bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Pressure on the Magnetic Transition of MnAsxSb1−x Solid Solutions
Authors: Edwards L. R.
Published: February 2004

The ferromagnetic transition temperatures of MnAsxSb1−x solid solutions for 0≤x≤1 have been measured as a function of pressure up to 4.5 kbar. Goodenough et al.1 have shown that for the alloys in the composition range 0.9≲x≤1 the magnetic transition is first order and is accompanied by a hexagonal to orthorhombic structural transformation, while for 0≤x≲0.9 the magnetic transition is second order. We find that this system exhibits a number of unusual features: (i) The change from first to second-order behavior occurs within a narrow concentration range 0.88<x<0.9; (ii) the initial pressure derivative of the transition temperature dTc/dP changes discontinuously in the concentration range 0.88<x<0.9; (iii) the transition temperature Tc exhibits a rather sharp minimum near this range. In the second-order regime dTc/dP decreases from −3 to −6.3°C/kbar as x increases. On the basis of an itinerant ferromagnet model it has been demonstrated that dTc/dP is related to Tc by the following equation2dTc/dP=ATc−B/Tc. We find for the alloys in the concentration range 0≤x≤0.75 this relation is obeyed. We have also studied in some detail the T—P magnetic phase diagram of MnAs0.9Sb0.1 and find it to be qualitatively similar to pure MnAs. The main difference is that the critical pressure to stabilize the orthorhombic phase is increased by approximately 1 kbar.
Localized Polarization on Sn Atoms in Ferromagnetic Transition Metals and Alloys
Authors: Huffman G. P. , Dunmyre G. R.
Published: February 2004

We have made 119Sn Mössbauer measurements on an alloy of Fe0.5Ni0.5 containing 1 a/o 119Sn from 4.2 K to the Curie point. 57Fe Mössbauer measurements were also made from 4.2 to 300 K. The hyperfine field at 119Sn nuclei behaves anomalously, decreasing much faster with temperature than does the magnetization, in a manner similar to that observed in Co. We interpret this anomalous behavior as being caused by a localized polarization associated with the Sn impurity and are able to fit the field-vs-temperature data well with a localized moment molecular field theory. A model of the Anderson type is outlined which indicates how localized polarization can form on a ``nonmagnetic'' impurity.
Magnetic Structure of Mn3O4 by Neutron Diffraction
Authors: Boucher B. , Buhl R. , Perrin M.
Published: February 2004

Mn3O4 is a tetragonal spinel I41/amd. It is ferromagnetic below Tc = 43°K. At 4.2°K neutron diffraction measurements on powdered samples show the presence of 8 sublattices in a unit cell a, 2a, c which is double the chemical unit cell. These 8 sublattices are arranged as follows: 2 sublattices at tetrahedral sites and 6 sublattices at octahedral sites. At 4.2°K the moments are 4.65 μB on A sites and 3.55 μB on B sites with a resulting moment of 1.85 μB/molecule along the (010) direction. The study of thermal variation of the structure shows that at 33°K a rearrangement of moments occurs such that the chemical and magnetic unit cells become identical.
Magnetic Structure of MnAs and MnAs0·92P0·08
Authors: Schwartz L. H. , Hall E. L. , Felcher G. P.
Published: February 2004

The similarity of the ordered magnetic structures of orthorhombic MnAs (stable at high pressure) and orthorhombic MnAs0.92P0.08 has been confirmed using neutron diffraction. Below the magnetic ordering temperature, Tc, a canted spin structure is found for both materials. Neutron diffraction measurements from magnetically ordered and disordered temperature regions show that in these materials the Mn magnetic moment varies with the volume of the Mn atom. The variation of the magnitude of the Mn magnetic moment is explained using the relation between Pauling valence and magnetic moment introduced by Mori and Mitsui. The results are in disagreement with the currently accepted interpretation of the susceptibility data.
Characterization of Magnetic Bubble Domain Garnet Crystals by X-Ray Diffraction: Symmetry and Compositional Gradients
Authors: Barns R. L.
Published: February 2004

At room temperature, selected pieces of Gd2.34Tb0.66Fe5O12 are magnetically uniaxial and have excellent characteristics for bubble domain devices; but x-ray powder, precession, rotation, and Weissenberg photographs show no corresponding uniaxiality. Bond's method of accurate lattice spacing measurement shows d-spacing gradients which can be as large as 0.065% over a distance of 1.3 mm. These gradients are large along the normal to the natural (211) faces. The lattice parameters of the two end members of this solid-solution crystal were measured. Application of Vegard's law allows quantitative estimation of the compositional gradients due to varying rare-earth atom ratios. X-ray fluorescence analysis mapping showed no variation in rare-earth atom ratios. A small piece was selected as having less than 2 ppm gradient along [211]. This was used to determine the shape of the unit cell by measuring the d spacings of eight reflections (widely separated in reciprocal space). A least-squares refinement assuming rhombohedral symmetry and a [111] direction along the unique magnetic axis gave a rhombohedral angle of 90°−0.9 arc sec, σ=0.04 arc sec. This very small distortion could be due to compositional gradients remaining despite precautions and may not be inherent in a homogeneous crystal. The previous report of a 1/3-min distortion was the result of an unrecognized gradient.
Magnetic Properties of CeBi, NdBi, TbBi, and DyBi
Authors: Nereson N. , Arnold G.
Published: February 2004

The magnetic properties of four REBi compounds, where RE is Ce, Nd, Tb, and Dy, were investigated by neutron diffraction on powder samples; all of these compounds are antiferromagnetic below Néel temperatures TN of 26, 25, 18, and 13°K, respectively. The magnetic structure of both CeBi and NdBi consists of (001) ferromagnetic planes coupled antiferromagnetically with the spin direction along the [001] axis. TbBi has a magnetic structure which consists of (111) ferromagnetic planes coupled antiferromagnetically with a [111] spin direction. The magnetic structure of DyBi could be either type A or B of MnO; the spin direction could not be determined from the present powder sample. CeBi and NiBi possess antiferromagnetic ordering of the first kind whereas TbBi and DyBi have the second kind. The development of antiferromagnetic ordering below TN follows a Brillouin function for CeBi and NdBi but TbBi and DyBi show considerable deviation. The saturation ordered moments for CeBi and NdBi are 6% less than the calculated values whereas for TbBi and NdBi the moments are 12% less than the expected values.
Field-Induced Spin Reorientation in YFeO3 and YCrO3
Authors: Jacobs I. S. , Burne Hugh F. , Levinson Lionel M.
Published: February 2004

Application of a sufficiently strong magnetic field Hx along the antiferromagnetic easy axis (x) of the isomorphic, distorted perovskites YFeO3 and YCrO3, results in the smooth rotation of the antiferromagnetic vector in the x-z plane, reaching the z axis at the critical fields Hcr=74±1 kOe and Hcr=40±1 kOe at 4.2°K, for YFeO3 and YCrO3, respectively. A detailed analysis of the magnetization curve mx(Hx) provides an unambiguous determination of the quartic and uniaxial-type anisotropy in the x-z plane of YFeO3 (spin= 52). In agreement with theory, quartic anisotropy terms are not found in YCrO3 (spin= 32). Only in the latter case are the uniaxial anisotropy and the reorientation field calculable from the initial susceptibilities. Comparison of mx(Hx) with mz(Hz) for H>Hcr provides a quantitative separation between the antisymmetric exchange (HD) and single-ion anisotropy (Hxz) contributions to the weak ferromagnetic canting. We find |Hxz/HD| <0.02 for YFeO3 and |Hxz/HD| <0.05 for YCrO3, at 4.2°K.
Anisotropic Properties Measured as a Function of Temperature
Authors: Flanders P. J.
Published: February 2004

Anisotropic properties have been measured with a rotating sample magnetometer as a function temperature on a sample, Fe3O4, in which K1(T) →0 as Ms(T) changes slowly, and on one, GdIG, in which Ms(T) →0 as K1(T) changes slowly. K2(T) for Fe3O4 was found from differences in lock-in output at 6 and 8 ω in a (110) plane disk; at 129 K where K1 is zero, V⊥(6ω) varied as K2/H. K1(T) and K1(T)/Ms(T) in GdIG were obtained from V⊥(2nω), at n=2, 4, and 6, for H>2K1(T)/Ms(T).
Noncubic Garnet Anisotropy from Growth-Induced Pair Ordering
Authors: Rosencwaig A. , Tabor W. J.
Published: February 2004

A growth-induced pair anisotropy model is presented to account for the pronounced noncubic anisotropies recently studied in flux-grown magnetic garnets. In this model the noncubic anisotropy arises from the presence of a relatively small amount of growth-induced short-range pair ordering. The resulting pair anisotropy consisting in general of both dipolar and pseudodipolar terms is shown to have many of the features of the observed anisotropy. In particular we perform a detailed calculation of the anisotropy energy under the {110} and {112} growth facets of the garnets when such short-range pair ordering occurs between ions of the rare-earth sublattice and those of the iron sublattices. Good agreement is obtained with presently available experimental data.
Theory of Infrared Absorption by Pairs of Cobalt Ions in MgF2
Authors: Halley J. Woods
Published: February 2004

The microscopic mechanism responsible for the electric dipole two-magnon absorption in rutile antiferromagnets remains in some dispute. Three mechanisms have been suggested which appear to make contributions of comparable orders-of-magnitude for some materials. As a contribution to the resolution of this problem we have studied the case of two next-nearest-neighbor Co2+ ions in a nonmagnetic rutile lattice. The results suggest some further experimental studies of the polarization properties of the observed pair absorption spectrum.
Exciton-Exciton Transitions in MnF2
Authors: Stokowski S. E. , Sell D. D.
Published: February 2004

We have seen absorption lines involving the simultaneous creation of two excitons in MnF2. The observed lines are the pure electronic transitions associated with the double exciton band (6A1+6A1→ 4T1+4T1) previously observed by Ferguson.1 These double excitons are combinations of the E1 (18 419.6 cm−1) and E2 (18 436.6 cm−1) single excitons. Line transitions identified as E2+E2 (36 789 cm−1) and the doubly degenerate E1+E2 (36 917 cm−1) were seen; however, the transition to the E1+E1 state was not observed. The identification was made with the aid of [001] and [110] uniaxial stress measurements; the energy shifts of the double excitons under stress are simply related to those of the E1 and E2 excitons. We show, on the basis of one-electron molecular orbitals, that the absence of the transition E1+E1 is probably due to a weak exchange interaction between the electrons involved in this particular transition. The double exciton lines are strongly polarized, which is not indicated by the space group selection rules, but is consistent with the Mn pair symmetry.
High Magnetic Field Investigation of Localized Magnons in Fe2+-Doped MnF2
Authors: Bernstein T. , Misetich A. , Lax B.
Published: February 2004

Using far-infrared absorption spectroscopy we have investigated the s0 localized magnon in 0.8% Fe2+-doped MnF2, at 1.4 K. We have followed this absorption with fields up to 138 kOe, and it disappears at the spin-flop transition. The spin-flop field is 103.5±1.0 kOe (as measured by observing the shift of the intrinsic two-magnon absorption), from which D′ = 10.1±1.1 cm−1 is calculated. Using this value, the localized magnon is expected to shift to 46.4±5.5 cm−1. This is in the intrinsic spin-wave band, which explains the observed disappearance.
Magnetic Circular Dichroism in Antiferromagnetic MnF2
Authors: Scarpace F. L. , Chen Ming Y. , Yen W. M.
Published: February 2004

The magnetic circular dichroism (MCD) properties of antiferromagnetic MnF2 in the 4T1(4G) region have been studied. We show that MCD is a useful technique in furthering our understanding of the spectra of these materials, particularly when complex assisted transitions are involved. Out of the complex band absorption, only a weak electric dipole feature at 18 536 cm−1 and the one-magnon sideband region exhibit magnetic circular dichroism. We present conclusive evidence that the weak electric dipole transition is a two-magnon sideband of the pure electronic line E2 in this manifold. The position and temperature dependence are in good agreement with other two magnon experimental data. The MCD splitting also yields an effective g factor for the two-magnon sideband which is in good agreement with existing data. We conclude that this three-center excitation is caused by a zone-center exciton plus two X2 zone-edge magnons. Fitting the observed MCD signal from the one-magnon sideband region to a calculated line shape gives us an estimate of the effective g factor for zone-edge magnons in MnF2.
Spin Waves and Excitons in Antiferromagnetic CoF2
Authors: Allen S. J. , Guggenheim H. J.
Published: February 2004

The large orthorhombic anisotropy field in antiferromagnetic CoF2 significantly alters the spectrum of spin-wave excitations that evolves from the effective S=32, Co2+ ground-state manifold. In addition to the usual twofold degenerate transverse spin-wave mode, a second twofold degenerate spin-wave mode appears at a higher frequency, as well as magnetic Davydov split longitudinal spin-wave excitations. Far-infrared absorption measurements of the k=0 modes have been extended to include all the excitations below 300 cm−1 as well as their Zeeman effect for H∥ and H⊥ to the spin axis. A theory of the uniform excitations is given which gives quantitative agreement with energies and magnetic-field splittings. The theory uses the effective S=32, single-ion anisotropy field and g factors obtained from Co2+:MgF2, a simple isotropic exchange interaction between the effective S=32 spins and the independently determined local spin-lattice coupling with the Eg phonons. The latter is essential to a quantitative description of the excitations.
Spin-Wave Dispersion Relation in Rare-Earth Metals
Authors: Nicklow R. M.
Published: February 2004

Recent measurements of the spin-wave dispersion relations for Gd, Dy, and Ho metal by triple-axis neutron spectrometry will be reviewed. Measurements along the c axis have been carried out for each metal at several temperatures, and for Gd additional measurements along the a and b axes have been made at 78°K. Information about the Fourier-transformed exchange interaction J(q) has been obtained from data analyses, which are based on a simple Hamiltonian containing only exchange interactions for Gd and a Hamiltonian containing exchange interactions plus appropriate anisotropy interactions (the usual frozen lattice model) for Dy and Ho. For both Dy and Ho a satisfactory analysis of the data requires the use of anisotropy interaction parameters which are not in good agreement with the results of macroscopic measurements. The neutron data suggest the existence of other anisotropy interactions, perhaps magnetoelastic, in addition to those usually considered in the frozen lattice Hamiltonian. The dispersion relation for Dy in the ferromagnetic phase has a pronounced minimum, and hence J(q) has a maximum, for q in the vicinity of the wave vector that is appropriate for the spiral structure just above Tc.
Magnetic Susceptibility of Au–Fe Alloys
Authors: Cannella V. , Mydosh J. A. , Budnick J. I.
Published: February 2004

Over the past years there has been considerable interest in the magnetic properties of the Au(Fe) system. Mössbauer measurements indicate that a complicated type of long-range ordering occurs below concentrations c of ∼12 at.% Fe and extends down to c<1%. Yet no definitive susceptibility study has been carried out over a complete range of temperatures and concentrations in order to characterize the magnetic ordering. We have measured the low-field magnetic susceptibility χ(T) for a series of eight Au–Fe alloys (1–22 at.% Fe), and we observe a definite peak in χ at those ordering temperatures determined from the Mössbauer data. The magnitude of χ greatly increases with c, while the shape of χ(T) in the region of the peak changes from a cusp-like behavior at low c to a behavior for c≳17% in which χ(T) gently rises, then sharply falls. These behaviors confirm the existence of a long-range order suggtesive of antiferromagnetism at low c (≤8%) with a more typical ferromagnetic ordering at high c. At intermediate c (≈12%), χ(T) seems to indicate the presence of a mixed type of long-range order.
Antiferromagnetism and Electrical Transport Properties of Chromium-Aluminum Alloys
Authors: Arajs Sigurds , Reeves Norman L. , Anderson Elmer E.
Published: February 2004

Electrical resistivity ρ of Cr–Al alloys containing 0.3-, 1.2-, 1.9-, 3.7-, and 6.2-at.% Al has been studied as a function temperature. The onset of antiferromagnetism causes small anomalies in the ρ vs T curves from which the Néel temperature TN can be determined. TN decreases rapidly with additions of small amounts of Al and then increases with larger Al concentrations. A minimum in the TN vs Al content curve occurs at about 1.2-at.% Al. This minimum results from the fact that below about 1.5-at.% Al level, the Cr–Al alloys possess an incommensurable antiferromagnetic structure. Above this concentration, the antiferromagnetic phase is of the commensurable type. The absolute thermoelectric power measurements on alloys containing 0.3 and 1.2-at.% Al support the determinations of TN from the electrical resistivity studies.
Paramagnetism of High-Concentration Manganese in bcc Vanadium
Authors: von Meerwall E. , Schreiber D. S.
Published: February 2004

We have studied the nuclear magnetic resonance and magnetic susceptibility in bcc V-Mn from 0% to 70% Mn. Above 45% Mn we find a rather sharp rise in a heretofore only weakly concentration-dependent paramagnetism, as well as decreases in both 51V and 44Mn Knight shifts. This increase in paramagnetism in V–Mn, as well as in V–Fe, is identified with the onset of occupation of the higher-lying 3d subband and occurs earlier near the solute atoms of higher nuclear charge. A simple model incorporating this solvent-solute difference in the band structure forms the basis for a partitioning of the susceptibility and the Knight shift. An emerging temperature dependence in χ becomes Curie-Weiss like at the highest Mn concentrations.
Magnetic Investigation of the Effect of Small Additions of Co and Mn on the Martensite Reversal in Fe–Ni Alloys
Authors: Krenzer R. W. , Baskes M. I.
Published: February 2004

Data on the temperature, magnetic field, and composition dependency of the magnetic moment and Curie temperature in several Fe–Ni–Co and Fe–Ni–Mn alloys have been obtained. The magnetization/temperature relationship was obtained for each alloy from 298°–873°K, following the change in magnetization through the transformation from martensite to austenite with increasing temperature. The magnetic moment of the alloys was also determined as a function of field at room temperature. The effect of Co and Mn additions to an Fe-30% Ni alloy on the transition temperature As the Curie temperature Tc, and the saturation magnetization at absolute zero σs0, has been determined. Values for As, Tc, and σ0, the magnetization at absolute zero, were obtained by fitting a Brillouin function to the respective contributions of austenite and martensite to the total magnetization. This technique represents a very sensitive method of obtaining transition temperatures and the respective amounts of each phase present in the alloys. The values of σ0 were then extrapolated to infinite field to obtain σs0. A theoretical prediction of σs0 and Tc was in agreement with the experimentally determined values.
Resistivity Minima in Paramagnetic V–Fe
Authors: Brodsky M. B. , Nellis W. J.
Published: February 2004

The electrical resistivities of V–Fe alloys containing 18–28 at.% Fe have been measured between 1.4° and 300°K. Magnetoresistivities of the alloys have been measured at 1.4° and 4.2°K in fields up to 19 kOe. Resistivity minima are found for compositions between 22% and 26% Fe. These alloys are paramagnetic but have magnetic contributions to the specific heat.1 No resistivity anomalies are found for 18% and 20% Fe, where essentially no magnetic contributions are observed in the specific heat. The resistivity of the 28% alloy has a change in slope near 12°K, and a positive dρ/dT throughout the temperature range, indicative of magnetic ordering. The specific heat, resistivity minima, and negative magnetoresistivities of paramagnetic V–Fe are analogous to Pd–U,2 only there are no localized moments in the latter case. These data are consistent with paramagnon-conduction electron scattering and not with ferromagnetic clustering. However, samples strained 25% in compression show an increase in the magnitude of their magnetic behavior which is better explained by magnetic clustering.
MnAlGe Films for Magneto-Optic Applications
Authors: Sherwood R. C. , Nesbitt E. A. , Wernick J. H. , Bacon D. D. , Kurtzig A. J. , Wolfe R.
Published: February 2004

MnAlGe is a uniaxial ferromagnetic compound with a saturation 4πMs of 3600 G, and Curie temperature of 245°C. We have studied polycrystalline thin films of this compound formed on various substrates by getter sputtering. The optimum substrate temperature to obtain films with uniform magnetic properties was 500°C. Films prepared at this temperature have a substantial component of magnetization normal to the plane of the substrate, and a coercive force of approximately 2000 Oe. Information was written into films approximately 700-Å thick by Curie point writing or with a fine permanent magnet wire, and read with good optical contrast by means of the polar Faraday effect. The relatively low Curie temperature is advantageous in reducing the power required for Curie point writing for magneto-optic memory or holographic applications.
Theory of the Nonlinear Polar Kerr Magneto-Optic Effect in Ferromagnetic Metals
Authors: Romagnoli R. J. , Ferguson P. E.
Published: February 2004

A theory of the nonlinear polar Kerr magneto-optic effect in ferromagnetic metals is developed. The material model is based on the classical equation of motion for a free electron with a finite relaxation frequency under the action of a Lorentz force. A second-harmonic current density is found of the form: J2=αE2+βh(H1)E1+ξ(E1V·E1)where α, βh (H1), and ξ are nonlinear conductivity tensors, E1 and H1 are the fundamental electric and magnetic fields, and E2 is the induced second-harmonic electric field. Results of this theory reduce, in the limit of a vanishing ferromagnetic state, to results obtained from the Boltzmann transport equation for conduction electrons subject to a potential barrier at the metal surface. As required, the theory reduces to the linear polar Kerr magneto-optic effect in the absence of second-harmonic generation. The second-harmonic reflection coefficients are derived. To the degree of approximations made, all four coefficients vanish at normal and grazing incidence. They are maximum at intermediate angles of incidence, depending upon the physical properties of the metal.
Variation of Stripe-Domain Spacing in a Faraday Effect Light Deflector
Authors: Johansen T. R. , Norman D. I. , Torok E. J.
Published: February 2004

Stripe-domain ferromagnetic films with high Faraday rotation and low optical absorption will rotate the angle of polarization of light transmitted through even-numbered domains an angle φ = FT and through odd-numbered domains an amount −φ, where F is the Faraday constant and T is the film thickness. The result of the differential rotation is that the film will act like a transmission diffraction grating. Since the orientation and spacing of the stripes may be altered by appropriate applied fields, the film may be used as a laser light deflector. A two dimensional model is proposed for stripe domains in some ferromagnetic films. This model differs from previous models (see Ref. 4–8) in that it includes the dependence of wall width on wall angle and thereby shows that variations in stripe-domain spacing of more than an order-of-magnitude are possible. Variations of this amount were observed experimentally in a YIG platelet which was used as a stripe-domain light deflector.
Optical Spectrum and Spin-Orbit Splitting of Nickel
Authors: Stoll Marc-Ph.
Published: February 2004

The optical conductivity of nickel has been measured on a single crystal, using different orientation of the magnetization vector. Weak structures in the region 2–2.6 eV on the low-temperature spectrum are assigned to the direct interband transitions X5→X4′ and L31→EF in the majority-spins band. A value of the spin-orbit parameter is deduced (ζ=0.12±0.01 eV), leading to exchange splittings ΔEd=0.55±0.07 eV and ΔEsp≲0.1 eV.
Magnetic Interactions in the Complex Fluorides AMIIMIIIF6
Authors: Banks E. , Berkooz O. , De Luca J. A.
Published: February 2004

Materials of the above type have been prepared in which A = Rb, Cs, Tl, and M is a first-row transition-metal ion. The majority of these materials, an example of which is RbFeVF6, have x-ray powder patterns consistent with the cubic pyrochlore type structure of similar fluorides first reported by Babel et al. Magnetic susceptibility and Mössbauer studies of these materials indicate the presence of magnetic ordering at very low temperatures, typically ∼5°K. Of particular interest are the non-cubic phases AFe2F6. For example, magnetic susceptibility data indicate that the material TlFe2F6 orders antiferromagnetically with a Néel temperature of ∼12°K. The Mössbauer study (4.2°–300°K) yields a magnetic hyperfine split pattern below the ordering temperature and also indicates that the transition metal ions remain in essentially discrete oxidation states over the temperature range investigated. Typical quadrupole patterns and isomer shifts are observed for Fe2+ and Fe3+ above the ordering temperature.
Back-Goudsmit Effect in Mössbauer Spectra
Authors: Viccaro P. J. , Oosterhuis W. T.
Published: February 2004

Paramagnetic iron ions with electronic spin relaxation times long compared to 10−7 seconds give the nuclear magnetic moment of 57Fe an opportunity to couple to the electron magnetic moment. This coupling between the nuclear and electronic moments may be broken by the application of an external magnetic field. This is accomplished by fields of the order of 100 Oe since the nucleus produces a field of about 10 Oe at the site of the electron. The effect of a small applied field is clearly exhibited in the Mössbauer spectra of several slowly relaxing paramagnetic iron materials with different electronic configurations. Examples to be presented include biological molecules, minerals, and inorganic salts. One can detect changes in the Mössbauer spectrum of a paramagnetic iron ion with applied fields as small as 10 Oe. Mössbauer spectra are calculated for various electronic configurations and compared with the appropriate experimental data.
Mössbauer Spectroscopy Study of the Spin-Flop Transition in Fe-Doped MnF2
Authors: Abeledo C. R. , Frankel R. B. , Misetich A. , Blum N. A.
Published: February 2004

Measurements of the hyperfine interaction in Fe+ + in MnF2 in external fields above the spin-flop field at 4.2 K are reported and a value of g⊥ = 2.13 is derived, in good agreement with theory.
Effect of Rare-Earth and Aluminum Ions on the High-Power Threshold of YIG
Authors: West Russell G. , Blankenship Alvin C. , Huntt Robert L.
Published: February 2004

The 9.4 GHz parallel pump microwave threshold field (hcrit) has been measured at 293°K for polycrystalline YIG and YA1IG spherical samples containing Ho3+, Dy3+, Ce3+, and Gd3+ singly or in combination. Low wave number spin-wave linewidths (ΔHk→0) were determined by adjusting the dc magnetic field to obtain a threshold field corresponding to the butterfly minimum. The experimental results justify a technical modification of the parallel pump instability equation from: hcrit = ΔHk→0ωp/ωm, to: hcrit = (ΣREΔHREk→0 + ΔHik→0) ωp/ωm, where ΔHik→0 is the intrinsic spin-wave linewidth of YIG and aluminum-substituted YIG, and ΔHREk→0 = E. NRE/4πMs is the effective spin-wave linewidth of each type of rare-earth ion present. ΔHREk→0 is directly proportional to the rare-earth ion concentration (NRE), and inversely proportional to the magnetization of the host material. E is a parameter of the constituent rare-earth ion which, for small doping levels, remains constant. Of major interest is the increased effect of a given NRE on the threshold field as the magnetization of the host material is reduced.
Microwave Resonance Linewidths in Substituted Single-Crystal Barium Ferrite
Authors: Dixon Samuel , Coin Thomas R. Au , Savage Robert O.
Published: February 2004

Ferromagnetic resonance linewidth measurements were performed at 37.6 GHz on substituted barium ferrite, BaZnx Tix Fe12−2xO19, where x varies from 1.0 to 2.5 in the melt. Crystals were synthesized by two growth procedures; a modified pulling technique and a free nucleation method from slow cooling BaO/B2O3 fluxes. The uniaxial anisotropy field Ha varied from 5400 to 11 100 Oe; Tc from 351° to 613°K, making the material of considerable interest for microwave device applications. Cavity perturbation techniques were used with polished spherical samples 15–20 mil in diameter. Variation in values of x have a large effect on the linewidths obtained. The linewidth decreases with increasing x to a minimum at 1.5 and then increases as x exceeds 1.5. At x = 1.5, resonance linewidths of 36 Oe on pulled crystals and 42 Oe on free nucleated crystals were observed.
Magnetic Properties of a Unique 18-Layer Hexagonal Ferrite
Authors: Tauber A. , Savage R. O. , Grebenau M. D.
Published: February 2004

The magnetic properties of a new 18-layer hexagonal ferrite Ba5Ti3Me2Fe12O31, (Me2+ = Zn, Mg) have been investigated in fields up to 15.5 kOe and temperatures from 4.2 K to Tc. Both the Zn and Mg compounds exhibit an easy plane of magnetization over the temperature range reported, Ea = K1 sin2θ+K2 sin4θ. At most temperatures the magnetization follows a σ = σ0+χH law. Zn-18 H has Tc = 310∓5°K, and nβ(H = ∞, T = 0) = 14.1 ∓0.6 μβ; Mg-18 H has Tc = 391 ∓3°K and nβ(H = ∞, T = 0) = 7.8∓0.5 μβ. A collinear spin model employing positive and negative exchange is proposed.
Broadband Linewidth Measurement of Low Q Hexagonal, Ferrimagnetic Resonators
Authors: Weller D. B.
Published: February 2004

Broadband linewidth measurement of high anisotropy planar ferrites (MnZnY) has been accomplished using an extension of the nonresonant matched method reported by Matthaei. This former method required 3-dB bandwidth measurements resulting from an approximate expression for Q. The present technique combines an exact expression for the unloaded Q of a bandstop filter with a linewidth representation for a high anisotropy planar ferrite. The resulting expression permits the calculation of linewidth over a broad range of frequencies for a low Q resonator, characteristic of hexagonal ferrites at high microwave frequencies. Calculation of linewidth can be obtained from essentially an arbitrary bandwidth and where the maximum rejection of a ferrimagnetic bandstop filter is less than 3 dB.
Magnetism, Metal-Insulator Transition, and Optical Properties in Sm- and Some Other Divalent Rare-Earth Monochalcogenides
Authors: Bucher E. , Narayanamurti V. , Jayaraman A.
Published: February 2004

In Sm2+X compounds (X = S, Se, Te) an unusualy large dependence of the low-temperature Van Vleck susceptibility on the ligand has been observed. SmSe, SmTe, and also TmTe undergo a continuous insulator-metal transition under pressure. In contrast, SmS shows a discontinuous transition to the metal at 6.5 kbar. In all cases the transition is accompanied by a large volume change of around 20%, which is due to the promotion of a 4f electron into the 5d-6s conduction band. Optical spectroscopy yields three distinct absorption peaks. They may be interpreted as transitions from 4f6↔4f55dt2g and 4f6↔4f55deg and probably an excitonic peak. The activation energy of a 4f electron is found to be 0.63, 0.46, 0.20, and 0.22 eV for SmTe, SmSe, SmS, and TmTe, respectively, from both the pressure-dependent electrical resistivity at room temperature and the observed absorption edge.
Neutron Crystal-Field Spectroscopy in Rare-Earth Metallic Compounds
Authors: Turberfield K. C. , Passell L. , Birgeneau R. J. , Bucher E.
Published: February 2004

The technique of inelastic neutron scattering has been applied to the problem of crystal fields in rare-earth metallic compounds. It is shown that in compounds where the Stark energies are somewhat greater than exchange energies, the complete energy-level diagram can be readily obtained from the inelastic neutron spectra and hence the corresponding crystal-field parameters may be deduced. In this paper we illustrate this by a series of measurements which we have performed on the praseodymium monopnictides, PrBi, PrSb, PrAs, PrP, and monochalcogenides PrTe, PrSe, PrS. It is found that the spectra can be reproduced in detail using ordinary crystal-field theory together with a simple approximation to the instrumental resolution function. In addition, all of the crystal-field levels in all seven compounds studied can be quantitatively accounted for using a nearest-neighbor point charge model with an effective charge of −2. This is in spite of marked variations in covalency, carrier concentration and, indeed, in the widths of the crystal-field transitions themselves over the series.
Residual Information in Magnetic Memory Devices
Authors: Taylor C. F. , Blades J. D. , Hewitt F. G.
Published: February 2004

A review of the magnetic phenomena that cause residual information in magnetic memory devices is presented. The types of devices discussed will be particulate medium devices, thin films, and core memories. Residual information is defined as any magnetic information that can be detected by laboratory techniques after normal clearing of the memory device. Some of the magnetization processes that lead to residual information problems are anhysteretic remanent magnetization, exchange anisotropy, thermal remanent magnetization, skew effects, magnetization creep, and partial switching. An attempt is made to relate these magnetization processes to the demagnetization techniques in magnetic memory devices.
Preparation and Structure of Fe-Doped EuO Films
Authors: Ahn K. Y. , Tu K. N. , Reuter W.
Published: February 2004

A large increase in ferromagnetic Curie temperature from 69.5°K to ∼190°K has been observed in EuO films doped with Fe. These films retain most of the large magneto-optic rotation of EuO (at 4.2°K) desired for beam addressable memories. However, the increase in Tc permits the operation of these devices at the more convenient liquid-nitrogen temperature. Films were prepared by simultaneous evaporation of Eu, Eu2O3, and Fe at pressure of 2×10−5 Torr. The amount of Tc increase is strongly dependent upon composition. For example, films with the highest Tc require Fe/Fe+Eu∼0.07 and excess Eu with a typical weight ratio of Eu/Eu2O3∼1.3 as compared to ∼0.9 for pure EuO. The analysis by Seeman-Bohlin x-ray diffractometer shows the same NaCl structure as that of pure EuO with a slightly larger lattice parameter (5.1564 Å). The doping also causes a reduction of grain size (from 200 to 120 Å) and a tendency toward preferred orientation. Results of electron microprobe spectroscopy and Mössbauer measurements show that the iron is predominantly present in the metallic state and the europium in the Eu+ + state. The dependence of physical properties on fabrication parameters will be critically examined.
Magnetic Susceptibility of Eu2O3
Authors: Kern S. , Kostelecky R.
Published: February 2004

Huang and Van Vleck have recently attributed the ``excess'' in susceptibility of Eu2O3 over that calculated from the spectroscopic data of Eu3+ diluted in Y2O3 to orbitally dependent exchange processes. Measurements of (EuxY1−x)2O3 by Grill and Schieber done above 95°K, on the other hand, have indicated that the susceptibility increases, rather than decreasing to the dilute calculated value, as x decreases. We have carefully remeasured the susceptibility of Eu3+ in Y2O3 down to helium temperatures and found that the susceptibility and crystal-field splitting remains relatively constant over the entire range of concentration. Calculations have shown that the effects of spin-orbit and crystal field mixing of states do not explain the magnitude of the discrepancy, nor would the presence of the monoclinic phase of the sesquioxide, which also exhibits a similar ``excess'' of susceptibility over the spectroscopically determined value.
Magnetic and Magneto-Optical Properties of Fe-Doped EuO Films
Authors: McGuire T. R. , Petrich G. F. , Olson B. L. , Moruzzi V. L. , Ahn K. Y.
Published: February 2004

EuO films with ∼8-wt% Fe have saturation magnetic moments of about 180 emu/g at 4.2°K and Curie temperatures (Tc) as high as 200°K (for pure EuO, σ=232 emu/g, Tc=69.5°K). The temperature dependence of the magnetization does not scale relative to pure EuO but deviates from the normal magnetization curve in that it exhibits a long tail extending from about 100°K up to Tc. Optical absorption data at 6°K in the range 0.3–2.5 μ indicate a characteristic peak at λ=0.6 μ (due to the 4f-5d transition) with α=2.2×105/cm, about 50% higher than pure EuO. The wavelength dependence of the normal Faraday rotation at 4.2°K is similar in shape to pure EuO; both peak at 0.7 μ but the peak rotation of the Fe-doped film (6×105 deg/cm) is about 30% lower than pure EuO. Mössbauer measurements of 151Eu show mainly Eu+ + with an isomer shift of −12.25 mm/s as in bulk EuO. At 4.2°K the 151Eu hyperfine field is 280.8±5.6 kOe (pure EuO≈300 kOe). The isomer shift of the doublet observed on the 57Fe resonance at 300°K is characteristic for metallic iron. We conclude that only a small fraction of the Fe is effectively doping the EuO films.
Annealing Study of EuO Films Doped with Iron and Europium
Authors: Suits J. C. , Lee Kenneth , Winters H. F. , Phipps P. B. P. , Kyser D. F.
Published: February 2004

Fe doped and Eu doped EuO films when annealed in vacuum exhibit large changes in the magnetic, electrical, optical, and magneto-optical properties. Annealing for 5 min at 500°C causes the Curie temperature to drop from 150° to 70°K. This effect is related to the insolubility of iron and excess europium in EuO. The annealing temperature for the iron is somewhat higher (500°C) than the annealing temperature for the excess europium (300°C).
Structural Disorder and Spin Polarized Electron States in EuS
Authors: Busch G. , Campagna M. , Siegmann H. C.
Published: February 2004

The electron-spin-polarization (ESP) analysis of the photoemission from ferromagnets is employed for investigating the spin polarized energy levels in EuS. We observe that EuS films, which were evaporated at 4.2 K in uhv, change considerably their magnetophotoelectric properties by annealing: the photothreshold increases by ∼0.8 eV and the tailing into the mobility gap disappears. The 4f7 levels then become the highest occupied energy states and the measured ESP was ∼53% for these electron states. By measuring ESP curves as a function of the external magnetic field for different photon energies we also observed the degree of polarization for the different energy states in disordered EuS.
Domain Structure During Magnetization of Grain-Oriented 3% Si–Fe as a Function of Applied Tensile Stress
Authors: Shilling J. W.
Published: February 2004

The longitudinal Kerr effect has been used to observed domain structure during dc and 60-Hz magnetization in conventional (110) [001] grain oriented 3% Si–Fe as a function of applied tensile stress parallel to the rolling direction. The observed domain processes indicate that the source of the Villari reversal in this material is demagnetizing fields occurring at grain boundaries and at the sheet surface. In grains where the [001] tilted out of the sheet surface, demagnetizing fields were produced when 90° flux closure domains were eliminated by applied tensile stress. During magnetization under applied tensile stress, these demagnetizing fields restabilized the original unstressed closure structure. High speed movies of the magnetization process in grains with perfect plane orientation revealed that although the 180° wall spacing was decreased by applied tensile stress the flux became very nonuniform due to the buildup of grain boundary demagnetizing fields and the average 180° wall velocity was not decreased. The observed domain processes explain the magnetic properties previously observed in this material under applied tensile stress, e.g., decreased maximum permeability, the appearance of negative magnetostriction and lack of improvement in core loss at stress levels in excess of 500 psi.
Observations of Magnetic Losses in a Single Crystal of a Ferromagnetic Conductor
Authors: Sun J. N. , Haller T. R. , Kramer J. J.
Published: February 2004

An exact correlation between material parameters and magnetic losses in ferromagnetic conductors has been very elusive, due partly to the fact that losses normally are measured on polycrystalline material. Even if the material is highly textured, the domain structure is sufficiently nonregular and wall motion is sufficiently sporadic that accurate correlation is very difficult. Recent observations have also shown that the dynamic domain structure can be significantly different from that observed statically. Thus, a technique was developed to measure magnetic losses on small single crystals with well-defined domains as a function of frequency and induction. Measurements were made on thin crystals of a 3% iron-silicon alloy {with an (001) [100] orientation} having a slablike domain structure parallel to one of the two 〈100〉 directions in the surface. Losses were measured in both 〈100〉 directions and were correlated with the dynamic domain structure observed by the Kerr magneto-optic effect and high-speed photography. The losses reflect the influence of the dynamic domain-wall spacing, wall nucleation, and annihilation.
Transfer Impedance of Soft Magnetic Materials
Authors: Young F. J. , Boomgaard D. J. , Colling D. A.
Published: February 2004

Transfer impedance of a variety of soft magnetic materials (Ni, Fe, Ni–Fe and Fe–Si alloys) has been measured for the frequency range 0.01 to greater than 100 kHz. At frequencies above about 10 kHz, it is shown that ferromagnetic materials can have lower transfer impedance than copper. In magnetic materials, the occurrence of low impedance appears to be related to magnetic softness, whether attained through choice of composition or through annealing treatments.
Very High-Temperature Permeameter
Authors: Barranger John P.
Published: February 2004

A new permeameter measures the magnetizing force and the corresponding magnetic induction up to the temperature of 1000°C in a vacuum or an inert atmosphere. Two massive symmetrical yokes close the magnetic path around the specimen which consists of a rod of solid material or a bundle of sheet material. The yokes are made of a specially processed alloy of 9% iron, 91% cobalt, a high-temperature soft magnetic material. A coil surrounding the specimen supplies a magnetizing force of up to 100 Oe and a separate coil is used to measure the magnetic induction. Auxiliary coils provide additional magnetizing force resulting in a longitudinal distribution of flux uniform to within 1%. The magnetizing force is calculated from the coil current while a fluxmeter is used for the induction. The null-balance-type permeameter utilizes the magnetic potentiometer principle with yoke compensating coils to cancel the effects of the reluctance of the yoke and the joint gaps. Very close agreement was obtained at room temperature when compared to the standards laboratory MH and Fahy type permeameters. Normal induction curves as a function of temperature for the yoke material are also presented.
Closed Grain-Oriented Magnetic Core
Authors: Pesch J. A. , Ward A. L.
Published: February 2004

Magnetic flux in ``E'' and ``L'' stampings made from cube-on-edge-oriented 3.25% Si–Fe must pass through the hardest magnetic direction at the corners of the ``E'' and ``L.'' This work shows how electron beam welding and grain growth can be used to form closed, flat, core specimens, in which the flux path is parallel with the easy direction of magnetization in all parts of the specimens. The magnetic properties of these cores are comparable with magnetic properties of Epstein specimens of the same material, having an induction of 19 800 G at 50 Oe magnetizing force, coercive force of 0.094 Oe, and maximum permeability of 53 000.
Magnetic Properties of Sputtered Single-Crystal Films of Terbium Orthoferrite
Authors: Sosniak J.
Published: February 2004

Magnetic domains have been observed in rf-dc sputtered films of TbFeO3 epitaxially grown on (001) YAlO3 and (011̄2) sapphire. The size of the domains in the demagnetized state increased with increasing film thickness, while the complexity of their form decreased. The coercivity of the films on YAlO3 was lower than of those on sapphire, with the lowest value of 10 Oe observed over very small areas.
Nanosecond Photographs of 90°–180° Switching in Biaxial Epitaxial Magnetic Thin Films
Authors: Kryder M. H. , Humphrey F. B.
Published: February 2004

Flux reversal in epitaxial Ni–Fe thin films has been studied with use of a 10-nsec exposure time Kerr magneto-optic camera. The epitaxial films exhibit biaxial anisotropy and both 90° and 180° switching may occur. When the switching field is applied antiparallel to the saturated magnetization, the switching processes are similar to the corresponding processes in polycrystalline films. When the field is applied at an obtuse angle to the saturated magnetization, stripe-like domains form that lie along the hard axis (45° to easy axes). With very low-drive fields the boundaries between stripes are 90° walls, but with higher fields the wall angle is much smaller, and the stripes appear like a large amplitude, large wavelength ripple. If the field is applied at an angle greater than 135° to the saturated magnetization, 180° domains nucleate and complete the switching after the stripes form. With angles less than 135°, the switching is completed by the formation of additional stripes and the rotation of the magnetization in nonswitched stripes.
Stripe Domains in Thin Co–Al Films
Authors: Norman D. I. , Lo D. S. , Johansen T. R.
Published: February 2004

Stripe domains were observed in sputtered Co–Al films 350–700-Å thick. This type of domain structure has been reported previously only in much thicker ferromagnetic films. The structure of the films determined by electron diffraction showed the stripe domains were associated with a bcc structure similar to iron. Saturation magnetization was measured with a vibrating sample magnetometer and was found to vary linearly with film composition, but had no relationship to the formation of stripes. The domains were observed by Lorentz microscopy and could be removed by a saturating field, but reappeared, contrary to the case reported on Ni–Fe films when an ac field was applied.
Ferroelectric/Photoconductor Memory Device
Authors: Mehta R. R.
Published: February 2004

Tests have shown that it is possible to switch a ferroelectric/photoconductor memory device between its ``1'' and ``0'' memory states in 10 μsec with 10 W/cm2 irradiance. Both a He–Ne laser and a CRT have been used to address the device which stores the bits of information as close as 25 μ apart. The device can retain stored information for more than 60 h with power off, and withstand 107 disturb pulses in the dark.