bluuebunny/crossref_metadata_2025 huggingface dataset:
Temperature compensated magnetic materials of the type Smx
R1−xCo5 (R=Tb,Dy,Er)
Authors: Martis R. J. J. , Gupta N. , Sankar S. G. , Rao V. U. S.
Published: February 2003

Permanent magnets made from SmCo5 exhibit negative reversible change in magnetization with increasing temperature, typically of the order of 0.04% per deg. C. between −100 and +200 C. It is desirable to improve this property by suitable substitutions. In the present study, a systematic examination of the preparation, structural and magnetic characterization of SmxR1−xCo5 (R=Tb, Dy and Er) has been undertaken. The ternaries were prepared by induction melting of the metals of proper stoichiometries. Magnetic studies were performed between 4.2 and 1000 K in applied fields up to 20 kOe. The results indicate that the best temperature compensation is achieved in the ternary SmxDy1−xCo5. Saturation magnetization and Curie temperatures are also reported.
Magnetic properties of EuSm2S4 and SrSm2S4
Authors: Holtzberg F. , Coey J. M. D. , von Molnar S. , Cornut B.
Published: February 2003

Crystals of EuSm2S4 and SrSm2S4 having the cubic Th3P4 structure are insulators, with a random distribution of Sr2+ and Sm3+ over equivalent sites. EuSm2S4 is a ferromagnet with Tc=2.7 K. SrSm2S4 does not order magnetically above 1.4 K. A sharp upturn in its specific heat below 4 K is attributed to splitting of the Γ8 quartet by a small non-cubic crystal field.
Spin dynamics and magnetic ordering in mixed valence systems
Authors: Shapiro S. M. , Mo/ller H. B. , Axe J. D. , Birgeneau R. J. , Bucher E.
Published: February 2003

Neutron scattering measurements are reported on the mixed valence compounds Ce1−xThx and TmSe. The χ″ (Q,ω) as derived from the inelastic spectra of Ce0.74Th0.26 shows a peak in the γ phase near 20.0 meV and shifts abruptly to greater than 70.0 meV at the transition to the α phase. The temperature independence of the susceptibility within the γ phase cannot be simply reconciled with the temperature dependence of the valence within the γ phase. TmSe is shown to order in a type I antiferromagnetic structure below TN∼3.2 K. The magnetic phase diagram is understood as a successive domain reorientation and a metamagnetic phase transition for T<3 K with increasing field. The mixed valence nature manifests itself in a reduced moment and a markedly altered crystal field. Another sample of TmSe with a lattice parameter implying 100% Tm3+ exhibits spin correlations characteristic of a type II structure but never achieves long range order.
Spin waves in ferromagnetic Tb0.76Y0.24
Authors: Wakabayashi N. , Nicklow R. M. , Child H. R.
Published: February 2003

The conduction electron susceptibility χ (q) is considered to play an important role in the magnetism of rare-earth metals and alloys. In order to obtain information about χ (q), studies of the spin waves in the alloy Tb0.76Y0.24 have been carried out in a magnetic field. The magnetic structure of this alloy was found to remain spiral down to liquid helium temperature with zero field. The spin-wave dispersion curve in this structure has already been studied along the c*-direction, and the results were analyzed successfully in terms of a susceptibility function corresponding to a one-dimensional system with a slight modification. In order to obtain somewhat independent information about χ (q), the spin-wave dispersion curve for the ferromagnetic phase has been studied. A field of 14 kG was necessary to transform the structure into a ferromagnet at liquid helium temperature. Spin-wave energies which are calculated in terms of the susceptibility function determined from the measurements in the spiral structure agree rather well with the observed energies. A large damping and softening of the spin wave has been observed near the wave vector q=0.16 which characterized the spiral configuration. The origin of the phenomenon may be related to the instability of the ferromagnetic structure.
Magnetostriction of amorphous TbxFe1−x thin films
Authors: Forester D. W. , Vittoria C. , Schelleng J. , Lubitz P.
Published: February 2003

A systematic investigation was made of magnetostriction and magnetization in amorphous thin films (∼1 micron) of TbxFe1−x with x=0 to 0.5 prepared by electron-beam co-evaporation. The amorphous or crystalline character of the films was determined using x-ray and Mössbauer techniques. Net magnetization, coercivity, and the initial in-plane and out-of-plane distribution of magnetization was determined using a vibrating sample magnetometer. Both the sign and magnitude of the magnetostriction was measured as a function of magnetic field using a capacitance method. Over most of the concentration range the amorphous samples have a positive magnetostriction with a maximum of Δl/l=285×10−6 at x=0.4 and going to zero at the compensation point (x=0.22) and near x=0.5 where the amorphous alloys are no longer magnetically ordered at room temperature. In the region x=0.1 to 0.2 the magnetostriction is more complex, being negative for fields up to 5 kOe and positive at higher fields. All the films studied with x?0.1 were magnetically very hard and required fields much greater than 15 kOe to saturate. The relatively large magnetostrictions compared with crystalline materials indicate that the large Tb single-ion magnetostriction mechanism continues to play a strong role in the amorphous lattice structure.
Neutron techniques for the observation of ferro- and antiferromagnetic domains
Authors: Schlenker M. , Baruchel J.
Published: February 2003

Neutrons are, because of their magnetic moment, a unique probe for the investigation of magnetic domains. They can be used to distinguish ferromagnetic domains through Larmor precession in simple transmission, and both ferro- and antiferromagnetic domains from Bragg diffraction experiments. This paper tries to review the neutron studies that were made on domains either in a statistical approach to get figures on the average size or population of domains, or in the more recent local approach in which maps or pictures of the domains are obtained. Neutron diffraction topography, in which the single-crystal sample is imaged through Bragg diffraction, is the main local approach technique. It has been used till now to investigate domains in chromium, nickel oxide and silicon-iron. New observations of antiferromagnetic domains in NiO and MnF2 are presented.
Fine particle Li-ferrite for APS millimeter-wave phase shifter
Authors: Tauber A. , Savage R. O. , Collins T. , Mitchell J. , Shappirio J. R. , Eckart D. W.
Published: February 2003

Powders composed of spheroidal particles 0.5–0.6 μm average size have been synthesized by rapidly quenching melts in the system Li2CO3-B2O3-Fe2O3. The flow characteristics of the powders are adequate to fabricate Li-ferrite ceramic bodies by arc-plasma-spraying (APS) the powders. Post annealing leads to densification and grain growth with concomitant decrease in Hc and increase in 4πMs and Br. Inversions in x-ray diffraction line intensity disappears with APS and annealing, yielding expected cation distribution. The inadvertent introduction of Zn accounts for the observed inverse relationship between magnetic moment and Curie temperature. The synthetic powder process requires further refinement to improve powder flow characteristics.
Gyrotropic susceptibility and effective anisotropy of unmagnetized polycrystalline ferrites
Authors: Courtois L.
Published: February 2003

A new gyrotropic susceptibility formalism of unmagnetized polycrystalline ferrites is presented. By using a ’’Lorentz field model’’, domain boundary dipolar charges are taken into account, especially ’’Polder-Smit dipolar charges’’. It is shown that the natural gyromagnetic resonance covers a large frequency range, the limits of which are clearly calculated. At high frequencies the microwave susceptibility seems definitively understood. At low frequencies a new susceptibility expression is proposed. This theory solves the effective anisotropy field problem, the value of which is shown to reduce finally to the crystalline anisotropy field value.
Surface oxidation of non-oriented silicon-aluminum electrical steels during annealing
Authors: Geiger A. L.
Published: February 2003

The structure of surface oxide layers formed during annealing of non-oriented silicon-aluminum electrical steels has been studied. For alloys containing from 1.5 to 2.5 percent silicon, a transition from internal to external oxidation is observed as the oxygen potential of the annealing atmosphere is decreased at constant temperature or as the temperature is increased in a constant atmosphere. Surface oxide structure has a significant effect on the rate at which decarburization and nitrogen absorption occur during annealing, the formation of an external oxide scale inhibiting both of these processes. The presence of a subscale (zone of internal oxidation) in electrical steel sheet results in an increase in core loss in comparison with subscale free sheet.
New ductile Cr-Co-Fe permanent magnet alloys for telephone receiver applications
Authors: Chin G. Y. , Plewes J. T. , Wonsiewicz B. C.
Published: February 2003

Cr-Co-Fe permanent magnet alloys have been investigated for potential replacement of Remalloy in the U-type ring armature telephone receiver. Of particular interest would be an alloy which could be cold drawn into cup shape. Small additions of Al, V, Nb, Ti and Zr were added to the basic 28%Cr–15%Co–Fe ternary in an attempt to suppress γ phase formation and improve cold formability. As a result of extensive investigation we have discovered two Zr bearing alloys that are highly promising for fabrication as receiver magnets. One alloy consists of 0.25%Zr–1%Al and the other 0.25%Zr–0.25%Ti–1%Nb. After suitable heat treatment they yield values of Br=9600 G, Hc=460 Oe, BHmax=1.9×106 GOe and Br=8900 G, Hc=440 Oe, BHmax=1.8×106 GOe respectively.
Thickness dependence of coercivity in LPE garnet films
Authors: Moore E. B. , Calhoun B. A. , Lee K.
Published: February 2003

We have observed that thicker than normal LPE bubble garnet films (14–17 μm) have lower coercivity than those of normal thickness (3–5 μm). We have investigated this thickness dependence of 4 film compositions in the SmCaGe garnet system. In thin films, coercivity is dominated by a high coercivity region near the substrate. As the film thickness increases, the coercivity decreases approaching a ’’bulk’’ value. The two portions of the film, with their different properties, produce a linear relationship of coercivity versus reciprocal thickness which should be taken into account when comparing coercivities of LPE garnet films.
Bubble film characterization by ac susceptibility measurements
Authors: Maartense I. , Searle C. W. , Mier M. G.
Published: February 2003

The use of low frequency magnetic susceptibility measurements as a means of characterizing bubble materials is illustrated. The parameters derived by this method agree to within a few percent with those obtained independently from optical measurements.
Non-Ohmic currents in LPE YIG films
Authors: Patterson R. W. , Adam J. D.
Published: February 2003

Measurements of the I-V characteristics of LPE YIG films have been made over several decades of current and voltage. Both Si-doped and undoped YIG were investigated. All films exhibited regions of non-Ohmic conduction, where I varied as Vα. Values of α ranging from 1.1 to 2.4 were observed. Evidence of carrier trapping was also found. The measurements are interpreted in light of the conduction mechanism through a two layer structure where the upper layer has a much higher resistivity than the bulk of the film. The model is shown to yield qualitative agreement with the experiments, and direct evidence supporting the model structure is presented.
The magnetic anisotropy of 111 oriented garnet bubble films
Authors: Eschenfelder Andrew H.
Published: February 2003

In order to tailor magnetic materials for bubble applications it is important to have a model that can be used to predict the effective anisotropy of a given composition or to select a composition that will have the correct anisotropy to achieve desired bubble size and Q. A model is described in this paper which seems to agree with observed anisotropies over the complete range of bubble sizes for 111 oriented films of mixed rare earth garnets. The elements of the model are as follows: (a) The total effective anisotropy, KT=KS+KG; (b) KS=−1012λ111Δa/2.9; (c) KG=𝒥ijKijxixj, where the sum is over all pairs of ions involving Sm or Eu, in amount xi, and smaller ions such as Y, Tm, Yb, Lu, in amount xj, where x is the atomic abundance (0–3) in the formula unit. (d) Both λ111 and KG are reduced by A/A0 corresponding to the dilution by Ga or CaGe. The paper gives values for Kij, λ111 and A/A0 to be used. A rationale for the model is also given although the principal justification for the model is its apparent success in projecting values of magnetic anisotropy in 111 oriented films.
Effect of in-plane field on the stripe end motion in LPE-garnet films
Authors: Nakao K. , Iida S. , Hirano M. , Tsushima T.
Published: February 2003

Contracting motions of stripe domains are studied by a real time observation method. The apparatus contains a high repetition rate Q-switched YAG : Nd3+ laser, polarizing microscope, highly sensitive image-orthicon TV camera system with a scan-conversion memory, TV monitor and TV control system. The bending of the stripe end during the contraction is observed. It always occurs in the as-grown film and sometimes in the YIG-coated and ion-implanted films. In the as-grown film, the bendings of the stripe end can be separated into two modes. In mode-1, the contracting velocity is about twice as large as in mode-2 when there is no in-plane field, and substantially increases when the in-plane field is applied. In mode-2 the velocity is scarcely influenced by the existence of the in-plane field. In the YIG-coated films, the contracting velocities have an asymmetry with respect to sense of the direction of the in-plane field.
Conductor and transfer-gate performance of single-mask field-current access magnetic-bubble devices
Authors: Dekker E. H. L. J. , van Mierloo K. L. L. , de Werdt R.
Published: February 2003

Bubble propagation has been investigated in conductor structures on 5 μm bubble (Y,Sm,Lu,Ca)3(Fe,Ge)5O12. The conductors consist either entirely of Permalloy or of a sandwich of Permalloy on gold. A static in-plane field is used for unidirectional bubble propagation. The dependence of bubble motion on current amplitude and in-plane field magnitude has been measured at low and high frequencies. The bubble motion was observed to consist of a first slow step where the current acts against the in-plane field, and a second quick step where both act together. Attainable frequencies increase with increasing in-plane field and current intensities up to a maximum of 1.1 MHz. The sandwich conductor has a 12% operating margin at 830 kHz frequency and 30 mA current. It performs better than the all-Permalloy conductor at the same overall spacing of the Permalloy to the epifilm. An improved transfer gate from current to field-access has an 18% margin, from field to current-access 16%, at 100 kHz. The overlap with the conductor margins is 7% at in-plane fields from 30 Oe. The gates can be combined to obtain a field-current swap gate.
Dynamic bubble characteristics in field access devices
Authors: Il’yashenko E. I. , Matveyev S. N. , Karmatsky N. I.
Published: February 2003

Some important characteristics of bubble behavior in field access control structures can be obtained directly in a new experimental system. Characteristics such as the phase angle of the drive field and bubble size variation through the structure can be obtained. The experimental system makes use of a mirror spacer combined with photoelectrical indication of the output signal of a moving bubble so as to obtain its position and dimensions. The procedure is illustrated with I-1 investigation of propagating structure. It is also shown how the system determines the characteristics of various propagation control circuits to estimate the degree of nonuniformity in bubble motion and delays in the coordinates of the drive field HR.
Microstructure and magnetic properties of electroless Co-P thin films grown on an aluminum base disk substrate
Authors: Chen Tu , Rogowski D. A. , White R. M.
Published: February 2003

The microstructure and magnetic properties of electroless Co-P films (∼100 to 1000 Å) deposited on an aluminum base substrate are examined. The squareness and coercivity characterizing the magnetic hysteresis are found to correlate with the size and nature of the microcrystallites making up the film. It is argued that this correlation is due to coupling between the microcrystallites.
High coercivity chromium dioxide
Authors: Hiller D. M.
Published: February 2003

Chromium dioxide in the 560–680 Oe coercivity range has been optimized for high density magnetic recording and is being produced at plant scale. The stabilized powders have residual magnetic moment of 33–35 emu/g, average crystal length of 0.6 μ, average aspect ratio of 20, and specific surface area of 20–40 m2/g. Magnetic tapes made with these oxides improve video output on state-of-the-art video cassette recorders by 2–4 dB and S/N by 1–3 dB, compared with current standard tapes, and also have very low audio noise. Magnetostrictive loss on replay is negligible, as on standard CrO2 tapes.
Computations of the micromagnetic dynamics in domain walls
Authors: Shir C. C.
Published: February 2003

A numerical model was developed to compute the temporal and spatial variations of the detailed micromagnetic structures of domain walls by numerical integration of the Landau-Lifshitz-Gilbert equation. Fundamental interactions due to anisotropy, exchange, and demagnetization are included. Preliminary results for the structure of a planar domain wall indicate that the wall width is much larger near the film surface than at the center of the film, because the demagnetization fields are significant near the surface and the side boundary of the domain wall. The instabilities of the numerical integration of the L-L-G equation are investigated. Several methods were developed to cope with the stiffness which arises when the damping parameter becomes small. The effects of non-dimensional film thickness and anisotropy parameters are similar and are less than 10 percent with these parameters varying by a factor of 2. On the other hand, the effects of an ion-implantation layer in the film on the wall structure are found to be very significant.
Phase separation as source of perpendicular anisotropy in amorphous GdCo
Authors: Herd S. R.
Published: February 2003

The source of perpendicular anisotropy (PA) in 0.05 μ thick, evaporated amorphous GdCo films was investigated by correlating the magnetic domain structure, as observed in the Lorentz mode with film structure, as observed with high resolution electron microscopy and diffraction, as functions of post deposition in situ anneal and elevated substrate temperature. A strong void network was found to anneal out above 500 °K at an apparent glass transition. PA was developed either together with this or at slightly higher temperatures and could be correlated to the appearance of 60–100 Å wide columnar arrays of two separate amorphous phases. The phase separation is evident also in a splitting of the single broad diffraction peak, normally observed in homogeneous amorphous deposits without PA, into two distinct components. Deposition at substrate temperatures above this glass transition results in amorphous films which crystallize on annealing without development of PA. From this, PA is thought to arise from anisotropically shaped Co-rich regions in a transition stage between the homogeneous amorphous and crystalline states.
O2 contaminated amorphous FeGd films
Authors: Schneider J. , Brunsch A.
Published: February 2003

Amorphous FeGd films were made by thermal evaporation in an ultra high vacuum system under controlled O2 pressures. The Gd necessary for magnetic compensation at room temperature increases from 20.2 to 23.8 at.% with increasing O2 pressure from 5×10−8 to 3×10−7 Torr. The perpendicular magnetic anisotropy Ku of films whose composition is about 1.5 at.% Gd deficient compared to the room temperature compensation composition decreases from 2.4×105 erg/cm3 at 8×10−8 Torr O2 to 1.2×105 erg/cm3 at 3×10−7 Torr where part of the magnetic material starts to develop in-plane anisotropy which increases with increasing O2 pressure to 100% at 5×10−7 Torr O2. Further O2 increase yields superparamagnetic films. Between 5×10−8 and 3×10−7 Torr O2 pressure Hc drops from ≳50 Oe to 2 Oe. The electrical resistivity exhibits an exponential increase above 2×10−7 Torr O2. A model to explain these findings will be proposed.
Magnetic and Mössbauer spectroscopic characterization of coal
Authors: Jacobs I. S. , Levinson Lionel M. , Hart H. R.
Published: February 2003

We sketch a role that solid state science, especially magnetic and Mössbauer spectroscopic characterization, can play in understanding coal, with its impurities. The Mössbauer characterization has potential impact on essentially all precombustion coal clean-up procedures. We review concurrent Mössbauer studies on coal in order to demonstrate that this technique has much to offer as an improved analytical method for determining forms of sulfur in coal. Our magnetization analysis throws light on the magnetic properties of coal impurities, ash and pyrite, which facilitate magnetic separation clean-up. It is demonstrated that simple crushing of coal can be responsible for transformations which aid in the separation. The two methods of analysis are shown to be useful for understanding coal liquefaction residues from the point of view of their removal magnetically.
Zero temperature dynamic structure factor for a classical RKKY model of CuMn
Authors: Ching W. Y. , Huber D. L.
Published: February 2003

We report the results of calculations of the zero temperature dynamic structure factor of a classical RKKY model of a metallic spin glass resembling CuMn (0.9 at.%). Our studies show that for the wave vectors considered, q=0.12 (1,1,1) Å−1 and 0.62 (1,1,1) Å−1, the spectral weight is largely confined to the region E?Ep where Ep is the peak in the density of states. Within the limits of the numerical analysis we find no evidence for propagating modes. We make use of our calculations in interpreting recent inelastic neutron scattering studies carried out on CuMn by Scheuer et al. The inelastic peak they observe is identified with the maximum in the density of states.
Spin waves in amorphous ferromagnets
Authors: Singh Vijay A. , Roth L. M.
Published: February 2003

Spin waves in a model of an amorphous Heisenberg ferromagnet are studied by means of an effective medium approximation (EMA) for comparison with observations in amorphous transition metal–metalloid alloys. For long wave length and low energy the EMA agrees with a quasicrystalline approximation for the spin wave energy, but gives a larger density of states than an extended chain approximation with corresponds to conventional spin wave theory. The EMA also gives finite wave vector structure in the spectral weight function.
NMR studies of metal and metalloid site hyperfine field distributions in magnetically ordered amorphous alloys
Authors: Raj K. , Durand J. , Budnick J. I. , Skalski S.
Published: February 2003

We report spin-echo NMR studies of hyperfine field (hf) distributions in a number of magnetically ordered Fe and Co-based amorphous systems. These distributions are broad and often complex due to the overlap of NMR signals arising from both metal and metalloid atoms. We show that by using isotopic substitutions it is possible to separate the metal and metalloid site hyperfine field distributions in Fe-based systems. In many instances it is possible to compare these results with those obtained on related crystalline compounds to identify the environments responsible for the hf distributions observed in the amorphous phase. We also present studies of annealing and cold working on electrodeposited amorphous Co-P samples. Local environmental models provide a good description of our results.
Magnetization of amorphous REx-Cu1−x alloys (RE=Gd, Tb, Dy, Ho)
Authors: Heiman Neil , Kazama N.
Published: February 2003

Films of amorphous RExCu1−x (RE=Gd, Tb, Dy, Ho: 0.30⩽x⩽0.60) were prepared by two source evaporation of the elements. Magnetization measurements were made at 4.2 K with a vibrating sample magnetometer in applied fields up to 70 kOe. In the case of the Gd alloys, the magnetization is consistent with a fully aligned moment of 7μB. The dependence of the Curie temperatures on x can be understood in terms of a nearest neighbor statistical model with a percolation limit of x=0.33. In the case of Tb, Dy, Ho alloys, the magnetization is considerably less than that expected for fully aligned moments. The degree to which the magnetization is reduced is proportional to the Stevens factor of the RE confirming that the reduction is due to local anisotropy effects. The field dependence of the magnetization is consistent with existing models but the dependence of Hc on D/J does not agree with the theory.
Magnetic phase diagram of the Gd-Al and Gd-Cu amorphous alloy systems
Authors: McGuire T. R. , Mizoguchi T. , Gambino R. J. , Kirkpatrick S.
Published: February 2003

Amorphous films of GdxAl1−x and GdyCu1−y where x and y vary from ∼0.2 to 0.8 have been prepared by sputtering. Magnetization measurements in fields from 0.1 to 18 000 Oe over the temperature range 4.2 to 300 °K allowed us to determine the magnetic phase diagram for these systems. Spin glass and ferromagnetic states as well as intermediate regions have been identified. For all compositions the paramagnetic Curie temperature is positive having values from 18 to 150 °K. When x ?0.40, GdxAl1−x displays a susceptibility cusp and relaxation effect characteristic of a spin glass. For compositions x=0.56 and 0.81 a peak in the low field susceptibility is found which is 30 °K below the ferromagnetic Curie temperature as estimated by an Arrott plot. Since magnetic saturation at 4.2 °K is not reached for these two alloys, we assign them to an intermediate state. The GdyCu1−y system also has spin glass like behavior at y=0.21 and y=0.31 but at higher concentrations only easily saturated ferromagnetism is found. Since anisotropy energies are usually small in Gd compounds, observations of a spin glass phase must reflect the presecnce of a wide variation of exchange interactions.
Magnetic neutron scattering from amorphous TmFe2
Authors: Rhyne J. , Pickart S. , Alperin H.
Published: February 2003

Elastic and inelastic neutron scattering was observed from the sputtered amorphous composition TmFe2, which on the basis of magnetization measurements exhibits a transition at T0?45 K. Total scattering isotherms taken over a range of temperatures bracketing this value show a magnetic component similar to YFe2, but not nearly as large as in TbFe2 and HoFe2. Energy scans taken at q=0.05 A−1 show very little change between 60 K and 10 K in the intrinsic linewidth (0.30 meV), suggesting that the spin diffusion does not change greatly on going through the transition.
Magnetic ordering and local random anisotropy in dilute magnetic glasses
Authors: Gruzalski G. R. , Patterson J. D. , Sellmyer D. J.
Published: February 2003

Magnetic susceptibility and high-field magnetization measurements are presented for amorphous Zr40Cu60−xMx (M denoting Fe, Mn, Gd, and Tb) and Nb50Ni50−xFex, with x ranging from zero to about ten. The alloys for M=Gd, Tb, and Fe develop low-temperature ordered states that are characterized as spin glass like, whereas the Mn alloy exhibits no evidence of order down to 1.3 K. The magnetic properties of these alloys are discussed in terms of local random anisotropy, fluctuations in the interimpurity exchange interactions, extremely short electron-mean-free paths, antiferromagnetic interactions between the localized moments and the conduction electrons, and moment instabilities.
Conduction electron polarization and moment perturbations in dilute Fe3Si based alloys
Authors: Stearns Mary Beth
Published: February 2003

The spatial variation of the s-conduction electron polarization in the Fe3Si system is determined from neutron scattering, magnetization saturation and hyperfine field measurements. This polarization is then combined with magnetization saturation and hff data for solute atoms Mn, V, Co, and Ni in Fe3Si to obtain the solute moments and host moment perturbations due to these impurities. The behavior of these solute moments and moment perturbations is seen to be very similar to those in binary Fe alloys. Since Fe3Si is closely related to Heusler alloys, it is suggested that their magnetic behavior is also governed by the same mechanism that determines the magnetic behavior of Fe; that is, the conduction d-like electron, not the s-like electrons cause the magnetic alignment.
Nuclear spin relaxation in Au51V: Spin dynamics of a Kondo alloy
Authors: Narath A. , Follstaedt D.
Published: February 2003

The temperature dependent spin dynamics of vanadium impurities in the Kondo alloy AuV (ϑK?300 K) have been studied by means of measurements of 51V transverse relaxation rates (T−12) for the temperature range 1–260 K and vanadium concentrations of 0.2 to 0.5 at.%. Contrary to published reports, we find the quantity T2T to increase markedly with increasing temperature. Its magnitude at 260 K [15(±5) msec K] exceeds the limiting low-temperature value by a factor of 10. The observed increase in T2T indicates a large reduction in the impurity spin-correlation time, e.g., τe(ϑK)/τe(0) ?0.2.
Matrix isolation studies of bimetallic molecules of transition metals (Fe-Co, Fe-Ni, Fe-Cu)
Authors: Montano P. A.
Published: February 2003

The matrix isolation technique has been used in conjuction with Mössbauer spectroscopy to study simple molecules of Fe-X (X=Cu, Ni, Co). The metal atoms were isolated in a solid rare gas matrix at 4.2 K and the molecules were formed in the matrix. It was observed that there is an increase in the electron density at the 57Fe nucleus in going from Cu to Ni. The Fe-Ni molecule is the weakest bond of all the studied cases. It has an isomer shift very close to that of the iron monomer in rare gas solids. In Fe-Ni the quadrupole splitting of the Mössbauer spectrum is half the value of the Fe-Fe molecule (4.05 mm/sec), indicating a different orbital ground state for the Fe-Ni molecule. By contrast Fe-Co is stronger bound than Fe-Ni, this being reflected in a more positive isomer shift. Iron-cobalt multimers were also studied and their magnetic hyperfine splitting determined. Samples of iron-cobalt isolated in solid argon with a 25 at.% metallic concentrations showed a very similar behavior to that of disordered Fe-Co alloys. The Fe-Cu molecule shows a large isomer shift and a small magnetic moment at the iron site.
Ferromagnetic resonance in periodic domain structures
Authors: Artman J. O. , Charap S. H.
Published: February 2003

We have recalculated the Smit and Beljers FMR mode frequencies for thin multi-domain magnetic platelets (disks) with uniaxial magnetocrystalline anisotropy K taking the finite aspect ratio of the domains into account. The magnetic anisotropy axis (z-axis) was taken to be perpendicular to the disk plane; the external magnetic field H was applied in the disk plane. The demagnetization energy coefficients of the periodic magnetic structures were found by the method of Kaczér and Murtinová. Below magnetic saturation the normalized FMR frequencies are: (a) for stripe domain arrays with H normal to the walls, Ω2+= (1−p)(1+2r−2p)−h2, Ω2−= (1−p)2−h2; (b) for bubble domain arrays, Ω2+= (1−p)(1+r−3p/2)−(1−r−p/2)(1−p)−1h2, Ω2−= (1+r−3p/2)[1−p−(1−p)−1h2], with HA=2K/M, Ω=ω/γHA,h=H/HA, r=2πM/HA and p=NzzM/HA. As the domain aspect (width/height) ratio tends toward zero, p→0 and the Ω2+, − expressions reduce respectively to (a) the stripe resonance expressions given by Smit and Beljers, (b) the first two bubble resonance expressions found in Kaczér and Gemperle. Our attempts to correlate these results with published experimental data are inconclusive; often the samples were too thick to support simple domain structures or relevant information was not provided.
Magnetostatic energy of stripe domain patterns
Authors: Spreen J. H. , Morgenthaler F. R.
Published: February 2003

The energy of an array of straight stripe magnetic domains, such as might be found in an epitaxial garnet (bubble) film, is examined theoretically by modifying and extending the results of Kooy and Enz. For a uniform pattern, the energy is conveniently expanded in a Taylor series, using variables which describe the relative widths of the stripe domains. The coefficients in the expansion are familiar transcendental functions of material and sample parameters. An immediate result is an expression for the linear susceptibility (to an applied field normal to the film plane) in terms of the sample thickness and zero-field domain width. The energies for non-uniform patterns, which are interpreted in terms of dispersion curves for waves of displacements of rigid walls from the zero-field positions, are calculated using two approaches. The results of a lattice dynamics model, in which the restoring forces are related to the expansion coefficients, are compared to the results of a model which uses an extension of Kooy and Enz’s result to general periodic domain patterns. The significant differences are attributed to the more accurate treatment by the second calculation of the long-range magnetostatic forces.
Transport properties of EuO at ferromagnetic resonance
Authors: Kaski K. , Kuivalainen P. , Stubb T.
Published: February 2003

Some transport properties of the magnetic semiconductor EuO have been measured at the ferromagnetic resonance (FMR). A static voltage appeared when the contacts on the sample were unsymmetrially located with respect to the external magnetic field. The induced static field was linearly proportional to the microwave power, the static electric field/microwave power ratio being 5×10−4 V/W mm. A change in sign of the static voltage was found when the angle between external magnetic field and microwave magnetic field was changed through 90 degree. To explain the appearance of the static voltage two models have been analyzed, electrodynamic interaction and magnon drag. The electrodynamic interaction model seems to fit better. A decrease in the sample resistivity at FMR was also observed, the change being 6 per cent.
Recent developments in the theory of spin glasses
Authors: Anderson P. W.
Published: February 2003

The actual behavior of real spin glass systems bears little resemblance to that computed by the mean field like theories of Edwards, Anderson and Thouless, and Anderson and Palmer. There is no singularity in the specific heat, and there is an anomalous sensitivity to the magnetic field, for example. The reason has long been expected to be much bigger in this case than for conventional ferro- or antiferromagnetics. I will give a simple argument showing that the Heisenberg spin glass (such as Cu-Mn) is at ’’lower critical dimensionality’’, the lowest dimensionality at which fluctuations allow a phase transition to exist. As a result, its nearest relative is the 2-dimensional x-y model recently solved by Kosterlitz, and I will show how similar the real properties of spin glass are to those computed for the x-y model.
The Hall effect in spin glasses
Authors: McAlister S. P.
Published: February 2003

Although the coupling betweenthe magnetic moments in the ideal spin-glass state is made via the itinerant electrons, it has been difficult to see conspicuous evidence of the state in properties that depend on the electrons’ motion. However, the temperature dependence of the anomalous part of the Hall effect, which arises from the spin-orbit coupling of the itinerant electrons with the local moments, is a transport property that in favourable alloys can show clearly the spin-glass transition. The conditions for the appearance of this anomalous component are presented. Features detected as the magnetic arrangement in a spin glass is altered suggest that independent spins and those coupled by direct exchange to at least one other spin are responsible for the behavior.
Magnetic properties of the rare-earth intermetallics RGa2
Authors: Tsai T. H. , Gerber J. A. , Weymouth J. W. , Sellmyer D. J.
Published: February 2003

The magnetic susceptibility (χ) of polycrystalline samples of RGa2, R=Ce, Pr, Nd, Gd, Tb, Dy, Ho, and Er, has been measured at low field, from 1.5 K to 300 K. The magnetization of these samples also has been measured up to 80 kOe at low temperatures. Antiferromagnetic behavior was observed for all the samples with Neel temperatures (TN) ranging from about 4.1 K for CeGa2 to about 14.8 K for TbGa2. Curie-Weiss fits to the high-temperature χ (T) data led to effective moments in good agreement with those expected for R3+ ions. The paramagnetic Weiss temperatures cannot be reconciled with the de Gennes theory based on free electron coupling of the R spins via the RKKY interaction. Electrical resistivity of selected polycrystalline samples has been measured, and the effects of spin-disorder scattering observed below TN. CeGa2 shows no evidence of Kondo behavior. Magnetization measurements for the polycrystalline samples show metamagnetic phase transitions when the antiferromagnetic R-R interactions are overcome. Measurements on a HoGa2 single crystal show that the [100] direction is the easy direction.
Magnetic properties of rare-earth magnesium compounds of the type RMg2
Authors: Buschow K. H. J. , Sherwood R. C. , Hsu F. S. L. , Knorr K.
Published: February 2003

The magnetic and crystallographic properties of rare earth compounds of the type RMg2 were studied. The compounds in which R represents La, Ce, Pr, Nd, Sm and Gd were found to be of the cubic Laves phase structure. The remainder of compounds of this series crystallize in the hexagonal Laves phase structure. For all compounds the lattice constants were determined. Most of these compounds order ferromagnetically at temperatures well below 100 K. Exceptions are LaMg2, YbMg2 and YMg2 which exhibit Pauli paramagnetism, whereas SmMg2 and EuMg2 order antiferromagnetically. From the magnetic properties and from the lattice constants it is concluded that Eu and Yb are both divalent in these compounds. A peculiar temperature dependence of the magnetization was observed in SmMg2. A sharp peak-like rise in the magnetization occurs within a temperature range of 10 K only, the magnetization being nearly temperature-independent otherwise. Details regarding the nature of the crystal fields in the cubic RMg2 compounds were derived from specific heat measurement performed on LaMg2, CeMg2 in the temperature range 1.5–40 K.
Appearance of magnetic moment in vanadium metal fine particles
Authors: Akoh H. , Tasaki A.
Published: February 2003

The magnetic susceptibility of vanadium metal fine particles (90 to 300 Å) which were prepared by the gas evaporation method was measured in the temperature range between 4.2 and 300 K. The magnetic susceptibility of these fine particles depends upon the diameter of the particle and it consists of two parts, one was the Pauli type and the other was the Curie-Weiss type overlapping the temperature independent one. The fact that the Curie constant estimated from the C-W part of the susceptibility is proportional to the reciprocal diameter of fine particle suggests that magnetic moment originates from surface of vanadium fine particles. Compared with vanadium fine particles, the magnetic properties of other metal fine particles were measured.
Linewidth of crystal-field excitations in metallic rare-earth systems
Authors: Becker Klaus W. , Fulde Peter , Keller Joachim
Published: February 2003

A theory for the linewidth of crystal-field excitations in metallic rare-earth systems is presented, where the damping is due to conduction electron-hole excitations. The results of that theory are presented by applying it to two cases. The first case concerns Ce impurities in LaAl2. A comparison with recent experiments is made. The second application is to a Γ1-Γ4 system. Special attention is paid to the behavior of the central peak near an induced moment phase transition. The theoretical predictions are in agreement with recent experimental findings on Pr3Tl.
On the properties and electronic structure of MnSb, CoSb and NiSb
Authors: Chen Tu , Rogowski D. , White R. M.
Published: February 2003

The resistivity, susceptibility, and thermopower of single-crystal MnSb, CoSb and NiSb are presented as functions of excess metal concentration. From these results, we propose that the electronic structure of the compounds may be described by metal 3d bands overlapping broader Sb p bands with the Fermi level lying near the top of the d bands in CoSb and above the d bands in NiSb. It is argued that the excess metal enters the structure as a neutral interstitial.
Order-disorder, magnetic interactions and corrosion behavior in stable and metastable Fe-Zn alloys
Authors: Montreuil C. , Evans B. J.
Published: February 2003

Hyperfine interactions, phase analysis, order-disorder phenomena and the behaviour to dilute acid immersions have been determined by means of 57Fe NGR at 298 K for a number of equilibrium, powder metallurgical and metastable, electrodeposited Fe1−xZnx alloys. The equilibrium alloys exhibit a linear dependence of Heff on Zn content in the α phase field. Even though the widths of the lines increase by a factor of 3 as x increases from 0 to 0.3, the lines remain structureless and symmetric. The Mossbauer spectrum of Γ phase exhibits an asymmetric, poorly resolved two-line pattern. For similar Zn contents the linewidths and Heff of the metastable, electrodeposited are larger than those of the equilibrium alloys. The electrodeposited alloys have extremely broad x-ray diffraction lines but are not completely amorphous and contain excess fractions of the α phase. Thermal annealing leads to a reduction of the Mossbauer and XRD linewidths in the α phase fraction and to an increase in Heff and δ. Immersion tests on the unannealed electrodeposited alloys show that the Γ phase provides the major sacrificial corrosion protection. For annealed alloys, the α and Γ phases are consumed at similar rates. These data provide an understanding of the static electrochemical behaviour of these alloys.
Europium barium titanate—A magnetic ferroelectric compound
Authors: Janes D. L. , Bodnar R. E. , Taylor A. L.
Published: February 2003

Eu1/2Ba1/2TiO3 was prepared with the intent of building both ferromagnetism and ferroelectricity into the same crystal lattice. Ceramic samples prepared at 1500 °C exhibit a magnetization of 59 emu/g at 1.8 °K and 5 kOe applied field. Possible crystallographic ordering of Ba2+ and Eu2+ ions is thought to permit positive interactions among the magnetic ions. The material also exhibits ferroelectric behavior with a Curie temperature of 165 °K and a polarization of 9.5 μC/cm2 at an applied field of 15.7 kV/cm and 35 Hz. Eu1/2Ba1/2TiO3 is the first compound known to us to exhibit simultaneously ferroelectricity and a magnetic moment of this magnitude.
Optical properties and electronic structure of UO2
Authors: Schoenes J.
Published: February 2003

The near normal incidence reflectivity of UO2 single crystals has been measured in the photon energy range from 0.03 eV to 13 eV. From the reflectivity spectrum the complex dielectric function ε (ω) =ε1(ω)+iε2(ω) has been derived by means of the Kramers-Kronig relation. In addition the absorption coefficient was determined from a direct transmission measurement on thin single crystal plates in the weakly absorbing spectral region below the absorption edge. An energy level scheme is proposed which allows a self-consistent assignment of the structure in ε2 with optical transitions between maxima in the density of states. The energy gap found at 2.1±0.1 eV is attributed to a 5f2→5f16deg transition. A crystal field splitting 10Dq=2.8 eV is derived for the 6d conduction states. Good agreement is obtained within this model with XPS measurements and a recent molecular cluster approximation. It disagrees with a previous interpretation of reflectivity data.
Crossover effects near the spin-flop multicritical point
Authors: Rohrer H. , Gerber Ch.
Published: February 2003

We report on the experimental investigation of two types of crossover in the ordered state near the spin-flop (SF) multicritical point in the orthorhombic antiferromagnet, GdAlO3. (a) The magnetization discontinuity, ΔM (t), at the SF transition increases with power β̃=0.88±0.02 close to the SF multicritical point. Close to a critcal edge point of the SF transition shelf, however, β̃≈0.32. The bicritical-critical crossover extends over several orders of magnitude. (b) The SF transition shelf was mapped out for different directions of H⊥. The resulting tetracritical point–bicritical line crossover appears to be rather complicated and the experimental results are not yet well understood.
Magnetic and structural phase transitions in NiTiF6⋅6H2O
Authors: Karnezos M. , Friedberg S. A.
Published: February 2003

At 300 K, NiTiF6⋅6H2O crystallizes in the trigonal NiSnCl6⋅6H2O structure with one axially distorted [Ni(H2O)6]++ complex per unit cell. This structure is retained on rapid cooling, enabling us to measure χ∥, χ⊥, and Cp between ∼0.05 and 4.2 K in a 3He-4He dilution refrigerator. χ∥ and χ⊥ are those of a uniaxial ferromagnet with Tc?0.14 K and the easy direction along the trigonal axis. These data, as well as Cp with H∥=300 and 1500 Oe are well described by an Oguchi model in which pairs of exchange-coupled spins are treated exactly and interactions among pairs are replaced by a mean field. The pair Hamiltonian is 𝒞H=D (S2zi+S2zj) −2JSi⋅Sj+gμB(Si+Sj)2. Heff where Si=Sj=1, Heff=H+2J (q−1)M/Ng2μ2B with q=6. We find D/k=−1.83 K, g=2.26 and J/k?+0.012 K. We have also measured Cp for NiTiF6⋅6H2O under equilibrium conditions between 1.7 and 270 K. A first order structural phase transition is observed at 136.5 K with a latent heat of ∼662 cal/mole.
Anisotropic behaviour of the magnetization of DyVO4 in the basal plane under Jahn-Teller distortion
Authors: Picard J. , Hubsch J. , Le Gall H. , Guillot M.
Published: February 2003

The purpose of this paper is to re-examine the magnetic properties of a single crystal DyVO4, mainly in the low temperature range (down to 1.5 °K) where anomalous behaviour of the magnetization and susceptibility are observed. As indicated by different authors the susceptibility along the tetragonal axis C4(Ha∥C4) is very small, but we have observed maximum of the magnetization at TD?19 °K which can be associated with the rise of the Jahn-Teller distortion. On the other hand, the magnetic behaviour of DyVO4 is more complicated in the basal plane (a-b) where a strong magnetic anisotropy appears in the in the temperature range TNeel<T<TD. In the temperature range 3.5–7.5 °K unusual spin flop with hysteresis is observed when the magnetic field Ha is applied along the antiferromagnetic (AF) a-axis. The anomalous magnetic behaviour of DyVO4 in the basal plane is described in detail for T<TNeel and T<TD.
Magnetic and superconducting transitions in GdxEr1−xRb4B4 and GdxY1−xRh4B4
Authors: Wang R. H. , Laskowski R. J. , Huang C. Y. , Smith J. L. , Chu C. W.
Published: February 2003

The magnetic and superconducting transition temperatures and upper critical fields have been measured for GdxEr1−xRh4B4 and GdxY1−xRh4B4. The pressure dependence of Tc for the Er system for x?0.05 is 0.5×10−2 K/kbar. Both systems exhibit reentrant behavior, that is a superconducting transition followed by a magnetic transition at a lower temperature that destroys the superconductivity. For the Er system, the initial additions of Gd actually raise the superconducting critical field followed by the expected decrease for greater additions.