bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetoresistivity of a Dilute Pt:(Co) Alloy
Authors: Shen L. , Schreiber D. S. , Arko A. J.
Published: February 2004

We report the magnetoresistivity of a giant-moment dilute alloy of Pt:0.07% (Co), which has shown evidence of being a Kondo system. The magnetoresistivity can be separated into a normal part and a spin part; the former follows Kohler's rule, and the latter is positive, increasing with decreasing temperature and increasing applied field. The results are examined in the light of a s-d exchange model and a two-band model.
Evidence for Quasibound States in a Kondo Superconductor
Authors: Edelstein A. S.
Published: February 2004

Previous electron tunneling measurements1 on Ce in La showed that there were many more states at low energy than predicted by the Abrikosov-Gor'kov (AG) theory of gapless superconductivity. Further measurements on this system show that it is gapless even at very low concentrations and temperatures. This contrasts with the prediction of AG that there is an energy gap for n≤0.9ncr where n is the impurity concentration in at.% and ncr is the concentration which destroys superconductivity. At low impurity (Ce) concentrations in La the number of states in the gap N(0, 0) = (0.51±0.17)n. This result is most easily interpreted by assuming that one is observing a single impurity effect and that the energy gap is a function of position. Using this interpretation and the experimental results one finds the density of states has its normal state value for a range of approximately 7.6 Å around each impurity. It is possible that these added states are quasibound states formed near each Kondo impurity.
High-Field Magnetoresistance in Dilute Alloys
Authors: DeGrave I. , Foner S.
Published: February 2004

Results of high-field magnetoresistance measurements are summarized for dilute alloys1 of Cu(Mn), Cu(Fe), Cu(Cr), and Rh(Fe). The temperatures range from 1.3°–20°K and fields extend to 200 kG. The general features show a negative contribution to the magnetoresistance for Fe, Mn, and Cr in Cu and a positive one for Fe in Rh. This is consistent with the temperature dependence of the resistance for those alloys. The magnetoresistance data for Cu(Fe) and Rh(Fe) demonstrate that the magnetic moment is not fully developed at 200 kG as expected from (our unpublished) high-field magnetic moment data and from microscopic Mössbauer measurements.2 The approach to magnetic saturation in Cu(Mn) is examined in detail by means of the magnetoresistance data. We also construct μ(B, T) for the other alloys. The results are compared with our magnetic moment measurements and with related studies of the spin-compensated state. The detailed results of these experiments will be published elsewhere.
Anomalous Temperature Dependence of the Hyperfine Field at 119Sn in Co
Authors: Cranshaw T. E.
Published: February 2004

The fall of Heff at the nucleus of 119Sn in fcc Co from −22 kOe at 4.2°K to −10 kOe at 500°K has been reported. We have now measured Heff between 900° and 1300°K and find values of 8–9 kOe. The sign was not determined, but following the trend of the earlier results leads us to believe that it is positive. We take up the suggestion that there is a component of Heff due to 5s | 3d overlap which has a temperature dependence due to the strong distance dependence of 〈5s|3d〉. If |〈5s|3d〉|2∝r−n=(d−x)−n where d is the distance between atoms, x the thermal displacement of an atom, and n large, then |〈5s|3d〉|2∝〈x2〉, neglecting thermal expansion and higher terms. Using for simplicity an Einstein model for 〈x2〉, we find that the results can be well fitted by Heff=σ(−27.8+5.1 coth TE/2T), where σ is the magnetization, and TE = 281°K is an Einstein temperature.
Hyperfine Field of 197Au in Au–Fe Alloys
Authors: Borg R. J. , Pipkorn D. N.
Published: February 2004

We have investigated the magnetic hyperfine splitting of 197Au by means of the Mössbauer effect in Au-rich Au–Fe alloys. The hyperfine field appears with the onset of the magnetic order and the magnitude increases with concentration of iron. The spectra are broadened and unsymmetric due to the variety of compositional environments of the Au atoms in the alloys.
57Fe Nuclear Transverse Relaxation Times in Fe and some Fe-Rich Alloys: Suhl-Nakamura Interaction
Authors: Stearns Mary Beth
Published: February 2004

We have shown previously by pulsed NMR experiments that in the domain walls of pure Fe the main mode of the nuclear longitudinal relaxation process, T1, is due to the emission or absorption of a single magnon. Here we report on the behavior of the transverse relaxation, T2. In pure Fe, at 4.2°K and higher temperatures, again the main mode of transverse relaxation is emission or absorption of a single real magnon. However, in Fe alloys with 1–4 atomic percent Al or Co, T1≫T2 at 4.2°K, indicating that some other relaxation mechanism is dominant. Here the spin-spin exchange interaction of the Suhl-Nakamura type appears to be the main mode of transverse relaxation.
Mössbauer and Resistivity Study of Dilute Sn-Transition Metal Alloys
Authors: Huffman G. P. , Schwerer F. C. , Dunmyre G. R.
Published: February 2004

We have measured the hyperfine field of Sn119 nuclei as a function of temperature in dilute (¼ at.%) alloy of Sn in Fe and Ni from 4.2°K to the Curie temperature. For Fe, the reduced field vs reduced temperature curve decreases more rapidly than the corresponding reduced magnetization curve. If one assumes s electron screening of the Sn atom, and that the Sn nuclei respond to a reduced magnetization predicted for nearest neighbors of a nonmagnetic impurity atom by the molecular field model of Lovesey and Marshall, the results can be partially explained as arising from a decrease in the strength of the Ruderman-Kittel interaction due to the decrease of the electronic mean free path at elevated temperatures. For Ni, the reduced field also decreases more rapidly than the reduced magnetization and agrees reasonably well with a curve obtained by applying the above mentioned Lovesey-Marshall corrections to the reduced magnetization of Ni. The results are consistent with the concept of Sn impurity screening by d electrons. Preliminary results for a dilute hcp Co–Sn alloy up to T/Tc = 0.47 show a much larger, more anomalous decrease of field with temperature, which might be associated with the formation of a localized moment at the Sn site. Additionally, measurements of the residual resistivity in the three alloys and of resistivity vs temperature for the Fe–Sn and Ni–Sn systems have been made and a discussion of the results is given.
Hyperfine Fields in Nickel Alloys Measured by the 61Ni Mössbauer Effect
Authors: Erich U. , Kankeleit E. , Prange H. , Hüfner S.
Published: February 2004

The hyperfine (hf) fields at the nickel sites were measured in the alloy series NixFe1−x (0≤x≤1) using the Mössbauer effect of 61Ni. The field at the 61Ni nucleus follows the relation Hhf = aμNi+bμ̄ with a≃ −20 kOe/μB and b≃−100 kOe/μB, μ̄ being the average magnetic moment of the alloy. This indicates that the conduction electron polarization produces the main contribution. In GdNi2 and ErNi2 intermetallic compounds the fields are less than 25 kOe as dededuced from linewidth.
Mössbauer-Effect Study of Single-Crystal Holmium
Authors: Reese R. Allan , Barnes R. G.
Published: February 2004

The magnetic structures of holmium metal were studied using the 80.6 keV transition of Er166. Erbium was introduced, as a dilute impurity, into the single-crystal holmium sources through neutron irradiation. Using a cubic, paramagnetic absorber of ErAl3, the intensities of the five magnetic hyperfine lines were studied as a function of temperature. In the ferromagnetic region (T<20°K), a five-line spectrum with a weak central line was obtained when the c axis of the crystal was aligned parallel to the gamma-ray beam. This spectrum is consistent with the ferromagnetic spiral structure determined from neutron diffraction data. The line intensities are insensitive to the distortion of the spiral in which the magnetic moments are grouped symmetrically about the easy directions of magnetization The maximum value of He (at 4.2°K) is the same as in erbium metal. At 20°K the central line was no longer observable, indicating that the magnetic moments are confined to the basal plane at this temperature. The temperature dependence of the internal magnetic field is also reported.
Hyperfine Interaction and Susceptibility in Some Actinide Metals and Intermetallic Compounds
Authors: Dunlap B. D. , Brodsky M. B. , Kalvius G. M. , Shenoy G. K. , Lam D. J.
Published: February 2004

Magnetic effects in a number of actinide metals and intermetallic compounds are being investigated utilizing the 59.6 keV Mössbauer resonance of 237Np in conjunction with bulk susceptibility measurements. The cubic Laves phase compound NpAl2 is found to be ferromagnetic. The paramagnetic moment is 2.30 μB, somewhat lower than in other cubic Np magnetic materials. The saturation magnetic hyperfine field is found to be (3155±50) kOe. Taking H(T)/H(0) = D[1−T/Tc]β, we find D = 1.48±0.10, Tc = 55.8±0.1°K and β = 0.355±0.017 for 0.994>T/Tc>0.83. At lower temperatures, departure from molecular field behavior is seen. In cubic actinide magnetic materials, an electric-quadrupole hyperfine interaction will be observed due to alignment of the unquenched orbital momentum. In NpAl2 we find e2qQ = − (27±1) MHz. For NpC, which has the NaCl structure, we obtain the hyperfine parameters Hi = (4789±50) kOe and e2qQ = (577±58) MHz at 4.2°K. Metallic neptunium (orthorhombic) and americium (hexagonal) show no magnetic hyperfine coupling at temperatures as low as 1.7°K.
Faraday Rotation in Rare-Earth Iron Garnets
Authors: Crossley W. A. , Cooper R. W. , Page J. L. , van Stapele R. P.
Published: February 2004

The Faraday Rotation of YIG, GdIG, and TbIG has been measured at 1.15 μ as a function of temperature between 100° and 450°K. The rotation has been analysed in terms of electric and magnetic dipole contributions from the various sublattices (Fe3+ octahedral and tetrahedral, and Re3+), and the contributions separated by a least-squares fit to magnetization data taken from published NMR results. (Both magnetic and electric contributions from an ion are proportional to the ionic magnetic moment). The electric dipole contribution from the two different Fe3+ sublattices were quite similar in YIG and GdIG, but those in TbIG showed a greater deviation. It is suggested that charge-transfer processes may account for this. The effect of a knowledge of the electric dipole contributions at 1.15 μ on published rotation results at longer wavelengths was investigated, and the assignment of the rotation entirely to magnetic-dipole effects was shown to be wrong. This affects deductions of magnetic g factors from long-wavelength rotation results.
Crystal Field in Samarium and Dysprosium Garnets
Authors: Grünberg P. , Hüfner S. , Orlich E. , Schmitt J.
Published: February 2004

The crystal-field energy levels of the 6H and 6F multiplets of Sm3+ and Dy3+ in yttrium aluminium (YAG) and yttrium gallium garnet (YGG) have been fitted to the Hamiltonian appropriate for the D2 site symmetry of the rare earth ion. A good fit has been obtained for both garnets. For the dysprosium garnets also the groundstate g factors were found to agree well with the calculated ones.
Angled Spin Configurations in YbIG
Authors: Clark A. E. , Buchanan R. A.
Published: February 2004

This paper presents spectroscopic evidence for the existence of angled spin configurations in ytterbium iron garnet (YbIG) near its compensation temperature (∼7.5°K). We measured the rare earth-iron exchange split single-ion transitions at 23.2 and 26.5 cm−1 in the far infrared as a function of magnetic field applied along the [111] easy magnetization axis. We find that these transitions do not decrease linearly with increasing magnetic field at 8.5°K as predicted from the g factors characteristic of splittings at higher temperatures.1,2 In fact from 30–50 kOe, the spectrum consists of 4 lines 21.1, 23.3, 25.5, and 27.4 cm−1 whose average energy is not appreciably different from that of the unsplit spectrum. All our observations are consistant with the prediction of a temperature range below 20°K where the sublattice magnetizations are not collinear, but where angles are developed between the sublattice magnetizations and the applied field.3 That the average splitting is not appreciably field dependent suggests that very little energy is needed to rotate the sublattice magnetizations.
Ultraviolet Magneto-Optical Properties of Single-Crystal Ferrimagnetic Ferric Oxide Compounds
Authors: Kahn Frederic J. , Pershan P. S. , Remeika J. P.
Published: February 2004

The first uv measurements of the complex polar-Kerr effect (rotation and ellipticity) are reported between 1.7 and 5.64 eV for representative ferrimagnetic ferric oxide compounds containing both octahedral (Feoct) and tetrahedral (Fetet) sites. Room-temperature measurements on bulk single crystals of pure and Ga-doped rare earth iron garnets, spinel ferrites, and magnetoplumbite are used to distinguish between the contributions of Feoct and Fetet to the magneto-optical spectra. Analysis shows that charge-transfer transitions at about 4 and 5 eV, associated with Feoct and Fetet, respectively, are responsible for the principal uv magneto-optical spectra of all the compounds studied. A model based on anisotropic orbital quenching explains why magneto-optical effects in the orthoferrites are of the same order of magnitude as those in the ferrimagnetic ferric oxide compounds, even though the net magnetizations of the latter are typically an order of magnitude larger.
Linear Magnetic Birefringence in Cubic Magnetic Crystals
Authors: Dillon J. F. , Remeika J. P. , Staton C. R.
Published: February 2004

For light traveling perpendicular to the magnetization in a ``cubic'' magnetic crystal, the normal modes are linearly polarized parallel and perpendicular to M. The difference in the velocities of these modes constitutes a Linear Magnetic Birefringence (LMB) which may be easily observed. Measurements of retardation for M∥ [100] and for M∥ [111] are needed to specify the LMB for a cubic crystal. These quantities R100 and R111 have been measured at 77° and 300°K for each of the rare-earth iron garnets. With the notable exception of TbIG and SmIG, there is evident a correlation between the LMB and the magnetostriction.
Resonance in Magnetically Ordered Crystals with Anisotropic g Factors
Authors: Gurevich A. G. , Sanina V. A. , Golovenchits E. I. , Starobinets S. S.
Published: February 2004

The equations of motion of the sublattice moments are discussed in the case of anisotropic g factors when the lengths of mechanical moments are conserved, or are not conserved. Experimental data on magnetic resonance in hexagonal ferrimagnet RbNiF3 and orthorhombic canted antiferromagnet NaNiF3 are interpreted on the basis of such equations with the suggestion that the lengths of mechanical moments are conserved. It is shown that for both crystals the g-factor anisotropy must be taken into account.
Magnetic Lag and Anisotropy Due to Interstitials in fcc Ferromagnetic Alloys
Authors: Adler E. , Radeloff C.
Published: February 2004

In fcc alloys, carbon and other interstitials occupy octahedral sites and hence were long believed to cause no lag, except for pairs of interstitials. In contrast to this the authors have recently found strong lag and anisotropy caused by single interstitials of carbon, hydrogen, and nitrogen. It is shown that this lag is due to the fact that in fcc solid solutions the environment of octahedral sites is noncubic. The induced anisotropy increases linearly with interstitial content. The symmetry axis of lattice defects are preferably the 〈100〉 directions in nearly pure metals and 〈110〉 and 〈111〉 directions in binary alloys with a high concentration of substitution solute atoms. In pure metals, induced anisotropy is only a small residual effect. The paper includes: Theory of this lag; experimental data of disaccomodation behavior; determination of activation energy; comparison with damping experiments and theories; aspects for technically useful materials.
Effects of AlN on the Primary Recrystallization Textures in Cold-Rolled-(110)[001]-Oriented Single Crystals of 3% Silicon Iron
Authors: Sakakura Akira
Published: February 2004

Cold-rolled-(110)[001]-oriented single crystals of 3% silicon iron containing AlN in solution develop a doublet {111} 〈110〉−oriented primary recrystallization texture consisting of grains with diameter of 0.5 to 1 mm after anneal at 550°C for 40 h followed by anneal at 1200°C. At the first anneal, very fine needle-like AlN precipitates, while (110)[001]-oriented primaries begin to originate at the surface of the sheet. At the heating process of the subsequent anneal, doublet {111} 〈110〉−oriented primaries originate at the middle of the sheet, and then grow at the expense of (110)[001]-oriented primaries. It is proved that very fine needle-like AlN precipitated after cold rolling is found to have a great effect on these primary recrystallization phenomena.
Dynamic Behavior of a Near-Ising System Near the Critical Point
Authors: Meijer P. H. E. , Edwards J. C.
Published: February 2004

Applying the master equation to an Ising model, equations of motion are obtained for the average of a single spin and for the average of a pair of spins. These equations relax to equilibrium values that predict a self-consistency relationship among the internal field, temperature, and exchange energy. The critical temperature obtained is that of the Bethe approximation, and is extended to include a static external field in the magnetization direction. With this, the relaxation of an Ising model near the Curie temperature has been investigated in a self-consistent manner. The results are similar to those of Suzuki and Kubo, but in the Bethe approximation instead of the Bragg-Williams approximation, and hence predict the relaxation of the correlation as well. In particular we studied a nearly Ising spin system that is a system with relatively small isotropic transverse coupling. An oscillating, linear, and external magnetic field applied transverse to the strongly coupled direction of the spins leads to lowering of the critical temperature.
Entropy and Susceptibility of a Pure Dipole-Dipole System (Cerous Magnesium Nitrate)
Authors: Meijer Paul H. E. , O'Keeffe David J.
Published: February 2004

The Van Vleck moment expansion is applied to a pure dipole system. On the basis of the long-range nature of the forces, sequences of diagrams are selected that give the dominant contributions in the lattice sums. A selection of diagrams contributing to the entropy and susceptibility is given. There are three different summations to be performed for each type of diagram: the trace over the spin variables, the lattice summation, and the summation over the Cartesian coordinates. The second is performed on the computer and the last by means of the Kramers-Wannier diagonalization. In order to obtain the contributions of diagrams of higher order a Fourier transform is performed. The calculations were performed for Cerous Magnesium Nitrate using a g factor that is zero along the c axis.
Magnetic Scattering of Neutrons from Heisenberg Antiferromagnets
Authors: Bennett Herbert S.
Published: February 2004

The magnetic scattering of neutrons from Heisenberg antiferromagnets in the paramagnetic state is discussed within the rigorous framework of a spectral representation for the longitudinal spectral weight function, low-order moments of this function, and sum rules. The longitudinal spectral weight function is expressed as a functional of the longitudinal diffusivity. The exact framework leads naturally to a phenomenological description of the neutron-scattering cross section in Heisenberg antiferromagnets. It is shown that replacing the longitudinal diffusivity by the sum of a Gaussian function and a resonating function which satisfies the sum rules gives the essential features for neutron scattering in the Hesienberg antiferromagnet RbMnF3.
Hydrodynamic Theory of Spinwaves
Authors: Halperin B. I. , Hohenberg P. C.
Published: February 2004

We have developed a hydrodynamic theory of spin fluctuations in an isotropic antiferromagnet, which is similar to the theory of two-fluid hydrodynamics for helium.1 In the long-wavelength limit, we find spin waves at any temperature below TN, with real frequency proportional to the wavevector k, and a dampling rate proportional to k2. The real frequency is given in terms of thermodynamic quantities and agrees with earlier predictions; the wavevector dependence of he damping, however, disagrees with earlier (microscopic) calculations.2 The results may be tested by neutron-diffraction experiments on RbMnF3. A similar hydrodynamic theory fo the isotropic ferromagnet predicts spinwaves with a frequency proportional to k2 and a damping proportional to k4.
Mobile-Electron Ising Ferromagnets
Authors: Fisher Michael E. , Scesney Paul E.
Published: February 2004

A general mobile-electron Ising model is described and its properties discussed: electrons migrate over a lattice of spin-½ positive ions; when there are k electrons on the bond (i, j), their energy is εk, and they induce an Ising spin coupling between the spins i and j. The mean number of electrons per bond, n, is determined by the condition of electroneutrality. The model is solved exactly in terms of the free energy of the underlying lattice; in three dimensions the magnetization, susceptibility and specific heat exhibit the renormalized1 critical-point exponents2 β=0.33−0.36, γ≃1.43, αs≃−0.14. The behavior of the simplest ferromagnetic model with k=0, 1 or 2, and n≤2 depends, for a fixed mode of electron-ion coupling, only on n and ε=2ε1−(ε0+ε2). When ε→−∞ (n≤1), bonds with k=2 are suppressed and the model becomes equivalent to Syozi's dilute ferromagnet.3 For ε<ε*= E0,0+E0,2−2E0,1 (where E0,k is the ground-state magnetic energy of a k bond) the model remains similar to Syozi's, having a critical concentration for the occurance of ordering nc=pc (determined by the underlying Ising lattice; see Ref. 3). However, when ε>ε* and 2pc>n>p*>pc a lower critical temperature arises, below which the spontaneous magnetization M0(T) again vanishes; this results from self-dilution on cooling owing to loss of k=1 bonds as T→0. When n=2pc this Tc, lower vanishes; for 2>n>2pc there is no lower critical point, but M0(T) at first increases with T. With the addition of direct ion coupling and antiferromagnetic interactions the model exhibits an even greater variety of behavior.
Effect of Magnons on Thermal Transport in Insulators
Authors: Rives J. E. , Dixon G. S. , Walton D.
Published: February 2004

Magnons can influence the thermal conductivity of insulators either by interacting with the phonons or by transporting heat. In a ferromagnet or ferrimagnet the magnon energies are raised by a magnetic field. The magnon-phonon interaction can suppress the contribution of phonons whose energy is close to that at which the magnon and phonon dispersion curves cross. A magnetic field moves the crossover to higher phonon energies. The phonon contribution is peaked at about an energy of 4 kT in a good crystal. Thus the phonon conductivity initially decreases with increasing field, then recovers to its zero field value at sufficiently high fields, but the magnon part does not. Similar effects occur in antiferromagnets. Using a 3He cryostat capable of reaching 0.2°K and a magnet capable of fields up to 50 kOe, we have observed these effects in MnCl2·4H2O, GdCl3, YIG, and Li Ferrite. In all the crystals except YIG and Li Ferrite, recovery to the zero field value eventually occurred, indicating that the magnon contribution had to be less than 2% of the heat current at zero field. In YIG the magnons contributed about 66% of the heat current. In Lithium Ferrite they contribute about 40%.
Anisotropy and Magnetostriction Measurements on (Ca+V+In)-Substituted YIG
Authors: Van Hook H. J. , Euler F. K.
Published: February 2004

Garnet crystals of the general composition {Ca2xY3−2x} [InvFe2−v] (VxFe3−x)O12 were obtained by flux growth in the ranges 0[equal to or less than]x[equal to or less than]1 and 0[equal to or less than]y[equal to or less than]0.35. The individual compositions of the crystals were determined by electron microprobe and confirmed by lattice parameter, magnetization Ms and Curie point Tc measurements. By microwave resonance techniques, magnetostriction constants λ100, λ111 (at room temperature) and magnetic anisotropy constants K1, K2 (with 4K[equal to or less than]T[equal to or less than]300K) were determined. The function |K1(x)| at T = 4K is nonlinear and exhibits a maximum at x≈0.20, as the well known Tc(x) does.1 The magnetostriction constants are both negative and vary between −1.5×10−6 and −4.3×10−6 with composition. These single-crystal data are supplemented by polycrystalline resonance lineshape studies on compositions with 0.8[equal to or less than]x[equal to or less than]1.3, at 4K<T<300K. With these new anisotropy data, the polycrystalline resonance linewidth follows the recent theoretical predictions of Schlömann2 over a wide range of ρ=K12/(21π2Ms4).
High Temperature Limit of the Thermal Conductivity of a Magnetic Lattice
Authors: Huber D. L.
Published: February 2004

The transport of energy in magnetic lattices at high temperatures is investigated. An approximate expression for the thermal conductivity is derived. The calculation involves a factorization of the thermal current correlation into a product of three two-spin functions and the use of a Gaussian approximation for the pair correlation function. Values for the conductivity are compared with corresponding values obtained from the expression CVDE, where CV is the specific heat and DE is the energy diffusion constant. Agreement within a factor of two is obtained for two and three dimensional spin one-half lattices with nearest-neighbor isotropic exchange interactions. The thermal conductivity of linear chains is studied in detail. Windsor's numerical calculation of the conductivity of a classical chain1 is compared with estimates based on the diffusion model and the factorization approximation. It is found that the diffusion model is in agreement with the numerical analysis. The factorization approximation fails to reproduce the longtime behavior of the correlation function and thus leads to an estimate of the conductivity which is too small by a factor of three. Energy transport in the spin one-half chain is shown to be nondiffusive. Details of the investigation will be published elsewhere.
Far-Infrared Ferromagnetic Resonance in Dysprosium and Terbium Metals
Authors: Marsh H. S. , Sievers A. J.
Published: February 2004

The surface impedances of polycrystalline Dy and Tb metals have been measured between 3 and 30 cm−1 as a function of temperature from liquid-helium temperature to 153°K. In zero magnetic field, the surface impedance in each case can be separated into two components. A broad background which increases with increasing frequency and temperature has been identified with conduction processes. A strong ferromagnetic resonance is superimposed on this background, and its frequency decreases monotonically with increasing temperature. The resonance frequency decreases from 24.2 cm−1 at 4.2°K to 9.2 cm−1 at 80°K in dysprosium, and from 13.7 cm−1 at 4.8°K to 4.7 cm−1 at 153°K in Tb. In the temperature ranges studied, both metals are planar ferromagnets with gaps in the spin-wave spectra due to large uniaxial and hexagonal anisotropies. Our results in both cases can be explained by the addition of a magnetoelastic contribution to the spin-wave energies first proposed by Turov and Shavrov and calculated by Cooper.
Spin-Wave Excitation Dependence upon Oxygen in Thin Nickel-Iron Layers
Authors: Blades J. D. , Lin C. J. , Cola R. A.
Published: February 2004

A clear-cut characterization of the role of oxygen present in 83 Ni–Fe vapor-deposited thin layers has been sought by a series of spin-wave resonance experiments upon samples that have been prepared under controlled ultrahigh vacuum conditions. Dryed oxygen was leaked into the vacuum chamber to obtain partial pressures of 1 and 5×10−8 and 1×10−7 Torr, prior to the formation of and during the cooling of the UHV condensed films. Of significance has been the response of the main peak resonance field strength, linewidth and intensity to the oxygen vapor point relative to a best vacuum, minimum oxygen, fabrication condition (<1×10−9 Torr). With an increase of oxygen the resonance field strength and intensity decrease and the linewidth increases. A direct influence of oxygen is observed to begin by extrapolation at 10−9 Torr partial pressure. Resonance line spacings were invariant to the controlled oxygen vapors. From the results that have been obtained, it can be surmised that the bulk magnetic properties of these thin layers are altered magnetically only slightly for oxygen content less than 10−8 Torr, and as the oxygen content increases, (1) it decreases the average magnetic moment of the layer through the formation of oxides; (2) a structural linewidth mechanism has been introduced; and (3) the basic spin-constraint mechanisms have not been altered.
Search for Magnetoelastic Effects in Tb Metal by Ferromagnetic Resonance at 2.5–3 mm
Authors: Wagner T. K. , Stanford J. L.
Published: February 2004

Recently magnetoelastic effects have been included in the Hamiltonian for the heavy rare-earth metals in a theoretical investigation by Cooper.1 We present data from a new, detailed study of single-crystal Tb extending over the temperature range 20°–240°K. The temperature dependence of the resonance field at 98.2 GHz is compared with the calculations of Cooper for 100 GHz for hexagonal anisotropy due to strain and for the case of unstrained hexagonal anisotropy. The experimental data fail to exhibit the rise of resonance field at low temperature required by either theory. The resonance can be followed down in field until, between 160° and 170°K, it disappears below structure believed to be associated with the onset of magnetostriction in our crystal (at ∼4 kOe). The resonance is not observed to rise above this structure in the temperature range 20°–160°K. Angular studies near 170°K reveal no hexagonal anisotropy to within the scatter of the data. Polarization studies at 98 GHz show that the amplitude of the absorption peak varies as the square of the sine of the angle between the rf and dc magnetic fields, the expected dependence for spin-wave excitation.
Spin-Wave Resonance of Irradiated Permalloy Films
Authors: Bailey G. C.
Published: February 2004

A study of the spin-wave resonance in the parallel and perpendicular orientations at 9.5 GHz has been made on a number of irradiated Permalloy films (thicknesses: 900 to 3100 Å; melt composition: 80% Ni–20% Fe). The films were evaporated onto fused-quartz and soft-glass substrates in a vacuum initially at 2×10−8 Torr, annealed in a magnetic field for 12 h at 250°C (the substrate temperature during evaporation), and irradiated with 3×1017 He3 particles per cm2. The resonance patterns of the films show a number of interesting features, including changes in the resonance fields, Hn, and intensities, In. In the perpendicular orientation, Hn generally decreased with irradiation except for the two thicker films where Hn=1,2 increased; in the parallel orientation, Hn generally increased. In the perpendicular orientation, the intensity changes of the modes varied both with the order number and with the film thickness. In general, as a function of order number and excluding the first mode, In odd initially decreased for the thicker films, In even initially increased, and then all In increased; for the thinner films, all In initially increased and then decreased for n>4 or 5. In the parallel orientation, the intensity changes were generally less than in the perpendicular case. Annealing the films at 200°C shows that some of the irradiation-induced changes are reversible. The observed changes occur as a result of changes in a number of parameters: the stress in the film (including stress changes both in the film alone and in the substrate), the magnitude and the inhomogeneity of the magnetization, and the surface anisotropy (and hence spin pinning).
Convenient Magnetostatic Mode Measurement of 4nM8 of Planar-Anisotropic Ferrites
Authors: Weller D. B.
Published: February 2004

A convenient stripline technique for generating the 210 magnetostatic mode has been used to measure the 4nM8 of planar-anisotropic ferrite materials. White has described the use of magnetostatic modes as a research tool. Precision measurements by Dillon, Fletcher, and others have used waveguide cavities to obtain rf field components required to excite the desired magnetostatic modes. These techniques have been extended to permit a simple 4nM8 measurement in a nonresonant transmission line. An rf strip transmission line with a hole in the center conductor will effectively couple to the 210 magnetostatic mode of a ferrimagnetic sphere centered within the hole. The 110 mode can also be excited by axially withdrawing the sphere to a linear rf magnetic-field location. The 4nM8 of high anisotropy, hexagonal ferrites as well as more conventional cubic (YIG) ferrites have been measured using this technique. It is seen that the resonance equations for the 210 and 110 mode in a spherical resonator may be solved in general for the saturation magnetization in terms of only the externally applied magnetic fields. (ω210/γ)2=[H210−(8πMs/15)+Tx][H210−(8πMs/15)−Tz]  (ω110/γ)2=(H110+Tx)(H110−Ty),=4πMs=(15/2)(H210−H110),where Tx and Ty represent anisotropy contributions. Measurement of pure YIG and MnZnY spheres indicate that the absolute values for 4nMs may be between 2 and 10% high, dependent on circuit dimensions. Additional material properties and measurement variables will be presented.
Experimental Test of Néel's Theory of Coercive Force due to Inclusions
Authors: English A. T.
Published: February 2004

Inclusions in soft ferromagnetic materials generally cause an increase in the observed coercive force Hc. The present objective was to determine whether the mechanism of this increase is the magnetostatic interaction of inclusions with moving domain walls, as originally proposed by Néel. Information on this point can be obtained by measuring Hc as a function of temperature in two-phase alloys which consist of a ferromagnetic matrix phase plus a distribution of ferromagnetic inclusions. For such alloys, Néel's theory predicts a peak in Hc at the Curie temperature of the inclusions. Previous experiments showed that a peak was sometimes present in samples of 0.8% C steel (α-iron plus cementite), depending on microstructure. The role of microstructure has now been clarified: the peak is always present if the inclusion size is about 0.1 μ, independent of the details of the inclusion morphology. The effect is not peculiar to Fe–C alloys, since it has also been observed in Fe-25%Ni. It is noteworthy that a substantial volume fraction of larger inclusions (diam. ≃1 μ) raises Hc, but apparently not via the magnetostatic mechanism.
Secondary Recrystallization of Silicon-Iron by Solute-Induced Boundary Restraint
Authors: Grenoble H. E. , Fiedler H. C.
Published: February 2004

The secondary recrystallization of silicon-iron requires that normal grain growth be restrained. This restraint has been attributed to dispersions of small inclusions usually identified as sulfides or nitrides. In this paper, it is shown that sulfur and nitrogen, when present together as solutes, will enable secondary recrystallization to occur.
Magnetic Properties of Textured Silicon-Iron Alloys with Silicon Contents in Excess of 3.25%
Authors: Ames S. L. , Houze G. L. , Bitler W. R.
Published: February 2004

Single-crystal- and polycrystalline-magnetic-property data available for silicon-iron alloys as a function of silicon content suggest that textured silicon-iron alloys with silicon contents in excess of that present in currently available commercial alloys (3.25%) would have improved magnetic properties. Because of processing difficulties, such alloys have not been produced and their properties reported. In this study 3.25%-silicon-iron alloys with a cube-on-edge texture were siliconized to uniform silicon contents of up to approximately 6.5%. For suitably prepared and annealed samples, enhanced magnetic properties were realized. Core loss, coercive force, and magnetostriction were considerably reduced. The increased silicon content also rendered the alloy amenable to improvement in core loss on magnetic annealing, presumably due to the greater tendency to atomic ordering at higher silicon levels. The decreased saturation accompanying higher silicon contents was reflected in increased excitation field necessary to attain inductions of 15 000 and 17 500 G.
High-Strength High-ductility Cobalt-Iron Alloys
Authors: Thornburg D. R.
Published: February 2004

Through careful control of final heat treatment, it has been found that commercial grade cobalt-iron alloys (49% Co, 49% Fe, and 2% V) can have both good room temperature mechanical properties and reasonable high field permeabilities in the partially recrystallized condition. As an example, on tensile samples from one commercial heat, an average yield strength of greater than 90 000 psi was obtained together with elongations in excess of 10% for one particular annealing treatment. Although the magnetic characteristics were somewhat degraded, the Btip (H = 100 oersteds) exceeded 22.5 kG. When similar samples were completely recrystallized, yield strength did not exceed 70 000 psi while ductility was never larger than 8%. An interesting feature of the investigation was the fact that the maximum ductility was obtained on samples with a partially-recrystallized structure. Possible mechanisms are discussed, which relate this phenomena to atomic ordering and recovery-recrystallization behavior.
Correlation of Magnetic Permeability and X-Ray Diffraction Line Broadening in Cold-Worked Iron
Authors: Rusnak R. M. , Cullity B. D.
Published: February 2004

The permeability of annealed and cold-worked iron (0%–3.8% plastic tensile strain) was measured at field levels up to 0.8 Oe. and found to obey the Rayleigh relationship, μ=μ0+vH. The results show that the reciprocal of either Rayleigh constant, μ0 or v, varies linearly with the square root of the plastic strain value and that their ratio (μ0/v) is essentially independent of the degree of plastic strain. X-ray diffraction lines were also recorded for each sample and the line width was found to vary linearly with the square root of the plastic strain. The x-ray line broadening produced by cold work is ascribed to small particle size, caused by dislocations with an average spacing of D. The constant μ0, taken as a measure of reversible domain wall motion, is shown to be directly proportional to D, in support of certain models which have been proposed for hindrances to wall motion.
The {111} 〈211〉 Texture in Silicon Steel by Secondary Recrystallization
Authors: Benford J. G. , Stanley E. B.
Published: February 2004

Secondary recrystallization in silicon steel is a phenomenon attributed to either a second-phase or surface-energy mechanism, and tertiary recrystallization is attributed to a surface-energy mechanism. The large-grained structure and preferred orientations resulting from these phenomena and reported in the literature have involved either a (100) or (110) plane in the plane of the sheet. Recently a {111} 〈211〉 or cube-on-corner texture, apparently developed by a secondary-recrystallization mechanism in the presence of selenium or selenide vapors, has been observed. The grain structure is reminiscent of that observed in cube-textured silicon steel and, in fact, when annealed in the absence of selenium or selenide vapors, cube texture did develop. Evidence is strong that a surface-energy mechanism is involved. Material with this texture is nearly magnetically isotropic as demonstrated by a maximum magnetic torgue of 7000 dyn·cm/cm3 compared to about 30 000 dyn·cm/cm3 for conventional nonoriented electrical steels. Magnetic tests on 5-mil-thick samples with the {111} 〈211〉 texture revealed a core loss of 0.44 W/lb/60 and permeability of 12 800 at 10 kG.
Effect of Dispersoid Parameters on High-Temperature Behavior of Cobalt and Iron +27% Cobalt
Authors: Towner R. J. , Pavlovic D. M.
Published: February 2004

The need for soft magnetic materials to operate at high temperatures in space electric-power systems requires a more fundamental understanding of the effects of nonmagnetic phases on basic magnetic behavior of synthetically strengthened metals. Coercive force (Hc) was measured at room temperature and 1200°F (649°C)–1600°F (871°C) on nineteen Co-base and ten Fe +27% Co-base extrusions dispersion-strengthened with 0.02–0.3 volume fraction (V) of oxide and boride particles ranging from 0.1 to 1.6 micron average diameter (d). The measured effect of this range of dispersoid parameters on Hc was correlated and interpreted by reference to equations of the form developed by Kersten, Néel, and Mager for particular inclusion sizes. The increase in Hc with V/d ratio was linear in most instances. Small changes in Hc resulted from the development of a fibrous subgrain structure by secondary working treatments (cycles of swaging and partial stress-relief annealing). These treatments provided both a substantial strengthening effect and thermal stabilization of the matrix for those materials containing finer dispersions, V/d≧0.75. Conclusions were reached concerning the limits of application and refinement of theoretical equations for predicting the influence of dispersoids and temperature on Hc.
Band Structure of Magnetic Semiconductors
Authors: Adler David , Feinleib Julius
Published: February 2004

A method is proposed for representing the effective one-electron density-of-states of materials in which some of the valence electrons are extremely localized. If some additional rules regarding nonconducting states and occupation-number dependent states are imposed, this scheme can be used to interpret both the electrical and optical properties of magnetic semiconductors. The materials NiO and CoO are discussed in detail.
Spin-Polarized Energy-Band Structure of Antiferromagnetic MnO
Authors: Wilson Timothy M.
Published: February 2004

A study has been made of the energy-band structure of antiferromagnetic MnO using a spin-polarized Augmented Plane Wave procedure. An earlier calculation, which was made using the form of the free-electron exchange potential originally proposed by J. C. Slater, predicted an energy gap of 2.7 eV. However, it also predicted the valence band to be composed of states having predominantly O2− 2p character. The results of the present calculation, which has been made using a modified form of the free-electron exchange potential, also leads to the prediction that MnO should be an insulator; however, in this case the valence band is predominantly composed of Mn2+ 3d states. These results are in better agreement with the observed optical properties of this compound. In both cases the conduction band is a mixture of Mn2+ d and s states. The energy gap separating the two Mn2+ d-bands can be shown to be in large part due to the intra-atomic exchange splitting of the d-level of the Mn2+ ion.
Temperature Dependence of Spin Structures Under the s-f Interaction
Authors: Fedro A. J. , Arai T.
Published: February 2004

A system of spins interacting through the s-f exchange coupling may exhibit an antiferromagnetic screw structure with temperature-dependent pitch parameter Q, but transform to a ferromagnetic state at a lower temperature. This behavior is shown to be explained by temperature-dependent distortion in the shape of the Fermi surface. The expression for the number operator which determines the chemical potential μ and the Fermi surface is calculated by the Green's function technique. A simple second-order perturbation treatment gives the expression involving a Kondo-like integral and yields the desired temperature dependence in kf in appropriate directions.
Spin Configurations in an Antiferromagnetic Slab
Authors: Shane J. R. , Lyons D. H.
Published: February 2004

The low-energy spin configurations of a two sublattice antiferromagnet have been examined for a sample of finite thickness. The model consists of layers of spins connected by isotropic nearest-neighbor exchange interactions. The applied field and the anisotropy field are assumed to be perpendicular to the layers; the molecular-field approximation is used to relate the orientations of the spins within a layer. The equilibrium equations and boundary conditions are found as a continuum limit of difference equations obtained by minimizing the energy with respect to the directions of the spins. It is found that a nonuniform spin configuration has a lower energy than the uniform antiferromagnetic state for applied fields above (2)−1/2Hc, where Hc is the critical field for the spin-flop transition that occurs in the usual treatment of the two sublattice model. In the new equilibrium state, the spins at the center of the slab are arranged in a spin-flopped configuration. At applied fields well below Hc, the configuration rapidly approaches the antiferromagnetic state with increasing distance away from the center of the slab. As the applied field is increased through Hc, the width of the ``flopped'' region near the center increases rapidly and the configuration approaches a uniform spin-flop state except in the regions near the surface. It is found that the surface spin-flop state1 does not occur as an equilibrium solution of the problem if all important contributions to the difference equations are retained.
Electron-Nuclear Double Resonance and Relaxation in RbMnF3
Authors: Ince William J.
Published: February 2004

Electron-nuclear double resonance has been observed in RbMnF3 at liquid-helium temperatures. Nuclear saturation, which was induced by applying a large amplitude UHF signal to the sample, was detected as a shift in the field required for AFMR at x-band frequencies. With the field applied in the [100] direction, saturation could be induced by pumping either the low-field or spin-flop modes. For a given x-band frequency, the effective nuclear temperatures for the low-field and spin-flop modes were in substantial agreement. The range of pumping frequency over which saturation could be induced was roughly 100 MHz, (≤686 MHz), and was a function of the Mn55 resonant frequency. Extrapolation of the experimental data to infinite nuclear temperature yields a value of 686.5 MHz for the unpulled nuclear hyperfine frequency, which agrees well with the value obtained from direct NMR experiments. Measurements of the saturation decay yielded a value of 50 msec for T1 at 4.2°K.
Nuclear and Electronic Spin-Wave Relaxation Rates in the Hexagonal Antiferromagnet CsMnF3
Authors: Seavey Marden H.
Published: February 2004

Nuclear and electronic spin-wave relaxation rates have been measured in the hexagonal antiferromagnet CsMnF3 in the flopped state using two kinds of parallel pumping experiments. In the first experiment, previously performed by Hinderks and Richards for RbMnF3, values of the product ηknηke are obtained from critical field data for simultaneous nuclear-electronic spin-wave instability using a 9.35 GHz pump. In the second experiment values of ηke are obtained by pumping at 17.5 GHz, twice the electronic spin-wave frequency. Reasonable agreement with a theory of Richards is obtained at 4.2° and 1.7°K for relaxation rates of the nuclear spin-waves having k ≈ 105 cm−1. For k ≈ 0 there is an order-of-magnitude discrepancy which may be accounted for if it is assumed that inhomogeneities strongly mix modes for k<105 cm−1. The electronic spin-wave linewidths for k ≈ 0 are much smaller than the AFMR which is independent of temperature from 4.2°–1.7°K. These results are consistent with a random strain-broadening interpretation of the AFMR width.