bluuebunny/crossref_metadata_2025 huggingface dataset:
Nuclear Magnetic Resonance Detection of a Spin-Wave Gap in Fe2B
Authors: Weisman I. D. , Swartzendruber L. J. , Bennett L. H.
Published: February 2004

Measurements of the 11B frequency vs temperature in the ferromagnetic intermetallic Fe2B for 4.2°≤T≤373°K give evidence of a spin-wave gap even in zero applied field. Above about 100°K, the reduced frequency is approximately proportional to T3/2 (with a small admixture of a T5/2 term). However at lower temperatures, a significant deviation of the reduced frequency from the T3/2 dependence is apparent. The deviation can be understood in terms of a spin-wave gap, Tg, which is present because of the relatively large magnetocrystalline anisotropy and magnetization.1 Assuming proportionality between reduced frequency and bulk magnetization, we have extracted1 the constants of proportionality in the spin-wave approximation, C (the coefficient of the T3/2 term) and D (the coefficient of the T5/2 term). We find that D/C=(1.0±0.4)×10−3. Our data set an approximate upper limit of about 1°K on Tg. These and other NMR and Mössbauer results on hyperfine magnetic fields and quadrupole interactions in both Fe2B and Fe2Zr will appear elsewhere.2 Anisotropy found in the Fe2B Mössbauer spectra can be interpreted as a super-position of hyperfine patterns arising from an anisotropic magnetic field and electric field gradient in combination with either two magnetically inequivalent Fe sites (such as was observed in Fe2Zr) or a two dimensional distribution of magnetization directions. The measured pressure variations ∂v/∂P of the 11B and 91Zr NMR frequencies in Fe2B and Fe2Zr, respectively, are (−21±2) and (31±2) Hz·bar−1.
Pressure Dependence of the Curie Temperature of Ferromagnetic Laves Phase Alloys
Authors: Alfieri G. T. , Banks E. , Kanematsu K.
Published: February 2004

The pseudobinary system (Zr1−xNbx)Fe2, with the cubic Laves structure, shows ferromagnetism for samples with x≤0.45. The lattice parameter decreases with increasing Nb content, but the major part of the change in TC is not due to this, as was seen in the case of (Zr1−xTix)Fe2. Zr(Fe1−xCox)2 behaves similarly. We have studied the effect of high pressure on the Curie temperatures of some of these alloys, using the method of McWhan. All of these samples show a linear decrease of TC with pressure. In the (Zr, Nb)Fe2 series, dTC/dP=−3.3°K/kbar for x=0.3 and −3.5°K/kbar for x=0.35. The permeability decreases with pressure, and the permeability-temperature curves behave as if the compounds become paramagnetic when the Curie temperature falls below 230°K. This is the Curie temperature (at 1 atm) of (Zr0.6Nb0.4)Fe2, which is the limiting composition of the ferromagnetic region. Zr(Fe1−xCox)2 behaves similarly, with dTC/dP=−4.7°K/kbar for x=0.35 and −6.6°K/kbar for x=0.4.
Effects of Magnetic Order on Refractive Index and Photoconductivity of Europium Chalcogenides
Authors: Bachmann R. , Wachter P.
Published: February 2004

The refractive index of the europium chalcogenides has been measured as a function of wavelength, temperature, and magnetic field and compared with dispersion theory. Attributing different oscillator strengths to the various substances, classical dispersion theory can account for the observed changes in the refractive index. To get more information about the electronic transitions involved, the spectral photosensitivity of EuO and EuS has been measured as a function of temperature and magnetic field. The results show that in EuO and EuS, electrons are optically excited into a conduction band both above and below TC. Spin-disorder scattering leads to large new magnetophotoelectric effects near the Curie point.
Magnetic Properties of the Europium Chalcogenides under Hydrostatic Pressure
Authors: Schwob P. , Vogt O.
Published: February 2004

The magnetic properties of the europium chalcogenides are commonly explained by a ferromagnetic nearest-neighbor exchange which is strongly volume dependent, and an antiferromagnetic next-nearest-neighbor exchange which varies slowly with distance. A qualitative confirmation of this model has been given by different authors who found an increase of the Curie temperatures of EuO and EuS by application of hydrostatic pressure. In the present work, pressure experiments have been extended to include the antiferromagnets EuTe and EuSe. There is no observable shift of the Néel temperatures with pressures up to 4 kbar (resolution 0.1°K for EuTe and 0.01°K for monocyrstalline EuSe). The metamagnetic transition of EuSe at T*=2.5°K to a ferrimagnetic structure is strongly pressure dependent: dT*/dp=−2.7°K/kbar. Measurements of the magnetization and the paramagnetic susceptibility of EuSe under pressure, both independently, indicate an increase of the ferromagnetic component of the order of +0.1kB °K/kbar. It is shown that the molecular field approximation is adequate for EuTe but needs modification in the case of EuSe.
Optical Absorption of K2CoF4, A Two-Dimensional Antiferromagnet
Authors: Maisch W. G.
Published: February 2004

The optical absorption spectrum of the two-dimensional antiferromagnet K2CoF4 (crystallographic space group D4h17) has been observed in the α, π, and σ polarizations, in the region 5000–50 000 cm−1, at various temperatures between 4.2° and 300°K. Axial-field splittings, present at all temperatures, are most prominent at low temperatures in the detailed structure of the 4T1(4F) → 4T2(4F) magnetic dipole transition near 7000 cm−1 and in the bands in the 17 000–23 000 cm−1 region of the spectrum [4T1(4F) → 2T1(2G), 2T2(2G), 4T1(4P), 2T1(2H), and 2A1(2G)] Three weak, narrow lines (Δν̃1/2≈10 cm−1) appear below 78°K in different intensities in the σ and π spectra in the region of the 2A1(2G) energy level (∼23 000 cm−1). A complete crystal-field calculation, using the tabulated matrix elements of Jesson, has been made for the d7 ion in a tetragonal environment. The parameters which give the best fit to the observed spectrum and also agree with the axial-field splitting of the 4T1(4F) ground state calculated by Folen et al. are, in cm−1, Dq=−785, Ds=170, Dt=−50, B=880, C/B=4.6, and ζ=−500.
Neutron Diffraction Study of NiS Under Pressure
Authors: Smith F. A. , Sparks J. T.
Published: February 2004

Recent neutron diffraction and resistivity measurements on the NiAs form of NiS show the existence of a first-order metallic to semiconducting, paramagnetic to antiferromagnetic transition at 265°K and and zero pressure, which has a large negative pressure dependence (dTN/dP)=−6.0°/kbar. Below TN the nickel moments, of approximately 1.7 μB, are coupled ferromagnetically in the basal planes and are aligned along the hexagonal axis. The coupling of adjacent basal planes is antiferromagnetic. The present work has examined the effect of pressures up to 8 kbar at temperatures T>TN, T=0.9 TN, T=0.25 TN using a time-of-flight neutron spectrometer. The results show that the compressibility of the lattice is small and essentially independent of temperature. In addition there is a migration of Ni atoms from their octahedral positions to tetrahedral interstitial sites with increasing pressure. In the region of 5 kbars, however, this process is reversed and there is a tendency towards perfect ordering of the NiAs lattice. At the same time there is an increase in the Ni moment towards its fully allowed value.
Antiferromagnetism in Chromium and its Alloys
Authors: Rice T. M. , Barker A. S. , Halperin B. I. , McWhan D. B.
Published: February 2004

Recent experimental and theoretical work on itinerant antiferromagnetism in Cr and its alloys is reviewed with particular emphasis on optical and pressure effects. At low temperatures, a peak appears in the infrared conductivity of Cr which is attributed to excitation of electrons across the antiferromagnetic energy gap. The maximum in absorption occurs at photon energy 5.1kTN, at low temperatures, which is substantially higher than the value 3.5kTN predicted by the simplest models. Both the position and shape of the absorption can be explained if the effects of electron-phonon scattering are incorporated in the model. The pressure dependence of the Néel temperature of Cr and alloys with Mo and V is described. The role of band structure is discussed, particularly its effect on the vanishing of antiferromagnetism under pressure.
Transition Temperature of the Two-Dimensional Heisenberg Ferromagnet with S=½
Authors: de Jongh L. J. , Botterman A. C. , de Boer F. R. , Miedema A. R.
Published: February 2004

The transition temperatures of a group of copper compounds of the general formula Cu(CnH2n+1NH3)2Cl4 have been obtained from ac susceptibility data. These compounds contain layers of CuCl2, separated by two layers of (CnH2n+1NH3)Cl. Also two compounds with the Cl−-ion replaced by Br− have been investigated. In the Cl-series, n was varied from 1–6, whereby the copper-copper distance within a layer remains practically constant, the distance between copper ions from adjacent layers increasing from 10 to about 20 Å. Values for the exchange parameter J have been derived from paramagnetic Curie temperatures and heat-capacity data at low temperatures. Whereas both the interaction between neighboring CuCl2-layers and the anisotropy clearly vary through the series of compounds, the values of J/kTc we obtained agree rather well to J/kTc=1.7. This suggests that the transition temperature is indeed characteristic for the layer-structure.
Anomalous Critical-Point Behavior in Europium Metal
Authors: Cohen R. L. , Hüfner S. , West K. W.
Published: February 2004

We have used Mössbauer-effect measurements of the hyperfine (hf) interaction in Eu metal to study the behavior of its sublattice magnetization just below the Néel temperature. From about 0.9≤T/Tc≤0.99, the hf field is accurately proportional to (1−T/Tc)β with β=0.20, but at 0.99Tc, the hf field falls from 0.4 of saturation to zero. This can be explained by the existence of a first-order transition coincident with the magnetic ordering.
Electron-Spin Resonance and Transferred Hyperfine Interactions in K2ZnF4:Mn
Authors: Folen V. J.
Published: February 2004

Electron-spin-resonance measurements at 24 Gc have been made on single crystals of K2ZnF4 doped with Mn. The spectra obtained in these measurements corresponds to Mn2+ in the Zn2+ sites (point group 4/mmm) in this material. The measured values of the spin-hamiltonian parameters are: g∥=2.0032, g⊥=2.0028, D=35.4×10−4 cm−1, A=−89.4×10−4 cm−1, B=−89.8×10−4 cm−1, a=5.9×10−4 cm−1 and F≅2×10−4 cm−1. In addition, the transferred hyperfine parameters (AsI, ApI, AsII, and ApII) were obtained from our measurements. These parameters, which result from interactions between the Mn2+ 3d electrons and F−, refer to the 4 equivalent nearest-neighbor F− ions in the (001) plane (Type I) and the 2 equivalent nearest neighbor F− ions along the four-fold axis (Type II). From the measured As values, the unpaired spin densities in the F− 2s orbitals were found to be 0.6% and 0.5% for Type I and Type II fluorines, respectively. These results are applicable to the estimation of overlap and/or covalent contributions to, for example, the D term in the spin-hamiltonian and to the estimation of the NMR frequencies of Mn2+ and F− in K2MnF4, an ideal two-dimensional antiferromagnet with large zero-point spin deviations.
Magnetic Properties of K2CoF4
Authors: Folen V. J. , Krebs J. J. , Rubinstein Mark
Published: February 2004

The compound K2CoF4 (as well as K2NiF4 and K2MnF4) is a two-dimensional quadratic layer antiferromagnet below its Néel point. We have investigated the fluorine transferred hyperfine interaction in K2CoF4 by nuclear magnetic resonance on the 19F nuclei, and performed EPR measurements on the Co2+ ion in the isomorphous compound K2ZnF4:Co2+. These measurements, as well as Srivastava's magnetic susceptibility measurements on K2CoF4,1 are in substantial agreement with theoretical calculations based on crystal field theory and the molecular field approximation. The experimental g values in K2ZnF4:Co2+ are g∥=6.30 and g⊥=3.13, while the calculated values (using parameters obtained from fitting to the temperature dependence of the susceptibility) are g∥=6.5 and g⊥=3.3. The super-hyperfine interaction constant measured for Co2+ in K2ZnF4 is in good agreement with the 19F Knight shift in K2CoF4 and the theoretical spin susceptibility. Results were also obtained for the nuclear resonance frequency of 19F in the antiferromagnetic state of K2CoF4. An account of this work has been published in Solid State Communications.2 Related work on the compound K2MnF4 has been published in Physics Letters.3
Mean Magnetic Moments in bcc Fe–Co Alloys
Authors: Bardos D. I.
Published: February 2004

Saturation magnetizations in the binary Fe–Co system were redetermined since an earlier investigation (P. Weiss and R. Forrer, Ann. Phys. 12, 1929) was made prior to the discovery of a CsCl-type ordered structure that has a wide solubility range. The alloys were quenched from 850°C at various rates in an attempt to suppress the ordering reaction. The magnetizations decreased as the quenching rate increased for alloys containing between 30 and 70 at.% cobalt. A maximum difference at 3% in the mean moment p was obtained for an equiatomic alloy quenched at the extreme rates. The mean moments for the ordered alloys are in good agreement with the previous investigation. The data for the fast quenched (presumably disordered) alloys indicate that the Slater-Pauling curve, in the electron-concentration range between iron and cobalt, has a maximum at about 28 at.% cobalt, compared with the 35 at.% suggested by the data of Weiss and Forrer.
Magnetization and Specific Heat of Fe–Be Alloys
Authors: Herr A. , Kuentzler R. , Meyer A. J. P.
Published: February 2004

Magnetic and electronic specific-heat measurements show that the s electrons of Be are not transferred to the d band in Fe–Be solid solution, but that this transfer occurs in the FeBe2–FeBe5 range at a rate of 0.6 electrons per Be atom while 1.4 electrons of Be remain in s state. This behavior is interpreted in supposing that the free-electron density of iron ns=0.9 has to be increased near ns=1.4 by the solute electrons before s→d transfer can occur. This model applies qualitatively to the observed data of Fe–Al and Fe–Si solid solutions.
Intrinsic Magnetization of Fe–Ni–Mn Alloys
Authors: Colling D. A.
Published: February 2004

The saturation magnetization of fcc Fe–Ni–Mn alloys was measured by a force technique at temperatures from 77°K to the Curie temperature. Additions of Mn were found to increase the atomic moment only for alloys with Ni-to-Fe ratio of 4/1. In this series, a maximum in atomic moment was observed for Mn concentration between 2.5 and 5.0 at.%. For Ni-to-Fe ratios of 3/2 and 2/3, Mn additions decreased the atomic moment, such decrease being more severe as iron content is increased. The effect of Mn on the Curie temperature is similar, except that no increase was observed in alloys with Ni-to-Fe ratio of 4/1. Results are satisfactorily explained using a Heitler-London model for the 3d electrons in which the atomic moment associated with each atom is determined by the principle of maximum spin and the sign of the interaction between neighboring pairs.
Use of Photoemission and Optical Methods to Determine the Electronic Structure of Solids
Authors: Spicer W. E.
Published: February 2004

Through measurement of the energy distribution of photoemitted electrons, it is possible to obtain a measure of the probability, P(hv, E), of an electron being excited by a photon, hv, to a given final state of energy, E. By studying P(hv, E) as a function of energy, information can be obtained on the optical selection rules. Where direct conservation of crystal momentum, hk̄, provides an important selection rule, it is possible to trace out the position in energy of the bands in particular regions of the zone. Where direct k̄ conservation doesn't provide an important selection rule, the optical density of states can be obtained. In many cases, the optical density of states appears to be directly related to the band density of states. Great care must be taken for surface cleanliness in the photoemission experiments; however, this method gives considerably better resolution than any of the other experimental methods used to probe electronic structure over a wide energy range.
X-Ray Photoelectron Spectroscopy on Magnetic Metals
Authors: Fadley C. S. , Shirley D. A.
Published: February 2004

Photoelectron spectroscopy offers one of the most direct methods for observing the density-of-states function N(E) in metals. We have used x-ray photoelectron spectroscopy (XPS) to study N(E) for the valence bands of Fe, Co, Ni, Cu, and Pt. X rays offer the advantage over lower-energy photons that the directly observable kinetic energy spectrum is probably more closely related to N(E). The final electron states are true continuum states, undistorted by the lattice potential, and they cannot affect the observed spectrum significantly. A disadvantage of x-ray photoelectron spectroscopy is the relatively poor resolution presently available. Photoelectrons were ejected from samples of the above metals by MgKα x rays from a specially-constructed nonmagnetic x-ray tube. The electrons were magnetically analyzed in the Berkeley Iron-Free Spectrometer. As the photoemission occurs in a region within only a few hundred angstroms of the surface, surfaces had to be cleaned by heating our sources in a stream of H2. The surface condition was monitored by observation of the oxygen 1s photoelectron line. The densities of states derived from these measurements showed a dominant peak near the Fermi energy for Fe and Co, in contrast to earlier ultraviolet photoelectron results.1,2 Our N(E) results for Ni and Cu are in good agreement with the results of soft x-ray emission spectroscopy,3,4,5 ion-neutralization spectroscopy,6 and more recent ultraviolet photoelectron studies.7,8
Photoemission Experiments on Ag(Pd), Ag(Mn), and Cu(Mn) Alloys
Authors: Norris C.
Published: February 2004

Photoemission experiments on bulk samples of Ag(Pd), Ag(Mn) alloys have clearly shown the occurrence and position of the virtual resonant bound states associated with the d electrons of the transitionmetal solutes. In Cu(Mn) the occupied resonant bound states of the Mn are not resolved, due to their overlapping the Cu 3d band. The significance for the magnetic behavior of Mn in Ag and Cu matrices is briefly discussed.
Ion-Neutralization Spectroscopy of Nickel
Authors: Hagstrum H. D.
Published: February 2004

The neutralization of ions of large neutralization energy such as He+ ejects electrons from solids in a two-electron, Auger-type process which extends to electrons quite deep in the band. The kinetic energy distribution of such electrons can be unfolded to give a function U (ζ) of band energy ζ called the transition density, which contains factors dependent on electronic state density in the solid and transition probability of the process. The method is a spectroscopy of solids (INS) which probes the local density of states in the surface region. The U (ζ) function for Ni shows a peak just below the Fermi level whose width agrees quite well with Mueller's theoretical result. It is possible that INS sees a somewhat narrower d band than other methods because the ion interacts principally with surface atoms, which have a weaker interaction with fewer neighbors than do bulk atoms. Ion-neutralization spectroscopy is also very sensitive to the presence of foreign atoms such as oxygen, and has been used to observe the virtual states of electrons in such atoms adsorbed in ordered monolayers on the solid surface.
Mössbauer Study of Electron Hopping in the Octahedral Sites of Fe3O4
Authors: Sawatzky G. A. , Coey J. M. D. , Morrish A. H.
Published: February 2004

A linewidth study of the Mössbauer spectra of 57Fe in A and B sites in Fe3O4 as a function of temperature has shown that relaxation effects due to electron hopping in the B sites are present. It is found that the linewidth of 57Fe in A sites is temperature independent, whereas that in B sites decreases rapidly with increasing temperature. Above room temperature, the temperature dependence of the B-site linewidth yields an activation energy close to that obtained by conductivity measurements just above the Verwey transition. Between the Verwey transition temperature and room temperature, the activation energy found from the B-site line width is considerably less than that above room temperature. These data indicate that there are two processes which influence the Mössbauer spectra. It is also found that below the Verwey transition temperature, the spectrum due to 57Fe in B sites cannot be interpreted as being due to one six-line spectrum for Fe2+ and another for Fe3+. This spectrum can be explained by assuming two Fe2+ spectra with an intensity ratio of 2:1.
Observation of the 169Tm and 27Al NMR in Thulium Aluminum Garnet
Authors: Jones E. D. , Schmidt V. H.
Published: February 2004

The observations of the 169Tm and 27Al nuclear magnetic resonances (NMR) in a single crystal of cubic thulium aluminum garnet are reported. The 27Al MNR was studied between 1.5° and 300°K, while the 169Tm NMR was observed only for T<4°K. From a study of the angular dependences of the 169Tm NMR fields, the (ξ, η, ζ) components of the Tm3+ susceptibility tensor were found to be highly ansiotropic and in units of emu/gram-atom, χ1=0.014, χ2=0.551, and χ3=0.03. The room temperature 27Al nuclear quadrupolar coupling constants e2qQ/h for the a and d sites were measured to be (0.892±0.005) and (6.155±0.005) MHz, respectively. The 27Al NMR frequency shifts for both sites were found to be angular and temperature dependent. A calculation for the observed angular dependences of the 27Al NMR frequency shifts in terms of dipolar fields is found to give reasonable agreement with experiment for the 1.5° and 300°K NMR data.
Nuclear Spin Echo Study of Mn2−xCrxSb
Authors: Houghton R. W. , Weyhmann W.
Published: February 2004

We have measured the NMR frequencies and nuclear relaxation times T1 and T2 of the Mn nuclei in ferrimagnetic Mn2−xCrxSb (x=0, 0.03) from 4°–300°K using nuclear spin echoes. Mn2Sb has two Mn sites: Mn(I) with μI=−1.77 μB and Mn(II) with μII=3.55 μB.1 We have identified these sites with frequencies of 144 and 126 MHz, respectively, at 77°K and have shown that the hyperfine interaction is negative and anisotropic. The NMR frequency of Mn(I) has an unusual temperature dependence; between 50° and 300°K it decreases linearly with temperature. This behavior is not described by spin-wave or molecularfield theories. It suggests the possibility of a strong temperature dependence of the electronic states which affects the hyperfine interaction. Between 4° and 200°K the ``intrinsic'' spin-lattice relaxation in the domains is given by T1T=30 msec °K and 17 msec °K for the Mn(I) and Mn(II) sites, respectively. Above 200°K, T1 decreases much more rapidly. In the region between 4° and 200°K, the transverse relaxation data are approximately fitted by the curve T2T0.44=186 μsec °K and 130 μsec °K for Mn(I) and Mn(II), respectively. Above 200°K they also begin to drop off more rapidly. These relaxation times are shorter than those reported for pure ferromagnetic metals.
Radio-Frequency Magnetically Induced Sidebands in Mössbauer Spectra
Authors: Heiman Neil D. , Pfeiffer Loren , Walker J. C.
Published: February 2004

The recently discovered, magnetically induced radio-frequency sidebands in the Mössbauer spectrum of metallic iron1 have been studied in more detail. Results of a survey to determine sideband intensity and location as a function of the experimental parameters are reported. In the earlier work1 the relative sideband intensities were fitted using Bessel functions Jn2(m), assuming that all the nuclei were vibrating with similar amplitudes. If, however, one assumes a Rayleigh distribution of amplitudes, the relative intensities should be proportional to exp(−m2)In(m2).2 A closer examination of the spectra indicates that either of these functions fits the data fairly well, although some intermediate distribution would seem to be more appropriate, particularly in light of a more elaborate model3 which relates the two functions cited above to sideband intensities at opposite extremes of phonon relaxation time (i.e., the time for a monochromatic vibration to spread into a wave packet characterized by kT). It should be stressed that fitting the data to either function yields essentially the same values for the physical parameters. Our original experiment1 was performed without a static field. When a static field is applied such that the rf field H1, the static field H0, and the plane of the absorber foil are mutually perpendicular, the presence of H0 has little effect on the sideband intensity for values of H0 up to 1 kG. Above 1 kG, the sideband intensity rapidly diminishes, falling to zero at H0≈2 kG. When H0 is oriented parallel to H1, we find that the sideband intensity diminishes rapidly, even for small fields (H0≈50 G), although a small sideband effect persists for fields as high as 1 kG.
Direct Evidence for Magnetic Domains in Silver
Authors: Condon J. H. , Walstedt R. E.
Published: February 2004

Pulsed NMR studies1 of 109Ag nuclei in a single-crystal specimen of Ag metal at helium temperatures in an applied field of 90 kOe reveal the presence of magnetic domains due to the de Haas-van Alphen magnetization. The H-A domains give rise to a measurable splitting of the 109Ag NMR line which appears and disappears with the H-A periodicity and has a magnitude slightly smaller than the H-A period (∼16.7 G with H0∥[100]) as expected. This effect is absent at 4.2°K and, on cooling down, sets in at about 2.2°K. Our results demonstrate the remarkable property, predicted by theory,2 that in the domain region of the H-A cycle the magnetic induction inside a planar specimen is independent of the applied field. The sharply resolved NMR lines give evidence for a large ratio of domain size to wall thickness and confirm the previously calculated positive wall energy.3
Nonlinear Properties of Magnesium Manganese Ferrite
Authors: Dixon Samuel , Leo Donald C.
Published: February 2004

Measurements have been taken on the ferromagnetic resonance properties of narrow-linewidth single-crystal magnesium manganese ferrite spheres at 9100 MHz and between 77°K and room temperature. The composition of the melt in mole percent was as follows: MgO 11.60%; MnO2 4.5%; Fe2O3 15.08%; PbO 34.41%; and PbF2 34.41%. This particular ratio of constituents was chosen in order to obtain an equal percentage of magnesium and manganese in the final samples. The actual composition of the samples investigated in this report was the following: Mg0.53Mn0.47Fe2O4. The low-power resonance linewidth (ΔH) measured along the easy axis [111] was 8.4 Oe at 295°K and rises to 24.7 Oe at 77°K. The threshold field (hc) for spin-wave excitation at 77°K was 250 mOe, while at room temperature it dropped to 100 mOe. From the room temperature threshold field, an intrinsic spin-wave linewidth (ΔHk) of 270 mOe was calculated.
Ferromagnetic Resonance in Ba4Zn2Fe36O60 (ZnU) and Mn-Substituted ZnU Single Crystals
Authors: Kerecman A. J. , AuCoin T. R. , Dattilo W. P.
Published: February 2004

Resonance experiments were performed on Ba4Zn2Fe36O60 (ZnU) and Mn-substituted ZnU single crystal spheres using a reflection technique and transverse pumping. The influence of surface polish on linewidth was studied from 26.5–40 GHz at 300°K. In general, ΔH was found to be only slightly dependent upon frequency. The lowest linewidth was 18.5 Oe measured on a Mn-substituted ZnU sample at 26.5 GHz. 4πMs, HA, ΔH, and γeff values are presented at 4.2°, 77°, and 300°K. A bandpass filter was constructed using a spherical resonator in an orthogonal configuration. The electrical characteristics are as follows: (1) Passband insertion loss, La=3.1–5.4 dB; (2) 3 dB bandwidth =200–380 MHz; (3) Stopband attenuation =30 dB, except spurious modes which are greater than 10 dB below main resonance.
Quick Evaluation Method for Microwave Ferrites Used in Analog Phase Shifters
Authors: Buck D. C. , Harris F.
Published: February 2004

A method is described in which the characteristics of a microwave ferrite pertinent to analog phase shifters are quickly determined. The method consists of recording the transmission resonant frequencies, Q's, and transmission coefficients of a reduced height, ferrite center-loaded waveguide resonator, for a range of applied field values. The guide is so dimensioned so as to pass only the Quasi-T E10 mode. Frequency shifts vs applied field can be expressed in terms of differential phase shift, and can be related to the state of magnetization. Magnetic losses can be directly seen by observing a reduction in the transmission coefficient at the low-frequency end of the band. An example of the method is given. A series of doped MgMn and Ni ferrites are tested and compared to performance in a Reggia-Spencer analog phase shifter.
Microwave Properties of Ferrites
Authors: Bady Isidore
Published: February 2004

Microwave properties of many ferrites have been measured using a novel method of measurement. The sample is a slab 2×0.3×0.04 in. and the sample holder is a ridge waveguide resonant cavity. Measurements were made at five or more resonant frequencies occurring between 4 and 10 GHz. It was thus possible to make measurements over a wide range of frequency without changing sample or sample holder. Since the filling factor approaches unity, considerably greater sensitivity and accuracy can be obtained than is possible with the conventional perturbation methods. Samples measured included garnets, and nickel, magnesium, and lithium spinels. 4πMs ranged from 750 to 5000 G. Magnetic susceptibility of unmagnetized ferrites: The test data indicates an approximate empirical formula for the real part, given by χ′ = −0.34[γ(4πMs+Ha) /ω]2 at frequencies where the quantity in the square brackets is one or less. The loss component decreases with frequency and the curves have a variety of shapes. Dielectric loss tangent: When the dielectric loss tangent is low (less than 0.0007), it does not vary with frequency; for larger values, it generally decreases with increasing frequency. Measurement accuracy is estimated at ±0.0001 or ±3%, whichever is higher.
Anisotropy and Ferromagnetic Resonance in NiFe2O4 with [111] Texture
Authors: van Groenou A. Broese , Beljers H. G. , Driessens F. C. M.
Published: February 2004

Grain-oriented materials are useful in magnetic applications such as transformers and microwave devices. We have prepared [111]-oriented NiFe2O4, which shows a deviation of texture axes of less than 5°. Typical values for the ceramic quantities are: grain size is 60 microns, porosity is 3.5%, and resistivity is 104 ohm·cm. In a polycrystalline material with one fixed [111] axis and randomly distributed [100] axes, the anisotropy energy is minimum for K1<0 along the texture axis (θ=0°), maximum at θ=50°, and again a minimum at θ=90°. The latter energy minimum has the nature of a preferential plane. This is found in [111] texture for K1<0, and is not present in [100] or [110] textures. Measurements of the static torque and x-band ferromagnetic resonance show the expected behaviour. The variation of the resonance field with θ is in good agreement with theory, using the static K1 value. The variation of linewidth with θ illustrates the expected spread in resonance field. For θ=0° and θ=90°, the linewidth is minimum, rising by 700 Oe when θ is changed to 50° where the resonance lines become highly asymmetric.
Summary Report
Authors: Smith D. O.
Published: February 2004

Three conferences on specialized topics in magnetism were held in the summer of this year; namely, (1) Magnetic Thin Films, Hakone, Japan, (2) Physics of Magnetic Films, Irkutsk, USSR, (3) Magnetic Oxides, Bucharest, Rumania. The limited attendance by American scientists at these International Conferences led to the suggestion that an informal report and discussion be given by people who were able to attend. The discussion leaders representing the respective meetings were: (1) D. O. Smith, M. I. T. Lincoln Laboratory, Lexington, Mass. 02173, (2) F. B. Humphrey, California Institute of Technology, Pasadena, Calif. 91109, (3) E. R. Callen, Dept. of Physics, American Univ., Washington, D.C. 20016. These people gave a general description and summary of the meetings and acted as moderators during question and discussion periods with other participants at the conferences as well as the general audience. This session represented an experiment by the Program Committee of the Conference on Magnetism and Magnetic Materials to disseminate information of interest to magneticians which does not appear or tends to get lost in the formal and accustomed channels. Judged by the audience response, it is fair to say that this objective was successfully reached. A list of American attendees and titles of the technical papers presented at the meetings was passed out to the audience and additional copies can be obtained by contracting the discussion leaders. The papers given at the Irkutsk meeting have appeared in book form (in Russian). Brief reports of the conferences have been written by the discussion leaders and will be published in the IEEE Magnetics Group Newsletter, Vol. 4, No. 4. (Dec. 1968).
Spin-Wave Excitations in the Conical and Spiral Magnetic Phases of Holmium Metal
Authors: Stringfellow M. W. , Holden T. M. , Powell B. M. , Woods A. D. B.
Published: February 2004

Spin-wave excitations propagating along the c and a axes of holmium metal have been studied by neutron inelastic scattering techniques, with a triple-axis spectrometer in both the constant Q and constant energy-transfer modes of operation. Measurements were made in the conical magnetic phase at a temperature of 4.6°K and in the spiral phase at 25°K. The dispersion curves for the two phases are similar in shape, although the spin-wave energies in the spiral phase are consistently lower than in the conical phase. For example, the energies of spin waves of wave vector (0, 0, 2π/c) are 3.97±0.21 and 3.48±0.21 meV in the conical and spiral phases, respectively, while those of spin waves of wave vector (0, 0, π/c) are 2.64±0.21 and 2.07±0.17 meV, respectively. The results give information about the Fourier-transformed exchange, J(0)−J(q), and the crystal field parameters.
Absence of Antiferromagnetism in Ti2O3
Authors: Moon R. M. , Riste T. , Koehler W. C. , Abrahams S. C.
Published: February 2004

The possible existence of antiferromagnetism in Ti2O3 has important theoretical implications associated with the explanation of the metal-to-semiconductor transition in this material. A previous neutron-diffraction study, using unpolarized neutrons, indicated that Ti2O3 was antiferromagnetic with the α-Fe2O3 structure. More recently, contradictory findings were reported which eliminated the α-Fe2O3 structure but could not rule out the type of ordering found in Cr2O3. We have reexamined this substance, using the new technique of neutron-polarization analysis. With this technique, the coherent scattering can be separated into nuclear and magnetic parts at a fixed temperature. It is possible to detect small magnetic contributions, even when the magnetic and nuclear peaks have the same scattering vector. At room temperature, we find no evidence for either the α-Fe2O3 or the Cr2O3 magnetic structure.
Spin Directions in Pure Chromium
Authors: Werner S. A. , Arrott A. , Atoji M.
Published: February 2004

We have carried out a triple-axis polarized-neutron-beam experiment with polarization analysis of the final beam and magnetic fields to 15 kG applied to a pure Cr single crystal. The purpose was to determine whether the spin axis in the transversely polarized spin-density wave state (122°K–38.5°C) is confined to the cube edges or whether in sufficient fields it can be made to lie in an arbitrary direction (perpendicular to the wave vector). The experiments show unambiguously that the latter is so. At 25°C, it is slightly more difficult to confine the spins to a single 110 axis than it is to a single 100 axis. At lower temperatures this anisotropy is enhanced. These results along with our previous results for the field dependence of the cube-edge components using unpolarized neutrons have been analyzed in terms of two different models. Both models have the spins in all directions perpendicular to the wave vector of the spin-density wave. One is the model of thermal activation of small domains. The other considers a domain structure with wall motion. In both models ansiotropy and magnetic field influence the net number of spins in any given direction.
Spin-Wave Spectrum of Nickel Metal
Authors: Mook H. A. , Nicklow R. M. , Thompson E. D. , Wilkinson M. K.
Published: February 2004

The spin-wave spectrum of nickel metal has been measured in the three principal symmetry directions by inelastic neutron scattering using the triple-axis technique. A large crystal of 60Ni was used to avoid incoherent scattering and reduce contributions from phonon scattering. The spin-wave dispersion curve rises quadratically in each of the three directions according to the relation E=Dq2 when D is about 430 meV Å2. The spin-wave intensity decreases slowly with increasing energy and then drops suddenly by more than an order of magnitude. This sudden decrease occurs at different energies for the three symmetry directions and in accordance with calculations is interpreted as the intersection of the spin-wave dispersion curve with a continuum band of excitations. In the [100] direction this intersection corresponds to an energy of about 100 meV and a q of about 0.4 A−1. These results along with band calculations by Hanus indicate a d band splitting of 0.57 eV. The measured spin-wave spectra are similar to those calculated with an interatomic exchange of 0.025 eV.
Spin-Wave Dispersion Relation for Holmium in the Spiral Magnetic Phase
Authors: Nicklow R. M. , Mook H. A. , Smith H. G. , Reed R. E. , Wilkinson M. K.
Published: February 2004

The spin-wave dispersion relation for the c direction of holmium metal in its plane-spiral magnetic phase has been studied by coherent inelastic scattering of thermal neutrons. Constant-Q measurements of neutron energy loss processes, with the scattered neutron energy held fixed at 8.5 meV, were made at 78° and 48°K. Preliminary least-squares analyses of the data indicate that the out-of-plane anisotropy constant is smaller than that for Dy and Tb, and that five interplanar exchange constants are required in order to fit the data satisfactorily. The resulting exchange constants are larger in magnitude than the anisotropy constant and are both positive and negative in sign as expected for the stability of the spiral structure.
Study of Yttrium-Cobalt Alloys by Polarized-Neutron Diffraction
Authors: Kren E. , Schweizer J. , Tasset F.
Published: February 2004

The magnetic moments in the ordered YCo5, Y2Co7 and YCo3 intermetallic compounds with closely related crystal structures have been investigated on single crystals using the polarized-neutron-diffraction technique. The ferromagnetically aligned magnetic moments on the cobalt atoms are influenced by the yttrium neighbors. They are the lowest in YCo3, which is the richest in yttrium, and at the sites having the most yttrium neighbors. Magnetic moments, induced by the ferromagnetic cobalt environment, were found on the yttrium atoms, too. The value of these moments, which are coupled antiparallel with the moments of cobalt, depends on the number of the cobalt neighbors and the magnitude of their moments. The induced magnetic moment of yttrium reaches a saturation value of about 1 μB. The form factor of yttrium was estimated, it was found to fall rapidly with sinθ/λ and to change sign near sinθ/λ=0.17. The resultant magnetic moment is in good agreement with the results of magnetic measurements. A full account of this work will be published in The Physical Review.
Strain Sensitivity of the Wall Coercive Force in Magnetic Films
Authors: Crowther Thomas S.
Published: February 2004

The change in the wall coercive force, Hc, of magnetic films on thin glass substrates has been measured as a function of uniaxial strain, e. Magnetostrictive alloys of Ni, Fe, and Co varying in thickness between 200 Å and 1500 Å were studied. Hc was generally found to be a linear function of strain with a sensitivity to strain less than half that of Hk, i.e. (dHc/de)/(dHk/de)<+0.5. The most interesting feature was a critical thickness at which the sign of the strain sensitivity reversed to a small negative value. Measured values of critical thickness of 800 Å for Bs=12,600 G and 650 Å for Bs=14,000 G agree well with the values of 760 Å and 680 Å predicted by Middelhoek for the transition thickness from cross-tie walls to Bloch walls for these saturation-induction values. Such a critical thickness is not observed in inverted films in which Hc>Hk, because the switching process here for easy-axis magnetization reversal occurs birotationally rather than as a simple wall motion.
History-Effect Memory: A Novel Ferrite Core Memory Using a Single Major Remanent State of One Polarity for Both Digital Information States
Authors: Hewitt Fred G.
Published: February 2004

The operation of this memory is based on the change in switching characteristics of the major remanent state when the saturating pulse is preceeded by a time-limiting pulse of the opposite polarity. The two-core memory cell records digital data by storing the history-enhanced switching characteristic in one or the other of the two cores. After writing, both cores are magnetized in the same polarity in the same major remanent state. Two test memories were built to demonstrate the operating principles. One was word organized with 4, 4-bit words, the other was bit-organized in a 4 by 4 array. The history-effect memory has very wide drive current and temperature operating margins. There are no current thresholds to limit switching speed. The application of this memory is limited by large noise, very close core tolerances, complicated wiring schemes, and high power consumption.
Role of Oxygen in Obtaining Complete Magnetic First-Order Transitions in FeRh Films
Authors: Lommel J. M.
Published: February 2004

In contrast to the sharp first-order transition between antiferromagnetism and ferromagnetism observed in bulk FeRh samples, thin films of the compound were previously reported to have a broad, incomplete, and hysteretic transition. It has now been discovered that when FeRh films are given a diffusion anneal in a good vacuum, and then a second anneal in a N2 atmosphere with a trace of O2 present, a complete transition develops. The improvement in the transition due to the O2 annealing can be removed by annealing in H2. Microstructural differences are also observed in the O2-annealed samples which have a complete transition. Under some annealing conditions, however, impurities can completely remove the transition characteristic from films.
Separation of Anisotropy Components in Magnetic Films by Study of the Temperature Dependence of the Anisotropy Field
Authors: Zappe H. H.
Published: February 2004

The temperature dependence of Hk is a measure of the strength of interaction of the anisotropy-generating atomic configurations. In a film having several different anisotropy components, Hk(T) is therefore expected to be a superposition of several temperature dependencies. To obtain a separation, Hk(T) was measured at different stages of a magnetic anneal, during which the anisotropy components were (beginning with those activated at low temperatures) gradually reoriented into a direction in which, as a result of a new technique, they became excluded from the measurement. The function Hk(T) changed, indicating superimposed components having different temperature dependencies. Electroplated Ni–Fe–Cu and evaporated Ni–Fe–Co films were investigated. It was found that two major anisotropy sources exist. One, responsible for the annealing effects, has such a strong temperature dependence that it is unlikely to originate from a diatomic directional order. The temperature dependence of this component is independent of the degree of easy-axis stabilization. The other component (possibly due to atom pairs), is only weakly dependent on temperature, and does not measurably respond to magnetic annealing in the considered temperature interval (25°–170°C).
Kondo Phenomenon in Dilute Lanthanum-Cerium Solid Solutions
Authors: Arajs Sigurds , Anderson Elmer E.
Published: February 2004

The manifestations of the Kondo effect in lanthanum-rich fcc lanthanum-cerium solid solutions, containing 0.9, 2.0, 2.5, 3.9, 6.0, 6.5, and 8.5 at.% Ce, have been studied by electrical transport property measurements. The electrical resistivity data as a function of temperature between 4° and 30°K clearly reveal a resistivity minimum in all above-mentioned alloys. The temperature at which the minimum occurs is almost independent of cerium concentration: it gradually changes from 5.8°–7.4°K, associated with 0.9 at.% Ce- and 8.5 at.% Ce-alloy, respectively. The depth of the resistivity minimum, measured with respect to 4.2°K, increases from 0.01 μΩ-cm (0.9 at.% Ce) to 0.13 μΩ-cm (8.5 at.% Ce) with increasing cerium content. The additional electrical resistivity due to dissolved cerium in lanthanum is proportional to ln T, where T is the absolute temperature, for temperatures below 12°K. The total electrical magnetoresistivity studies at 4.2°K, made with longitudinal magnetic fields up to 60 kOe, show the following behavior: The resistivity increase with increasing fields is positive for pure normal lanthanum, almost independent of field for 0.9 at.% cerium alloy, and negative for all other lanthanum alloys. The absolute value of the magnetoresistivity increases with increasing cerium concentration. All these observations result from the localized magnetic moments associated with cerium dissolved in lanthanum.
High-Field Magnetoresistance of Dilute Cu–Mn and Cu–Fe Alloys
Authors: Rohrer H.
Published: February 2004

We have measured the magnetoresistance of dilute Cu–Mn and Cu–Fe alloys with impurity concentrations ranging from 0.14–0.12 at.% Mn and 0.04–0.40 at.% Fe, respectively, in the temperature range 1.3°–88°K and in magnetic fields up to 200 kOe. In Cu–Fe it is found that an appreciable part of the magnetoresistance is due to the field dependence of the scattering amplitudes. In the case of Cu–Mn, the magnetoresistance does not exhibit the expected saturation in high fields.
Resistivity and Susceptibility of Rh–Ru Alloys Containing Fe
Authors: Knapp G. S. , Sarachik M. P.
Published: February 2004

The susceptibility and resistivity have been measured as a function of temperature for several Rh–Ru alloys containing Fe. It is found that the θ's derived from the susceptibility data show no dependence on iron concentration, and change only moderately as the host composition is varied from Rh to Rh0.75 Ru0.25. Thus, the interpretation of these results as evidence for a Kondo quasibound state with TK depending exponentially on the density of states does not hold. It is also found that the linear behavior of ρ with Tχ(T), which led to the formulation of the two-band model, breaks down for ternary Ru–Rh–Fe alloys.
Local Moment Formation and Resistivity Minima in CoAl Alloys
Authors: Caskey G. R. , Sellmyer D. J.
Published: February 2004

Measurements of electrical resistivity, thermoelectric power, and magnetoresistance have been made from 1.4° to 300°K in alloys of 48%–57% cobalt in aluminum. At the equiatomic composition, CoAl has the CsCl structure. Resistance minima were observed in the vicinity of 30°K for cobalt concentrations between 50.4% and 51.5%. Below the resistance minima there is a temperature region where the dependence is approximately logarithmic before it saturates at about 1.4°K. The depth of the minima [ρ(1.4°K)−ρ(Tmin)] and the thermopower at 4.2°K both show rather sharp peaks as a function of concentration in the vicinity of 50.5% cobalt. The magnetoresistance of the samples showing minima is negative or T<Tmin and its magnitude increases with field up to 150 kG. These results and earlier susceptibility measurements for this system are discussed in terms of several current theories of the electronic effects of magnetic impurities in metals.