bluuebunny/crossref_metadata_2025 huggingface dataset:
The healing behavior of nuclear tracks in yttrium iron garnet films
Authors: Heitmann H. , Hansen P.
Published: February 2003

The irradiation of yttrium iron garnet films with 181-MeV xenon ions (1.4 MeV per nucleon) creates paramagnetic cylinders around the path of the ion with a radius of about 7.5 nm. These nuclear tracks consist of needle shaped regions of high crystalline defect density reaching 10 μm deep into the garnet material. The saturation magnetization decreases exponentially with dose. However, its temperature dependence remains unchanged by the irradiation except for small deviations near the Curie temperature. Owing to the creation of paramagnetic volumes, the Faraday rotation is also reduced, but contrary to the behavior of the saturation magnetization, the temperature dependence is changed. The reduction at low temperatures is much smaller as would be expected from the saturation magnetization. The optical absorption is drastically increased by the irradiation. Annealing leads to heal-out of the irradiation induced effects. The saturation magnetization is restored after 10 h annealing at 833 K. The Faraday rotation at T=4.2 K, however, is then twice as large as that of the unirradiated film. This additional rotation nearly disappears after annealing at 1223 K. The additional optical absorption induced by the irradiation exhibits a similar behavior as the additional Faraday rotation.
Electrical resistivity in spin glass C
uMn
Authors: Huang F. S.
Published: February 2003

The electrical resistivity is discussed, providing a direct measurement of the critical exponent β for a spin glass CuMn. CuMn alloys with magnetic impurity concentrations ∼0.7–4.5 at. % exhibit the characteristic spin glass cusp in low field ac susceptiblity at temperature TF. The magnetic contribution to the resistance of this alloy increases with temperature below Tf and is constant above Tf. By using the exchange interaction between the conduction electrons and the unpaired electrons localized on the Mn ion as a perturbation and by applying the Boltzmann transport equation, the electrical resistivity is shown to be related to the order parameter q. Below the freezing temperature, scattering can be caused by deviation of the spin from its ground state. As the temperature rises, the resistivity will increase, too. Above the freezing temperature, each spin behaves perfectly independently and gives rise to a constant resistivity. So the critical exponent β of spin glass order parameter q can therefore be determined by fitting the theory to measured data. It also can be shown that specific heat is related to the temperature derivative of ρmag(T) for ordered magnetic moment material.
Singular behavior in the random anisotropy model in a nonzero magnetic field
Authors: Cullen J.
Published: February 2003

We study a model of an amorphous magnet in which the disorder is described by a randomly varying easy magnetization axis. We assume that the system has a net anisotropy, not withstanding the randomness. With a magnetic field applied perpendicular to this axis, we show that the system behaves as a spin glass, i.e., there is no long-range magnetic order when the field is close to the anisotropy field. It is this effect which may ultimately limit the response of transversely field-annealed ribbons.
Crystal field splittings in dilute amorphous rare earth alloys
Authors: Rainford B. D. , Samadian V. , Begum R. J. , Lee E. W. , Burke S. K.
Published: February 2003

Inelastic neutron scattering has been used in an attempt to characterize the crystal field of isolated rare earth ions in an amorphous matrix. Amorphous yttrium copper alloys in which 5% of the yttrium was replaced by Ce, Pr, and Er were studied using neutron time-of-flight spectroscopy. Both the Ce and Pr alloys showed quasielastic paramagnetic scattering at all temperatures between 15 and 300 K. The Er alloy however displayed a well defined inelastic peak centered at 2 meV at low temperatures which was identified with a crystal field transition. To our knowledge this is the first observation of a well-defined spectroscopic transition for rare earths in an amorphous environment.
Chemical bonding and local symmetry in cobalt- and iron-metalloid alloys
Authors: Corb B. W. , O’Handley R. C. , Grant N. J.
Published: February 2003

A model is proposed that quantitatively accounts for the moment variation in transition metal–metalloid (T–M) crystals and glasses. The model, formulated from the valence bond theory, assumes that each Co atom surrounding an M atom contributes a d orbital to participate in p–d hybrid bonding. The hybridized d orbital is then considered to be nonmagnetic. Hence the moment variation in Co–M alloys is determined by the local symmetry of the M atom and not by the valence of M. The moment reduction is caused by orbital transfer rather than charge transfer. Excellent quantitative agreement is found when the model is compared with experimental data for crystalline and amorphous Co–M alloys. It is found that amorphous alloys retain the same local environment around the metalloid atom as in the crystalline cases and that the bonding is equivalent. The bond model predicts zero moment change for dilute bcc Fe alloys because the bonding levels in the Fe band have no uncompensated spin. Reasonable agreement with experiment is obtained, but the size of the metalloid affects the Fe–Fe atom exchange which in turn affects the magnetic moment. The bond model for Ni–M alloys is presented in another paper.
High magnetic moment of Fe–Au–B sputtered amorphous alloys
Authors: Fukamichi K. , Satoh T. , Masumoto T.
Published: February 2003

Fe-base amorphous alloys have been prepared by high-rate sputtering and melt quenching, and the magnetic moment, the Curie temperature, the saturation magnetization at room temperature, and the crystallization temperature have been investigated. Some elements which are located at the right hand side in the periodic table such as Au, Pt, and Pd increase in the magnetic moment. These elements also increase the room temperature saturation magnetization in dilute concentration ranges. The crystallization temperature is increased by addition of the elements which have a high heat of fusion, except for Pd and Rh.
Effect of large in-plane fields on potential wells of bubbles under charged walls
Authors: DeLuca J. C. , Malozemoff A. P.
Published: February 2003

At small values of in-plane field Hp magnetic bubble domains can reside under charged walls at the edge of a nonimplanted disk. When Hp is increased along the charged wall and exceeds a critical value Hpcrit1, the stable bubble position moves many microns away from the disk. The maximum gradient of the well along this direction also goes to zero at this value, but the apparent field well depth Hw goes to zero at a lower value Hpcrit2. Between Hpcrit1 and Hpcrit2, Hw can actually be negative. A phenomenological theory is developed to show how this can occur. The maximum gradient of the well perpendicular to the charged wall is also studied. It is found to be asymmetric at low in-plane fields, to decrease with increasing in-plane field, and to be roughly a factor of two larger than the maximum gradient along the charged wall.
Effect of grain geometry on electrical properties of snow at frequencies up to 100 MHz
Authors: Denoth A.
Published: February 2003

The complex dielectric constant of snow samples with different stages of metamorphism and different densities and liquid water contents has been measured in the frequency range of up to 100 MHz. Both the static dielectric constant and the loss factor at frequencies between 1 and 100 MHz depend strongly on the snow texture. The shape of the snow grains or clusters has been found to be an important texture parameter; it is particularly suited for snow classification. A significant influence of the size of the grains on the electrical properties has not been observed. Under the condition of a low ionic conductivity, shape factors to classify snow samples can be derived from the static permittivity. Compared to the determination of shape factors from thin snow sections, the dielectric method is most suitable for application to wet snow.
Optical absorption coefficient and minority carrier diffusion length measurements in low-cost silicon solar cell material
Authors: Swimm Randall T. , Dumas Katherine A.
Published: February 2003

The optical absorption coefficient of silicon solar cell material grown by three low-cost growth methods was measured in the wavelength interval 0.8≤λ≤1.0 μm, the wavelength region of interest in surface photovoltage measurements of the minority carrier diffusion length. The square root of the absorption coefficient was found to vary linearly with photon energy over the wavelengths studied, and the measured data agree with a linear empirical fit to within 0.5% RMS. The absorption coefficients obtained are slightly lower than those reported by Runyan, with the greatest disagreement at long wavelengths. Minority carrier diffusion lengths computed using the present absorption coefficients are approximately 16% greater than those calculated using Runyan’s data. Excellent sample-to-sample agreement within and between lots indicates that for two of the growth methods studied, material quality as judged by optical properties has not been sacrificed by the use of low-cost growth methods. Samples grown by the third growth method studied showed measurably poorer optical quality.
Damage thresholds in laser-irradiated glass
Authors: Batteh Jad H.
Published: February 2003

A model is developed for determining the laser fluence required to damage glass. In particular, damage thresholds for elastic stress failure and surface relaxation phenomena are determined based on the temperature and stress profiles in the glass. The temperature profile is calculated from the one-dimensional diffusion equation with an exponential source term to account for absorption of laser radiation. An effective heat transfer coefficient is used to approximate surface heat losses due to natural convection and radiation. Stress profiles in the glass are calculated based on the plane stress approximation. The model is used to calculate damage thresholds for continuous wave DF and CO2 irradiation of BK-7 glass for times ranging from 10−5 to several seconds. It is found that the absorption coefficient at the laser wavelength plays a significant role in determining the mode of damage and the damage threshold. The effects of surface losses and glass width on the damage threshold are also discussed.
Magnetic properties of hydrides of rare earth–transition metal glasses
Authors: Robbins C. G. , Chen* Z. D. , Zhao* J. G. , O’Shea M. J. , Sellmyer D. J.
Published: February 2003

The effect of hydrogen on magnetic properties of metallic glasses of the form (R80Ga20)1−xTxHy where R=Pr, Nd, Gd, Tb, Er; T=Cr, Fe, Co, B; 0≤x≤0.3 and 0≤y≤1.7 is reported. The anisotropic rare earth glasses without H all exhibit speromagnetic (spin-glass-like) transitions and the effect of hydrogen, in most cases, is to lower the peak in χac significantly but leave TC relatively unchanged. For the Gd glass with T=Fe and x=0.1 the introduction of H at the level y=0.55 causes a large decrease in TC and a significant increase in local random anisotropy. Models for these phenomena are discussed.
Hydrogen in amorphous magnetic alloys
Authors: Coey J. M. D. , Ryan D. , Gignoux D. , Liénard A. , Rebouillat J. P.
Published: February 2003

Iron-rich Y1−xFex amorphous alloys have been charged electrolytically with hydrogen to an H:Y ratio of approximately 3. The alloys are originally asperomagnetic, with spin freezing temperatures below 110 K, but they become soft ferromagnets on hydrogenation with Curie temperatures in excess of 400 K. The iron moment in a–Y12Fe88 changes from 1.96 to 2.24 μB in the hydride and the isomer shift increases by 0.15 mm/s. However, it appears that the main effect of the hydrogen is to shift a broad, mostly ferromagnetic exchange distribution with some antiferromagnetic interactions to an overwhelmingly ferromagnetic one. This is attributed to dilation of the iron–iron nearest-neighbour distances. By contrast, no significant effects on magnetic moment or exchange were detected on hydrogenating amorphous Fe40Ni38Mo4B18 (Metglas 2826 MB), but the in-plane anisotropy was modified and the soft magnetic properties degraded.
Noncrystalline ferromagnetic iron-gallium oxide
Authors: Coey J. M. D. , Devlin E. , Gambino R. J.
Published: February 2003

Conductivity, magnetization, and Mössbauer spectra have been measured for a thin film of composition Fe0.50 3+Fe0.19 2+Ga1.37O3, sputtered from a target of FeGaO3. The film shows thermally activated electrical conductivity in the range 150–300 K with activation energy 0.26 (2) eV, and a room temperature resistivity of 3×104 Ω-cm. Signs of electronic relaxation typical of inhomogeneous mixed-valence materials appear in the Mössbauer spectra, but the activation energy there is smaller. The oxide orders ferromagnetically around 155(10) K. At 4.2 K, hysteresis is observed with a coercivity of 4.7 kOe, and a reduced remanence of 0.46. The ferromagnetism of the amorphous oxide is attributed to ferromagnetic interactions associated with Fe2+↔Fe3+ electron transfer, which are stronger than the usual Fe3+–O–Fe3+ antiferromagnetic superexchange.
Low field magnetic properties of amorphous (FeyB1−y)1−2xRExLax alloys
Authors: Geohegan J. A. , Koon N. C. , Das B. N.
Published: February 2003

The low field magnetization curves of amorphous (Fe82B18)90RE5La5 alloys (where RE=Pr, Sm, Gd, Tb, Dy, and Er) were measured at room temperature. In the as-cast state these alloys have low coercive forces (50 to 1800 mOe) and high initial susceptibilities. Stress relief annealing studies show that much of the coercivity is due to strain induced anisotropy. We present the effects of annealing two new alloys, (Fe78B22)96Tb2La2 and (Fe75B25)96Tb2La2. Transverse field annealing of the first of these alloys induces an anisotropy, as derived from M–H curves, of 360 J/m3. The largest effective magnetomechanical coupling constant of the transversely annealed samples was 0.45.
Nonmagnetostrictive glassy Co–Fe–Ni–Mo–B–Si alloys
Authors: Hasegawa Ryusuke
Published: February 2003

Magnetic properties of glassy (Co1−x−yFex–Niy)100−a−b−cMoaBbSic are presented where 0.03≤x≤0.10, 0≤y≤0.10, 0≤a≤6, 11≤b≤18, 0≤c≤14, and 18≤(b+c)≤26 atomic percent. Many of these alloys are nearly zero-magnetostrictive and exhibit properties comparable with or superior to crystalline zero magnetostrictive supermalloys. For example, heat-treated glassy Co67.4Fe4.1Ni3Mo1.5B12.5Si11.5 ribbon (25 μm thick) exhibits core loss (L) of 4 W/kg and permeability (μ) of 23 000 at f=50 kHz and Bm=0.1 T, which are superior to those (L=8 W/kg and μ=19 000) of a corresponding supermalloy. In these materials, high B–H squareness ratio close to 1 and low coercivity of 20 A/m at 50 kHz have been observed, which are useful in such devices as switch-mode power supplies. Furthermore, the glassy alloys with Si/B ratio close to 1 have been found to be relatively stable magnetically. For example, the activation energy for the kinetics at magnetization reorientation increases from 1×10−19 J to about 2×10−19 J when Si/B ratio changes from 0 to about 1.
Neutron diffraction studies of diluted magnetic semiconductors (invited)
Authors: Dolling G. , Holden T. M. , Sears V. F. , Furdyna J. K. , Giriat W.
Published: February 2003

The nature of the spin correlations in Zn1−cMncTe alloys for several values of c has been studied by neutron powder diffraction as a function of temperature T between 2 and 300 K. Results have been obtained for c=0.376, 0.565, 0.594, and 0.68. The correlations are weak at low c and high T, but intensify progressively as c increases and/or T decreases. For c as high as 0.68, the experiments do not indicate any phase transition to a fully ordered magnetic structure, but the appearance of broad, intense magnetic diffuse scattering peaks at particular positions suggests a strong tendency towards antiferromagnetic ordering of type III. The results are analyzed in terms of a theory of the magnetic scattering from magnetic ions surrounded by near-neighbor shells of correlated spins. Comparison is also made with the correlations expected from an ordered type III structure modified by various exponential functions of a correlation length κ(c). Application of a magnetic field up to 2 Tesla to the c=0.594 specimen produced no measurable effects on the neutron diffraction patterns.
Raman scattering from magnetic excitations in diluted magnetic semiconductors (invited)
Authors: Ramdas A. K.
Published: February 2003

Alloys of II–VI semiconductors with magnetic semiconductors like MnS, MnSe, MnTe—the diluted magnetic semiconductors—occur in a homogeneous phase with the zinc blende or wurzite structure, over a large composition range. Thanks to the presence of the substitutional Mn++ and in turn, a strong Mn++–Mn++ and Mn++–band electron exchange interaction, these alloys exhibit striking magnetic properties. Raman scattering is a powerful technique for their investigation. This is illustrated with results on Cd1−xMnxTe which exhibits (1) Raman lines associated with ΔmS=±1 as well as ΔmS=±2 paramagnetic transitions within the Zeeman multiplet of the S=5/2 ground state of Mn++ (2) the paramagnetic transitions in combination with LO-phonons (3) spin-flip transition of a bound electron (4) evolution of the paramagnetic line of Mn++ into the high frequency component of the magnon line split into a doublet by the magnetic field. The magnon line has been studied as a function of temperature, composition, and magnetic field.
Neutron spin echo study of spin glass dynamics (invited)
Authors: Mezei F.
Published: February 2003

The neutron spin echo technique allows us to obtain direct, model independent information on spin relaxation in the time domain of 3×10−12 to 3×10−9 sec. The experimental results on a variety of spin glass samples reveal a number of common characteristic features. Namely (a) the relaxation kinetics correspond to a broad distribution of relaxation times; (b) the slowing down of the relaxation can be described by an Arrhenius law above the freezing temperature, but not around and below; (c) the absence of momentum dependence in the relaxation dynamics indicates that nonexchange type interactions play a fundamental role in this dynamics.
Small angle neutron scattering studies of critical correlations in alloys (invited)
Authors: Rainford B. D. , Burke S. K.
Published: February 2003

Neutron small angle scattering (SAS) data are compared and contrasted for three different types of transition metal alloys which display a critical concentration cF for the onset of ferromagnetism. In Cr Fe alloys and in amorphous (Fe Mn) PC alloys near cF the scattering intensity rises dramatically below the Curie temperature. This ‘‘subcritical’’ scattering is not found in Pd Ni alloys. While the physics of the onset of order is quite different in the three cases, the behavior of the correlation range as a function of temperature and concentration is very similar in the three alloy systems.
Spin-freezing below the ferromagnetic transition determined by the imaginary component of ac magnetic susceptibility
Authors: Goldfarb R. B. , Fickett F. R. , Rao K. V. , Chen H. S.
Published: February 2003

The temperature dependences of the real and imaginary components of ac magnetic susceptibility have been measured for a number of amorphous Fe-Mn and Fe-Ni alloys. The alloys have paramagnetic, ferromagnetic, and spin-glass intervals as a function of decreasing temperature. The spin-freezing temperatures Tfg are identified by examining the imaginary susceptiblility χ″. With decreasing temperature, χ″, representative of losses, begins to increase at the Curie temperature TC, and reaches a peak at a temperature identified as Tfg. No peak is seen at TC. The real susceptibility χ′ increases rapidly at TC but decreases before reaching Tfg. For frequencies of 10 and 20 Hz, the peak magnitude of χ″ is about half that of χ′. The results suggest that Tfg may be unambiguously defined by a peak in χ″ in the case of spin glasses with intervening ferromagnetic states.
Critical indices in the magnetic ordering of iron–chromium–boron metallic glasses
Authors: Olivier M. , Strom-Olsen J. O. , Altounian Z. , Williams Gwyn
Published: February 2003

We have measured the ac magnetic susceptibility and the dc magnetization as a function of field and temperature in a series of Fe8 0-xCrxB2 0 metallic glasses. Samples with x≤28 show ferromagnetic ordering which follows scaling law predictions, yielding well defined values of the critical indices δ and γ are quite similar for all samples, lying between 1.43 and 1.60, but values of δ increase from about 4 in the strongly ferromagnetic alloys to about 7 in the weakly ferromagnetic ones. Samples with 29≤x≤32 show a spin-glass-like phase, whose remanent magnetization exhibits characteristic time dependence.
Magnetostriction measurements on the mixed valence compound CeSn3
Authors: Edelstein A. S. , Koon N. C.
Published: February 2003

Magnetostriction measurements have been performed on a polycrystalline sample of the mixed valence compound CeSn3 between 4 and 14 K in magnetic fields up to 60 kOe. The volume magnetostriction is positive, larger than the ordinary magnetostriction, and is only weakly temperature dependent.
Low temperature electrical resistance of single crystal NdB6 and PrB6 and critical scattering near their Néel temperatures
Authors: Ali N. , Woods S. B.
Published: February 2003

We have measured the electrical resistance of NdB6 and PrB6 single crystals in the temperature range 2–20 K. NdB6 and PrB6 order antiferromagnetically at TN=7.74 and 6.99 K, respectively. For the lowest temperatures the resistance varies as T2 which we believe is due to electron–electron scattering, while for temperatures near but still below TN the resistivity varies as T4 which is characteristic of electron–spin wave scattering. The temperature derivative of the resistance shows a very sharp maximum at TN. Analysis of resistance data using r=r0+Bt+A±‖t‖1−α, where t=(T−TN)/TN yields α=−0.017 and −0.019 for NdB6 and PrB6, respectively, which agrees well with the recent renormalization group theory calculation for d=3 and n=2.
Magnetic properties of some new Co–Nb–B metallic glasses
Authors: O’Handley R. C. , Corb B. W. , Hara Y. , Grant N. J. , Hines W.
Published: February 2003

Several new amorphous metallic alloys based on cobalt or iron and stabilized with up to 10 at.% boron and up to 14 at.% niobium have been melt spun to ribbon form. Notable are Co80Nb14B6, Co84Nb10B6, and Fe81Nb5B14. The cobalt moment and Curie temperature reductions due to niobium are stronger than those due to boron. These new glasses show attractive soft ferromagnetic properties—similar to those of the familiar transition metal/metalloid glasses—while offering improved thermal stability despite the reduced metalloid content.
Low temperature magnetic, thermal, and electrical properties of amorphous (Co100−xMnx)76B24 alloys
Authors: Onn David G. , Obi Y. , Wang L. Q.
Published: February 2003

The low-field ac magnetic susceptibility (1.5–300 K), low temperature specific heat Cp (0.8–40 K), and electrical resistivity (ρ/ρ300) of the amorphous alloys (Co100−xMnx)76B24 with (0<x<50) have been determined using samples with a common origin. As the magnetic state changes from ferromagnetic to spin-glass the linear contribution to Cp increases by more than a factor of 3. Near the magnetic tricritical point concentration (x≂35) a new sharp discontinuity in the Debye temperature θD(0) is reported. Parallel changes in (ρ/ρ300) occur, and the Debye temperatures obtained from the latter are in excellent agreement with those obtained from CP for the ferromagnetic alloys.
Magnetization studies of Cr concentration effects in amorphous Fe–Ni–Cr–B–Si ribbons
Authors: Krishnan R. , Dancygier M. , Tarhouni M.
Published: February 2003

We report here our results on magnetization (σ) studies of amorphous Fe40−x/2Ni40−x/2CrxMo2B8Si10 ribbons with 0<x<5 (vacuum-schmelze) in the range 4.2 to 300 K and in applied fields up to 150 kOe. Both magnetization and TC are decreased with the addition of Cr the former amounting to 0.05 μB/at.Cr at 4.2 K. For x=0, taking μFe=2.2 μB, we find μNi=0.25 μB. The decrease in moment at 4.2 K with x is discussed assuming a constant Fe and Ni moment. Though a value of −4 μB for Cr gives the best fit this value is considered unreasonable. Friedel’s model describes fairly well the decrease in μ due to Cr addition. However, the situation ought to be more complex. The temperature dependence of σ follows Bloch’s law for the range T/TC=0.4 to 0.6 D/TC is found to be constant which indicates that Cr does not modify the range of exchange interaction. High field susceptibility is also described.
Magnetic properties of a glassy Ni81.5B18.5 alloy
Authors: Bakonyi I. , Panissod P. , Hasegawa R.
Published: February 2003

The amorphous Ni81.5B18.5 alloy prepared by rapid quenching has been studied by magnetization measurements up to 50 kOe and by 11B nuclear magnetic resonance. The magnetization of this alloy is dominated by ferromagnetic component saturating above 20 kOe at about 2 emu/g at 4.2 K and contains also a linear term with a temperature-independent susceptibility of about 3×10−6 emu/g. From the combined magnetic and 11B NMR studies it could be concluded that the observed ferromagnetism may be attributed to the presence of small magnetic particles (amounting to about 2 to 3% of the sample volume) which are embedded in a paramagnetic Ni–B amorphous matrix. These data indicate that for a homogeneous Ni–B system the critical concentration for the appearance of ferromagnetism should be below 19 at.% B.
Research on structural relaxation of Fe78Si10B12 amorphous alloy
Authors: Yu J. , Wu Y. , Wang R.
Published: February 2003

Several physical properties of quenched Fe78Si10B12 amorphous alloy, such as electrical resistivity, Curie temperature, maximum permeability, and coercive force, have been measured before and after annealing at different temperatures for one hour. The results show that with different annealing temperatures the properties of these specimens change in different ways. The annealing temperatures below ∼380 °C may make the alloy more stable and better qualities, while the annealing temperatures above ∼380 °C make the alloy more unstable and degrade the qualities compared with the as-quenched state. The possible mechanism of the different changes have been discussed and two kinds of structural relaxation have been suggested.
Magnetic and crystallization studies of splat-cooled praseodymium–gallium–iron alloys
Authors: Hadjipanayis G. C. , Wollins S. H. , Hazelton R. C. , Lawless K. R. , Prestipino R. , Sellmyer D. J.
Published: February 2003

Magnetic hysteresis and crytallization studies are reported for several (Pr80Ga20)100−xFex metallic glasses, where 30≤x≤80. Thermomagnetic data show the presence of two magnetic phases which are probably responsible for the relatively high coercive fields observed at cryogenic temperatures. As the iron content of the sample is increased, the magnetic moment increases substantially but the coercivity is drastically reduced. In (Pr80Ga20)70Fe30 the observed coercive fields are strongly temperature dependent indicating strong thermal activation effects which are consistent with the magnetic viscosity measurements. The hard magnetic properties disappear after crystallization and the samples appear to be paramagnetic at room temperature.
In-situ crystallization studies of co-evaporated amorphous Fe–Zr thin films
Authors: Valenzuela R. , Huanosta A. , Medina C. , Krishnan R. , Tarhouni M.
Published: February 2003

Amorphous Fe100−xZrx(x=7, 8) thin films were deposited by coevaporation in ultrahigh vacuum on NaCl crystal substrates held at room temperature. In-situ crystallization studies were carried out by transmission electron microscopy. First evidence of crystallization as obtained in the electron diffraction pattern at 763 K for x=7 and 840 K for x=8. The first obtained crystalline phase was αFe and for high temperatures, αFe coexisted with a fcc, a ≂11 Å phase for x=7, whereas for x=8, besides these two phases, a third one was obtained (also fcc, a≂6.5 Å). These two phases can be identified as Fe3Zr and Fe2Zr, respectively. These results are discussed on the basis of the Fe–Zr phase diagram.
Studies of amorphous soft magnetic materials with extra low core loss at high frequency
Authors: Chang Wu-Shin , Han Yung-chu
Published: February 2003

In this work we report that amorphous alloy (Fe6Co88Ni3V3)75Si10B15 is suitable for transformer at high frequency, transformers. It has been found that optimum performance at high frequency can be achieved by high temperature annealing. The core loss at 20 kHz and 5 kG is about 18–20 W/kg. Optimum core loss is equal to 15 W/kg, which is the lowest value ever reported. This kind of amorphous alloy has good thermal and mechanical stability.
Kinetics of reorientation of induced anisotropy in amorphous and crystalline alloys
Authors: Ho Kai-Yuan
Published: February 2003

Isothermal magnetic annealing with the field applied alternately along two different axes has been used to study the kinetics of the reorientation of the induced magnetic anisotropy in a zero-magnetostriction amorphous alloy and in a 50Ni–50Fe crystalline alloy.
Some microstructurally dependent magnetic properties of amorphous FeBSi alloys
Authors: Parker S. F. H. , Grundy P. J. , Jones G. A. , Tebble R. S.
Published: February 2003

Amorphous ribbons of two Fe82(B, Si)18 alloys have been furnace-annealed at temperatures ∼400 °C for times up to 25 h. The coercivity increases sharply at first, passes through a maximum, and then reaches a plateau after about 4 h anneal time. The saturation magnetization of the ribbons also increases slightly. These changes have been correlated with the microstructure observed with high voltage transmission electron microscopy. It is clear that the major factor is the formation of iron dendrites whose size and number density increase with time up to a saturation value. The volume fraction of crystallized material is directly related to coercivity. The interactions of dendrites with moving domain walls have also been studied: direct evidence of pinning effects when the dendrite size is of the order of the wall width is presented.
Properties of amorphous Co–Ta and Co–W films deposited by rf sputtering
Authors: Naoe M. , Kazama H. , Hoshi Y. , Yamanaka S.
Published: February 2003

Magnetic and thermal properties of Co100−xTax(11≤x≤25) and Co100−xWx(13≤x≤25) amorphous films deposited by rf diode sputtering have been investigated. In both systems, structural changes of these films from crystalline to amorphous lead to a drastic decrease of their coercive force Hc and the absolute value of saturation magnetostriction λs, where λs is negative. Since magnetic properties and structure of the amorphous Co–Ta and Co–W films depend significantly on the argon gas pressure PAr, the PAr must be adjusted to the proper value during sputtering to obtain films with soft magnetic properties. Typical magnetic properties of Co–Ta and Co–W amorphous films are as follows: (i) Co–Ta: 4πMs≤11 kG, −λs≤2×10−6, Hc≤0.4 Oe. (ii) Co–W: 4πMs≤11 kG, −λs≤8×10−6, Hc≤4.0 Oe. The crystallization temperature Tx of the amorphous Co–Ta films is above 700 K and Tx increases with the increase of Ta content in the films. Tx of amorphous Co–W films is above 940 K. In this alloy system, however, structure relaxation occurs at much lower temperature than the Tx, which causes an increase of Hc. This causes the soft magnetic properties of the amorphous Co–Ta films to be more thermally stable than those of the amorphous Co–W films.
Magnetic permeability after-effect in Fe–Cr–B and Fe–Cu–B amorphous systems
Authors: Allia P. , Turtelli R. Sato , Soardo G. P. , Vinai F. , Lovas A.
Published: February 2003

Room temperature measurements of magnetic permeability after-effect, specific magnetization, and linear magnetostriction are performed on amorphous ribbons of compositions Fe80−yCryB20, Fe80−yCuyB20, Fe85−yCryB15(0≤y≤5) to study the role of compositional and structural contributions to magnetic time effects of amorphous ferromagnets. The aftereffect is found to decrease with decreasing Fe content. Its behavior, however, is clearly independent of the type of transition metal added to the Fe–B matrix, although Cr and Cu interact quite differently with boron atoms. These results show that the magnetic aftereffect of amorphous alloys is not related to the ordering of metalloid atoms. The experimental data are instead discussed in terms of a new theory, relating the aftereffect to the magnetostrictive interaction between the atomic-level shear stress fluctuations frozen in rapidly quenched alloys, and the magnetization direction. The agreement between the present results and the theory gives further support to the hypothesis of a structural nature of the aftereffect measured in amorphous ferromagnets.
Elimination of disaccommodation in zero-magnetostrictive FeCoSiB amorphous alloys
Authors: Jagielinski T.
Published: February 2003

The disaccommodation of magnetic permeability in amorphous zero-magnetostrictive alloys occurs due to gradual pinning of domain walls by the induced anisotropy. To eliminate the disaccommodation one should induce the perpendicular anisotropy in order to fix the position of walls and to control magnetization by rotation process. However, if the magnitude of the perpendicular anisotropy is too large, the value of μ becomes reduced. Therefore a very careful heat treatment is necessary. The optimum values found, so far, for Fe4.7Co70.3Si15B10 are μ=1.3×104 and D3=0.6%.
Nonlinear domain wall dynamics in yttrium and thulium orthoferrites
Authors: Chetkin M. V. , Akhutkina A. I. , Kuzmenko A. P. , Gadetsky S. N.
Published: February 2003

The domain wall velocities in yttrium and thulium orthoferrites plate cut perpendicular both to the optical and c axis were investigated using high speed photography. The observed V(H) dependencies are considerably nonlinear. The critical domain wall velocities for Bloch, Néel and intermediate type are the same and equal to 2×106 cm/s in accordance with theory. Apart from transversal sound and critical velocities the V(H) dependence possesses other pecularities. The form of moving domain wall strongly depends on its velocity and mobility. Up to transversal sound velocity and under low mobility condition its form remains straight. After this, velocity domain wall motion becomes two-dimensional and unsteady.
Dragging of domains by an electric current in Metglas 2826 MBa)
Authors: Hsu Y. , Berger L.
Published: February 2003

A steady, unidirectional motion of stripe domains, caused by hydromagnetic forces, has been observed in ribbons of Metglas 2826 MB traversed by an electric current at 300 K. A half-wave rectified 60 Hz current density of peak value jp≂20 A/mm2 is sufficient to induce this ‘‘domain drag’’ motion. A dc current density with smaller superposed 60 Hz sinewave ac current, does it too. Because of the very low coercivity (Hc=7 mOe), these jp values are ∼103 times smaller than those needed for domain drag in Gd–Co films, but comparable to those in Co crystals at 4 K. A reversal of current reverses the sense of wall motion. As predicted by theory, wall motion is in the same direction as the motion of effective charge carriers, shown by the sign of the Hall effect to be holes.
Point contact spectroscopy of intermediate valence compounds
Authors: Frankowski I. , Wachter P.
Published: February 2003

We measured the dynamic resistance dU/dI (U) of point contacts with intermediate valent (IV) ‘‘gold’’ SmS and IV ferromagnetic TmSe0.82Te0.18 at liquid helium temperatures. Similar as for IV SmB6 and TmSe, on which we reported earlier, dU/dI (U) for ‘‘gold’’ SmS exhibits a strong resistance peak at zero bias with a width of 6.5 mV, which we take as further evidence for a f–d hybridization gap in the electron density of states in these compounds. The results on TmSe0.82Te0.18 support our measurements on TmSe, where we found that a gap exists in the antiferromagnetic but not in the ferromagnetic phase. In addition we report on point contact measurements on CePd3.
Temperature dependence of the field induced magnetic form factor of the intermediate valence compound CePd3
Authors: Stassis C. , Loong C.-K. , Zarestky J. , McMasters O. D. , Moon R. M. , Thompson J. R.
Published: February 2003

Polarized neutron scattering techniques have been used to obtain information regarding the ground state electronic properties of the intermediate valence compound CePd3. The spatial distribution of the magnetization induced by a magnetic field of 42.5 kG in a single crystal of CePd3 has been studied at 100 and 4.2 K. We find that at 100 K the measured form factor is in good agreement with the free-ion 4f magnetic form factor of Ce3+. At 4.2 K on the other hand, deviations from a 4f magnetic factor were observed. An adequate fit to the experimental data taken at 4.2 K can be obtained by assuming that the induced magnetization contains a significant component (∼17% of the total) of Ce–5d electronic character.
First- and second-order phase transitions in Potts models: Competing mechanisms (invited)
Authors: Berker A. Nihat , Andelman David
Published: February 2003

Many condensed matter systems, ranging from adsorbed surfaces to bulk magnets, are microscopically modelled by interacting q-state Potts spins, arrayed in d dimensions. A changeover from second-order phase transitions at q≤qc(d) to first-order transitions at q≳qc can be understood as a condensation of effect vacancies, which are patches of local disorder favored by entropy. Accordingly, the renormalization-group treatment of Potts models is within context of Potts-lattice-gas models, where critical and tricritical fixed points occur at low q, but merge and annihilate at qc. This picture has led to exact tricritical exponents in two dimensions. It is also consistent with recent experimental results on intercalated systems in three dimensions. Effective vacancies in pure Potts models have also been studied by Monte Carlo simulation. Their effective chemical potential can be controlled by a four-point interaction, which proved useful in Monte Carlo renormalization-group studies.
Microwave transmission measurement of the critical exponent beta in iron and iron-silicon
Authors: Abeles J. H. , Carver T. R. , Alexandrakis G. C.
Published: February 2003

Using the ferromagnetic antiresonance transmission (FMAR transmission) technique with ‘‘zero’’ applied field, a new measurement of the critical exponent beta in iron has been made. The results described were made attainable by the development of a new high-temperature microwave (9.4 GHz) transmission spectrometer, designed to operate to and above the Curie temperature at 770 °C. The result is β=0.372±0.014 for a reduced temperature range of 0.0002<ε<0.004, in agreement with renormalization group calculations giving β−0.365. This close approach to the critical regime is a consequence of the large low-temperature saturation magnetization of iron, relative to the frequency of the spectrometer divided by the magnetomechanical ratio. The critical exponent β was also measured for an iron-silicon alloy (6% Si), yielding β=0.383±0.016. The agreement of these two values supports universality.
Critical behavior in Ni3Fe1 and Ni3Mn1
Authors: Orehotsky J. , Sousa J. B. , Pinheiro M. F.
Published: February 2003

Critical behavior of the temperature derivative (dρ/dT) of the electrical resistivity was investigated in two order-disorder magnetic alloys: Ni3Fe1 and Ni3Mn1. In the Ni3Fe1 alloy system, the temperature derivative displays a very sharp λ peak at the Curie temperature and a poorly resolved peak at the order-disorder temperature. Both peaks are characterized by positive values of dρ/dT. The results in the Ni3Mn1 alloy system showed a small peak at the Curie temperature and a large inverted peak characterized by negative values of dρ/dT at the order-disorder temperature. The inverted peak displayed an unexpected fine structure that appeared to be related to the degree of long range order in the specimen. The contrasting behaviors of dρ/dT for these two alloys are examined in terms of current ideas on critical phenomena based upon free electron models.
Comparison of dynamical critical behavior in isotropic ferromagnetsa)
Authors: Hohenemser C. , Chow L. , Chowdhury A. R. , Collins G. S.
Published: February 2003

Neutron scattering linewidth measurements in Ni, Fe, and Co at T=TC have consistently yielded a dynamical critical exponent z=5/2. In contrast, perturbed angular correlations above TC and nuclear magnetic resonance studies below TC exhibit crossover from z=5/2 to z=2 near a reduced temperature of t=10−2. We show that the latter behavior, while not inconsistent with the neutron results, cannot be attributed to dipolar perturbations as in the case of EuO. We show further that the behavior of critical fluctuations, as measured by the spin autocorrelation time τc, is within experimental error symmetrical about TC.
Pressure dependence of the phase diagram of metamagnetic Ni(NO3)2 ⋅ 2H2O
Authors: Salem-Sugui S. , Ortiz W. A. , Paduan-Filho A. , Missell F. P.
Published: February 2003

From differential magnetic susceptibility measurements we have determined the magnetic phase diagram of the metamagnetic system Ni(NO3)2 ⋅ 2H2O, for several hydrostatic pressures (P) up to 10 kbar. The zero temperature transition field Hc(0,P) and the Néel temperature TN(P) were determined for all pressures, both increasing almost linearly with P. Using Mean Field Theory one can obtain expressions for TN(0) and Hc(0,0) as a function of the exchange parameters, which leads to the dependence of these parameters as a function of P. At atmospheric pressure we observed an anomaly in the phase diagram, occuring near the previously determined tricritical point. The anomaly is present for all pressure, and is probably associated to the tricritical point.
Magnetic ordering in Nd(OH)3
Authors: Ellingsen O. S. , Bratsberg H. , Mroczkowski S. , Skjeltorp A. T.
Published: February 2003

The ac susceptibility of Nd(OH)3 has been measured for a wide range of temperatures (0.05–35 K) and fields (0–5 kOe). The results show for the first time an antiferromagnetic ordering near TN=265 mK. This temperature is much lower than what is expected from the measured Curie-Weiss theta of −3.4 K (sphere). The data indicate a considerable amount of short range order above TN in the form of a broad peak. This is due to competing nondipolar interactions between successive neighbours and the high symmetry of the hexagonal structure. These results will be discussed in relation to earlier results found in the isostructural NdCl3.
Magnetic properties of quasi two-dimensional ferric stearate
Authors: Pomerantz M. , Aviram A. , Taranko A. R. , Heiman N. D.
Published: February 2003

Results are given of measurements of magnetic susceptibility, electron spin resonance, and Mössbauer effect of ferric stearate. The stearates have long chain hydrocarbons separating by about 50 Å the planes of metal ions. Thus they are excellent examples of quasi two-dimensional magnetic structures. An interesting sample seems to contain some hydroxy-ferric stearate. In this sample we observed that at high temperatures (295 K≥T≥60 K) the magnetization scaled as H/T, as for superparamagnets. Below 60 K there were deviations from this scaling, shifts in electron spin resonance fields, and splittings of the Mössbauer spectrum, indicating a transition to a state of time-independent magnetic order.
Systematics of d-dimensional hypercubic spin-1/2 Ising ferromagnets: Critical temperature and critical energy
Authors: Nath K. , Frank B.
Published: February 2003

The critical temperatures Kc and the nearest-neighbour correlation functions Uc have been calculated for the d-dimensional hypercubic Ising ferromagnet for d=4 to d=30, by generalizing a recent theory reported for d=3. The results are of relevance for Monte Carlo Renormalization Group work involving critical properties in random fields, which calls for a knowledge of Kc in the limit of zero field. As d becomes large, Kc and Uc are found to approach the spherical model values. Polynomial expressions in 1/d are fitted to the calculated values, using the analogous spherical model expressions as guide. Comparison is made with the corresponding expressions of Fisher and Gaunt. Uc/(1−Kc), independent of d for the spherical model, is investigated; it is seen to be approximately independent of lattice structure for d=2 and for d=3.
Amorphously packed, frustrated hierarchical models: Chaotic rescaling and spin-glass behavior
Authors: McKay Susan R. , Berker A. Nihat , Kirkpatrick Scott
Published: February 2003

Hierarchical Ising models have been constructed with competing ferromagnetic and antiferromagnetic interactions, and solved exactly. As frustration is increased, a low-temperature phase is encountered, characterized by chaotic renormalization-group trajectories. This spin-glass phase is microscopically described in terms of subsets of spins which are strongly correlated, yet noncontiguous. Further, the amorphous packing of real systems is approximated in these models by a random distribution of shapes at various hierarchical levels, which eliminates unphysical limit cycle behavior in favor of chaos.
Recent advances in simulation of magnetic systems (invited)
Authors: Stauffer D.
Published: February 2003

Large but simple systems have been simulated by Monte Carlo methods. For spin 1/2 Ising lattices, up to 216 million spins were used in three dimensions; for percolation, up to 1225 million sites in the triangular lattice. Possible applications include the evaluation of the nucleation rate in the Ising model as function of supersaturation, and of corrections to scaling for percolation cluster numbers.
Numerical simulation of spin-glass transition phenomena (invited)
Authors: Walstedt R. E. , Walker L. R.
Published: February 2003

Results are presented from a continuing investigation of spin-glass transition effects by numerical simulation. The model is one of classical unit vectors randomly distributed on an fcc lattice, with RKKY exchange coupling and nearest-neighbor dipolar coupling in an approximate representation of dilute Mn in Cu. Results for system energy and for dipolar energy as a function of temperature show no resolvable features at the freezing temperature TG* in accord with the high-precision specific heat data of Fogle, Boyer, Phillips, and Van Curen. Additional details of shattered susceptibility behavior in the vicinity of the ground-state transition are presented. Further data on freezing temperatures as a function of dipolar coupling strength D show a trend toward macroscopic behavior (i.e., TG* independent of D) with a sample of 4928 spins. Finally, a moderately sharp onset of freezing transverse to an applied magnetic field is found, as predicted by the mean-field calculations of Toulouse and Gabay. As expected, this transition is unrelated to transverse susceptibilities.
Computer simulation studies of three-dimensional tricritical behavior
Authors: Herrmann H. J. , Rasmussen E. B. , Landau D. P.
Published: February 2003

Monte Carlo and Monte Carlo renormalization group methods are used to study tricritical behavior in a variety of layered Ising metamagnets and the next-nearest-neighbor Ising antiferromagnet in three dimensions. For ferromagnetic intrasublattice coupling which is strong compared with the antiferromagnetic intersublattice coupling we find tricritical exponents which are in agreement with the predicted classical behavior. For smaller intrasublattice interactions the observed exponent behavior is consistent with the breakup of the tricritical point into a double critical endpoint and a critical endpoint as predicted by mean field theory; however, we cannot detect any change in the phase diagram itself.