bluuebunny/crossref_metadata_2025 huggingface dataset:
Crystallographic Angle and Temperature Dependence of Giant-Anisotropy Ferrimagnetic-Resonance Linewidth
Authors: Tittmann B. , Sparks M.
Published: February 2004

Ferrimagnetic resonance linewidths were measured as a function of angle θ from a [100] axis in a (110) plane for an yttrium iron garnet sample doped with 0.1 at.%Ho. Near the [100] and [110] directions the linewidth has a single peak at 4.2°K which becomes a double peak at 27° and 77°K, as predicted by Sparks.
Conduction-Electron Polarization in Rare Earth-Platinum Alloys
Authors: Vijayaraghavan R. , Rao V. Udaya Shankar , Malik S. K. , Marathe V. R.
Published: February 2004

Nuclear magnetic resonance studies of 195Pt in the rare-earth-platinum intermetallic compounds of the composition RPt2 and RPt5 (R≡La, Ce, Pr, and Nd) have been made in the temperature range 80° to 300°K. They have the cubic (MgCu2 type) and the hexagonal (CaCu5 type) Laves structures, respectively. In RPt5 componuds, there are two inequivalent platinum sites and correspondingly, two 195Pt resonances are observed in each compound. The platinum Knight shifts which are positive, are strongly temperature dependent in all but the lanthanum compounds. The magnetic susceptibilities have been measured in the same temperature range. The Knight shift (K) versus susceptibility curves are straight lines, intersecting the K axis at K0, corresponding to the lanthanum compounds.

The EPR of Gd3+ in GdPt2 has been observed and a g value of 1.8735 has been obtained. The paramagnetic Curie temperatures are positive for RPt2 compounds and negative for the others. The results have been discussed in terms of the RKKY theory and the Anderson-Clogston mixing. Values of J(0) have been obtained for the two sets of intermetallic compounds.
Temperature Dependence of the Eu3+ Spin 〈S(T)〉 in EuP
Authors: Jones E. D.
Published: February 2004

The temperature dependence of the Eu3+ spin 〈S(T)〉 in the NaCl-type intermetallic compound EuP has been studied by the observation of the phosphorus nuclear magnetic resonance (NMR) between 100° and 600°K. The phosphorus Knight shift consists of two contributions: (1) a temperature-independent term K0 equal to the Knight shift in the nonmagnetic isomorph LaP and (2) a temperature-dependent term K(T), proportional to the Eu3+ spin 〈S(T)〉. The temperature dependence of the Eu3+ spin 〈S(T)〉 was calculated for a Eu3+ ion in an octahedral crystal field and an exchange interaction of the form 2βHe xS(He x=λ〈S〉). Good agreement between the calculated and observed temperature dependence of the Knight shift was obtained for E1 (the energy separation between the J=0 and J=1 states) and λ in the range E1/k=525°K, λβ/k=0°K to E1/k=475°K, λβ/k=5°K. An analysis of the Knight shifts showed that these data are relatively insensitive to the effects of the crystal field interaction. Using the uniform-conduction electron spin-polarization model for the Knight shift, the resulting s-f exchange energy for EuP was calculated to be Jsf≃−0.37 eV, in good agreement with the other rare-earth phosphides.
Magnetic Behavior of Cobalt and of Nickel in Compounds with Rare Earth Metals
Authors: Lemaire R. , Paccard D. , Pauthenet R. , Schweizer J.
Published: February 2004

We discuss the value of the intrinsic magnetic moment of cobalt in intermetallic compounds of the formula RxCov, where R is a rare earth element or yttrium. The experimental values of this moment are determined from the results of neutron-diffraction studies and those of measurements of the absolute saturation magnetization on certain compounds: R2Co17, RCo5, R2Co7, RCo3, and RCo2. The electronic configuration of cobalt is greatly modified, both by the addition of the conduction electrons of the rare earth atoms or yttrium and by the magnetic interactions resulting from these atoms. This behavior of cobalt permits the explanation of certain apparent anomalies in the properties of the alloys, viz., the differences between the Curie temperatures of the compounds of the same series are too large to be attributable to the interactions between the rare earths along; the magnetizations and Curie temperatures of the alloys with cerium are smaller than those of the corresponding compounds with yttrium; and certain compounds RCo2 present a ferrimagnetic-paramagnetic first-order transition.

The variation of the Curie temperatures of the compounds RxNiv, as a function of rare earth percentage, can be explained by the behavior of the moment of nickel analogous to that of cobalt.
ESR in Gadolinium-Group V Compounds
Authors: Allenson M. B. , Taylor K. N. R.
Published: February 2004

Exchange narrowed paramagnetic resonance lines have been observed in GdP, GdAs, GdSb, and GdBi, at 9.3 GHz over the temperature range 17°–400°K. The exchange parameter derived from the linewidth by the theory of Anderson and Weiss has been expressed as a combination of nearest-neighbour superexchange and a temperature-dependent term. This latter term shows good agreement with the theory of Karpenko and Berdyshev and indicates that the predominant exchange, over the temperature range examined, is an indirect interaction via the impurity semiconductor current carriers. In all the compounds the impurity level excitation energy is found to be about 10−2 eV.
Magnetic Properties of the Intermetallic Compounds DyxY1−xFe2
Authors: Piercy A. R. , Taylor K. N. R.
Published: February 2004

Measurements of the bulk magnetization have been made between 4.2°K and the Curie points for eleven compounds in the series DyxY1−xFe2. The Curie temperatures increase continuously through the series. The compounds near to x=0.3–0.4 exhibit temperature compensation points, and the saturation moments show that the equilibrium concentration occurs at x≃0.28. In addition, the coercivity increases rapidly in this region and has a value in excess of 10 kOe at x=0.35, T=4.2°K.

If both the Fe and Dy moments remain constant or vary linearly through the series, the equilibrium concentration would occur at x≃0.35. Consideration of the results of these and other similar compounds indicates that the Fe moment varies nonlinearly with x. It is suggested that the Fe moment is approximately 1.4 μB for x<⅓ and increases gradually for larger x to about 2 μB. It is further proposed that this behavior may be explained by the presence of a shallow minimum in the density-of-states curve, sufficient to stabilize the moment for x<⅓, but such that the increased coupling allows the moment to increase for higher Dy concentrations.

The Fe moments in other RE Fe2 compounds are correlated with this model, taking the Curie temperatures as a measure of the exchange energies.
Spin-Density Wave in Chromium and its Alloys
Authors: Motizuki K. , Shibatani A. , Nagamiya T.
Published: February 2004

Sinusoidal, helical, and antiferromagnetic spin-density waves are derived by the self-consistent Hartree-Fock method on the assumption of a simplified band structure consisting of octahedral electron- and hole-Fermi surfaces, and it is found that the sinusoidal spin-density wave has the lowest energy. To consider alloys, the sizes of the electron- and hole-Fermi surfaces are varied. A possible flow of electrons from other bands into these electron and hole bands in the process of the formation of the sinusoidal and antiferro-magnetic spin-density wave is considered. Then, it is found that the wave number of the spin-density wave jumps and approaches 1, i.e., comes closer to the antiferromagnetic wave, at a certain alloy concentration on the Cr–Mn side. The exact antiferromagnetism appears only when the electron- and hole-Fermi surfaces have the same size.
Local-Moment-Conduction-Electron Exchange Coupling and RKKY Spin Densities in Metals
Authors: Watson R. E. , Freeman A. J.
Published: February 2004

The local-moment-conduction-electron exchange coupling J(k′k), important for all problems involving so-called s-d(s-f) exchange, has been assumed always to be either a constant or at best, a function only of Q(= |k′−k|). In this paper we extend our earlier work assuming J(Q) behavior1 and examine, in some detail, the actual k′, k dependence of the exchange; these results are then applied to the spin densities obtained within lowest order Ruderman-Kittel-Kasuya-Yosida (RKKY) theory. The J (k′, k) were obtained using realistic local moment wave functions (Hartree-Fock 3d and 4f orbitals for Fe and Gd) and conduction electrons. Results, for Fe and Gd local moments, are reported and spin densities are compared for a range of assumed Fermi momentum (kF) values (0.3<kF<1.0). The spin density at a nuclear site in a metal differs from the bulk density behavior due to the penetration of the s shells in an ion core by the Bloch electrons and our calculations indicate this difference to be severe (a purely Q dependent correction2 for this core penetration is found to be inadequate). Our results suggest that spin densities sampled at nuclear sites by NMR and Mössbauer measurements need not be correlated with the bulk behavior, determined by neutron diffraction.
Concentration Dependence of the Spin-Density-Wave Periodicity in Antiferromagnetic Chromium Alloys
Authors: Falicov L. M. , Penn David R.
Published: February 2004

The dependence of the periodicity of the spin-density waves in antiferromagnetic metals upon the number of conduction electrons is studied theoretically. It is seen that the commensurate structure, i.e., the structure for which the wavevector q equals half a reciprocal lattice vector G, is the state of minimum energy over a finite range of electron densities. The effect, which has been observed experimentally, is essentially due to the presence of two energy gaps which coalesce into one in the commensurate state. The theory gives quantitative relationships which are in good agreement with the experimentally determined values for the chromium-rich Cr–Mn and Cr–Re alloys.
Indirect Exchange in Many-Valley Semiconductors
Authors: Cullen James R. , Callen Earl , Luther Alan H.
Published: February 2004

The effect of intervalley transitions on the indirect exchange interaction in magnetic semiconductors is considered. Using second-order perturbation theory, we derive an expression for the spin-spin coupling energy in terms of the susceptibility χ(R12) for one valley. When the spins are located on lattice sites, and a local s-f exchange interaction is used, the coupling energy reduces to a especially simple form. Calculations are based on a two-valley model, for simplicity. The resulting coupling is used to study the paramagnetic Curie temperature and ferromagnetic spin-wave spectrum for a lattice of spins. The latter quantity is shown to be especially sensitive to the ratio of Fermi wavenumber to the separation of valley minima. The paramagnetic Curie temperature θ is shown to be independent of the direction and of the valley separation. Using the number of valleys as a parameter, we have fit the variation of θ with concentration in EuxGd1−xSe and EuxGd1−xTe. In this way we obtain four for the valley number in Se and sixteen for the case of Te.
Analysis of the Magnetic Properties of Dilute Fe and Mn in Cu Alloys
Authors: Housley R. M.
Published: February 2004

We analyze available magnetic data in these alloys on the basis of expectations derived from the s-d exchange model. The experimental data are consistent with the general expectation of a singlet ground state. This allows a unified interpretation of Mossbauer and NMR data on very dilute Fe in Cu alloys and qualitatively explains previously puzzling features of the Mössbauer data in more concentrated alloys. Nuclear orientation measurements on Cu–Mn alloys are reinterpreted to suggest that a singlet state may form in that system below ∼0.1°K.
Spin-Wave Theory and CuK2Cl4·2H2O
Authors: Loly P. D.
Published: February 2004

The magnetization and specific heat of this salt are analyzed using self-consistently renormalized spinwave theory including second-neighbor effects. Unlike previous work, we embody in our calculations the fact that the Curie temperature is 0.88°K and the relation of exchange constants to TC afforded by the results of high-temperature expansions. If the magnetisation data is plausibly modified, we find good agreement up to 0.85TC for that property and tolerable agreement for the specific heat to the same temperature. The required sums over the Brillouin zone have been evaluated by a novel method.
Neutron Scattering from Paramagnetic Chromium Halides
Authors: Rao L. Madhav , Murthy N. S. Satya , Venkataraman G. , Iyengar P. K.
Published: February 2004

Energy distribution of neutrons scattered from chromium tribromide and chromium trifluoride in their paramagnetic phase have been measured using the time-of-flight technique. Chromium tribromide is an ionic ferromagnet with a Curie temperature of 37°K, while chromium trifluoride is an ionic antiferromagnet with a Néel temperature of 80°K. At large momentum transfer the second moment of the energy distribution is directly related to the exchange integral J, according to de Gennes. de Gennes' prescription is strictly valid for a system of localized magnetic moments which arise purely out of the spins of the unpaired electrons. Furthermore, the method is eminently suitable for those substances characterized by only one dominant exchange integral. Both CrBr3 and CrF3 satisfy these conditions. Measurements have been made at suitable momentum transfer values and the exchange integrals are extracted from these measurements. J = 4.66°±0.9°K for CrBr3 and J = 7.2°±1.2°K for CrF3.
Neutron Scattering from Magnetite below 119°K
Authors: Samuelsen E. J. , Bleeker E. J. , Dobrzynski L. , Riste T.
Published: February 2004

A neutron-scattering experiment to look for spin-wave excitation-energy changes of magnetite at the transition point 119°K showed no such change. During this work we discovered, however, that the low-temperature structure gives rise to weak extra neutron-diffraction lines that can be indexed as (h, k, l±½) in cubic indices. From the observed neutron polarization sensitivity of the intensities and the increasing structure factors with increasing sinθ/λ, we conclude that the extra reflections are not directly due to magnetic ordering (ferrimagnetic spirals or Fe2+–Fe3+ ordering on the octahedral sites). Rather they are caused by a lowering of the crystal symmetry.
Excitations of Cobalt Fluoride near the Néel Temperature
Authors: Martel P. , Cowley R. A. , Stevenson R. W. H.
Published: February 2004

The temperature dependence of the branch of magnetic excitations with lowest frequency in cobalt fluoride has been measured by inelastic scattering of slow neutrons. The triple-axis crystal spectrometer at the C5 facility of NRU was used throughout in its `constant-Q' mode of operation. Measurements of the dispersion relation in the a and c directions were made at 11 different constant temperatures between 4.5° and 80°K, and at 11 different momentum transfers around the (001) reciprocal lattice point. As the temperature was increased from 4.5°K, the frequencies of the excitations decreased and the widths of the neutron groups increased. The excitations were still observed above TN, although they then had very short lifetimes, and on a further increase of the temperature the scattering gradually approached that expected from a paramagnet. Some typical frequencies (units 1012 Hz) for momentum transfer (0, 0, 1.4)2π/c at temperatures of 0.11, 0.77, 0.95, 1.09, 1.39, 2.1 TN are: 1.88±0.02, 1.68±0.03, 1.41±0.05, 1.0±0.1, 0.75±0.3, 0±0.4, while the corresponding half-widths of the observed neutron groups are: 0.16±0.05, 0.29±0.05, 0.41±0.08, 0.52±0.1, 0.75±0.2, 1.0±0.2, respectively.
Neutron-Scattering Determination of Spin-Wave Dispersion Relations in FeF2
Authors: Guggenheim H. J. , Hutchings M. T. , Rainford B. D.
Published: February 2004

Spin-wave dispersion in antiferromagnetic FeF2 has been investigated by inelastic neutron scattering at 4.2°K. Incident neutrons of 122 cm−1 energy were used to excite spin waves in a {010} plane, and the energies of the scattered neutrons determined by time-of-flight techniques. The single mode observed has a rather flat dispersion lying between 53 and 79 cm−1. The measured energies were fitted to a theoretical expression to determine values for the single ion anisotropy constant D, (Hsi=−DSiz2), and the exchange interactions between the ions Jl, (Hex12=J lS1·S2). We find D = 6.46(+0.29, −0.10) cm−1, J1 (coupling neighboring ions along the c axis) = −0.048 (±0.060) cm−1, J2 (coupling neighboring ions at the corner and body center of the cell) = +3.64(±0.10) cm−1, and J3 (coupling neighboring ions along the a axis) = +0.194(±0.060) cm−1.
Magnetic Study of the Manganous Sulfates MnSO4 and MnSO4·H2O
Authors: Allain Y. , Krebs J. P. , de Gunzbourg J.
Published: February 2004

The magnetization measurements up to 420 kOe made on antiferromagnetic powder specimens of MnSO4 and MnSO4·H2O between 1.6° and 70°K have revealed saturation fields of 250 and 320 kOe, respectively. The saturation value of the magnetization is in good agreement with the theoretical value for Mn2+(5 μB). The moment before saturation does not vary linearly with the applied field. This fact could be explained by spin-wave theory or by a biquadratic term in the exchange energy. The anisotropy and the exchange fields have also been estimated from our experiments. The susceptibility versus T plot has given the Néel temperature TN and the effective moment which corresponds to the S state of Mn2+.

Specific heat measurements have also been accomplished on MnSO4. They confirm our value for TN (11.5°K) and show three other peaks below the Néel temperature, two of which could correspond to the transitions theoretically forseen for this magnetic structure (cycloidal cone spiral) by Solyom.
Shape Dependence of the Specific Heat of Magnetic Systems with Long-Range Interactions
Authors: Levy Peter M. , Landau David P.
Published: February 2004

The shape dependence of the free energy in an applied field and thereby the specific heat, has been determined for magnetic systems with long-range interactions. For ellipsoidal bodies the specific heat at constant applied field, CH0, can be related to the shape-independent specific heat at constant internal field, CHi, by; CHi(Hi, T)=CH0(Hi, T)+[DT(∂M/∂T)H02]/[1−D(∂M/∂H0)T]where D is the classical demagnitization factor. Detailed experimental knowledge of M(H0, T) and CH0 (H0, T) is required in order to find the derivatives accurately and to determine CH0 (Hi, T). In dysprosium aluminum garnet (DAG) dipolar interactions account for about 70% of the energy and therefore shape effects should be important. By using new and available magnetothermal data on DAG we have calculated CHi (Hi, T) from the CH0 (H0, T) measured for two different shapes; we find that the CHi agree to within experimental error. We also find that the maximum specific heat changes with shape by as much as 40% and the temperature corresponding to this maximum can vary drastically. We conclude that it is important to reduce experimental results to the specific heat for a long thin needle aligned parallel to H0; for this shape CH0 and CHi are identical.
Magnetic Properties of Hexagonal RbNiF3 with Substituted Ions
Authors: McGuire T. R. , Shafer M. W.
Published: February 2004

Transparent RbNiF3 is analyzed in terms of ferrimagnetic spin ordering. It has the hexagonal BaTiO3 structure and the magnetic ion (Ni2+) is located in the center of fluoride octahedra on two nonequivalent sites. We have replaced nickel in the hexagonal structure with both nonmagnetic and magnetic ions [Ca, Cd, Mg, Co, and Mn] to further elucidate the magnetic structure. In the substitution of Mg for Ni there is a small preference of a sites and the solid solution retains ferrimagnietc order up to RbNi1/3Mg2/3F3. Calcium substituted for nickel has a strong preference for a-sites probably because it is larger and prefers a site with higher local cubic symmetry. Because of the a-site preference the moment increases from 21 emu/g for pure RbNiF3 to 27 emu/g for RbNi3/4Ca1/4F3. At ⅓ Ca, magnetic ordering has disappeared, consistent with the absence of magnetic ions on a sites. The only ion which completely replaced rubidium while retaining the hexagonal structure is Tl+. TlNiF3 is also ferrimagnetic with TC = 129°K and σ = 13 emu/g. Alhough our results are consistent with a ferrimagnetic model, recent neutron-diffraction results [S. J. Pickart and H. A. Alperin, J. Appl. Phys. 39, 1332 (1968).] indicate the possibility of a canted arrangement.
The Heat Capacity of Cu(NO3)2·2.5H2O at Low Temperatures
Authors: Friedberg S. A. , Raquet C. A.
Published: February 2004

The heat capacity CP of powdered Cu(NO3)2·2.5H2O has been measured between 0.5° and 4.2°K. In zero applied field, CP exhibits a Schottky anomaly having its maximum value of 0.51R at 1.82°K. The data are quantitatively described by assuming that Cu2+ ions exist in this salt in isolated pairs (binary clusters) coupled by isotropic antiferromagnetic exchange with J/k = −5.18°K. The same model was previously found to give a good fit of the observed magnetic susceptibility. The present results, however, clearly exclude the possibility that Cu2+ ions in this material are coupled in extended linear chains. CP measured in an applied field of 8.7 kG was found to be as predicted by the pair model. As a result of the isotropy of the pair interaction and the small single-triplet separation, it has been possible to cool this salt by adiabatic magnetization of the powder in relatively small fields.
OH Groups and Fe Valence in Hydrothermal and Flux-Grown YIG
Authors: Wood D. L. , Kolb E. D. , Remeika J. P.
Published: February 2004

In the transparent region of Yttrium Iron Garnet (YIG) in the infrared, it has been shown that Fe2+ and Fe4+ both give broad optical absorption accompanied by electrical conductivity. The conductivity is n-type for Fe2+ ions and p-type for Fe4+ ions, both involving a hopping mechanism. Heat treatment of YIG in a reducing atmosphere produces Fe2+ at rather low temperatures, and in hydrogen gas the equilibrium is controlled by temperature rather than the diffusion rate. At the same time the Fe2+ is formed, OH groups appear in the structure, and their optical absorption near 3 μ affords another way of monitoring the reversible changes in iron valence for this treatment.

Hydrothermal YIG is formed with OH groups already present, but with all Fe ions trivalent. The amount of OH present in crystals grown from KOH is much less than for crystals grown from NaOH, and the primary mechanism for admitting the proton into the structure involves substitution of an alkali or a vacancy for the Fe3+ ion. Removal of the OH by heat treatment in oxygen produces Fe4+ ion, and p-type conductivity. Fourteen distinct lines in the 3 μ region are seen in the infrared spectra of crystals containing protons introduced in various ways, including a small amount even in flux-grown crystals. These lines arise from OH groups in different environments in the lattice.
Absorption Spectrum of MnCO3
Authors: Stevenson Richard
Published: February 2004

The absorption spectrum of MnCO3 at 4.2°K in the 4060 Å region is shown. The intense absorptions associated with the 6Γ1→4Γ1, 4Γ3 transitions show no splitting in an external magnetic field and appear to be magnon sidebands. Groups of weak subsidiary lines are shown to arise from Raman-active vibrations of the carbonate molecule. In each group, the subsidiary lines are spaced at odd multiples of the magnon excitation energies, and these lines may be appearing because of multimagnon excitation.
Role of Exciton Dispersion and Exciton-Magnon Interactions on the Shape of Magnon Sidebands in Stressed MnF2
Authors: Misetich A. , Dietz R. E.
Published: February 2004

We have previously1 studied the effect of stress on 4T1 excitons E1 and E2 in the optical absorption spectra of MnF2 and magnon side bands of them. The effect of stress on the zone-center excitons (k=0) was understood as well as some features of the magnon side bands. However the shape of the side bands, the peak positions and the relative intensities remained unexplained within a single exciton theory, as well as changes in the side bands with stress. This disagreement may be due to exciton dispersion or exciton-magnon interaction since in absorption an exciton and a magnon are created simultaneously and they may interact. However a magnon side band in the emission spectra corresponds to the simultaneous creation of a magnon and annihilation of an exciton and they do not interact: any anomaly in this case will be due to exciton dispersion. We have analyzed both, emission and absorption spectra under (100) stress, and the conclusion is that the main effect is the exciton-magnon interaction. Any exciton dispersion must be smaller than 1 cm−1. Using a simple model for exciton magnon interaction we are able to explain the observed σ side bands in the absorption spectra. The main contribution derives from interaction between second neighbors in second-order perturbation.
A New Interpretation of the Anomalous Magnetic and Optical Behavior of Copper Acetate Monohydrate
Authors: Bose A. , Bagchi R. N. , Sengupta P.
Published: February 2004

Interpretation of the extensive magnetic and optical measurements of copper acetate monohydrate on the basis of a C4v symmetry of the complex by different workers are, to some extent, incomplete and often lead to contradictions. Starting with the electronic states of each half of the complex, assumed to have a C2v symmetry as shown by ESR. data, we find that the bonding between the two halves is a mixture of σ- and δ-type as against a pure σ or δ bonding for a C4v symmetry. Operation of H=Hex+HLS+βH(L+2S) on the valence bond states of the whole complex by usual perturbation technique then gives us the expressions for the singlet-triplet separation (J), the spectroscopic splitting factors and the magnetic susceptibilities. It is found that the last two quantities and the optical absorption data can be correlated to a good extent and the ligand field parameters obtained in the process yield a value of − 138 cm−1 for J, which is fair enough under the approximations employed. In this calculation we have found it necessary to consider the dimeric band at 28 000 cm−1 to be a Laporte forbidden type under a strong anisotropic ligand field.
Spin-Wave Sidebands in Manganese Fluoride
Authors: Tanabe Yukito , Gondaira Ken Ichiro
Published: February 2004

It is pointed out that the spin-wave sideband of MnF2 has some peculiar features. If the ion is excited optically, the total spin of the ion and the exchange coupling with the neighboring ions will be changed. A general formula is developed to take this effect into account and to calculate the line shape. Possible approximations are discussed to make the actual calculation feasible.
Quantitative Study of the Magnetization Ripple in Ferromagnetic Ni–Fe Alloy Films
Authors: Suzuki T. , Wilts C. H.
Published: February 2004

Magnetization ripple in Ni–Fe thin films has been investigated by several workers, but no systematic study of the ripple structure over a significant range of alloy composition, substrate deposition temperature, and measurement temperature has been published. The present report describes the results of such a study. Room-temperature measurements of the ripple amplitude θ0 and wavelength λ have been measured as a function of alloy composition from 50% Ni to 90% Ni for films deposited at room temperature. In addition, θ0 and λ have been measured from 25° to 450°C for 76% Ni films evaporated at temperatures from −180° to 400°C. For all data, θ0 and λ are in order of magnitude agreement with Hoffmann's calculations (10−2 rad and 1 μ, respectively). As a function of alloy composition, the ripple amplitude exhibits a minimum in the vicinity of 73% Ni. The wavelength is independent of alloy composition. For 76% Ni films deposited at −180°C, the ripple wavelength is independent of measuring temperature. The amplitude θ0 decreases to zero at about 330°C and does not reappear at higher temperatures, contrary to the reappearance reported by others. For higher deposition temperatures, the scatter in the data is much higher than for −180°C and ripple could be observed as high as 450°C.

The ripple amplitude increases with substrate deposition temperature, as expected from the increase in grain size. Two points concerning the present data should be emphasized. (1) The results are in reasonable agreement with Hoffmann's theory. (2) The data constitute a systematic description of magnetization ripple in Ni–Fe films.
The Transverse Susceptibility of Single-Crystal Ferromagnetic Films
Authors: Prutton M.
Published: February 2004

A single domain theory is outlined for the transverse susceptibility χ of magnetic films with both biaxial and uniaxial anisotropies. It is shown how values for the anisotropy constants and the angle between the anisotropies can be obtained from plots of χ vs sample orientation and χ vs applied field. The theory is applied to a magneto-optic method and (100) Ni single crystals and a value of K1=−3.4×104 erg/cc is reported.
Structural Properties and Ferromagnetic Resonance Linewidth in Single-Crystal Nickel Ferrite Films
Authors: Schröder H. , Glauche E.
Published: February 2004

We have prepared single-crystal nickel ferrite films, several microns thick, on cleaved MgO surfaces both by chemical transport and by reactive sputtering. The structures were characterized by x-ray diffraction and by measurements of the static magnetic moment. The resonance field strengths parallel and perpendicular to the (100) plane of the films, and the linewidths were measured. Though the static film properties were in accordance with the corresponding values of bulk material, the resonance quantities varied over a wide range. In comparison with the theoretical values for ideal nickel ferrite films according to the Kittel resonance equation, the measured resonance fields for a smooth film may be explained by an additional quasi-isotropic internal field; a rough or granulated film, also obtained by chemical transport, is best described by a strong internal field (≥1300 Oe) which is anisotropic with regard to parallel and perpendicular film directions. The films prepared by reactive sputtering show some peculiarities. The linewidths of all films are relatively large (700–1700 Oe). We suggest two-magnon scattering for the line broadening, and for the line shape, superimposed magnetostatic and spin-wave modes excited by demagnetization fields.
Susceptibility and Magnetization Ripple in Polycrystalline Magnetic Films
Authors: Leaver K. D.
Published: February 2004

The magnitudes of the magnetic susceptibility components χi and χt of a uniaxial magnetic film, measured parallel to and perpendicular to a hard direction applied field, respectively, are determined by the magnetization-ripple distribution. They can be shown theoretically to be related directly to one another only if the longitudinal magnetostatic interactions in the ripple are negligible. Experimental results are presented to show that they are related over a rather wide range of applied field.
Ripple Relaxation Times in Thin Magnetic Films
Authors: Hoper J. H.
Published: February 2004

Basically two different models have been proposed to characterize the effect of ripple on magnetization reversal. One of them assumes a long ripple relaxation time compared to thin-film switching times, the other short. To determine which model best describes switching phenomena, a small-angle fallback experiment has been devised which detects the change of the ripple reaction torque due to ripple rearrangements. From these data, a ripple relaxation time of 1.1±0.2 nsec was found which was relatively independent of angular dispersion. A theoretical calculation was made similar to that by K. J. Harte except loss was included. Using typical thin-film values, a 1.3 nsec ripple relaxation time was obtained which is in good agreement with experimental data. Therefore, except for the initial high-speed rotational process, the fast-relaxation model should best describe noncoherent rotational-switching behavior.
Epitaxial Growth of Metal Oxides
Authors: Hanak J. J. , Johnson D.
Published: February 2004

Results of three methods of growing epitaxial layers of metal oxides and ferrites are reported. One of these is a vapor-solid displacement method which involves a partial or a total displacement of the metal ions in a given oxide by other metal ions present in gaseous form as halides. An example of this technique is the formation of MgFe2O4 from Fe3O4 via the reversible reaction MgCl2(gas)+Fe3O4(solid) lim 1000°CMgFe2O4(solid)+FeCl2(gas).Further displacement of iron by magnesium results in the formation of MgO. Single-crystal epitaxial films of MgO have been grown in this manner on single-crystal manganese ferrite and manganese zinc ferrite. The other two methods are variations of chemical transport which were used to grow single-crystal films of manganese ferrite on MgO substrates. One of these involves a close-space transport in which sintered manganese ferrite is used as a starting material and HBr as a transporting gas. In another variation, the oxides MnO and Fe2O3 are separately brominated in a stream of HBr diluted with helium; the deposition of ferrite takes place when water vapor is injected into the resulting gas mixture. By this technique, a wide range of compositions of manganese ferrite can be deposited which have varying magnetic properties and resistivities ranging over five orders of magnitude.
Lorentz Microscopy of Iron Films Epitaxially Deposited onto Lead Telluride Substrates
Authors: Blackburn W. J. S. , Ferrier R. P.
Published: February 2004

Epitaxial iron films in (100) orientation and in the thickness range 300–1200 Å have been prepared by vapor deposition on to heated lead telluride substrates in a vacuum of 10−5 Torr. Calculations of the stray field surface energy densities for 90° and 180° Néel walls in such films have been made and the results are used in the interpretation of some features of the domain structure of the films as revealed by Lorentz microscopy.
Experimental Manifestations of Localized States in Metals
Authors: Jaccarino V.
Published: February 2004

A brief survey is presented of some of the experimental evidence on localized states in metals. Particular regard is given to studies of magnetic impurity states that are associated with dilute transition-metal solutes in either transition or nontransition metal matrices. An attempt at classification of the experimental methods and their results is made according to whether they are direct or indirect and microscopic or macroscopic. It appears that present-day theory offers only a qualitative understanding of the observed phenomena, a situation not unlike that which exists in regard to the ferromagnetism of certain of the transition metals.
Spin Impurities in Heisenberg Antiferromagnets
Authors: Walker L. R.
Published: February 2004

Work on the effects produced by a single spin impurity placed in a uniform spin system which interacts through Heisenberg exchange and with anisotropy fields is considered. The problem is formulated in terms of a two-time Green's function, whose equation of motion is simplified by the rpa. An infinite set of equations arises which contains the spin magnetizations as parameters; these are to be found consistently in terms of the Green's functions using the Callen-Shtrikman algorithm. At low temperatures an approximation equivalent to that of spin-wave theory reduces the set of equations to nine in the bcc case. These may be solved and permit a discussion of the modes of excitation of the impurity host system. These may be localized, above or below the spin-wave band, or act as resonant modes within it. Explicit expressions for the spin deviation at any site may also be given. Exactly similar equations may be used at higher temperatures if it is assumed that in the equations all spins save the impurity have the same magnetization. The impurity magnetization itself may be found by solving iteratively the equations for the impurity Green's function and the magnetization. This model is very useful for general qualitative discussions. Magnetization vs. temperature curves have recently been obtained (with D. Hone and H. E. Callen) for various impurity situations, using a method previously applied by the same authors to ferromagnetic hosts. This model determines only the impurity magnetization, but the first shell of down-spins is allowed to depart from the host magnetization, although it is only treated approximately. Self-consistency is achieved, however, for the impurity. The convergence is excellent. Some vigilance has to be exercised in searching for localized modes and in doing integrations over the sharp peaks which may occur in the Green's functions. Examples of magnetization curves are given for systems with resonant modes, with localized modes above and below the spin wave band, with levels which change from resonant to localized as the temperature changes and so forth. In the absence of anisotropy, some of the features of the zero-point deviation of the impurity which appear may be predicted by the use of second-order perturbation theory treating the transverse exchange as a perturbation.
Magnetic Anisotropy in Flat Ferromagnetic Films: A Review
Authors: Wilts C. H. , Humphrey F. B.
Published: February 2004

A review of those characteristics of the anisotropy found in thin Fe–Ni–Co films that are important from a practical viewpoint are presented. Previously published data are supplemented to form a composite ternary diagram of anisotropy field Hk as a function of composition for the alloy system Fe–Ni–Co for 250°C substrate temperature. Anisotropy fields as a function of composition for the three binary alloy systems at other substrate temperatures are included. A composite diagram showing anisotropy field as a function of measuring temperature illustrates the need for temperature stability. Magnetic annealing and aging is discussed. Finally the importance of magnetostriction as a source of the anisotropy is discussed in detail as well as pair ordering. It is concluded that no single source or combination satisfactorily describes the origin of the anisotropy.
Mössbauer Measurements in ZnY (Ba2Zn2Fe12O22) and Mn0.625–ZnY Ferrites
Authors: Albanese G. , Asti G. , Lamborizio C.
Published: February 2004

By means of the Mössbauer technique, the hyperfine magnetic fields and the electric quadrupole interactions in ZnY (Ba2Zn2Fe12O22) and Mn0.625–ZnY planar ferrites have been investigated.

From the obtained spectra it is deduced that the Zn ions are randomly distributed over the tetrahedral sites of both S and T blocks and that Mn is substituting for Fe3+.

The magnetic transition temperature for Mn0.625–ZnY turns out to be TC = (143±5)°C, not much different from that of ZnY, where TC = 135°±5°C.

In these compounds the angle between the magnetic moment and the electric-field gradient differs from 90° showing the presence of angles between the magnetic moments of iron ions.
Axial Magnetic Anisotropy in the Heavier Rare Earth Sodium Molybdates
Authors: Holmes L. , Schieber M.
Published: February 2004

The magnetic susceptibilities of the scheelites R1/2Na1/2MoO4, with R = Gd, Tb, Dy, Ho, Er, Tm, and Yb, have been measured between 2° and 300°K. The compounds are paramagnetic and show large, axial anisotropy at low temperatures. The wavefunctions and energy levels are deduced for the Yb compound and compared to values which have been obtained in CaWO4. The variations in magnetic anisotropy from ion to ion are correlated with the crystal field inferred for the Yb compound.
Cation Distributions in Octahedral and Tetrahedral Sites of the Ferrimagnetic Spinel CoFe2O4
Authors: Sawatzky G. A. , VAN DER Woude F. , Morrish A. H.
Published: February 2004

Mössbauer spectra of CoFe2O4 show that this spinel is not completely inverse and that the degree of inversion depends on the heat treatment of the material. The magnetic moments of the slowly cooled and the quenched material are 3.4 and 3.9 μB per unit chemical formula, respectively, and the Néel temperatures are 798°K and 792°K, respectively. From the width and the shape of the absorption lines of the Mössbauer spectra several magnetic hyperfine fields have been identified with different B sites and the temperature dependences of these fields have been determined. The different hyperfine fields have been attributed to 57Fe nuclei in B sites with different ratios of iron and cobalt ions in the six nearest-neighbor A sites.
Magnetic Study of the Manganate Phases: CaMnO3, Ca4Mn3O10, Ca3Mn2O7, Ca2MnO4
Authors: MacChesney J. B. , Williams H. J. , Sherwood R. C. , Potter J. F.
Published: February 2004

Two series of manganate phases have been prepared and their magnetic properties measured. The first series consists, in addition to CaMnO3, of three phases having layered structures. In these, tetravalent manganese ions are contained in single or multiple perovskite layers, which are separated from each other by nonmagnetic calcium-oxygen layers. Magnetic exchange of the type Mn4+–O–Mn4+ is disrupted between layers and decreased Néel temperatures would be expected to result. In a second series of phases, the size of the CaMnO3 unit cell was increased by partial substitution of strontium for calcium. Increased separation of manganese ions produced by this means was expected to reduce Néel temperatures. However, contrary to these expectations, Néel temperatures remained approximately constant for the first series of phases and increased for the second.

This apparent enigma can be viewed in terms of the effect of chemical substitution and lattice geometry upon the strength of exchange interactions. As pointed out by Goodenough,1 the overlap integral is increased as the result of partial substitution of larger A-site cations for calcium. On the other hand, geometrical influences are important to understanding the insensitivity of Néel temperatures to decrease in the number of near-neighbor magnetic ions that occurs as nonmagnetic layers are inserted in the perovskite structure.
A Localized-Electron to Collective-Electron Transition in the System (La, Sr)CoO3
Authors: Raccah P. M. , Goodenough J. B.
Published: February 2004

Crystallographic, magnetic, and electrical studies of the system La1−xSrxCoO3.00±0.01 for 0≤x≤0.5 give indirect evidence for the presence of chemical inhomogeneities separating strontium-free regions, where localized ``3d'' electrons occur at thermally excited high-spin Co3+ ions, from strontium-rich regions, where the ``3d'' electrons are collective and give ferromagnetism at low temperatures. These different regions occur within the same rhombohedral perovskite crystal and appear to represent two different electronic phases within the same crystallographic phase. A schematic band model for the ferromagnetic phase is presented.
Strain-Sensitive Thin Magnetic Films
Authors: Onyshkevych L. S.
Published: February 2004

For the sonic film memory highly strain-sensitive ferromagnetic thin films are required with magnetic properties comparable to those of good Permalloy memory films. Research has shown that films prepared by evaporation from 60% Ni, 25% Fe, 15% Co melts meet the requirements.

These films have Hc and Hk values below 15 Oe and are usually inverted. They are well oriented with good squareness in the easy axis. X-ray diffraction measurements show them to have a single phase (fcc).

The strain-sensitivity is about an order of magnitude higher than that of the most sensitive Ni–Fe alloys with comparable values of Hc and Hk. Typically, a strain of about 5×10−5 causes: (1) a rotation of the easy axis by ∼25°, (2) a significant change in the values of Hc, Hk, and (3) a decrease in the switching threshold by at least a factor of two. The change in Hk and the rotation of the easy axis agree in general with theoretically predicted behavior.

Dynamic strain measurements show these films to be suitable for memory use with coincidence writing (strain pulse—magnetic field pulse) and nondestructive read.
Low-Temperature Beam-Addressable Memory
Authors: Fan G. Y. , Greiner J. H.
Published: February 2004

In this paper, the work on a low-temperature laser-beam addressable memory will be presented. There are several advantages for a low-temperature beam addressable memory. First, the memory medium, an EuO film, gives large magneto-optic effects which result in a fast readout rate. Second, at a low operating temperature, the specific heat of the material is small since the lattice and electronic specific heats are proportional to T3 and T, respectively. Thus, thermowriting requires much less energy at low temperature than at room temperature. Third, because of the low-energy requirement for the read-write transducer, injection lasers with fast switching speeds can be used. Fourth, the films that were investigated can sustain small-area magnetization reversals. Using injection lasers as transducers and EuO films as memory-storage elements, reading and writing experiments were carried out. Bits of <3 μ in diameter were written with a 10-mW laser in 10 nsec by using thermal writing. The laser energy required to write such a bit is 10−3 erg; and since no substantial magnetic spread was observed in a thin film of EuO, the density of packing is essentially limited by optics. High-speed reading experiments were also carried out. Since the magneto-optic conversion efficiency is very high, a good S/N ratio for detection was achieved by a 1-mW laser pulse of a few nanoseconds duration.
A Coupled Magnetic Film Device for Associative Memories
Authors: Wang C. P.
Published: February 2004

It is well known that a pair of magnetostatically coupled films with easy axes at 90° to each other exhibit biaxial anisotropy. However, when an external bias magnetic field is applied along the easy direction of one of the films, only two states of the coupled system have minimum energy. It can be shown that these two stable states are not collinear in magnetization orientations and the resulting switching characteristic is quite different from that of a uniaxial coupled film device.

A new associative memory device based on the above-mentioned switching characteristics is presented in this paper. Nondestructive content interrogation is feasible on this device by applying a current on the strip line intervening between two magnetic layers. When the polarity of the interrogation current mismatches the state of the device, a signal is induced in a detection strip line orthogonal to the interrogation line and located on top of both magnetic films. On the other hand, when the current polarity matches the device state, none or very little flux change is experienced by the detection line. The mismatch signal is always of one polarity independent of the device state.

A device sample with electroplated magnetic and conductive layers and photoetched strip lines has been fabricated. The scheme of two storage cells per bit is adopted to cancel capacitive noise. Two 2-bit (4 cells) words have been successfully operated in a parallel by bit content search mode. The measured mismatch to match ratio for a single bit is better than eight.
A New Method of Propagating Domains in Thin Ferromagnetic Films
Authors: Michaelis P. C.
Published: February 2004

A new mode of controlled magnetic-domain propagation has been discovered. With this technique either serrated domain boundaries or small single-wall domains can be propagated along the hard axis of an anisotropic thin film. The drive line for either case is a hairpin-shaped wire located adjacent to the film and parallel to both the film plane and the hard axis. Bipolar current pulses applied to the drive line in conjunction with a dc or pulsed hard-axis bias field are used to control propagation. The bias and drive fields are chosen to provide the necessary asymmetry for preferential propagation. Displacement of domain-wall boundaries in one direction of 2000 to 5000 Å per cycle are obtained. Both modes of propagation have been observed in 900 to 2250 Å NiFe and NiFeCo films. NiFe and NiFeCo films used for the experiments had dispersions (α90) ranging from 0.5° to 5°. Varying the film to drive-line spacing from 0.5 to 5 mil or skewing the film ±20° with respect to the drive line did not prevent domain propagation. Interpretation of these effects and experimental data defining operating conditions are given.