of thorium with the heavy rare-earth metals Ho and Er, as part of an investigation of the nature of the exchange interaction in these materials. At room temperature, the heavy rare earths in question crystallize in the simple hcp structure; thorium, in the ccp structure. Alloys containing more than about 80 at. % rare earth are found in the hcp structure, and those with less than about 50 at. % are found in the ccp arrangement. The three outer electrons of the rare-earth metals (5d16s2) are presumed to form conduction bands, and it is generally accepted that magnetic coupling in the rare-earth metals occurs via an indirect interaction involving a polarization of the conduction electrons. Thorium, a tetravalent diluent (outer electron configuration 6d27s2), provides a means of changing the effective number of conduction electrons on alloying of the rare earths. In contrast to the effect of trivalent yttrium and lutetium as diluents, small additions of thorium tend to stabilize the ferromagnetic state in the hcp structure. Attempts at correlation of the results with the Ruderman-Kittel-Kasuya-Yosida theory have been made but with indifferent success.
Magnetic Properties of Rare-Earth Compounds
Authors: Busch G.
Published: January 2005

The magnetic properties of binary rare-earth compounds are reviewed. The influence of crystal field and exchange interaction on the magnetic properties is shown to vary systematically in the group of LnX compounds [Ln=Lanthanide atom, X=N, P, As, Sb]. Crystal-field parameters are calculated.

The europium-chalcogenides are of particular interest. From measurements of the magnetic susceptibility at normal and under high pressure it is concluded that EuSe is antiferromagnetic above 3°K approximately with a Néel temperature of 4.6°K, but it assumes a ferro- or ferrimagnetic structure at lower temperatures.

The optical absorption of EuO, EuS, EuSe, and EuTe was measured as a function of temperature. Energy gaps and their variation with temperature were determined. A giant decrease of the gaps was observed below the Curie and Néel temperatures, respectively. The change of the gaps is shown to be proportional to the magnetization of the specimen. This effect yields a new method to measure the spontaneous magnetization without a magnetic field. A long tail of the spontaneous magnetization above the Curie temperature is found.
Magnetic Properties of PrAl2
Authors: Olsen C. E. , Arnold G. , Nereson N.
Published: January 2005

Neutron diffraction powder patterns have confirmed that the compound PrAl2 undergoes a magnetic transition to a ferromagnetic structure at a Curie temperature of 38°K. The ordered moment at saturation on the Pr atom sites is 2.94±0.05 μB which is close to the full moment of 3.2 μB expected for the free Pr+3 ion. No detectable moment is observed for Al. The present results for the total moment per molecule are in satisfactory agreement with previous magnetization measurements. The shape of the magnetic form factor for the Pr3+ ion was determined over the range from (sinθ)/λ=0.1 Å−1 to 0.5 Å−1 and is in good agreement with calculated values.
Hysteresis Evaluation of Microwave Ferrites at Audio Frequency with Large Dynamic Range
Authors: Weiss Jerald A. , Betts Foster
Published: January 2005

The evaluation of ferrites and ferrimagnetic garnets for use in microwave switches and digital phasers requires, in addition to microwave examination, determination of saturation and remanent magnetization, coercive field, and a measure of squareness, including the dependence of these properies on amplitude of actuating fields, temperature, and internal and externally applied stresses. We have developed a novel method which combines the required accuracy and convenience, and by which we are able to examine, on a single specimen, both the low-field details of hysteresis and the approach to saturation at high fields. The field is produced by a nickel—ferrite electromagnet excited at 60 or 400 Hz, generating a field at amplitudes up to 1000 Oe. The specimen may be a rod, toroid, or other shape. Flux sensing is conventional; sensing of internal field is done by a magnetic potentiometer of special design. Integration is performed by a system incorporating amplifiers which were selected for gain, bandwidth, noise, and drift characteristic adequate to yield substantially distortion-free hysteresis loops under the stringent requirements of high-field excitation.
Lightweight High-Power TE01 Mode Duplexes
Authors: Greenwood R. E. , Heithaus W. C.
Published: January 2005

This paper describes a lightweight high-power TE01 mode duplexer in which weight reduction is achieved by using hexagonal ferrites. This duplexer operated at 35 GHz and has been tested at 150 KW peak power. Transmitted power loss is typically less than 0.5 dB. This device is basically a ``zero dB'' coupler using circular waveguide for the primary line and ferrite loaded rectangular waveguide for the secondary line. Hexagonal ferrites in the secondary waveguide produce the desired nonreciprocal phase shift. The ferrite is a (NiCo)2W compound with Hanis=6500 Oe. The method of selecting material and configuration is discussed, along with the effects of ferrite properties, configuration and location on performance and magnetic-field requirements.
Magnetic and Microwave Properties of Aluminum- and Gadolinium-Substituted Calcium Vanadium Garnets
Authors: Wilson W. R. , Hodges L. R. , Rodrigue G. P. , Harrison G. R.
Published: January 2005

Polycrystalline ferrimagnetic pentavalent vanadium garnet compositions have been prepared for both the Bi and Y compounds. In this study, aluminum was substituted for iron in the BiCaVIG compounds and gadolinium was substituted for yttrium in the YCaVIG compounds. In particular, the following compositions were formulated, prepared and evaluated: Bi0.4Ca2.6V1.3AlwFe3.7−w O12 for w values in the range of 0 to 0.5; (Y0.5Gd0.5)3−2xCa2xVx Fe5−xO12 with x values from 0.6 to 1.2. The following magnetic and microwave characteristics were measured and reported on these compositions: lattice constant, density, 4πMs, Curie temperature, linewidth, and g factor. Linewidth, g factor and 4πMs as a function of temperature are also given. The properties of these materials are compared with those of the pure BiCaVIG and YCaVIG compounds and those in the yttrium iron garnet family.
Ferromagnetic Resonance Effects under Mode-Segregation Conditions
Authors: Chow K. K. , Buffler C. R.
Published: January 2005

Measurements are reported that verify the mode-segregation effect of Hines and Chow. This effect occurs when the uniform precessional mode is made to move below the k=0 extrapolated lower limit of the spin-wave manifold by means of an interaction with a dielectric cavity mode, or by means of propagation effects.

The measurements reported show a radical change in both the nonlinear behavior and the linewidth of ferromagnetic resonance as the k>0 spin-wave states are eliminated from the relaxation process.

It is believed that these experiments indicate new avenues of approach for studying basic relaxation mechanisms as well as new areas of practical high-power device operation.
Thin Ferrite Phase-Shifters for Integrated Microwave Devices
Authors: Roome G. T. , Hair H. A. , Gerst C. W.
Published: January 2005

Theoretical and experimental investigations have been conducted to determine the feasibility of microwave devices which utilize the remanent magnetization characteristics of dimensionally thin magnetic materials. A technique for producing phase-shift (both reciprocal and nonreciprocal) was theoretically developed and proven experimentally.

By investigating the thin sample geometry (ferrite slabs 5 to 20 mils thick), we had the opportunity to use commercially available materials to prove the theory and at the same time extend it to a device configuration which is topologically close to the thin film. Phase-shifting elements composed of a meander line circuit deposited on a thin ferrite slab have been built and tested. By a modification of the meander-line-circuit dimensions and the direction of the ferrite magnetization relative to the circuit, both reciprocal and nonreciprocal devices can be made. A microstrip arrangement of the device was adopted so that the theory could be proved in a structure which closely approximates the ultimate thin-film application.
Frequency Dependence of Initial Permeability of Ferrites near the Onset of Low Field Loss
Authors: Sandy F. , Green J. J.
Published: January 2005

Measurements have been made of the initial permeability, μ=χ0+1, on a series of ferrites as a function of frequency above ωM=γ4πMs. The reciprocal of the real part of the susceptibility, 1/χ0′, was found to be linear in ω over a wide frequency range and reasonably independent of everything except ωM. This behavior is shown to be consistent with a model describing the susceptibility as an integral over a distribution of Lorentzian modes with frequencies from zero to ωM. It was also found that (χ0″)−1/2 was linear in ω over a smaller frequency range and that the initial slope and subsequent shape depends strongly on the magnitude of the intrinsic loss of the material and its frequency dependence. This behavior is also consistent with the above model.
A New Low-Level Limiter for Centimeter and Millimeter Waves
Authors: Courtois L.
Published: January 2005

A new type of ferrimagnetic limiter which is almost as efficient as the coincidence limiter and which can be used even at very high frequencies is presented. It is based on the coincidence of dimensional sample resonance and optimum conditions for parametric excitation of spin waves at ω/2. Its characteristics are compared to other known limiters, particularly at high frequency.
Low-Temperature Nonlinear Effects in High-Saturation Magnetization Ferrites
Authors: Dixon Samuel
Published: January 2005

Single-crystal nickel zinc (Ni0.5Zn0.5Fe2O4) and lithium zinc (Li0.35Fe2.35Zn0.5O4) ferrite were used in an experimental investigation of ferromagnetic nonlinear effects with incident power at both room temperature and 77°K. All data were taken at a constant frequency of 9.0 GHz. The lowest measured linewidths (ΔH) were 10 and 15 Oe at room temperature on nickel zinc and lithium zinc, respectively. These linewidths are reduced approximately 50% at 77°K. The saturation magnetization of the samples was in the order of 5000 ±150G at room temperature. This magnetization is increased approximately 20% above the room temperature value at 77°K. Variation of the incident power in oersteds over the range 1×10−6 to 10 Oe yielded the following general results: A substantial reduction in threshold field for nonlinear effects was measured on both lithium and nickel zinc ferrite at 77°K. Spin-wave linewidths (ΔHk) calculated at 77°K also yielded large reductions from those observed at room temperature. These enhanced values of saturation magnetization, along with the low threshold fields observed in nickel zinc ferrite, have important applications in the design of microwave-power limiters operating in the coincidence mode.
Miniature Ferrite Nonreciprocal Device
Authors: Friedman A. N.
Published: January 2005

This paper describes the design philosophy of a novel miniature nonreciprocal ferrite device using a resonance detuning principle and presents some experimental results. Early in the investigation an isolator was constructed at 1.2 GHz which showed 2 dB loss and 13 dB isolation while occupying a space 0.25 in. by 0.40 in. by 0.07 in. exclusive of biasing magnet. Also, a two-element structure occupying approximately twice the volume was constructed at 400 MHz and showed 2 dB forward loss and 25 dB isolation. The large loss is not intrinsic to the device. It is a combination of copper loss and lack of saturation in the ferrite at resonance and is subject to improvement. Miniaturization is made possible by the use of a lumped element 3-dB quadrature hybrid coupler. The coupler provides the quadrature phase needed to excite orthogonal windings and produce a circularly polarized magnetic field at the ferrite element. One sense of circular polarization couples strongly to the ferrite resonance spoiling an exciting circuit resonance. The resulting impedance change alters the scattering characteristic of the resonator. The other polarization sense, produced by exciting another port of the coupler, leaves the scattering unchanged. This is the basic nonreciprocity upon which circulators and isolators can be constructed. An isolator makes use of one coupler with two loads to absorb the energy transmitted past the resonators. A four-part circulator results when this energy is recollected by a second coupler.