bluuebunny/crossref_metadata_2025 huggingface dataset:
Neutron-Diffraction Studies of Magnetic Structures in Ho-Er Alloys
Authors: Shirane G. , Pickart S. J.
Published: April 2005

Neutron-diffraction studies were made on a single crystal of Ho0.5Er0.5 as well as on two polycrystalline samples, Ho0.7Er0.3 and Ho0.4Er0.6. The magnetic structures of these alloys at 4°K are ferromagnetic cone spirals propagating along the c axis, as in both end members. The magnitude of observed magnetic moments indicates that these alloys form uniform magnetic structures with respect to the cone angle. This conclusion is in contrast to the model in which the magnetic-moment direction of each constituent atom is mainly determined by its own anisotropy with an average cone angle and spiral periodicity. The temperature dependence of magnetic intensities of the Ho0.5Er0.5 crystal has been studied in detail. The cone angle of the ferromagnetic cone structure increases with temperature and the structure transforms to a pure spiral mode at 33°K without a noticeable discontinuity in the total moment value. The spiral structure is retained up to the Néel temperature at 104°K in contrast to pure Er where an additional sinusoidally modulated phase was observed below the Néel point.
Critical Magnetic Scattering from KMnF3
Authors: Cooper M. J. , Nathans R.
Published: April 2005

Critical magnetic scattering experiments on the simple ionic antiferromagnet KMnF3 are described. The observed intensity distributions are compared with those calculated from the Van Hove theory for quasi-elastic scattering using an experimentally determined resolution function. Excellent agreement is obtained with the Ornstein-Zernike form for the radial dependence of the correlation function in the temperature range 1.002<T/Tc<1.1. The correlation range is found to increase from 12 Å at T/Tc=1.1 to 200 Å at T/Tc=1.002 and the inverse staggered susceptibility is found to follow very closely a 43 power law dependence on T−Tc. The results are also compared with recent results on ferromagnetic metals.
Magnetic Structure of MnP
Authors: Felcher G. P.
Published: April 2005

Neutron diffraction measurements confirm that MnP is ferromagnetic between 50° and 291°K, with 1.3 μB/Mn atom directed along [001] of the orthorhombic Pbnm cell. Previous measurements at low temperatures indicated that the compound was metamagnetic; neutron diffraction measurements in zero magnetic field reveal a modulated structure in which ferromagnetically coupled pairs of Mn spins are arranged in a spiral whose axis of propagation and rotation is [100]. A preliminary account is given of the magnetic behavior of the compound at the metamagnetic-ferromagnetic transition point.
Transient Growth of Spin Waves under Parallel Pumping
Authors: Joseph R. I. , Hartwig C. P. , Kohane T. , Schlömann E.
Published: April 2005

We have experimentally observed the transient absorption during the application of a microwave pulse in a high-purity single-crystal YIG sphere at X-band and dc fields on the order of 900 Oe when the rf power level exceeds the threshold only slightly (less than 1 dB). Detailed calculations of the transient absorption coefficient based upon a previously proposed theory of Schlömann and taking into account the reaction of the sample upon the field in the resonant cavity agree reasonably well with the experimental data.
Spin-Wave Linewidth of Garnets Determined with Relative Power Measurement
Authors: Goldstein H. L. , Boxer A. S. , Ollom J. F. , Baldwin V. M.
Published: April 2005

A new technique is described for determining spin-wave linewidth (ΔHk) by a purely relative power measurement. In this method, first the threshold power P1 for instability under parallel-pump excitation with a single frequency is measured. Then the threshold power P2 is found when the sample is excited by two signals of equal amplitude with a frequency difference of Δω. The ratio P2/P1, is a function of Δω. It varies approximately from ½ to 2. For large Δω, spin waves with half the frequency of the two applied signals are excited. For small Δω, the two frequencies jointly excite a single spin wave. In this region, the observation of instability does not depend on the secular growth of the unstable spin wave. Rather, the spin wave oscillates in amplitude between the thermal level and a level nk0 exp B at which its effect on the microwave signal is just detectable. These considerations are supported by oscilloscope traces of the transmitted signal: For small Δω, instability is observed on each oscillation of the difference frequency. For large Δω, P2/P1 is a function of Δω/ηk, where ηk=γΔHk/2 is the spin-wave relaxation frequency and γ the gyromagnetic ratio. Thus ηk can be determined directly from a measurement of the power ratio in this region. For small Δω, P2/P1 is a function of BΔω/ηk. This makes it possible to find B when ηk has been measured before.
Longitudinal Susceptibility of Porous Polycrystalline YIG at Microwave Frequencies
Authors: Kohane T. , Schlömann E.
Published: April 2005

A theory of the longitudinal susceptibility (response to an rf field applied parallel to the dc field) of magnetic materials with a nonuniform saturation magnetization is described. According to this theory the imaginary part of the longitudinal susceptibility χ″ considered as a function of dc magnetic field, should show an absorption peak whose height is proportional to the porosity, whereas the width is substantially independent of porosity and approximately given by 2π 〈M〉, where 〈M〉 is the average saturation magnetization. The real part of the susceptibility is negative on the low-field side, positive on the high-field side, of the absorption peak. Measurements on porous, polycrystalline YIG at room temperature and X band are reported. The data agree quite well with the theoretical predictions, provided that allowance is made for the damping of the spin waves that give rise to the longitudinal susceptibility.
Dependence of the Magnetic Properties of Y3Fe5−xGaxO12 and Y3Fe5−xAlxO12 on Thermal History
Authors: Leo D. C. , Lepore D. A. , Nielsen J. W.
Published: April 2005

The saturation magnetization, Curie temperature, compensation point, and ferromagnetic resonance linewidth of Y3Fe5−xMxO12, M=Ga or Al, depend upon the thermal history of the sample. For example, a single crystal of YGaIG, x=1.26, will exhibit a room-temperature 4πMs between 220 and 88 G as it is quenched from temperatures ranging downward from 1275°C and finally slow-cooled to room temperature. Tc will decrease 3.5°C. The results can be explained by assuming the Ga or Al concentration on octahedral sites increases with increasing temperature. The direction of the change in Curie temperature is predicted by Gilleo's theory.

The results are important to the control of magnetic properties of garnets in applications requiring closely matched samples.
Permanent Magnets in Use Today
Authors: Luborsky F. E.
Published: April 2005

The present status of our concepts as to the origin of the structure and behavior of permanent magnet materials now in use is discussed. It is shown that domain theory can at least qualitatively explain the properties of all these permanent magnet materials. In some cases quantitative agreement between theory and observed properties has been achieved, e.g., with elongated single-domain particle magnets and with iron and iron-cobalt whiskers smaller than about 1000 Å in diameter. Such cases are shown to improve our understanding of both the structure and properties of the more complex Alnico alloys.
Observations of the Structure of Alnico V by Thin-Film Electron Transmission Microscopy
Authors: Dash J. , Bitler W. R.
Published: April 2005

A new technique for the preparation of thin films of Alnico V for electron transmission studies is described. Using films prepared by this method it has been possible to observe domain boundaries and superdislocations typical of ordered structures in samples water quenched from 1250°C. Second-phase particles which have a structure-of-lattice parameter much larger than the matrix-lattice parameter have also been observed. It is thought that these particles originate in the temperature range 850° to 1200°C.
Some Measurements of Inhomogeneous Permanent Magnets by the Pole-Coil Method
Authors: Steingroever E.
Published: April 2005

The pole-coil method for measuring demagnetization curves of permanent magnets is applied to inhomogeneous magnets. It allows the analysis of different causes of inhomogeneities: differences in the intrinsic magnetic properties within one test sample, in the degree of orientation of otherwise homogeneous material, in the effectiveness of magnetic heat and annealing treatment; inclusion of holes or nonmagnetic contaminations; unequal cross sections of the tested magnet, e.g., with conical shape.

By the pole-coil method inhomogeneities can be recognized by differences in remanence and coercivity. But in the case of serial arrangement of different components the resulting coercivity of an inhomogeneous sample is an average value of the coercivities of the components and nearly unaffected by the location of the measuring spot. The measurement of a magnet with different cross-sectional areas on both faces yields data for immediate magnetic circuit design.
First- and Higher-Order Magnetic Phase Transitions in Dysprosium Aluminum Garnet
Authors: Keen B. E. , Landau D. , Schneider B. , Wolf W. P.
Published: April 2005

Dysprosium aluminum garnet is a highly anisotropic (Ising-like) antiferromagnet which, in an applied field, undergoes a transition to the paramagnetic state without spin flopping. To investigate the nature of this transition we have made high-resolution measurements of the isothermal magnetization M and we have measured the specific heat CH as a function of temperature in different constant magnetic fields up to 14 kOe. The results show that for temperatures between 1.66°K and 1.14°K (and probably below) the transition is of first order, with dM/dH accurately constant and equal to 1/D, where D is the demagnetizing factor. The latent heat corresponding to this first-order phase change was calculated from the Clausius-Clapeyron equation and compared with direct measurements of the isothermal heat of transformation. Good agreement was found. From 1.66°K up to the Néel point (TN=2.53°K) the transition is of higher than first order with a point of inflection in the M(H) isotherms and slightly rounded λ-type peaks in the CH(T) curves. Close to TN the phase boundary is found to fit Hcint=A(1−T/TN)n, with n=0.50±0.02 and A=6.52 kOe. Our results show that the theory of a simple Ising model with nearest-neighbor interactions is only partially successful in predicting the behavior of a real material which also has magnetic dipole interactions.
Neutron Diffraction Determination of the Intermediate-Field Magnetic Structure of CoCl2·2H2O
Authors: Cox D. E. , Shirane G. , Frazer B. C. , Narath A.
Published: April 2005

Recent magnetization measurements have shown that antiferromagnetic CoCl2·2H2O undergoes two metamagnetic transitions when a magnetic field is applied along the monoclinic b axis. At 4.0°K and 32 kOe there is an abrupt increase in magnetization to 1 μB per Co2+ ion followed at 46 kOe by a second increase to 3 μB per Co2+ ion, which is believed to correspond to the ferromagnetic state. Neutron diffraction data have been obtained with fields of up to 46 kOe applied along the b axis of a single crystal mounted within a split-coil superconducting magnet. At the first transition, magnetic reflections characteristic of the antiferromagnetic phase disappear, and a number of new reflections, based upon a unit cell in which the a axis is tripled, are observed. These are in good agreement with a simple collinear ferrimagnetic model recently proposed in which the moments are parallel within (100) planes, which in turn are ordered in the sequence −++−++ in the a direction. The observed moment is about 3.3 μB per Co2+ ion.
Relaxation in Antiferromagnets due to Spin-Wave Interactions
Authors: Harris A. Brooks
Published: April 2005

For an antiferromagnet it is shown that within perturbation theory the Holstein-Primakoff and Dyson-Maleev transformations do not lead to identical results for either the static or dynamic properties. By examining the spin Green's functions we justify the use of the Dyson-Maleev transformation when there are few spin waves present. Using second-order perturbation theory we find the antiferromagnetic resonance linewidth to be Δω0=(64ωAω0/π3S2ωE)(kT/ℏωE)2exp(−ℏω0/kT)  for  kT≪ℏω0and Δω0=[40ωAζ(3)/π3S2](kT/ℏωE)3  for  ℏω0≪kT≪ℏωE,in qualitative agreement with the experimental results for MnF2.
Antiferromagnetic Resonance in RbMnF3 below the Spin-Flop Transition
Authors: Ince William J.
Published: April 2005

Antiferromagnetic resonance in RbMnF3, with the magnetization in the flopped state, has been reported previously. This paper reports an investigation of resonance for the low-field region 0–5000 Oe. For applied fields less than about 3000 Oe, the static equilibrium position of the sublattice magnetizations is in general multivalued, due to the cubic anisotropy. Experimental results are presented which show the resonance, at 4.2°K, as a function of magnitude and direction of the applied field with respect to the cubic lattice. A theory of antiferromagnetic resonance for cubic materials is also presented. With appropriate choice of coordinates, the linearized equations of motion permit the normal mode frequencies to be derived. By considering the magnetization to be locally uniform, and confining the applied field to a symmetry plane, solution of the static equilibrium problem has been obtained. The model has been used in conjunction with the resonance analysis to calculate the resonant frequencies. There is good agreement between theory and experiment for some of the observed resonances.
Resonance at 70 Gc/sec Near the Néel Point in RbMnCl3
Authors: Shane J. R. , Kedzie R. W. , Kestigian M.
Published: April 2005

Magnetic resonance has been observed at 70 Gc/sec as a function of temperature near the Néel point (∼88°K) in RbMnCl3. Below the ordering temperature, the antiferromagnetic resonance line moves rapidly downfield with decreasing temperature. At zero field, the line broadens and disappears. This resonance is identified as the high-frequency mode of a hard-axis antiferromagnet; it has not been observed at lower frequencies. At X band and at K band, the paramagnetic resonance line broadened and disappeared above TN such that continuous observation of the resonance through the Néel point was not possible. The 70-Gc/sec measurements in this temperature region display an interesting hysteresis effect. Below TN, the AFMR line was observed at higher fields for an increasing field sweep than for a decreasing field sweep. Above 88°K, the field for resonance is independent of temperature but the amplitude of the PMR depends upon the direction in which the field is swept through resonance. Over a temperature interval of 1.5° below 88°K, the sample appeared to be ordered during a decreasing field sweep; but only the paramagnetic line was observed as the field was swept in the opposite direction. Possible explanations for this behavior are presented.
Magnetic Susceptibility Tensor and Harmonic Generation in CuCl2·2H2O at the Critical Field
Authors: Naiman C. S. , Lawrence T. R.
Published: April 2005

The differential susceptibility tensor of an antiferromagnet is a highly nonlinear function of orientation and magnetic field near the critical field Hc for the spin-flopping transition. An interesting feature of this susceptibility is a cross term χyx which produces magnetic coupling in a pair of orthogonal coils if the axis of one coil is parallel to the easy axis and the other is parallel to the next-to-easiest axis. We have measured the components of the susceptibility tensor in CuCl2·2H2O and found that the general features of the experimental data are predicted by the molecular-field approximation. Some of the discrepancies between the experimental measurements of the components of the susceptibility tensor and theoretical predictions could be reconciled by assuming that the easy-axis orientation and the values of Hc varied slightly throughout the volume of the crystal with the average deviations being estimated at 2×10−3 rad and 15 Oe, respectively. Asymmetries exhibited by the experimental data are discussed. Also, the integral of χyxdHx over the transition region does not vanish when H is very nearly parallel to the easy axis, indicating a change in My during the transition. The nonlinearity of the critical field susceptibility has also been studied by observing the second-harmonic generation (SHG). The amplitude of the SHG as predicted follows the square of the input signal over most of the transition region. However, very close to Hc it deviates from this value, being closer to the cube.
A Three-Sublattice Theory of Weakly Ferromagnetic α-M4+δFe2+δFe3+ 2(1−δ)O3
Authors: Searle C. W. , Morrish A. H.
Published: April 2005

A model of α-M4+δ Fe2+δ Fe3+2(1−δ)O3 has been developed in which the ensemble of ferrous ions is treated as a third sublattice coupled to the two ferric sublattices. By assuming that the ferrous sublattice is highly damped and that it couples antiferromagnetically to the two ferric sublattices, it is found that the model consistently describes the magnetic resonance data on hematite doped with tetravalent ions. The effect of the third sublattice on the spontaneous magnetization and other properties is discussed.
Design of Two-Pole dc Motors using Segment-Shaped Ceramic Magnets
Authors: Ireland J. R.
Published: April 2005

Speed versus torque and current versus torque are linear relationships in these motors under conditions of constant applied voltage and constant temperature. The designer must first establish the speed versus torque relation toward which he will design. At this point equations are given for evaluating the efficiency and the current, which will be realized in the final design. The designer now chooses one or more armature diameters based on available laminations or desired maximum motor diameters. Equations are given and procedures described, enabling the designer to make one or more trial magnet designs and to calculate the flux per linear inch of the armature which will be obtained from them. Additional relations are given so that the designer may establish: (1) the required product of flux and conductors, (2) armature resistance, (3) minimum axial length of armature so as to avoid demagnetization during stall, (4) wire size, and (5) total number of conductors. A method is shown to determine feasibility of winding such an armature and adjustments to be made, if necessary. Since turns per coil must be an integer, the designer may end up with a small deficit of magnet flux. A new relation is shown, permitting the designer to determine the amount of magnet overhang necessary to provide this additional flux.
Considerations in the Design of Permanent Magnets for Use with Microwave Tubes
Authors: Underhill Earl M.
Published: April 2005

The use of ``microwave magnets'' dates, in this country, from about 1939, when the first Alnico magnets were made for magnetron tubes. Permanent magnets for this application usually involve more engineering and encounter more production problems than any other usage. All crossed-field tubes and all tubes using a magnetic field to focus a beam of electrons depend for their operation on the basic reaction between a moving charge and a magnetic field: F=ev×B, essentially the motor reaction. The electrical efficiencies of all electromagnetic, dynamic devices depend, in a complicated fashion, upon the magnetic energy density within the interaction volume. This underlies the fundamental design problem connected with microwave tube magnets.

The solution of this problem sometimes requires special design techniques, and normally demands much in the way of special manufacturing equipment and procedures. Because of the large magnets usually involved, maximum stored energy is important, but maximum stored energy per dollar of purchaser's over-all cost remains paramount. High energy combined with high operating field strength is important for magnets to be used for focusing.

The newer columnar grades of Alnico, of both medium and high coercivity, offer excellent opportunities for improved tube designs, and for an expansion of applications not yet predictable. These alloys, however, have introduced many new problems related to their manufacture and control of quality, not all of which have, as yet, been completely resolved. It is important that the design of any microwave magnet be carefully integrated with that of all the other components of a tube.
Effect of Electroplating Parameters on Magnetic Properties of Ni-Co Alloys
Authors: Kefalas J. H.
Published: April 2005

Relations between crystal structure, composition, and coercive force of Ni-Co, Ni-Co-P, and Co-P alloys have been reported. These relations are very useful for the understanding of the magnetic properties of Ni-Co alloys. However, their practical application is limited because the dependence between plating parameters and magnetic properties of the deposit were not established. In this paper, relations between magnetic properties and plating parameters of Ni-Co films varying in composition and thickness are reported. A relation between coercivity and stress of deposit is shown. The coercivity for a particular thickness of deposit and particular composition and concentration of solution increases from 130 to 250 Oe as the plating temperature increases from 25°C to 40°C, then the coercivity decreases as temperature increases from 40°C to 85°C. Similar relations have been found between magnetic properties and plating current density, Ni/Co ratio of solution (for various concentrations), and thickness. These results are reproducible and have been plotted. The effect of pH is also reported. With these experimental results, the optimum plating conditions for Ni-Co materials with coercivity ranging from 100–550 Oe can be found. Ni-Co alloy with 500 Oe coercivity was deposited on drums and bit density of 5000-flux reversals was obtained.
Anomalously High Remanence in (γ−Fe2O3)1−x· (α−Fe2O3)x Particles
Authors: Gustard Brian , Schuele William J.
Published: April 2005

The remanent magnetization of acicular γ−Fe2O3 particles partially converted to hematite by heating in air was measured after saturation and ac demagnetization using a vibrating-sample magnetometer. It is possible that commercial γ−Fe2O3 recording tapes could undergo this partial conversion which may result in a deterioration of their magnetic properties. The complete composition range from pure γ Fe2O3 to hematite was studied. The composition was determined by interpolation of the saturation magnetization of the sample and of the values for pure γ Fe2O3 and hematite. The remanent magnetization increases as a function of hematite composition. At 90% hematite there is a peak in the remanent magnetization which is a factor of 2 greater than the remanence of the two components. The coercivity was approximately constant, 320 Oe, as a function of composition except that pure hematite had a value of 635 Oe. Partially converted particles were examined using dark-field electron microscopy to indicate the method of conversion.
Localized Moments (?)
Authors: Geballe T. H. , Matthias B. T. , Clogston A. M. , Williams H. J. , Sherwood R. C. , Maita J. P.
Published: April 2005

The magnetic properties of dilute solutions of Fe in face-centered-cubic (fcc) alloys made from the elements Os, Ir, and Pt bear a strong resemblance to the behavior of Fe in solutions of corresponding 4d shell elements. The localized state associated with the Fe atom shows no magnetism until the 5d band of the host matrix is fuller than that of Ir. The occurrence of superconductivity in the host matrix is found to correlate with the occurrence of the nonmagnetic state of Fe. In pure Ir, the isolated Fe state is at most weakly magnetic, although it contributes a very large density of states at the Fermi level. Solutions containing 5% Fe show definite magnetic properties. In Pt and Pt rich alloys the magnetic Fe state develops a ``giant moment'' which is a function of the host lattice susceptibility.
Theory of Localized Magnetic States in Metals
Authors: Anderson P. W.
Published: April 2005

Recent developments have shown that the many-body theory of localized magnetic states can lead to much greater complications than appear in the simple Hartree treatments. We discuss the question as to whether the virtual state model actually has a moment at absolute zero, reviewing the work of Suhl, Nagaoka, Abrikosov, and others. If time permits, the subject of interaction of localized moments and the relation to magnetism in metals will also be reviewed.
New Texture in Iron and Iron Base Alloys
Authors: Aspden R. G. , Berger J. A. , Trout H. E.
Published: April 2005

The observation of a new orientation in iron and iron base alloy sheets is reported. This texture is prepared by annealing iron and iron base alloys, characterized by a gamma to alpha transformation, in the gamma region and slowly cooling through the phase change. The new texture is {001} 〈uvw〉. The occurrence of this structure is documented with the use of etch pits, domain patterns, and an x-ray method.

The magnetic characteristics for iron sheet with the {001} 〈uvw〉 texture are compared with those of iron sheet with a weakly oriented texture resulting from primary recrystallization and normal grain growth. Iron sheet with this new texture is easier to magnetize and has lower losses. The improved magnetic characteristics are ascribed to the elimination of grains having a hard direction of magnetization in the surface of the sheet. Iron and iron base alloys with this texture should find application in rotating electrical equipment.
Application of Soft Magnetic Materials and Specialty Alloys
Authors: Olson R. D.
Published: April 2005

Many advancements recorded by the electrical and electronic industries in the past two decades can be directly attributed to advancements in magnetic materials technology. Efficiencies of power generation and conversion systems have improved through the development of lower energy loss and grain-oriented magnetic alloys. Control systems have become smaller and lighter due to improved flux-carrying capabilities of static magnetic components.

Requirements placed on magnetic materials by the military and space efforts have been ably met by existing materials. Elevated temperature data are presented showing magnetic design data for temperatures to 1400°F. Examination of these data and elevated temperature mechanical data indicate where advances in materials technology are needed.

Two factors are significant in the processing of materials into components. These are: correlation of basic material parameters to device performance and the effects of processing various magnetic geometries on basic material characteristics. Technological improvements in these areas offer further gains for control and power systems.

Future demands on magnetic materials to meet the growing needs of the electrical and electronic industries dictate that a higher degree of sophistication will be required in alloy design, material fabrication, apparatus design, and materials processing.
Secondary Recrystallization in High-Purity 49% Ni-Fe
Authors: Casani R. T. , Klawitter W. A. , Lykens A. A. , Ackermann F. W.
Published: April 2005

In 1962 Benford and Lindsay showed that secondary recrystallization temperature in a 49% Ni-Fe alloy of commercial purity depends upon the degree of texture developed as a function of penultimate grain size (PGS) and percent of last cold reduction. The objective of this investigation was to determine the effect of these variables in a 49% Ni-Fe alloy of high purity. An electrode, prepared from Fe and Ni powders, was vacuum-consumable melted, forged, and hot-rolled. Cold rolling was done with intermediate anneals to produce two penultimate grain sizes followed by reductions of 86.6%, 90.0%, and 93.0% to 0.014 in. thick. Permeability measurements, magnetic anisotropy measurements, macrostructure examinations, and Laue transmission patterns were made on samples annealed at different temperatures in dry hydrogen. The results show that both PGS and percent cold-reduction influence sharpness of the primary recrystallized texture, which agrees with the earlier work. This study, however, indicates that sharp primary textures result in higher secondary recrystallization temperatures. It is concluded that high initial permeability, after annealing at moderate temperatures, requires a large PGS and lesser percent final cold reduction. The results further suggest that for square hysteresis loop characteristics over a relatively broad annealing range, one should start with a small PGS and greater percent cold reductions.
Effect of Composition on Growth Rates of Secondary {100} Grains in Si-Fe Sheets
Authors: Foster K.
Published: April 2005

Growth rates of surface-energy-controlled secondary {100} grains were measured in sheets containing from 2 to 4 wt % silicon in iron and in sheets containing 3% silicon with soluble ternary additions. A linear decrease of {100} growth rate was observed with increasing silicon content. Additions of Ni, Mn, and V had about the same effect as an equivalent wt % of Si. Additions of Mo and Cu decreased the growth rate more than Si.
Effect of Structure on Magnetic Properties of High-Temperature Alloys
Authors: Pavlovic D. M. , Clark J. J.
Published: April 2005

Direct-current magnetic behavior of several high-temperature alloys was studied at various temperatures up to 600° or 760°C and after cooling to room temperature. Overaging of intermetallic precipitates and partial reversion of the martensitic matrix to austenite, both reactions commencing at temperatures near 500°C, appear to be responsible for the increase in coercive force and flattening of the magnetization curve in 15% Ni and 18% Ni maraging steels. The continuous decrease in magnetic hardness of H-11 tool steel is dependent on the structural changes primarily associated with agglomeration of the carbide particles. A similar behavior is shown in a precipitation-hardened 23%-Ni-Co-base alloy.
Magnetic Anisotropy in Mo-Permalloy Crystals Induced by Plane-Strain Compression
Authors: Chin G. Y. , Nesbitt E. A.
Published: April 2005

Magnetic properties of molybdenum Permalloy single crystals have been studied in terms of the Chikazumi-Suzuki-Iwata (CSI) theory of slip-induced directional order. The crystals were deformed in a plane-strain-compression apparatus which restricts lateral spreading of the specimen. This type of deformation is similar to that of ordinary rolling. However, the operating slip systems required for analysis are more readily determined in plane-strain compression, which permits slip line observations as well as analysis of specimen shape change. In this work, 4–79 Mo-Permalloy crystals were compressed on the (110) plane and constrained to elongate in the [1̄12] direction. This orientation is particularly suitable for study in that slip occurs on only two systems {(111)[101̄] and (111̄)[011]} and that the orientation remains stable with deformation, hence avoiding possible complications due to lattice rotation. A simple analysis based on the CSI theory predicts for this orientation a slip-induced uniaxial anisotropy with the easy axis lying between [1̄11] and [1̄10] directions on the (110) compression plane, depending on the type of ordering in the alloy. Magnetic torque measurements on disks cut from the deformed crystals indicate the presence of both long-and short-range order. The induced anisotropy energy Ku was found to increase with thickness reduction to a value of 120×103 erg/cm3 after 50.5% reduction. Similar results were obtained with crystals deformed by rolling.
Uniaxial Anisotropy Induced by a Low-Temperature Magnetic Anneal Following Electron Irradiation
Authors: Sery R. S. , Gordon D. I.
Published: April 2005

We have shown previously that an electron radiomagnetic treatment (electron irradiation in the presence of an applied magnetic field) can bring about a high degree of uniaxial anisotropy in low Hc nickel-iron alloys. A number of samples so treated at temperatures of 105°C±30 C° attained high Br, μmax, and rectangularity with only small changes in Hc. Our new data show that the same properties can be achieved by an alternative process: irradiation with or without an applied field at 65°C±25 C°, followed by a low-temperature (<200°C) magnetic anneal of ≈ 1 h. Polycrystalline samples of Mumetal and 5–80 Mo-Permalloy, subjected initially to 0.8 to 1.1×1017 2-MeV-electrons/cm2 with a 0.22-Oe field and in the range of 40° to 90°C did not generally exhibit the high Br and μmax of those treated at the higher temperatures. However, subsequent isochronal anneals (one hour per anneal in steps of 25° or 50C° and from 100° to 500C°) in a 0.22-Oe field did bring about high rectangularity and high values of Br and μmax. For example, in a typical sample, Br and μmax increased by 30% and 82%, respectively. Improvements in properties started at <100°C for Mumetal. These results emphasize three important factors in the production of radiation-induced magnetic anisotropy: (1) irradiation, the mechanism for producing excess vacancies; (2) temperature, the condition which permits a high enough diffusion rate to enable the orientation to occur within a reasonable time; and (3) applied field, the orienting agent for alignment of like-atom pairs to produce uniaxial anisotropy. The results also show that the irradiation phase need not be simultaneous with the orienting phase nor need it have an applied field present.
EPR of 0.1% Mn in Single Crystals of Copper in the Region of 1.6° to 4.2°K
Authors: Geschwind S. , Devlin G. E. , Wernick J. H.
Published: April 2005

In the classic work of Owen et al.,1 the EPR of Mn in Cu was studied in single crystals of Cu at a concentration of 1.4 at. % Mn. Studies were also made at lower concentrations in polycrystalline materials. In line with the recent interest in local moments in metals, the question arises as to whether hyperfine interactions or anisotropic crystal field splittings might have been exchange narrowed by long-range exchange interactions between the Mn ions in the more concentrated materials. The absence of hfs in the more dilute polycrystalline materials which still show relatively narrow lines (∼100 G) places an upper limit on the hfs but the question remains as to whether a resolved hfs within these limits could be observed in a dilute single crystal. We have, therefore, re-examined the EPR spectrum of 0.1 at. % Mn in a single crystal of copper. Linewidths of 80 G are found, but no hfs is observed. In addition, any anisotropy in g value is found to be less than 1 part in 4000. Nor is any variation of g shift with temperature observed in the temperature range of 1.6° to 4.2°K. From this latter result one is able to place an upper limit of 1 part in 3000 on the second-order g shift, λ2χpMd as discussed by Hasegawa.2
Influence of an External Magnetic Field on Nuclear Resonance in Ferromagnetic Materials
Authors: Bennett Lawrence H.
Published: April 2005

The reduction in the amplitude of the nuclear magnetic resonance signal, as well as a change in line shape, upon the application of an external steady magnetic field has been measured for metallic nickel at room temperature. Both the transverse and longitudinal configurations (steady field and rf field perpendicular and parallel, respectively) were measured for a sample of nickel powder and for bulk nickel. The signal amplitude drops faster in the longitudinal configuration than in the transverse for each specimen. The reduction in amplitude is considerably less for the pellets than for the powder. There is no sign of a critical field as previously reported. A comparison of the resonance results with the apparent permeabilities is presented. The difference in behavior of the nuclear resonance signal for the transverse and longitudinal configurations is related directly to the difference in the behavior of the permeabilities for the two configurations.
Anisotropic Hyperfine Interactions in ZrFe2 and GdFe2 from a Nuclear Magnetic Resonance Study
Authors: Gegenwarth R. E. , Budnick J. I. , Skalski S. , Wernick J. H.
Published: April 2005

We have studied the nuclear magnetic resonance of 57Fe nuclei in the magnetic state of both ZrFe2 and GdFe2, using the technique of spin echoes. The broad spectrum from the iron nuclei in ZrFe2 at 4.2°K could be resolved into one weak and one strong line located at 28.9±0.2 Mc/sec and 30.6±0.1 Mc/sec, respectively. The frequencies of these lines are in good agreement with the Mössbauer results in this system which show two lines, with an intensity ratio of 3 to 1, arising from nuclei in domains. The application of magnetic fields less than 4π/3 Ms to the stronger Zr resonance at 77°K produces a detectable frequency shift and a decrease in intensity of the spin-echo signal. In GdFe2, a ferrimagnet, a similar spin-echo spectrum for the iron is observed with one weak and one strong line at 31.3±0.3 Mc/sec and 32.4±0.1 Mc/sec, respectively. The difference between this system and ZrFe2 may be understood in terms of the contribution from the magnetic gadolinium sublattice. We conclude that in these systems, the anisotropy observed by the Mössbauer technique is detectable in nuclear spin-echo spectra.
Conduction Electron Polarization in Mixed Scandium Laves Phases with Cobalt and Nickel
Authors: Barnes R. G. , Beaudry B. J. , Lecander R. G.
Published: April 2005

The Knight shift K and linewidth δH of the 45Sc NMR in the cubic Laves phase intermetallic system Sc(CoxNi1−x)2, where 0≤x≤1, have been investigated at 300°K. In accord with the probable simple Pauli paramagnetism of ScNi2, K=+0.39%, whereas in ScCo2, K=−0.43%, indicative of a d-spin contribution to K from the Co° (d9) ions. In ScCo2, δH may be interpreted as resulting from the exchange-narrowed dipolar field of the Co ions, with J/k=0.44°K. In the mixed compounds, δH varies linearly both with applied field H and composition x above and below x=0.5, and the average K varies smoothly, but not linearly, between the ScNi2 and ScCo2 values. The field and composition dependence of δH may be interpreted in terms of a distribution of K values resulting from the random distribution of Co neighbors. Preliminary measurements of the volume susceptibility indicate that the Knight shift and susceptibility may be directly correlated.
27Al Knight Shift and Hyperfine Interaction in GdAl2
Authors: Jones E. D. , Budnick J. I.
Published: April 2005

A new 27Al NMR has been observed in the paramagnetic state of GdAl2 between 350° and 575°K. The 27Al NMR linewidth δH was found to be strongly temperature-dependent. Data are presented which suggest that the previously reported 27Al NMR in GdAl2 is probably due to a small amount of some other Gd–Al compound. The 27Al Knight shift is temperature-dependent, varying from about −6% to −3% between 350° and 575°K, respectively. The temperature-dependent part of the Knight shift obeys a Curie-Weiss law, i.e., K(T) α (T−θ)−1, with θ≃150°K. The temperature-independent part of the Knight shift is consistent with the value measured for the nonmagnetic isomorph LaAl2. Extrapolating the Knight shift data to 300°K and combining K(300) with the room-temperature susceptibility χ(300) yields an effective 27Al hyperfine field Hhf≃−6.8 kOe per Bohr magneton. An 27Al hyperfine field in the ferromagnetic state is thus calculated to be 27H≃−46 kOe in good agreement with experiment. The s-f exchange energy is calculated to be Jsf=−0.13 eV. The 27Al nuclear quadrupolar coupling constant was measured to be (e2qQ/h)≃4.27 Mc/sec.
Neutron Diffraction Study of Dilute Chromium-Base Alloys
Authors: Koehler W. C. , Moon R. M. , Trego A. L. , Mackintosh A. R.
Published: April 2005

The magnetic properties of chromium alloys containing small amounts of members of the 4d (Nb, Mo, Tc, Ru, and Rh) and 5d (Ta, W, and Re) transition groups have been studied by powder, and in some cases, single-crystal neutron-diffraction techniques. Selected composition of alloys with 3d group metals V and Mn, which had been investigated previously with polycrystalline samples have been reexamined with single-crystal specimens. For elements which increase the electron-to-atom ratio, the magnetic moments and Néel temperatures of the alloys increase with concentration of the alloying element and reach maximum values of 0.75 μB and 700°K as compared to 0.40 μB and 310°K for pure Cr at 2%–5% of the diluent. Alloys containing less than about 1% of diluent exhibit a simple commensurate antiferromagnetic structure at high temperatures and the transverse and longitudinal oscillatory structures characteristic of pure Cr at lower temperatures. The spin-flip temperature falls quickly below that of pure Cr (121°K) until for concentrations between 1% and 1.5% only the simple antiferromagnetic structure and the transverse oscillatory structure are found. In alloys with more than 1.5% diluent the commensurate structure is found at all temperatures. The periods of the oscillatory structures, where they exist, are larger in these alloys than in the pure metal. In alloys of Ru and Re, the Néel temperature and average moment decrease from their maximum values and tend toward zero at about 15 and 20 at. %, respectively. Of the compositions in the range which were studied all exhibited the simple antiferromagnetic structure. For alloys with V, Nb, and Ta in which the electron-to-atom ratio is reduced, and those with Mo and W, where it remains constant, the Néel temperature, spin-flip temperature and average moments are diminished-Mo, W, V, and Nb, and Ta being more efficient in that order in modifying the properties of Cr. In each of these cases the oscillatory structure with period smaller than in the pure metal is observed. Some, but not all, of these observations are in qualitative agreement with predictions based on the spin-density wave models for chromium due to Overhauser and to Tachiki and Nagamiya.
Magnetic Switching in Ni-Fe Single-Crystal Films
Authors: Lo D. S.
Published: April 2005

Quasistatic magnetic switching in Ni-Fe single-crystal films has been studied by Lorentz microscopy. The results show that the switching mechanism is different for two different types of single-crystal films and for different orientations of the reversal fields. For type A single-crystal films, in which the ratio of the coercive force to the biaxial anisotropy field (Hc/H1) is relatively large, the switching mechanisms are similar to those of the uniaxial polycrystalline films.1 However, switching by two consecutive switching stages was observed in the single-crystal biaxial films, each stage corresponding to a different easy-axis direction. The change of the mechanism can be explained by the discontinuities of the critical curve derived from the Stoner-Wohlfarth coherent model. For this type of film 90° switching takes place by a different process than the one reported in the literature.2 For type B single-crystal films, in which the ratio of Hc to H1 is relatively small, switching takes place by the motion of 90° and 180° domain walls similar to those walls observed in single-crystal iron films.3 Both types of films studied, 840 and 1640 Å thick, respectively, are 81 Ni-19 Fe and were epitaxially grown on rocksalt. Transmission electron diffraction, transverse-biased-permeability measurements, torque measurements, and Lorentz microscopy indicate that the films have a good single-crystal structure as well as biaxial anisotropy properties. Although both films had nearly zero magnetostriction and a good single-crystal structure, both films exhibited magnetization ripple in the Lorentz micrographs.
One-Dimensional Zero-Degree Double Bloch Walls in Thin Films
Authors: LaBonte Anton E. , Brown William Fuller
Published: April 2005

The magnetization M (x) in a ferromagnetic film is approximated by a discrete distribution for which the magnetostatic energy can be calculated exactly, without restrictions on the functional form of M (x). The minimum internal energy (exchange, anisotropy, and magnetostatic) and related magnetization distribution for two parallel Bloch walls with opposite senses of rotation are computed for various fixed spacings between the wall centers. The two walls repel one another because of their magnetic interaction. As a consequence, an energy barrier separates the energetically more favorable state of uniform magnetization from the stable 0° double Bloch wall configuration. The results show that the energy at the peak of the barrier is about 12.5% above the energy of two corresponding isolated 180° walls. The applied field necessary to maintain an equilibrium distribution for a given wall spacing is calculated as a function of the wall separation. It is found that a field of at least H0=0.204 Ms (163 Oe if Ms=800 emu) is required to overcome the energy barrier and collapse the distribution to a state of uniform magnetization.
Crystal Field Effects for Ce3+ and Yb3+ in the Garnets
Authors: Herrmann G. F. , Pearson J. J. , Wickersheim K. A. , Buchanan R. A.
Published: April 2005

We show that the methods used by Hutchings and Wolf for fitting the Yb3+ spectra in the garnets can be employed, with suitably modified spin-orbit and crystal-field parameters, to calculate the energy levels and wave functions of the electronically similar ion Ce3+. The results are in sufficient agreement with infrared data to verify our interpretation of the Ce3+ spectrum and at the same time to support strongly the Hutchings and Wolf results for Yb3+.
Anisotropy of the Rare-Earth-Iron Exchange Interaction in Garnets
Authors: Levy Peter M.
Published: April 2005

We have evaluated the exchange splittings of the lowest 2F5/2 and 2F7/2 doublets of Yb3+ in YbIG, in terms of the exchange potential parameters given by us in a previous article, by using the wave functions of Yb3+ in YGaG. As there are ten exchange potential parameters and only six experimental splittings, it was necessary to reduce the number of unknowns by assuming: (1) that the RE-Fe exchange interaction takes place through the neighboring eight oxygen ions, and (2) that the rare-earth-oxygen (RE-O) exchange potential is axial about the RE-O axis. Defining A (ml) by: Hex=−2ΣA(ml)S(RE)·S(Fe),we find a good four-parameter fit of the experimental exchange splittings by assigning the values A (ml=0) = 6.41 cm−1, A (ml=±1) = 6.52 cm−1, A (ml=±2) = −29.6 cm−1, A (ml=±3) = 6.17 cm−1 to the RE-Fe exchange interactions that take place through the next-nearest oxygen ions, and by adopting essentially zero values for the RE-Fe exchange iuteractions that take place through the nearest oxygen ions. This result corroborates qualitative conjectures based on superexchange bonding anglcs.
Frequency-Dependent Anisotropy in Si- and Ca-Doped YIG and LuIG
Authors: Tchernev Dimiter I.
Published: April 2005

The magnetic anisotropy of small spherical samples of Si- and Ca-doped single-crystal yttrium and lutetium iron garnets has been studied at 10 and 25 kMc/sec over the temperature range from 4.2° to 300°K. The experimental results have been compared with similar data from static torque measurements. There is a considerable difference between the microwave and static magnetic anisotropy in doped garnets, while for pure garnets the agreement between the microwave and static data is very good. In particular, the microwave first-order anisotropy constant in Si- and Ca-doped garnets is less negative than the static anisotropy constant, which is independent of doping, and the difference between the two types of measurements is linearly proportional to the doping density. In Ca-doped garnets the microwave anisotropy constant becomes zero at about 5.5% doping density, and for larger Ca concentrations changes sign and becomes positive. The same effect, although of lesser magnitude, is observed in Si-doped garnets. The frequency dependence of the microwave anisotropy is confirmed by measurements at two different wavelengths. As expected, the deviation of the microwave anisotropy constant from the static one is larger at 25 than at 10 kMc/sec.