bluuebunny/crossref_metadata_2025 huggingface dataset:
An Integrating Type of Electronic Hysteresigraph
Authors: De Mott E. G.
Published: April 2005

An electronic hysteresigraph, which integrates without recourse to electromechanical means and is free of drift, has been developed. In operation, a search coil surrounds the magnetic specimen to be tested, and the specimen is then subjected to a change in externally applied magnetic field strength. The time integral of the potential induced in the search coil is a measure of the magnetic flux change in the specimen. The induced potential is applied to a solid-state voltage-to-frequency converter which produces a series of output pulses, the number of which is proportional to ∫edt. These pulses are summed on a digital counter to give a measure of the flux change. A digital-to-analog converter then provides a dc output which drives the Y axis of an X-Y recorder.

A signal proportional to the applied magnetic field strength is simultaneously fed to the X axis of the recorder and a continuous B vs H plot is obtained. This is a real-time mode as the response of the various measuring elements is practically instantaneous.

In considering the integrator, it is interesting to note that absolute accuracy traceability in calibrating the voltage-to-freqency converter is referred directly to the volt, as represented by the standard cell, and to the second, as represented by a crystal-controlled time base. This is in contrast to the generally used secondary standards of mutual inductance and current shunt millivolt drop.
Magnetostatic Modes in Antiferromagnets and Canted Antiferromagnets
Authors: Beeman D. E.
Published: April 2005

The resonance frequencies of the magnetostatic modes are calculated for an antiferromagnetic sphere with a dc magnetic field applied along the direction of easy magnetization. For resonance at a fixed frequency, the separations between the various modes are of order 0.2 (2HexHA)½4πM/Hex Oe. The magnetostatic modes of canted antiferromagnets of the α-Fe2O3 type are also investigated. Application of the magnetostatic conditions and solution of the differential equation for the magnetic scalar potential for a spherical sample reveals separations between modes of order 0.1 (H0+HDM) 4πM/Hex Oe. These modes are associated with the low-frequency resonance near ω1=γ[2HexHA′ + H0+HDM)]½.
Origin of High Coercivity in Chemically Deposited Cobalt-Phosphorus Films
Authors: Speliotis D. E. , Judge J. S. , Morrison J. R.
Published: April 2005

Films of Co-P, varying in composition from 2.5% to 5% P and varying in thickness from 200 to 2500 Å, were prepared by chemical deposition. The coercivity of these films was found to be a function of both P content and thickness. The particle size of these films increased with increasing thickness and was a function of the P content. The films were annealed in a reducing atmosphere at various temperatures up to 500°C. The low-coercivity films undergo a transformation to films exhibiting coercivities of ∼250 Oe at a temperature of 250°C. The intermediate-coercivity films remain essentially unchanged, whereas the high-coercivity films drop sharply in coercivity at ∼400°C to this apparent ``equilibrium coercivity'' of ∼250 Oe. Etching experiments on these samples show no drastic effects on coercivity. The coercivity merely proceeds back along the original coercivity-versus-thickness curves. Structural and magnetic evidence indicates the existence of an equilibrium magnetic structure in these films which is primarily dependent on particle size.
Anomalous Scattering Due to s-d Interaction
Authors: Kondo Jun
Published: April 2005

Higher-order effects of the s-d interaction on the scattering probability of conduction electrons are investigated. A picture of one-electron scattering which takes no account of the presence of other electrons is not sufficient in higher-order effects due to the dynamical character of the s-d interaction. Pauli's principle must be taken into account in selecting the intermediate states for a scattering process of one-electron type. This results in a logarithmic temperature-dependence of resistivity. The dynamical character of the s-d interaction also causes a two-electron scattering, which results from two successive one-electron scatterings. This type of two-electron scattering does not occur when the interaction is a static one. The electrical resistivity arising from this scattering diverges even at finite temperature, when the scattering probability is calculated by a simple perturbation theory. The situation is quite analogous to that of scattering of a light quantum by an atom. By analogy we introduce a finite lifetime of the intermediate state and obtain a finite result. The electrical resistivity is found to be linear in T when T<Ta≅cTF, where c is the fraction of magnetic atoms. This term, combined with the logT term, accounts for the experimental result on a Cu-Mn alloy quite well.
Properties of the Hyperfine Structure of Dilute and very Dilute Fe in Nonmagnetic Metallic Hosts
Authors: Kitchens T. A. , Craig P. P.
Published: April 2005

The Mössbauer effect has proven fruitful for investigating the magnetic properties of dilute concentrations of Fe in metals. Measurements of the magnetic hyperfine field Hhf at Fe impurities in nonmagnetic metal hosts yield information relating to the formation of localized moments and to the onset of impurity-impurity interactions. These studies fall into two classes: (A) Systems in which the impurity concentration is sufficiently low (or the measurement temperature sufficiently high) that impurity-impurity interactions play a negligible role and the Hhf depends only upon the nature of the impurity and of the host. (B) Systems in which interactions play a significant role and magnetic transitions can occur. In the first category, measurements on a number of cubic transition metals and alloys will be compared with other experimental data and with theories of the formation of localized magnetic moments. In the second category, dilute alloys of Fe with Au, and Pd will be compared with the results of other experiments and with theoretical concepts of direct and indirect exchange interactions.
Effects of Alloy Additions to 4–79 Molybdenum Permalloy
Authors: Lykens Armand A.
Published: April 2005

It is generally agreed that to obtain highest initial permeability in 4–79 molybdenum Permalloy, one must cool the alloy at a critical rate through the atomic-ordering temperature range during the final hydrogen anneal. Chegwidden and Ashworth have shown that this rate decreases with decreasing nickel and increasing molybdenum. The purpose of this investigation was to determine the effects of small alloy additions to vacuum-melted 4–79 molybdenum Permalloy upon the optimum cooling rate (CRopt) and maximum obtainable initial permeability. Varying amounts up to 1% by weight of aluminum, chromium, niobium, tantalum, titanium, and tungsten were added to small vacuum-melted heats. The cast ingots were processed to 0.006-in.-thick strip from which were obtained ring lamination samples. These were annealed at 2150°F for 4 h in pure dry hydrogen and cooled at different rates between 14F°/h and an estimated 10 000F°/h through the ordering range (1112° to 572°F). Sixty-cycle ac initial permeability (u0) was measured at 40-G induction. It has been found that chromium, niobium, and titanium decrease the CRopt and increase the maximum obtainable u0, e.g., 0.62% chromium increases the u0 from 56 000 at a CRopt of about 3700F°/h to 94 000 at an CRopt of about 550F°/h; and 0.56% niobium increases the u0 from 51 000 at a CRopt of about 3700F°/h to 90 000 at a CRopt of about 1100F°/h. The optimum addition for the three elements is approximately 0.50% to 0.70%. Aluminum, tantalum, and tungsten at the levels studied have no appreciable effect on either the CRopt or the maximum obtainable u0.
Magnetic Properties of Nickel-Iron Alloys Bombarded by Neutrons in a Magnetic Field
Authors: Nesbitt E. A. , Chin G. Y. , Williams A. J. , Sherwood R. C. , Moeller J.
Published: April 2005

Single crystals of three compositions in the Fe-Ni system (30% Ni, 50% Ni, and 76% Ni) were irradiated with neutrons (0.5×1018 neutron/cm2) in the presence of a magnetic field of 2000 Oe. Neutron irradiation affected the properties of all three compositions. In the 30% Ni alloy, the temperature at which the martensitic transformation starts was raised by neutron irradiation from 213° to 262°K while the temperature range for almost complete transformation was greatly broadened from a 9° to a 139° width. These effects of changing the transformation that were produced by neutron irradiation were simulated by cold rolling. The 50% Ni alloy showed a uniaxial anisotropy which is maximum when the magnetic field was directed in the [001] direction and a minimum in the [111] direction. This behavior which differs from the usual magnetic annealing effect tends to substantiate the work of Pauleve et al. The latter have shown the existence of an ordered phase in the 50% Ni alloy. As a result of neutron irradiation, the 76% Ni alloy became highly ordered and a high value of crystal anisotropy was obtained in a relatively short period of time. This work indicates that neutron irradiation at the proper temperature is a powerful method of obtaining long-range ordering in certain alloys of the Ni-Fe system.
Observation and Theory of New Line in Far-Infrared Absorption in Antiferromagnetic FeF2
Authors: Halley J. Woods , Silvera I.
Published: April 2005

A many-ion spin-orbit interaction in magnetic materials is pointed out which explains the existence of a previously anomalous infrared absorption line at a frequency of 154 cm−1 in antiferromagnetic FeF2. The interaction also provides a possible explanation for the existence of a magnon sideband recently observed in the antiferromagnet MnF2. The experiments on FeF2 are described and compared with the theory.
Optical Transparency of Rare-Earth Iron Garnets
Authors: Wood D. L. , Remeika J. P.
Published: April 2005

Optical absorption and electrical resistivity have been measured for single-crystal flux grown rare-earth iron garnets doped with Si4+, Sn4+, Ge4+, and Ca2+. Strong optical absorption near 9000 cm−1 is observed due to relaxation mechanisms involving transfer of an electron from Fe2+ ions in the case of Si, Ge, Sn doping, or a hole from Fe4+ ions in the case of Ca doping to Fe3+ ions in the vicinity. This is accompanied by n-type electrical conductivity for crystals containing Fe2+ introduced by Si, Sn, Ge, and by p-type conductivity for those containing Fe4+ produced by Ca doping. We find that pure rare-earth iron garnets contain small amounts (0.004 atom/formula) of Fe4+ producing undesirable optical absorption, and this can be eliminated by small additions of tetravalent Si, Sn, or Ge.
55Mn NMR in Mn3O4
Authors: Houston T. W. , Heeger A. J.
Published: April 2005

We report here a study of the NMR of 55Mn associated with the Mn2+ ion located on the A site of the tetragonal normal spinel structure of Mn3O4. From the dependence of the signal on external magnetic field, it is clear that in this highly anisotropic crystal, only the NMR signal from nuclei within domain walls is sufficiently enhanced to be detected. There is nevertheless a well-resolved quadrupole splitting into five lines (I=52). A unique electric field gradient is possible in such a case for a tetragonal crystal only if the electronic spins within the domain walls rotate in the plane transverse to the c axis. Thus even within the domain walls the spins remain perpendicular to the primary hard axis. The central line of the spectrum is found at 557.4 Mc/sec at 4.2°K with the interval between satellite lines being 1.45 Mc/sec. The half-widths of these lines follow very closely the expression 〈Δν2〉12∼(I−Iz)2(I+Iz+1)2+2(2Iz+1)2,for Iz↔Iz+1 transition as expected for the quadrupole dependence of a Suhl—Nakamura width.
Radio-Frequency Resonance Echoes in Magnetic Materials
Authors: Stauss G. H. , Rubinstein M.
Published: April 2005

A resonance-echo effect not involving nuclear spins in magnetically ordered materials has been investigated at radio frequencies. The echo amplitudes and relaxation properties have been studied by varying the temperature, frequency, rf intensity, and external static magnetic field for several magnetic conductors and insulators. In a zero external magnetic field, the echoes occur throughout the available frequency range (5–110 Mc/sec) and relax exponentially with relaxation times roughly inversely proportional to temperature or applied frequency through most of the range of either parameter. With an external field they exhibit peaks in amplitude vs field strength. Physical mechanisms which possibly produce these effects (domain wall motion or intradomain ferromagnetic resonance modes) are discussed.
Hyperfine Fields and Isomer Shifts in Magnetically Ordered Europium Compounds
Authors: Wickman H. H. , Nowik I. , Wernick J. H. , Shirley D. A. , Frankel R. B.
Published: April 2005

The Mössbauer technique was employed to study hyperfine fields in several ordered divalent europium compounds at low temperatures. The intermetallics EuCu2, EuAl2, and EuAl4 were ordered at helium temperatures and the observed fields and isomer shifts were 189(8) kOe, −0.88 cm/sec; 278(8) kOe, −0.97 cm/sec; and 290(8) kOe, −1.14 cm/sec, respectively. Comparison of these results and previous measurements with EuO, EuS, and Eu metal indicates a possible correlation between isomer shift and internal field. With the exception of EuCu2 the internal fields increase with increasing magnitude of isomer shift. Interpretation of this trend with a core polarization model yields a value of 120±20 kOe for the field per 6s valence electron.
Domain Wall Motion in Multilayered Magnetic Thin Films
Authors: Patton Carl E. , Humphrey Floyd B.
Published: April 2005

In order to determine whether increased domain wall mobility is a possible explanation for the anomalously fast flux reversal observed in laminated films, the details of wall motion have been investigated for multilayer samples with from one to five 350-Å Permalloy layers separated by 100-Å layers of SiO, as well as for thick 1500-Å films. Kerr effect quasistatic wall mobility measurements were made for the one- and two-layer 350-Å films and the 1500-Å films, yielding mobilities of 9.2×103, 6.0×103, and 8.6×103 cm/sec·Oe, respectively. Bitter patterns were used to confirm the existence of Néel walls in the single-layer 350-Å films. The pulse conditions for these measurements produced locked Néel walls in the double films, as confirmed by Kerr effect observations. Bloch walls occur in the 1500-Å films. Low-drive domain-wall-motion flux-reversal experiments were performed for all the laminated films, yielding Sw's of 1.9, 1.7, 1.9, 1.8, and 2.1 Oe·μsec, respectively. For linear switching curves the slopes (1/Sw) are taken to be proportional to the domain-wall mobility. The measured mobilities for the single and double 350-Å films and the 1500-Å films do not differ significantly. The Sw values for all the laminated films are nearly equal. This mobility and switching data indicate that the anomalously fast flux reversal in laminated films can not be attributed to a mechanism involving domain wall motion.
Magnetic Film with Helical Anisotropy
Authors: Thompson D. A. , Finzi L. A. , Chang H. , Albert P.
Published: April 2005

A helical anisotropy film is characterized by the induced anisotropy of the form K sin2[π(z)−2πz/d], where K is the anisotropy constant, θ is the magnetization orientation, z is the coordinate along the direction of film thickness, and d is the film thickness.

It has been predicted by solving Euler's equation that for film thickness greater than the critical value 2π(A/K)½ (A=exchange constant), stable states may occur in which the magnetization orientation θ follows approximately the helical variation of the easy axis. The magnetic characteristics of a helical film can be clearly demonstrated by the M-H loops of the top or bottom layers, as obtainable with a Kerr magneto-optic apparatus. The transitions from a saturated state to a helical state and from one helical state to another result in multiple-threshold M-H loops.

Nonmagnetostrictive Permalloy films have been electroplated onto a slowly rotating substrate in the presence of a dc orienting field. Samples of 3 μ or more thickness show the helical anisotropy characteristics while a sample of less than 0.5-μ thickness behaves as a uniaxial film. Furthermore, control samples of each thickness have also been electroplated on a stationary substrate. They only show the usual uniaxial anisotropy property.
Perpendicular Anisotropy in Polycrystalline Ni-Fe Thin Films
Authors: Iwata Takao , Prosen Richard J. , Gran Burton E.
Published: April 2005

A magnetostatic model for perpendicular anisotropy (i.e., the anisotropy resulting from the rotation of the magnetization out of the plane of the film) is presented on the basis of columnar grain structure in ferromagnetic thin films. The calculation shows that the anisotropy constant is proportional to the square of saturation magnetization and the proportionality factor should decrease with increasing ratio (d/D) of the grain boundary layer thickness to the columnar grain diameter. The surface relief accompanying the columnar structure is also a significant factor. Although measurements of d are not available at present, the model appears to explain the observed magnitude as well as the concentration and substrate temperature dependences of perpendicular anisotropy. Measurements are made on the thickness and grain size dependences of perpendicular anisotropy in 81% Ni-Fe films. The observed results agree qualitatively with predictions based on the present model.
Effect of Magnetostatic Interactions on the Real and Imaginary Parts of the Transverse Biased Permeability in Thin Ni-Fe Films
Authors: Oredson H. N.
Published: April 2005

It has been found that the rapid fall off of μ′ (the imaginary part of the permeability) on the low-field side of μ′ vs HT is due to the formation of locking domains, and that in this region the probability density function is not proportional to μ′.

This fall off can be predicted from μ (the real part of the permeability) by assuming that the fall off in μ is due entirely to the effects of locking domains. When this is done, and Δ90, the inhomogeneity in anisotropy magnitude, is determined from the corrected probability density curves the relationship arc sin Δ90=4α90 is found nearly to hold, but a coefficient of 5 gives a better fit to the data. It is suggested that the 5 comes from anisotropies of order higher than 2 due to higher-order interactions. These interactions are responsible for triaxial anisotropy introduced by etching a polycrystalline film into small triangles, and for higher-order anisotropies found by etching small rectangles.

A theoretical expression for the permeability has been found as μ−1=HT−H̄K+Mdπ−1[2A/(HT−H̄K)M]−12[δHb/(1.64)8(HT−H̄K)]2,where HT is the transverse bias field, H̄T is the average anisotropy field, M is the saturation magnetization, d is the film thickness, A is the exchange constant, and δHb is the inhomogeneity in the magnitude of the anisotropy, defined as Δ90 H̄K. This expression gives a very good fit to the data.
Magnetization Creep in Nickel-Iron Films via the Lever Mechanism
Authors: Olson A. L. , Torok E. J.
Published: April 2005

Nickel-iron films exhibit creep in a combination longitudinal dc and transverse ac field. It has been found experimentally that the creep threshold curve is not fixed in field space like the rotational switching curve, but can be displaced along the transverse field direction by an amount equal to an extra transverse dc bias field. Thus the creep threshold is a function of only the oscillating component of the transverse field. The dc component of the transverse field can be increased with little change in the shape of the creep threshold curve until the creep threshold coincides with the switching threshold curve. This has been found so far to hold for films up to 10 800 A thick. These results can be explained by a simple theory based on the ``lever'' mechanism for creep proposed last year: The additional field which causes creep originates from the induced magnetic charge on the wall due to the applied fields rotating the parallel and antiparallel domains through different angles. This theory predicts creep threshold curves which coincide with the experimental curves. The lever mechanism is unique among proposed creep models in explaining this transverse displacement of the creep threshold.
a-c Exchange in the Garnets
Authors: Burns G. , Giess E. A. , Blazey K. W.
Published: April 2005

In the ferrimagnetic garnets the a-d (octahedral-tetrahedral) exchange is the dominant one and reasonable values of the other exchange values are difficult to obtain. Thus, direct measurement of some of the smaller exchange constants is of interest because of the ambiguity of the values obtained by molecular field analysis. In this paper an optical technique is used to measure the a-c exchange of Cr3+-Gd3+ in the garnet Gd3Ga2(GaO4)3. The 16a site is octahedrally coordinated and the rare earth is on the 24c site. The structure on sharp redline fluorescence from the Cr3+ ions is measured. The fluorescence transitions are from the excited 2E state to the ground 4A2 state; thus the exchange constant in both states can, in principle, be determined. The analysis of the a-c interaction was done by assuming a Heisenberg Hamiltonian H= ∑ i=16JSCr·SGdi,where the sum is over the six nearest-neighbor Gd3+ ions each with a span 72. The most probable value of ∑ i=16SGdiis 8. The Cr3+-Gd3+ exchange splitting in the 2E state of Cr3+ is just resolvable. A detailed fitting of the lines gives J=0.32 cm−1 (0.46°K). The Cr3+-Cd3+ exchange splitting of the Cr3+ ground state is not resolvable. However, the low-temperature linewidth is much too wide to be due to anything except an exchange splitting. Fitting the line one obtains an exchange value in the ground state approximately half the excited state.
High-Temperature Electronic Relaxation at the Rare-Earth Ions in Garnets
Authors: Caspari M. E. , Ray F. D.
Published: April 2005

The electronic relaxation times at Tb3+, Sm3+, and Tm3+ ions in magnetic iron and nonmagnetic gallium and aluminum garnets have been studied by gamma-gamma angular correlation experiments. The relaxation time of Tb3+ in iron garnets reaches a minimum value of ∼10−11 sec at higher temperatures, considerably larger than similar values for the Sm3+ and Tb3+ ions in iron garnets. The Tb3+ ion relaxation time in iron garnet was independent of temperature from below room temperature to 1100°K. This result suggests that the transitions which determine the relaxation time occur between closely spaced levels. In Sm3+ in iron garnets the relaxation time τs∼[exp(Δ/KT)−1] with Δ/K=250°K, while in Tm3+ τs∼T−1. No significant differences were observed between the relaxation times in magnetic iron and nonmagnetic gallium or aluminum garnets at room temperature. In the case of Sm3+ and Tm3+ where no temperature saturation effects have been observed this result seems to indicate that processes involving spin magnon interactions and phonon modulation of the exchange field do not play a dominant role in the rare-earth ion relaxation process in rare-earth iron garnets at room temperature.
Ferromagnetic Metals in High Magnetic Fields
Authors: Freeman A. J. , Blum N. A. , Foner S. , Frankel R. B. , McNiff E. J.
Published: April 2005

High-field susceptibility results are presented for Mössbauer measurements on iron at low temperatures in fields up to 135 kOe and magnetization measurements on iron and nickel single crystals in fields up to 148 kOe with vibrating sample magnetometers. The Mössbauer measurements give the hyperfine field Hn= Hint− (H0−HDM)+ΔH, where Hint is the hyperfine field at zero applied field, H0 is the applied field, HDM is the demagnetizing field, and ΔH is a term which would reflect a change in the magnetization at high field, i.e., ΔH/Hn=ΔM/M. The Mössbauer results at 4.2°K are equivalent to χ=2±7×10−5 emu/cc. The magnetization experiments give χ≤4×10−5 for iron and χ≤1.1×10−5 for nickel at 4.2°K. We discuss the various contributions to the total susceptibility χ, give estimates of χd based on theoretical band calculations, and discuss various uncertainties in both the theoretical calculations and in values of the molecular field parameter which make detailed comparisons difficult. Finally, we compare with predictions based on Herring's phenomenological description of χ for ferromagnets.
Magnetic Structure Properties of Tb-Sc Alloys
Authors: Child H. R. , Koehler W. C.
Published: April 2005

The results of a neutron-diffraction study of the magnetic structure properties of the Tb-Sc alloy system are reported. Five binary alloys with Tb content from 90 at. % to 25 at. % have been examined by powder techniques from 300°K down to liquid-helium temperatures to determine the magnetic ordering temperatures and the magnetic structures. The dilution by Sc causes the spiral magnetic phase of Tb to remain stable over a temperature interval larger than in the pure metal. This effect is the same general behavior as that found in the Tb-Y system previously reported. However, the Néel points of the Tb-Sc alloys fall well below those found for Tb-Y and the initial turn angles are smaller in this system. TN falls more rapidly for Tb-Sc alloys than for Tb-Y alloys as a function of the effective spin variable x=c(g−1)2J(J+1), where c is the atomic percent of Tb, and reaches 0°K at x about 2.5. The 25% Tb alloy shows no visible magnetic order down to 1.3°K in contrast to the Tb-Y system where magnetic order was observed with as little as 5 at. % Tb. The universal curve of TN vs x previously found for rare-earth alloys is not obeyed in the Tb-Sc system.
Effect of Pressure on the Néel and Curie Temperatures of the Tb-Y Alloy System
Authors: McWhan D. B. , Corenzwit E. , Stevens A. L.
Published: April 2005

Measurements of the Néel and Curie temperatures of the alloy system TbxY1−x have been made from 5 to 90 kbar by an ac method in which the sample forms the core of a small transformer. The results are compared with similar measurements on the elements Gd, Tb, Dy, and Ho. In the alloy Tb0.95Y0.05 the temperature range over which the spiral structure exists (TN−Tc) increases slightly with increasing pressure. For alloys with more than 70% Tb, a transition ocurs at high pressure which by analogy to pure Tb is from the hcp to the Sm-type structure. No ferromagnetism is observed in the Sm structure above 77°K. The percent change in TN at 30 kbar varies smoothly with concentration from 14% in Tb to a constant value of 7% below the 70% Tb alloy. This variation implies that the relation TN∝c⅔, where c is the concentration of Tb, does not hold at high pressures.
Effects of Deposited Copper Coatings on Drive Current Margins of Permalloy Film DRO Storage Elements
Authors: Shimek Ronald J. , Rausch William V.
Published: April 2005

The object of this study is to obtain film storage elements exhibiting the expanded digit current margins required for improved storage element densities while maintaining the nominal drive current amplitudes. Copper films varying in thickness from 200 to 50 000 Å were deposited on conventional film elements at substrate temperatures, during copper deposition, of 190° to 330°C. Increases in element coercive force of up to 75% can be attained without significantly changing other basic magnetic properties of the elements. The disturb threshold of the elements can also be increased by nearly 75% with the write thresholds increasing only 10% to 15%. Average digit current margins of the copper-coated elements are consistently greater than the margins of the comparable uncoated Permalloy control elements with the same nominal drive currents. Worst-case margin comparisons of coated and uncoated arrays indicate no appreciable change in the uniformity of element switching properties. Irreversible and reversible temperature-induced changes in the margins are discussed.
A Magnetic Film Memory Element for Fully Unipolar Operation
Authors: Hohl J. , Middelhoek S. , Mohr Th.
Published: April 2005

The most generally known mode of operation of a thin-film memory uses unipolar field pulses in the hard direction and positive and negative field pulses in the easy direction for writing. For reading, unipolar field pulses are applied in the hard direction, and according to the stored information, a positive pulse followed by a negative one or vice versa are induced in a sense line. The circumferential electronic circuitry is rather complex, as bipolar bit drivers and sense detectors are required. Savings in driving and detecting circuitry are possible with an element which requires bit drive pulses of only one polarity, and produces a sense signal for a binary ``1'', but no sense signal for a binary ``0''. An element satisfying the above requirements will be described. It consists of two magnetic Ni-Fe layers evaporated on top of each other, which are separated by a thick SiO layer. The easy axes of both magnetic layers form a small angle with each other. Preliminary experience with this new memory element, with respect to its preparation, physical behavior, and pulse operation, is discussed.
First-Order Magnetic Transition in UO2
Authors: Frazer B. C. , Shirane G. , Cox D. E. , Olsen C. E.
Published: April 2005

The antiferromagnetic transition in UO2 at 30.8°K has been examined in a neutron diffraction study. Magnetic intensity changes measured through the Néel temperature revealed that the transition is an extremely sharp one: 50% magnetization is established within ΔT/TN=0.001. As a further test of the first-order nature of the transition, the magnetic scattering above the Néel temperature was studied to see if critical scattering could be observed. While, as would be expected in any case, some short-range correlation in magnetization density was indicated by the observation of a diffuse peak, the absence of the sharp critical scattering characteristic of a second-order transition confirmed the first-order nature of the phase change. In addition to the above measurements, an extensive study of the magnetic structure was carried out at 5°K to determine the U4+ form factor. Magnetic ordering of the first kind on the face-centered cubic sites occupied by the U4+ ions in the fluorite-type structure was reported earlier by Henshaw and Brockhouse,1 and this was confirmed in the present study. The form factor, determined from 23 independent (hhl) single-crystal intensity measurements over a sin θ/λ range extending to about 0.8, indicate a 5f2 electronic configuration with an effective U4+ moment of 1.75±0.05 μB and some degree of asphericity in magnetization density. Details are to be published in The Physical Review.
Magneto-Optical Properties of Materials Containing Divalent Europium
Authors: Suits J. C. , Argyle B. E. , Freiser M. J.
Published: April 2005

A variety of relatively transparent materials containing Eu+ + have become available, thus enabling a study to be made of the magneto-optical properties of the Eu+ + ion in widely different environments. The following materials are reviewed: Eu2SiO4 (orthorhombic structure with a ferromagnetic Curie temperature Tc of 7°K), dilute Eu+ + in CaF2 (fluorite structure), EuF2 (fluorite structure, Tc≈0), EuO−Al2O3−B2O3 glasses (Tc=0), EuSe (NaCl structure, Tc=7°K), and EuO (NaCl structure, Tc=69°K).

We discuss the magneto-optical properties of the ``nonmagnetic'' materials (CaF2: Eu+ +, EuF2, Eu glasses) in terms of an intra-atomic 4f7→4f65d transition. Using this transition, calculation of the Faraday and Cotton-Mouton birefringence in EuF2 gives reasonable agreement with experiment. The magneto-optical properties of the ``magnetic materials'' (Eu chalcogenides) are discussed in terms of an interatomic (4f7) (4f7) → (4f6) (4f75d) transition. This transition gives reasonable agreement with the observed magnitudes of the magnetic absorption edge shifts in EuSe and EuO.
Crystallographic Study of Chromium Spinels
Authors: Raccah P. M. , Bouchard R. J. , Wold A.
Published: April 2005

Several chromium spinels have been prepared and regular x-ray diffraction intensities were measured on the powders. A Fortran program was developed in order to process the data. It appeared that the results, so obtained, were comparable to those from neutron diffraction techniques. A plot of the U parameter versus a0 for the thiochromites shows that metallic CuCr2S4 is exceptional. For its value of U, it has a much lower a0 than would be expected from a comparison of Mn, Fe, Co, and Zn thiochromites.
Effect of Chemical Stoichiometry on the Copper Ferrite Phase Transition
Authors: O'Bryan H. M. , Levinstein H. J. , Sherwood R. C.
Published: April 2005

Previous studies on copper ferrite report conflicting data as to the effect of quenching temperature on the transformation temperature. Data of the present study reveal that the reason for this disagreement has been insufficient attention to the influence of chemical stoichiometry. The transition temperature of copper ferrite with Fe/Cu=2.00 has been shown to be determined primarily by the distribution of the Cu atoms between the A and B sites of the spinel lattice. However, this distribution is not determined uniquely by the quenching temperature, as has been previously reported. Instead it is shown that the Cu distribution is also strongly affected by the oxygen stoichiometry. For constant quenching temperature, the amount of Cu on B sites increases with decreasing oxygen deficiency, and for the same oxygen content, the B-site Cu increases with decreasing quench temperature. The change in transition temperature produced by varying the oxygen content for a 900°C quench is comparable to the temperature change produced at constant oxygen content by varying the quench temperature from 900° to 500°C. In these studies the Cu distribution was determined from the saturation magnetization at 1.4°K. The temperature of the phase transformation was determined by x-ray diffractometer measurements. In view of these data it is clear that a systematic investigation of this diffusionless transition requires control both of stoichiometry and of thermal history.
Temperature-Dependent Localized Spin-Wave Modes in Impure Ferromagnets
Authors: Hone Daniel , Callen Herbert
Published: April 2005

A spin impurity in a Heisenberg ferromagnet can produce a localized spin-wave mode if its spin or its exchange is sufficiently large. By assuming the effect of the perturbation to be very localized, and the local mode frequency to be so high that its thermal excitation is small, we obtain an estimate of the temperature dependence of the local mode frequency. It is found to decrease with temperature, but more slowly than the host magnetization. Furthermore, a mode which is nonexistent at low temperatures can appear at higher temperatures.
Application of the Rudermann—Kittel Interaction to Metals
Authors: Smit J.
Published: April 2005

The indirect exchange interaction of magnetic cores via the conduction electrons has been calculated on the basis of a simple model, and the original Rudermann—Kittel result was found provided that (3m/4πℏ2) × J SkF≪1, where J is the exchange interaction between the conduction electrons and the magnetic core electrons, and kF the radius of the Fermi sphere. For the usual values J = 5 eV·Å3, kF = 1 Å−1, and the spin S = 3, this parameter is 0.5. The zero points of the oscillatory interaction from this analysis may be particularly unreliable.
Effect of the Band States Near the Fermi Surface on the Magnetic Properties of Anderson's Extra-Orbital Model
Authors: Scalapino D. J.
Published: April 2005

The magnetic properties of Anderson's ``extra-orbital'' model are investigated. An exact ground-state solution is obtained for the simple case in which the conduction band is replaced by a single effective band state. Using this solution, a criterion for a magnetic ground state is determined. The possible existence of a magnetic ground state is found to be critically dependent upon whether the energy level of the effective band state is on the Fermi surface or not. To study this critical behavior associated with band states near the FS, the full Anderson (continuum) model is investigated. It is shown that the ``extra-orbital'' spin—flip scattering processes associated with band states near the FS produce a lnk T/Γ damping which prohibits the occurrence of a Hartree—Fock magnetic ground state.
Variation of the Critical Temperatures of Ising Antiferromagnets with Applied Magnetic Field
Authors: Bienenstock Arthur
Published: April 2005

High-temperature expansions of the free energy of Ising ferro- and antiferromagnets on the square, simple cubic, and body-centered cubic lattices have been derived directly from the corresponding low-temperature expansions using a generalization of the technique proposed by Domb. These lattices, being loose-packed, can be divided into two identical sublattices, α and β, such that every α site has only β sites as nearest neighbors. The high-temperature expansions treat the finite magnetic fields on the α and β sites as independent quantities. With these series, which extend to eleventh order in the appropriate energies divided by kT, the high-temperature expansions of the staggered susceptibility (the susceptibility with respect to a magnetic field whose sign on the α sites is the negative of its sign on the β sites) has been evaluated for finite applied constant magnetic field. This staggered susceptibility shows a strong singularity at the antiferromagnetic critical temperature, and is analagous to the normal susceptibility of an Ising ferromagnet. The variation of the critical temperature has been obtained numerically for various ratios of the applied magnetic-field energy to the coupling energy using the method of Padé approximants. The results are well described by an expression of the form Tc(H)/Tc(0) = [1 — (H/Hc)2]ξ, with ξ = 0.87, 0.35, and 0.36 for the square, simple cubic, and bcc lattices, respectively. Here, Hc = —zJ/m, where z is the coordination number, J is the spin coupling energy, and m is the magnetic moment.
Thermal Properties of Spin-Wave Impurity States
Authors: Wolfram T. , Hall W.
Published: April 2005

The effect of dilute magnetic impurities on the thermal properties of an ideal simple cubic spin ½ Heisenberg ferromagnet has been investigated. It is shown that for a small ratio ε of impurity—host to host—host exchange low-lying ``s-type'' virtual spin-wave states result which cause a large density of states to occur at low energies. These low-energy states lead to an accumulation of spin disorder at and near the impurity site. Consequently the impurity magnetization decreases far more rapidly than that of the host. This effect is accompanied by a large increase in the low-temperature spin-wave specific heat. Analytic solutions to the Green's function equations are calculated for temperatures near T = 0 and near T = Tc, the Curie temperature. Self-consistent numerical solutions are presented for both the magnetization and spin-wave specific heat as a function of temperature. For small ε the impurity magnetization is approximated by the Brillouin function mI=μβ tanh [(μβH+6J′〈S1z〉)/kT],where J′ is the host-impurity exchange and 〈S1z〉 is the thermal average for the impurity nearest-neighbor spins. 〈S1z〉 is found to be depressed from the bulk value by an amount which increases with temperature and is about 0.84 of the bulk value as T→Tc.

A detailed account of these calculations will be published elsewhere.
Composition Dependence of Irradiation-Induced Uniaxial Anisotropy Energy of Permalloy Films
Authors: Williams C. M. , Schindler A. I.
Published: April 2005

The composition dependence of irradiation-induced uniaxial magnetic anisotropy energy has been examined in Permalloy thin films over the range from 40% to 90% Ni. The uniaxial anisotropy was developed at 60°C by irradiating the films with 2-MeV 3He particles in the presence of an orienting magnetic field. The values of the uniaxial anisotropy constant Ku were found to range from a maximum of 1.9×104 erg/cm3 for 52 Ni-48 Fe to a minimum of 1.3×103 erg/cm3 at 90 Ni-10 Fe. In the range from 40% to 70% Ni the values obtained are significantly greater than those found for films evaporated or annealed in the presence of a magnetic field. Because of radiation-enhanced diffusion, directional short-range order can occur at temperatures considerably lower than those necessary for magnetic annealing, with a concommitant increase in the uniaxial anisotropy energy. These data were compared with the theoretical relationship, as derived by Néel and Taniguchi, and with a related semiempirical expression of Ferguson: K0 = A′ (Tc−Ta) n2 (1−n)2, where n is the fraction of Fe atoms, Ta is the annealing or deposition temperature, and Tc is the Curie temperature. Both expressions agree with the data fairly well for nickel compositions above 70%, but for compositions of nickel between 40% and 70% the expression developed by Ferguson does not account for all of the observed anisotropy.
Exchange Anisotropy Properties in Sulfided Iron Films
Authors: Greiner J. H.
Published: April 2005

Exchange anisotropy, manifested by a shifted B-H loop and a sinθ torque, has been observed in sulfided Fe films. At room temperature, loop shifts along the H axis up to 7 Oe were measured. The B-H loop was shifted in the direction of the field applied during sulfiding and symmetrical about zero H for a field applied perpendicular to this direction. A sinθ torque was present at room temperature in fields up to 20 kOe. At high fields the sinθ torque decreased and the rotational hysteresis increased. The amplitude of the sinθ torque and the B-H loop shift corresponded to an unidirectional anisotropy energy of 0.1 erg/cm2 of apparent interface. Sulfiding of ∼100 Å of a 1000-Å Fe film was sufficient to produce a 7-Oe shift of the B-H loop.
Properties of Thin Films of High-Permeability Alloys
Authors: Flur B. L. , Griest A. J.
Published: April 2005

A number of commercially available high-permeability nickel-iron-base alloys with low values of coercive force, magnetostriction, and crystalline anisotropy are of potential interest as materials for thin-film memory elements. Because of their compositional complexity, however, films of these alloys are not easily prepared by vacuum deposition. By use of bias sputtering, thin films of Mumetal, Conetic AA, Supermalloy, and 4–79 Permalloy have been successfully prepared. The effects of substrate temperature (100°–400°C) and film thickness (500–1000 Å) on the properties of wall-motion threshold H0, anisotropy field Hk0, dispersion α90, skew β, magnetostriction, and sheet resistivity have been experimentally determined.

In general, for the same thickness and substrate temperature, the high-permeability alloys show lower H0 and Hk0 than the binary 81% Ni-19% Fe alloy. The data show that the reduction is most pronounced in the molybdenum-containing alloys, less so in Conetic AA, and least in Mumetal. Molybdenum additions appear to be the most effective in inhibiting the rate of increase of dispersion with increasing H0/Hk0 ratio; e.g., a Supermalloy film was deposited with H0/Hk0=0.9 Oe/0.4 Oe and α90=4.5°.
Magnetic and Electrical Properties of FeRh Thin Films
Authors: Lommel J. M.
Published: April 2005

Thin films of the intermetallic compound FeRh were prepared by vacuum depositing alternate layers of Fe and Rh and then giving them a diffusion anneal. Magnetization, coercive force, and electrical resistance measurements show the presence of a phase transition at about 50°C. In contrast with bulk samples, the films exhibit a broad transition and a large thermal hysteresis. It has been shown that the transition characteristics are not associated with clamping of the film to the substrate. Codeposited and sputtered films showed little evidence of the phase transition.
Theory of Linear Ferrite Devices for Microwave Applications
Authors: Von Aulock W. H.
Published: April 2005

Linear ferrite devices for microwave applications include phase shifters, switches, isolators, circulators, and others whose operation is independent of the applied rf signal level. In this paper, propagation through an infinite ferrite medium is treated first, and points of operation for various ferrite devices are established on a normalized plot of effective permeability vs biasing field. Transfer matrix techniques are used to analyze slab configurations with transverse magnetization, such as those found in differential phase shifters for circulators, field-displacement isolators, and certain latching phase shifters. These techniques permit computation of optimum geometry, field configurations, phase shift, and cutoff conditions. Suhl and Walker's analysis of the completely filled cylindrical waveguide is applied to the ferrite-filled coaxial line and extended to study Faraday rotation, phase shift, and cutoff conditions in cylindrical rod geometries. Of particular interest is a simplified analysis of the Reggia-Spencer phase shifter which predicts frequency dependence and critical geometry with good accuracy.
Reduced Manganese Moment in Manganese Chromite
Authors: Dwight K. , Menyuk N. , Feinleib J. , Wold A.
Published: April 2005

The net magnetization, magnetic susceptibility, 55Mn nuclear magnetic resonance, and neutron-diffraction properties of MnCr2O4 have been reinvestigated. Our results are in general agreement with earlier findings. The neutron-diffraction pattern of MnCr2O4 evidences appreciable deviation from a pure spiral configuration. Furthermore, the susceptibility data indicate that the Mn+ + ions possess a reduced magnetic moment of about 4.3μB, rather than the previously assumed value of 5.0μB. Given the hypothesis of an admixture of quartet states with quenched orbital momentum into the 6S free-ion ground state, the reduced value of the 55Mn hyperfine field observed in manganese chromite is consistent with this low value for the manganese moment.

The interpretation of the NMR result in terms of a ferrimagnetic spiral ground-state spin configuration remains essentially unchanged, a manganese cone angle of about 61° being indicated. The use of 4.3μB for the Mn+ + moment improves the agreement between the theoretical and observed neutron-diffraction patterns, but the best fit is still obtained with a much smaller value for this cone angle, namely 33°. Within the spiral model, the observed magnetic-diffraction intensities are incompatible with the larger cone angle; the NMR findings are incompatible with the smaller. Other discrepancies are also discussed.
Neutron Diffraction Study of Helimagnetic Spinel ZnCr2Se4
Authors: Plumier R. J.
Published: April 2005

Neutron diffraction experiments under magnetic fields up to 15 kOe are performed on the helimagnetic spinel ZnCr2Se4. For fields of about 3 to 4 kOe, switching of 90° antiferromagnetic domains occurs. In the same field range, there is also a tilting of the spins rotation axis towards the field direction. In the field range 10 to 15 kOe, canting of the spins towards the field direction occurs as shown experimentally. Hysteresis effects of the boundaries motions are studied. Exchange coefficients are determined, together with estimates of the potential energy associated with the Bloch walls and of the magnetic anisotropy energy.