bluuebunny/crossref_metadata_2025 huggingface dataset:
The Electrodeposition of Thin Magnetic Permalloy Films
Authors: Girard R.
Published: January 2005

The work of Wolf has shown that electrodeposited magnetic films, above a thickness range of a few hundred Angstroms, could be obtained on flat metallized glass substrates, with properties adequate for computer memories. New problems arise when one tries to prepare very thin films (<300Å) or to deposit on flat or cylindrical metal substrates.

The preparation of very thin films is interesting for studies such as creep, or to insure that thicker films do not present unwanted composition gradients or stresses. The influence of the nature of the plating bath on the amplitude and extension of the composition gradients and on the stresses, and consequently, on the magnetic properties (Hc, HkΔ) are examined.

The deposition on metallic substrates has an obvious interest when using ground planes or wires. In this case the crystalline structure of the substrate has as much importance as its chemical activity, and we will show the usefulness of an intermediate layer of controlled grain size and isotropy.

The results of these studies are related to the aging behaviour of plated films.
Cu Diffusion in Electrodeposited Permalloy Films
Authors: Von Neida A. R. , Hagedorn F. B.
Published: January 2005

The diffusion of Cu into electrodeposited Ni-19% Fe films has been studied over the temperature range 325°−426°C by measuring the loss of magnetic flux associated with the interdiffusion of Cu and NiFe. The Permalloy films, nominally 4800 Å thick, were electroplated on top of a 1-μ-thick layer of Cu, which had previously been plated on an 0.005-in.-diam wire. Precision measurements of flux were made with a vibrating sample magnetometer using an applied field of 8 kOe along the wire axis. Principally, the flux loss and hence the penetration depth at all temperatures varies as the square root of the diffusing time in agreement with classical diffusion theory. There is, however, an initial flux loss due to a relatively rapid process which occurs with a relaxation time described by τ=τ0 exp (Q/RT), where τ0=8×10−14 sec and Q=51.6 kcal/mole. In view of this high activation energy Q, it is proposed that the initial flux loss is due to an oxidation reaction which occurs from oxygen trapped in the film during plating. The diffusion process is characterized by a diffusion coefficient D=5.2 exp (−47 300/RT). The Q obtained is considerably higher than that previously reported (34 kcal/mole) for diffusion of Cu into evaporated Permalloy films. To check the validity of the technique, the interdiffusion of electroplated Cu and Ni was investigated with the technique described above. A similar two-stage process is observed with Q=33 kcal/mole for the diffusion process, close to the Q=35.4 kcal/mole reported for diffusion of Cu in bulk Ni.
Uniaxial Anistropy and Rotational Hysteresis in Thin Gadolinium Films
Authors: Livesay B. R. , Grismore F. L. , Scheibner E. J.
Published: January 2005

The planar anisotropy and rotational hysteresis of thin films of gadolinium have been studied using torque measurements. Films ranging from 300 to 700 Å were prepared by evaporation at normal incidence onto heated quartz and glass substrates and overcoated with SiO. Electron- and x-ray diffraction patterns show a finite fraction of crystallites have a canted preferred orientation of the c axis, which probably accounts for the uniaxial anisotropy observed. The films were found to have a dominant sin 2θ-torque behavior for fields above 3 kOe and a sin θ-dependence below 300 Oe. The uniaxial anisotropy constants measured for these films are 104−105 erg/cc. The films show a unidirectional rotational hysteresis. Peak loss occurs at field strengths between 0.5 and 1 kOe, and losses remain significant up to 10 kOe. A magnetic model based on a magnetization ripple structure is proposed to explain the observed data.
Thickness Dependence of the Composition in Electroplated Ni–Fe Cylindrical Films
Authors: Doyle W. D.
Published: January 2005

The thickness dependence of the average composition in electroplated cylindrical Ni–Fe films was determined from a measurement of the torsional strain sensitivity. It was found that from 200–2500 Å the average Ni fraction varied about 4% which is considerably less than that previously reported for flat films. It is attributed to the extremely high agitation which can be achieved conveniently in the wire plating geometry.
Thermally Induced Parallel Magnetic Coupling in Coupled Thin Films
Authors: Suiter W. B.
Published: January 2005

Previous investigators reported parallel magnetic coupling between ferromagnetic thin films separated by Pd up to 300 Å thick. They also reported that parallel coupling, while temperature dependent, displayed no thermal hysteresis between − 180° and 300°C. Reported in this paper are: (1) the introduction of large irreversible increases in the parallel coupling field by heat treating the samples between 260° and 345°C, and (2) the irreversible development of parallel coupling through Pd films up to 1500 Å thick, where antiparallel coupling existed prior to heat treatment. The structures on which these effects are observed most readily are similar to those used by the earlier investigators except for their greater Pd thicknesses and deposition at room temperature. However, irreversible increases in the parallel coupling field were also observed for samples with preparation essentially identical to previous work. For a typical sample (two 1000- Å ferromagnetic layers, Hc = 1.5 Oe and 16 Oe, respectively, and a Pd layer 940 Å thick) the coupling field, before heat treating, was 0.3 Oe antiparallel. After treating at 310°C for 4 h, the coupling field was 1.1 Oe parallel. The temperature and time dependence of the development of the parallel component of the coupling field cannot be described by a classical diffusion process characterized by a single activation energy, which suggests a mixture of grain boundary and volume diffusion. The ability to achieve a desired value of parallel coupling by heat treating provides a convenient method for establishing the required coupling for device applications.
Magnetoelastic Coefficient and Temperature Relationship in Thin Ni–Fe Films
Authors: Tolman C. H. , Oberg P. E. , Rubens S. M.
Published: January 2005

Measurements of the magnetoelastic strain coefficient of nickel-iron thin films on soda-lime glass substrates have been made at temperatures from −40° to 200°C. The composition of the films ranged from 1% Ni rich to 1% Fe rich, with respect to the nonmagnetostrictive composition near 81% Ni, 19% Fe. Films with positive magnetostriction became less positive, and films with negative magnetostriction became less negative with a temperature increase. In some cases the magnetostriction changed from negative to positive when heated. The composition that displayed the least change in magnetostriction upon heating from −40° to 200°C is 0.1%. Fe-rich as compared to the nonmagnetostrictive composition. Changes in the coercive force and the anisotropy field with temperature are also reported.
Zero Magnetostriction Composition of NiFe Films
Authors: Reekstin J. P.
Published: January 2005

Measurements of the magnetoelastic strain sensitivity of evaporated NiFe films in the range 64.1–84.1 wt % nickel show the average zero magnetostriction composition (ZMC) to be 81.5±0.2% nickel for films in the vicinity of 1000 Å. This result agrees with the ZMC reported by Wolf and Crowther for electroplated and evaporated 1000- Å films, but disagrees with the value of 80.3% nickel reported by Long for 10 000- Å electroplated films, even though the same analyst and analytic techniques were used. In an attempt to resolve this difference, the effect on the ZMC of a uniform composition gradient is examined. Strong exchange coupling is assumed to make the magnetization direction uniform throughout the film. A quadratic expression is fitted to the nonlinear magnetoelastic strain coefficient vs composition data. It can then be shown that the apparent ZMC, as a function of film thickness and composition gradient, may be represented by ZMC=55.86+[− (G2T2/12)+657.4]½, where G is the gradient in nickel concentration in weight percent Ni per 1000 Å and T is the film thickness in thousands of angstroms. The apparent discrepancy with Long's result would be resolved if a composition gradient in the order of 2.7% 1000 Å existed in the electroplated films. Since a gradient of this magnitude is not unreasonable in an electroplating process even with agitation, the ZMC of 80.3% Ni reported by Long is consistent with the model proposed here. It is concluded that the ZMC of NiFe films is 81.5% Ni in the absence of a gradient, although whatever mechanisms are responsible for Metzdorf's recent findings may also be significant here.
The Magnetic Susceptibility of Neptunium Oxide and Carbide between 4.2° and 350°K
Authors: Ross J. W. , Lam D. J.
Published: January 2005

The magnetic susceptibilities of the dioxide and monocarbide of neptunium have been measured from 4.2 to 350°K. The inverse susceptibility of neptunium dioxide is linear in temperature above 60°K with an effective paramagnetic moment of 2.95 μB. A peak in the susceptibility-vs-temperature curve is observed at 25°K, in agreement with the maximum observed in the specific heat of NpO2. The neptunium monocarbide becomes ferromagnetic below 200°K. A peak in the susceptibility-vs-temperature curve at 310°K indicates a transition from a magnetically ordered arrangement to a paramagnetic one. The effective moment per NpC unit for the ferromagnetic and paramagnetic states is 1.4 μB and 3.37 μB, respectively.
Magnetic Structure of NiCl2·6H2O
Authors: Kleinberg Robert
Published: January 2005

Neutron diffraction data of NiCl2·6H2O have been taken at 1.5° and 4.2°K on the (h0l) zone. The magnetic reflections observed at both temperatures indicate that the magnetic structure consists of antiferromagnetic (001) planes, with an antiferromagnetic coupling between planes, to give a magnetic cell with cm = 2c. Using the results of the NMR experiments, the magnetic space group is concluded to be Ic2/c. A study of the relative intensities of the magnetic reflections indicates that the spin direction is not along the a′ axis as has previously been assumed, but is approximately 22.5° from the a′ axis toward the a axis.
Canted Antiferromagnetism of CuCl2·2D2O
Authors: Umebayashi H. , Shirane G. , Frazer B. C. , Cox D. E.
Published: January 2005

Canted antiferromagnetism in CuCl2·2D2O has been confirmed in a neutron diffraction experiment. The neutron data agree well with the theoretical predictions of Moriya for a minor magnetization component of about 0.1 μB parallel to the c axis. The angular dependence of the neutron data indicates that the spatial distribution of minor magnetization is quite different from that of the main component.
Magnetic Ordering in Mn(HCOO)2·2H2O and Related Compounds
Authors: Pierce R. D. , Friedberg S. A.
Published: January 2005

The heat capacities of the isostructural dihydrated formates of Mn2+, Fe2+, and Ni2+ have been measured between 1.4° and 20°K. Sharp peaks associated with long-range spin ordering are found at 3.72°K for Mn(HCOO)2·2H2O, 3.74°K for Fe(HCOO)2·2H2O, and 14.5°K for Ni(HCOO)2·2H2O. An additional sharp anomaly in Cp is found at 1.72°K for the Mn+2 salt, while Cp of the Ni+2 salt exhibits a Schottky-like maximum at 3°K. Each of these anomalies can be correlated with some feature of the observed magnetic susceptibilities.

A unit cell in these salts contains two each of two inequivalent metal ion sites, types A and B. Formate groups constitute AA and AB bridges and appear to mediate the dominant superexchange couplings. A simplified molecular field treatment of Mn(HCOO)2·2H2O in which JAA = 0.65 k, JAB = −0.10 k, and JBB = 0 provides interpretations of several striking effects. In particular, it shows that below a common transition temperature, B spins order much more slowly than A spins and are nearly ``free'' at 1°K as seen in both magnetic and thermal data. Analysis of the data for the Ni+2 and Fe2+ salts suggests that the effective spins of A and B ions may differ in a given substance.
Magnetic-Susceptibility Studies on the Magnéli Phases of the Titanium-Oxygen System
Authors: Keys L. K. , Mulay L. N.
Published: January 2005

A magnetic-susceptibility study of the Magnéli phases of the titanium-oxygen system shows an anomalous dependence on the stoichiometry. The magnetic susceptibility has been fitted (where applicable) to a Curie-Weiss law of the form χ = C/(T+θ) +A, using a least-squares analysis. The Curie constant C increases with increasing stoichiometry despite the apparent increasing magnetic dilution (addition of Ti4+ ions) of the Ti3+ ions. Some of these phases exhibit an antiferromagnetism; others show an apparent paramagnetic behavior; and several show semiconductor-to-metal transitions.
Magnetic Properties of FexO as Related to the Defect Structure
Authors: Koch F. B. , Fine M. E.
Published: January 2005

The magnetic properties of FexO with long-range order of defects was studied. The crystal structure appears to consist of periodically spaced complexes of vacant octahedral and occupied tetrahedral sites, with most of the octahedral ions in an ideal NaCl-type environment. The Néel temperature, determined from measurements of susceptibility and modulus, increases very slightly as x is decreased. Octahedral-tetrahedral ion exchange interactions are proposed to account for the increase in TN. The molar susceptibility obeys a Curie-Weiss law, χ = 3.56/(T+136). With θ = 136°K and TN about 200°K, θ/TN is less than one. According to a treatment by Van Vleck one expects θ/TN greater than one for negative first-near-neighbor and second-near-neighbor interactions. A positive first-near-neighbor interaction may possibly arise through double exchange between Fe2+ and Fe3+.
Magnetic Susceptibility of Vanadium Difluoride
Authors: Stout J. W. , Lau H. Y.
Published: January 2005

Measurements have been made of the magnetic susceptibility of VF2 at temperatures between 1° and 300°K. This compound was previously found [J. Appl. Phys. 37, 966 (1966)] to have the rutile structure and to have a gradual maximum in magnetic heat capacity at 27°K and a sharp heat-capacity peak at 7.0°K associated with the development of long-range order. The data were interpreted as indicating that the major exchange interactions between vanadium ions couple together one-dimensional chains of atoms parallel to the c axis. We have measured the magnetic susceptibility of powdered samples and of an oriented crystal sample made by stacking together small needle-like single crystals. The high-temperature susceptibility data show that the net exchange interactions are antiferromagnetic. There is a gradual maximum in magnetic susceptibility near 40°K, consistent with the development of a large amount of one-dimensional short-range order. At 77°K and lower temperature the susceptibility parallel to the c axis is greater than that perpendicular to this direction.
Field-Dependent Magnetic Susceptibility of MnO
Authors: Bloch D. , Feron J. L. , Georges R. , Jacobs I. S.
Published: January 2005

The field dependence of the magnetic susceptibility of MnO powder has been studied in continuous fields up to 50 kOe, between 4.2° and 200°K. Each isotherm is measured from a virgin magnetic state to avoid hysteresis and viscosity complications. Above the antiferromagnetic Néel point, the susceptibility is field independent with a maximum value of (83±1)×10−6 emu/g at 122°K. At 4.2°K, the susceptibility saturates with field at a value of 79×10−6 emu/g. This is identified as the transverse susceptibility. It drops slightly with temperature to a broad minimum at 55°K. An attempt to analyze the field dependence using the model of Keffer and O'Sullivan suggests that the weak in-plane anisotropy, K2, has orthorhombic symmetry. This model is rejected because it ignores domain wall displacement. A rough estimate of K2 at 4.2°K is 9×103 erg/cc, assuming trigonal symmetry.
Faraday Rotation and Gyromagnetic Effects of Trivalent Europium Ions
Authors: Sander L. , Kittel C.
Published: January 2005

The electronic magnetization of Eu3+ ions at low temperatures is associated with Van Vleck temperature-independent paramagnetism; the ground state has J=0. We have calculated the Faraday rotation for this ion. A contribution from the Van Vleck paramagnetism is partially cancelled by the usual diamagnetic term. The resulting rotation should be observable in Eu3+ in the microwave and infrared regions. In the appropriate limits we find for the rotation per unit length Δθ/Δx=(48μB2N/ℏν)(ℏω/Δ)4(μBH0/Δ)[1−(ℏω/Δ)2]−2,where N is the concentration, v is the velocity of light in the medium, and Δ is the splitting between J=1 and J=0. We give the appropriate modification of this formula in a crystal field. We calculate the gyromagnetic ratio g′; at low temperatures the calculations of Frank have to be corrected to take into account nuclear effects.
Far-Infrared Spin-Wave and Anomalous Phonon Absorption in Antiferromagnetic Uranium Dioxide
Authors: Allen S. J.
Published: January 2005

The far-infrared spectral response of antiferromagnetic UO2 has been studied between 10 and 220 cm−1 as a function of temperature, magnetic field, and uniaxial strain. In the ordered state, resonant absorption is observed at 17.5, 79.0, 99.0, 110.5, 184.0, and 216.0 cm−1. The resonances at 79.0 cm−1 and 99.0 cm−1 are shown to be nondegenerate antiferromagnetic modes. Absorption by zone-boundary magnons within domain walls is believed responsible for the structure at 17.5 cm−1. The remaining modes appear to be anomalous phonon absorptions which appear in the ordered state by virtue of the strong magnon-phonon interaction.
Temperature Dependence of Co2+-Ion Absorption Transitions in Magnetic Host Crystals
Authors: Holloway W. W. , Kestigian M.
Published: January 2005

The temperature dependence of Co2+-ion absorption-band maxima has been studied in crystals of RbCoF3, KMn0.975Co0.025F3 and KNi0.75Co0.25F3. Shifts in the cobalt-band maxima are superimposed on changes of purely thermal origin. The additional changes in the band maxima are attributed to the magnetic properties of these materials. In pure cobalt salts the magnetically induced changes begin, with decreasing temperature, at the Néel temperatures of the materials. Similarly, in salts where the cobalt ion is not a major constituent, the shifts in the Co2+ bands appear approximately at the Néel temperature of the host.
Magneto-Optical Effects
Authors: Pershan P. S.
Published: January 2005

The general theory of magneto-optical effects is reviewed and it is shown that one can describe these phenomena in terms of a macroscopic dielectric tensor by setting μ=1. This is true even when the microscopic origins of the dielectric constant are magnetic-dipole transitions. For the case of electric-dipole transitions, the dispersive magneto-optical effects (i.e., Faraday or Voigt effects) can be interpreted in terms of an effective Hamiltonian which is related to the macroscopic dielectric tensor in a very simple manner. The form of this effective Hamiltonian follows from symmetry considerations. From the measurements of the magneto-optical effects, one determines the constants of the effective Hamiltonian and from these one can predict the cross section for Raman scattering of light by spin excitations.
Thermal Conductivity and Far-Infrared Absorption of UO2
Authors: Aring K. , Sievers A. J.
Published: January 2005

The thermal conductivity of single-crystal UO2 has been measured from liquid-helium temperature up to room temperature. The sample temperature was determined, with a helium gas bulb thermometer, and the temperature gradient was measured with Au–Co vs Manganin differential thermo-couples. In the vicinity of the Néel temperature, TN=30.8°K, the conductivity is depressed by two orders of magnitude, from that expected for a similar diamagnetic crystal. The experimental results demonstrate that a strong phonon-magnon coupling exists in this crystal. The far-infrared transmission of the same UO2 crystal has been measured from a frequency of 5–115 cm−1 at 3°K. A grating monochromator and a Strong-type lamellar interferometer have been used for these measurements. A sharp absorption line has been found at 17.63±0.1 cm−1. Broader absorption lines have been observed at 19.2, 23, 79, and 100 cm−1. Transmission measurements in which a 50-kG magnetic field is applied to the sample or the sample temperature is varied indicate that impurity-induced absorptions occur at 19.2 and 23 cm−1, and the three remaining lines can be identified with the antiferromagnetic state of UO2.
Magnetic Effects on the Optical Absorption of EuO and EuS
Authors: Methfessel S. , Freiser M. J. , Pettit G. D. , Suits J. C.
Published: January 2005

The relationship between optical absorption and ferromagnetic order has been investigated on single crystals and thin films of EuO and EuS. The 4f7-4f65d transition can be identified in evaporated films as an absorption peak of ∼105 cm−1 at 2.1 and 2.4 eV, respectively, which tails out exponentially to lower energies. The onset of the ferromagnetic order is accompanied by an unusually large red shift of the absorption peak which superimposes on the normal magneto optical dichroism. The detailed temperature dependance of this shift does not relate exponentially to the variation in magnetization as found earlier by Busch et al. for powdered samples,1 but is approximately proportional to the nearest neighbor spin correlation function 〈S1S2〉/S2. This is in agreement with an exciton like model for the excited state in which the electron is localized in 5d-orbitals at the excited Eu-ion and its 12 nearest Eu neighbors. The exchange interaction of the excited electron with the neighboring 4f7-spins causes the red shift which is much larger (EuO:0.23 eV; EuS:0.11 eV) and extends to higher temperatures than one expects for the effect of a molecular field on excited electrons in a conduction band.
Magnetic Measurement Techniques for Thin Films and Small Particles
Authors: Humphrey Floyd B.
Published: January 2005

Techniques which are particularly useful for magnetic investigations involving thin films and small particles are reviewed. Measurements of torque are discussed from an instrument point of view and from a measurement point of view, including those measurements such as Mr, Ms, and Δ90 which are peculiar to thin films. Extensions to the standard loop tracer method that are necessary to investigate thin films include a very sensitive integrator, a very slow drive, and the extra coils for measuring α90 and Δ90. For fast flux reversal, the equipment is outlined and various methods of taking data are discussed. Optical techniques involving the Kerr magneto-optic technique are reviewed along with the use of the electron microscope for both Lorentz and Bitter pattern transfer observations.
Biological Applications of Magnetism
Authors: Lang George
Published: January 2005

For some time NMR and ESR have been applied to the study of biological materials. Two somewhat distinct applications have developed: as a means of detecting a given complex and following it through a reaction, and as a source of information on the electronic state and structure of a material. Mössbauer spectrometry has recently been applied to biological studies, principally in the latter mode. Unfortunately, the method may be used only on atoms with suitable nuclear properties. Work has been reported on hemoglobin, myoglobin, various cytochromes, ferritin, ferridoxin, and xanthine oxidase, all of which contain iron. Hemoglobin has been the most intensively studied. The magnetic compounds (e.g., the azide, fluoride, nitric oxide) are sufficiently dilute that reasonably well-resolved hyperfine spectra are seen at low temperatures. Many are consistent with ESR data and one (the azide) can be predicted from the g values. Recent measurements in applied magnetic fields confirm the original interpretations. The nitric oxide spectrum provides information on the spread of the unpaired NO spin onto the iron ion. Some spectra are not yet understood, with Mössbauer and ESR spectra indicating different spin states. A number of interesting problems relating to these, to spin-spin interaction, and to other cooperative iron-iron effects remain to be investigated.
The Range of Ferromagnetic Exchange Interactions
Authors: Trousdale W. L. , Longworth G. , Kitchens T. A.
Published: January 2005

Experimental investigations on the characteristic length over which two magnetic atoms interact in a nonmagnetic metal have been carried out. Two methods are used: (a) measurement of the transition temperature as a function of the magnetic atom concentration in zero field, and (b) study of the magnetization distribution in alloys in the region just below the transition temperature as determined from the magnetic hyperfine field distribution.

These experiments have been done using palladium as the nonmagnetic and iron as the magnetic atoms. In the FePd alloys it is found that the transition temperature and the nature of the magnetic transition depend strongly on the method of sample preparation and in particular on the annealing of the samples. Samples quenched from the melt to room temperature show a diffuse transition and a relatively slow rise in magnetization with decreasing temperature. Those which have been annealed show a relatively sharp transition and a narrower magnetization distribution below the transition temperature, indicating that the process of annealing produces a more homogeneous distribution of the iron atoms. Interpretation of this phenomenon and its relation to the range parameter are discussed.

Assuming that the magnetic interaction between two iron atoms is due to the overlap of the matrix polarization, the range obtained in this investigation from a simple statistical model is in excellent accord with neutron diffraction measurements.
Ferroelectricity
Authors: Matthias B. T.
Published: January 2005

Ferroelectricity is a very general phenomenon. Yet it is possible to divide it into three main groups with essentially three different mechanisms: the order-disorder of hydrogen bonds, the trigger effect of nonspherical radicals, and the 4π/3 catastrophe due to high electronic polarizabilities. Recently it has been realized that some of the metallic bronzes crystallizing in the perovskite structure may also be ferroelectric. At present, it is very difficult to determine ferroelectricity in these metals.
Domain Theory and Observation
Authors: Craik D. J.
Published: January 2005

The relevance of domain studies to both intrinsic and technical magnetic properties and the reasons for the continued interest and activity in the subject are discussed. The particular advantages of certain of the many methods of observing domains are noted, without attempting any comprehensive survey. Reference is made to some recent developments using x-rays, to the interpretation of powder patterns, and to dynamic studies. There is no general domain theory, i.e., no theory which predicts the domain structure which will exist in a specimen with specified shape and intrinsic properties. However, it is possible to evaluate, with varying degrees of approximation, the energies corresponding to some observed or postulated structures. Domain observations can then be used to verify magnetostatic calculations, and can give measurements of certain intrinsic properties. Also, precise calculations of magnetization curves can be made for postulated structures in the hope that these will elucidate the technical properties of real materials.
Magnetic Symmetry and Spin Waves
Authors: Brinkman William
Published: January 2005

In general, the symmetry of the spin-wave spectra is determined by the magnetic space group characteristic of the spin order in the crystal. For many magnetic materials, however, interactions such as dipole-dipole, antisymmetric exchange, and higher-order anisotropic exchange are quite small, so that most of their properties are essentially determined by isotropic Heisenberg exchange plus a few crystal field parameters. It was pointed out previously that this fact is reflected in the spin-wave spectra in terms of additional symmetry not predicted by the magnetic-space-group theory and that this symmetry is describable in terms of spin-space groups which include independent spin and space rotations. In this paper the theory of magnetic space groups and spin-space groups and the characterization of the spin-wave spectra in terms of their representations is briefly reviewed. The effect on the spin-wave spectra of the various types of interactions that have been proposed for the rare-earth metals is then analyzed in detail and compared with the recent experimental data for Tb. The calculation of selection rules for neutron scattering is also discussed and applied to Tb.
Ferromagnetism in Compounds with Pyrochlore Structure
Authors: Bongers P. F. , Van Meurs E. R.
Published: January 2005

The compounds (RE)23+Cr3+Sb5+O7 (RE=Y or a rare earth except Ce, Pm, Lu) with pyrochlore structure have asymptotic Curie temperatures between 4° and 16°K; Ho2CrSbO7 and Dy2CrSbO7 are ferromagnetic below Tc=10°K and Tc=16°K, respectively. The moments of the chromium and the rare-earth ions are oriented parallel in these latter two compounds. The positive Cr3+–Cr3+ interaction in the pyrochlore structure is compared to the interaction between chromium ions in other compounds.
Magnetic Phase Equilibrium in Cr-Substituted CaFe2O4
Authors: Corliss L. M. , Hastings J. M. , Kunnmann W.
Published: January 2005

The structure of CaFe2O4 has orthorhombic symmetry (space group Pnam-D2h16) and is characterized by Fe–O–Fe–O chains within which the Fe–O–Fe bond angle is ∼130°. These chains are cross linked by means of Fe–O–Fe bonds in which the angle is ∼99°. The compounds (Ca (CrxFe1−x)2O4, with 0≤x≤0.5, have been found, by means of neutron measurements, to exhibit two magnetic structures in each of which the chains are internally antiferromagnetic, with spins alternating +−+− along the chain. In one structure the chains are linked ferromagnetically through the 99° bonds, with magnetic symmetry Pn′a′m, and in the second they are antiferromagnetically coupled, corresponding to the space group Pna′m. A phase diagram has been constructed showing both single-phase regions and a region in which the two phases exist in equilibrium. Transition temperatures as well as the temperature dependence of magnetic moments and phase concentration have been determined as a function of chromium content. The problem posed by the coexistence, at equilibrium, of two magnetic phases belonging to a single-crystal structure will be discussed.
Semiconducting and Optical Properties of Ferromagnetic CdCr2S4 and CdCr2Se4
Authors: Lehmann H. W. , Harbeke G.
Published: January 2005

Electrical conductivity, Hall effect, magnetoresistance and thermoelectric properties have been studied on a number of undoped and doped polycrystalline CdCr2S4 and CdCr2Se4 samples. Undoped CdCr2S4 and CdCr2Se4 are n-type and p-type, respectively. With suitable doping, the conductivity of CdCr2Se4 can be changed by about six orders of magnitude [10−5 to 10 (Ω·cm)−1] without changing the magnetic properties. In Ag-doped p-type CdCr2Se4 the mobility at room temperature is 32 cm2/V·sec and rises with decreasing temperature. By doping with In, CdCr2Se4 can be made n-type. The mobility of electrons is found to be two orders of magnitude lower than the mobility of holes. The conductivity of p-type CdCr2Se4 decreases monotonically with decreasing temperature without any anomaly around the Curie temperature (Tc=130°K1). However, the conductivity of n-type CdCr2Se4 has a minimum at 146°K and rises sharply with further decreasing temperature. This n-type material also exhibits a large negative transverse magnetoresistance effect which has a maximum at the Curie temperature (Δρ/ρ0=−0.8 for H=6 kG). The magnetoresistance of the p-type material is positive in the paramagnetic range and negative in the ferromagnetic range. Optical transmission experiments on thin single crystals show that the absorption edges of CdCr2S4 and CdCr2Se4 are at 1.6 and 1.3 eV, respectively, at room temperature.2 For the ferromagnetic range an anomalously strong shift of the absorption edge takes place to higher energies in CdCr2S4 and to lower energies in CdCr2Se4. The edge is shifted further in both materials by an externally applied magnetic field. This additional field shift exhibits a linear magnetic dichroism and has its maximum at the Curie temperature. The observed anomalous optical properties and also the strong increase in conductivity of n-type CdCr2Se4 in the ferromagnetic range are closely related to magnetic ordering. Apparently the strong shift of the absorption edge decreases the energy difference between the donor level and conduction band and results therefore in an increase of the carrier density. A complete account of this work will be published elsewhere.
Some Magnetic Properties of Fe2SiO4 from 4°K to 300°K
Authors: Kündig Walter , Cape J. A. , Lindquist R. H. , Constabaris G.
Published: January 2005

Mössbauer spectra of 57Fe in Fe2SiO4, which has iron atoms in two distinct crystallographic sites, have been obtained from 9°K to 300°K, a temperature range in which two magnetic transitions occur as indicated by magnetic susceptibility measurements. Above the first transition temperature, 66°K, the spectra consist of a pure quadrupole split line. Below this temperature Zeeman splitting is observed, resulting in composite spectra attributed to the two different iron sites. Magnetization curves indicate the presence of weak ferromagnetism between 66°K and the second transition temperature, 20°K. Below the second transition temperature Fe2SiO4 is an ideal antiferromagnet. The hyperfine spectra were analyzed by numerical solution of the complete interaction Hamiltonian. From this analysis values of the magnetic fields, the electric field gradients, and their relative orientations are obtained. These results are compared with the spin assignments that have been made on the basis of neutron diffraction studies.
Ferromagnetic Resonance of Single Crystals of CdCr2S4 and CdCr2Se4
Authors: Berger S. B. , Pinch H. L.
Published: January 2005

The ferromagnetic resonance of single crystals of CdCr2S4 and CdCrSe4 has been investigated as a function of temperature at 9.49 and 24.24 GHz. The CdCr2S4 crystals were grown by vapor transport, and the CdCr2Se4 crystals were grown from CdCl2 flux. The magnetocrystalline anisotropy and linewidth were found to be dependent on sample. The K1 at 4.4°K varied between 3.8×103 and 4.4×104 erg/cm3 for CdCr2S4 and 2.2×103 and 1.8×104 erg/cm3 for CdCr2Se4. These values are in good agreement with those based on a calculation using the single-ion model of anisotropy. The linewidth of the more anisotropic samples was found to be orientation-dependent and broad compared to the less anisotropic samples. The narrowest linewidth observed at 4.4°K was 37 Oe. This value is higher than expected for these materials and may be caused by crystalline imperfections. It is suggested that the observed variation of properties with sample may be due to small concentrations of divalent chromium.
Magnetic Properties of GdCl3 from Gd3+ Pair Measurements in LaCl3 and EuCl3
Authors: Birgeneau R. J. , Hutchings M. T. , Wolf W. P.
Published: January 2005

Previous EPR measurements on Gd3+ pairs in LaCl3 have shown that the interactions between nearest and next-nearest neighbors are accurately described by isotropic bilinear exchange and magnetic dipole coupling, and they indicated that the ferromagnetic ordering of GdCl3 at 2.2°K is due to dominant next-nearest neighbor exchange. Similar measurements have now been made using EuCl3 as the host lattice. The results are similar to those in LaCl3, and since the lattice spacing in EuCl3 is very close to that of GdCl3, it is now possible to use the interaction constants measured for the Gd3+ pairs to make quantitative predictions of magnetic bulk properties of GdCl3. Excellent agreement is found for the high-temperature susceptibility; for the specific heat, there is a small discrepancy. The measured interaction constants are close to one of a set of values recently used by Marquard to predict some highly anomalous spin-wave spectra for GdCl3.
Ferromagnetic Resonance and Other Properties of Cadmium Chromium Selenide
Authors: LeCraw R. C. , Von Philipsborn H. , Sturge M. D.
Published: January 2005

Magnetic and electrical measurements are reported on single crystals of CdCr2Se4. The measurements include ferromagnetic resonance linewidth and magnetic moment vs temperature, magnetic anisotropy constant K1 and g-factor at 4.2°K, and the sign of the Seebeck coefficient at 300°K. A theoretical calculation of K1 at 4.2°K is also presented.
High-Resolution Specific-Heat Measurements on Dysprosium Aluminum Garnet
Authors: Keen B. E. , Landau D. P. , Wolf W. P.
Published: January 2005

Measurements of the specific heat have been made on three samples of dysprosium aluminum garnet in the critical point region of 2.5°K, using large optical-quality single crystals and temperature steps down to 50 μdeg. The results for all three samples were very similar but they could not be fitted unambiguously to any of the presently proposed singular functions. In all cases, rounded maxima 2 to 3 mdeg wide were found, with peak values between 4.2 and 5.1R. Below these maxima, the results could be fitted to simple laws of the form C=A_ln | T−TN− | +B_, but above the maxima a logarithmic form could only be fitted by choosing TN+ more than 5×10−3 °K higher than TN−. Even then the agreement was not very good, and an apparently better fit could be obtained using the law of the form C=A′(T−TN)−α+B′ with TN+=TN− and α=0.31±0.02. This value of α would be considerably larger than predicted by any of the present theories. These experiments suggest that small broadening effects present even in apparently homogeneous samples can lead to considerable uncertainties in the analysis of critical-point behavior.
Neutron-Diffraction Studies of Terbium
Authors: Arrott A. , Werner S. A. , Cooper M. J. , Nathans R. , Shirane G.
Published: January 2005

A neutron-diffraction study of antiferromagnetism and the wave-vector-dependent susceptibility of Tb near its Néel temperature shows a susceptibility which can be represented over a range of temperatures by χq−1=χQ−1 + (qz−Q)2/(eq0)2 + (qx2+qy2)q02 with e=2.6 and q0=0.017 (4πb3) and with a χQ which roughly follows the expression [(T−TN)/T1]−4/3, with T1=6°K. There is a more rapid decrease in χq than predicted by the Lorentzian form for large values of (qz−Q) and a less rapid decrease than predicted for large values of qx. The wave vector for which χq is a maximum shifts further away from ferromagnetism the higher the temperature.
Surface of Magnetization, Field, and Temperature for Nickel near Its Curie Temperature
Authors: Noakes J. E. , Arrott A.
Published: January 2005

A nickel single-crystal sphere is placed in a solenoid with a 100 axis along the solenoid axis. The solenoid is placed in an electromagnet with the field at right angles to the solenoid axis and along another 100 axis of the nickel crystal. A detector coil is placed with its axis parallel to the solenoid in order to measure the change in the component of the magnetization of the sphere along the solenoid when the 20-G field in the solenoid is reversed. This component is measured as a function of the transverse field of the electromagnet to obtain the effective susceptibility in applied fields from 20 to 5000 G. A sufficient time is allowed between each change of the electromagnet field for the large magnetocaloric effects to decay and the sample to return to the furnace temperature. The temperature dependence of the spontaneous magnetization in zero internal field and of the initial rate of increase with field of magnetization above the spontaneous magnetization below the Curie temperature, the temperature dependence of the initial susceptibility above the Curie temperature, and the field dependence of the magnetization at the Curie temperature and at a number of nearby temperatures are obtained. The single-crystal results show sharper indications of the spontaneous magnetization than do identical measurements on polycrystalline Ni. The difference is attributed to Dzialoshinski interactions at grain boundaries. Analytic representations of some of the data are given.
On the Possible Phase Transition for Two-Dimensional Heisenberg Models
Authors: Stanley H. E. , Kaplan T. A.
Published: January 2005

Recently the authors presented evidence suggesting the presence of a phase transition for two-dimensional Heisenberg models with nearest-neighbor ferromagnetic interactions and S>½. Here we further analyze the first six coefficients of the high-temperature series for the zero-field susceptibility, and incorporate the results of recent calculations beyond sixth order into the arguments for a phase transition. It is found that the higher-order coefficients support the previous suggestion concerning the existence of a phase transition for S>½, and are consistent with a zero critical temperature for the particular case S=½. Finally, two preliminary calculations on the nature of the low-temperature phase are described. The first of these, due to Dyson, is an intuitive generalization of spin wave theory. The other is an approximate calculation for the rectangular net within the classical Heisenberg model: Considering this net to consist of linear chains, the intrachain interactions are treated exactly, while the interchain interactions are treated via a molecular field approximation. Both of these calculations support the original suggestion of a phase transition for two-dimensional Heisenberg models.
Dependence of Critical Properties of Heisenberg Magnets upon Spin and Lattice
Authors: Stanley H. E. , Kaplan T. A.
Published: January 2005

High-temperature expansion methods have recently been used to predict the form of the divergence of the zero-field static susceptibility χ at the critical temperature Tc. These studies have suggested that χ∼A (T−Tc)−γ, with γ=43 independent of both lattice structure and spin quantum number S. Here we argue that the proposal γ=43 for all S is unjustified; we find a slow but nevertheless clear variation of γ with S. We further point out that there exists at least one physically interesting lattice—a normal cubic spinel with nearest-neighbor ferromagnetic B—B interactions—for which the theoretical evidence indicates that if the power-law form of divergence is correct, γ may differ from43 by as much as 50%.
Magnetic Critical-Point Behavior of CrO2
Authors: Kouvel J. S. , Rodbell D. S.
Published: January 2005

The magnetization σ of the ferromagnetic compound CrO2 was measured as a function of field H and temperature T near the Curie point Tc. From isotherms of σ2 vs H/σ, the initial susceptibility χ0 above Tc was obtained, which when tested against the relationship χ0−1 ∝ (T−Tc)γ gives a constant γ of 1.63±0.02 from just above Tc (386.5°K) up to about 1.15 Tc. This γ value contrasts with the values near43 recently computed for the Heisenberg model and later found experimentally in various ferromagnetic metals and compounds. At higher temperatures the effective γ decreases rapidly towards unity. Up to the highest field used (25 kOe), the critical isotherm obeys the relationship σ∝H1/δ with δ=5.75±0.05, which differs markedly from the theoretical δ values of 3 (molecular field) and 5.2 (3-dimensional Ising) and from various experimental values. Gradual departure from this relationship below 1.5 kOe is attributed to the magnetocrystalline anisotropy that persists at Tc. Furthermore, we find that all the σ(H, T) data for CrO2 just above Tc can be represented by a universal function of the form, σ/σ′=f(H/H′), in which σ′ ∝ (T−Tc)λ and H′ ∝ (T−Tc)λ+γ, where λ=0.34. This ``corresponding states'' representation is the exact magnetic analog of an equation of state recently proposed by Widom for a fluid near its critical point.
First-Order Phase Transition in a Rigorously Solvable Magnetic System
Authors: Blume M. , Watson R. E.
Published: January 2005

We have considered the paramagnetic—ferromagnetic transition for the Ising system with ``infinite range'' interactions (i.e., each spin interacts equally with all other spins) and in the presence of a single-ion anisotropy term: H=−2jΣ lim i>i SizSjz+ΔΣ lim i Siz2−gμHΣ lim iSiz. Kittel and Shore1 have shown that this system (in the absence of the term in Δ) is exactly soluble, and leads rigourously, in the limit of an infinite number of particles, to the equations of the molecular-field approximation, and to a second-order phase transition. The single-ion term can cause the transition to become first order2,3 in that there is a discontinuity in the magnetization as a function of temperature. We have solved for the relevant thermodynamic parameters as a function of temperature for the case of ions with spin one. The development of the first-order transition as a function of the number of particles will be discussed. This work will be submitted for publication in the Physical Review.
Behavior of Mössbauer f and Thermal Shift of 57Fe in Nickel near the Curie Temperature
Authors: Howard D. G. , Dash J. G.
Published: January 2005

Using an enriched black absorber, measurements of the recoilless Mössbauer fraction for 57Fe in nickel at the Curie temperature have yielded f=56%±2%. Further measurements above and below this temperature indicate that no abrupt change greater than the error quoted above occurs. These measurements are consistent with a change in the Debye temperature no larger than 14°K, and such a change is not sufficient to explain an observable shift in the center of the Mössbauer pattern. Our data is consistent with a shift of about 0.04 mm/sec, the pattern moving in the opposite direction from that reported for 57Fe in iron. These measurements seem to support the suggestion of Alexander and Treves that the sudden thermal shift at the Curie temperature results from a shift of the absolute position of the Fermi level.
Effect of Ordering on Rolling-Induced Magnetic Anisotropy in FeCo-2V
Authors: English A. T. , Chin G. Y. , Von Neida A. R.
Published: January 2005

Rolling-induced magnetic anisotropy has been measured on polycrystalline FeCo-2V as a function of initial degree of order. The latter was varied by isothermal heat treatment at 450°C after quenching from 800°C (disordered). Torque measurements show that a uniaxial anisotropy, with the easy axis in the transverse direction, is developed in all samples by cold-rolling. Anisotropy energies up to 1.25×105 erg/cm3 are obtained following 20% reduction in thickness. The results appear to be explainable only in terms of the slip-induced directional order theory of Chikazumi—Suzuki—Iwata, which has been extended recently to B2 (CsCl) alloys. The largest anisotropies are obtained in material initially quenched from above the order—disorder temperature. From this it appears that short-range order gives rise to larger induced anisotropy than long-range order.
Thermal Expansion of ZnS from 2° to 317°K
Authors: Reeber R. R. , Powell G. W.
Published: January 2005

Thermal expansion of the wurtzite phase of ZnS was measured using a back-reflection Debye-Scherrer x-ray camera. Experimental results indicate that retrograde behavior is exhibited both perpendicular and parallel to the c axis at 60°±5°K. The molar volume decreases approximately 0.30% from 300° to 60°K and then increases slightly upon further cooling. Lattice parameters obtained at 25°C are a0=3.8226±0.0003 Å and c0=6.2605±0.0015 Å.