bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of hydrogen on the magnetic properties of iron-rich metallic glasses (invited)
Authors: Coey J. M. D. , Ryan D. H. , Boliang Yu
Published: February 2003

Melt spun and sputtered amorphous alloys from the a FexM100−x series with M=Y or Zr can be electrolytically hydrogenated up to a maximum of about 3 hydrogens per M, while retaining their mechanical integrity. Hydrogen uptake has been monitored in situ during hydrogenation by following the increase in length of the melt-spun ribbons. Values of up to 7% have been found, and the corresponding increase in volume per absorbed hydrogen is approximately 0.5 Å3. Hydrogen diffusion constants have been estimated from the mechanical relaxation, and activation energies of order 0.4 eV have been deduced. The binding energy is about 1 eV per hydrogen. Desorption at elevated temperatures preceeds crystallization of the alloys studied, and the hydrogen-loaded materials retain much of their charge at room temperature for periods of order one year. Iron-rich yttrium alloys have a moment close to 2 μB/Fe, but they are asperomagnets, the iron moments freezing in a random noncollinear arrangement which possesses a net moment, below their spin freezing temperature of about 100 K. On hydrogenation they become excellent soft ferromagnets with a Curie point at 400–500 K, although there is little change in the magnitude of the iron moment. The effect is attributed to a shift in the exchange distribution towards more positive values on dilation of the interatomic spacings. Iron-rich zirconium alloys are quite different. They are essentially weak itinerant ferromagnets with a greatly reduced iron moment, and pure amorphous iron, judging from a FexM100−x as x→100, would be nonmagnetic. On hydrogenation however they tend towards the same ferromagnetic state as the hydrogenated yttrium alloys.
Reversible structural transformation in cobalt-base amorphous alloys
Authors: O’Handley R. C. , Corb B. W. , Grant N. J.
Published: February 2003

A reversible, displacive transformation in the short-range order of cobalt-rich amorphous alloys has been inferred from magnetic measurements. The issues of reversibility and possible phase separation are discussed with new analysis. Comparison is made with magnetic effects accompanying the hcp-fcc transformation in crystalline cobalt and cobalt-rich alloys. An electronic model for the transformation is proposed.
Magneto-optics and electronic structure of uranium monochalcogenides
Authors: Reim W. , Schoenes J. , Vogt O.
Published: February 2003

Magneto-optic Kerr-rotation and ellipticity measurements of US, USe, and UTe at magnetic saturation reveal very large signals compared to other metals. This enhancement is attributed to the increased f-d overlap and the large spin-orbit energy of 5f and 6d states. For energies up to 5 eV, the diagonal and off-diagonal conductivity spectra are interpreted in terms of two interband (d→f and f→d) transitions and a free electron part. The f states behave similarly for all three uranium chalcogenides and are found to be delocalized. The conduction electron spin polarization is shown to be negative and it decreases from −40% to −35% to −20% going from US to USe to UTe.
Spin dynamics of the cerium and uranium monopnictides studied by neutron scattering (invited)
Authors: Hälg B. , Furrer A.
Published: February 2003

The spin dynamics of the cerium and uranium monopnictides studied by diffuse and inelastic neutron scattering is reviewed. The diffuse scattering above the antiferromagnetic ordering temperature largely corresponds to longitudinal spin fluctuations which are highly anisotropic. For CeAs, CeSb, and UAs multicritical behavior has been found, i.e., the symmetry of the critical scattering above TN differs from the actual type of magnetic ordering below TN. In the ordered state the magnetic excitation spectrum of UN and UAs exhibits only a broad response, whereas well defined spin-wave branches have been observed for USb and the cerium monopnictides. A very detailed study of the magnetic excitations has been performed for CeAs, where the spin-wave dispersion is split into two modes of transverse polarization due to the exchange anisotropy. One of these modes exhibits nearly zero energy gap and quadratic dispersion which has not previously been observed in antiferromangets. A generalized random-phase-approximation calculation taking into account anisotropic exchange interactions consistently describes the transverse magnetic excitations for TTN. In USb, CeSb, and CeBi the magnetic excitations display similar feature as the spin-waves in CeAs and can be understood in close analogy to the treatment applied to CeAs.
Paramagnetic spin waves in the one-dimensional antiferromagnet CsMnBr3
Authors: Collins M. F. , Gaulin B. D.
Published: February 2003

CsMnBr3 is a quasi-one-dimensional hexagonal antiferromagnet. We report on inelastic neutron scattering measurements that show well-defined spin-wave modes at a temperature of 15 K, which is almost twice the Néel temperature for three-dimensional ordering. The spin waves at large wave vectors have similar energies to those found in the three-dimensional ordered state at 4 K. At small wave vectors a mode is observed with energy 1.8 meV at zero wave vector, which is not seen in the three-dimensional state. The presence of dipolar interactions explains this effect qualitatively but not quantitatively. Measurements are also presented showing the effects of raising the temperature on the spin waves. At small wave vectors there is an apparent renormalization upwards of the spin wave peaks with increasing temperature, as has been predicted theoretically.
Magnetic correlation in itinerant magnetic materials above T
C (invited)
Authors: Brown P. J. , Ziebeck K. R. A. , Déportes J. , Givord D.
Published: February 2003

Although the properties of magnetic insulators are relatively well understood, the same cannot be said of materials in which the unpaired electrons participate in the Fermi surface. A number of conflicting theories exist which all give a more or less satisfactory account of the ground state properties of magnetic metals but give widely different descriptions of magnetic fluctuations above the ordering temperature (TC). The paramagnetic state of a material can be characterized by the spin-density spin-density correlation function (SDSDCF) which is accessible to measurement through the magnetic scattering cross section. We have made measurements of the paramagnetic scattering from the transition metals Cr, Mn, Fe, Ni, and a number of intermetallic compounds over a wide range of temperature. Polarization analysis was used to separate the magnetic part of the scattering cleanly. In all cases where atoms with open d shells are in contact we have found significant structure in the SDSDCF over a range of several interatomic distances. This has loosely been called ‘‘short range order above TC.’’ The resolution of the spectrometer for the majority of the measurements was some 12 THz FWHM, so that although the true equal time SDSDCF is not obtained, essentially all contributions with a lifetime greater than 5×10−10 s are included and in particular most of the thermal fluctuations up to kTC. The paramagnetic scattering results are coherent with inelastic neutron scattering data both above and below the transition temperature. It has been found difficult to give a consistent account of all these results using theories based on extensions of the Heisenberg model. The fluctuating band models, in which correlations in the paramagnetic phase appear naturally, seem more appropriate.
Investigation of the paramagnetic phase of bcc iron using polarized neutron scattering
Authors: Wicksted J. P. , Shirane G. , Steinsvoll O.
Published: February 2003

Recent neutron scattering experiments performed at Brookhaven on Ni and Fe (4% Si) above TC have demonstrated that a simple paramagnetic scattering function S(Q,ω)∝[1/(κ21 +q2)]×[Γ/(Γ2+ω2)] can explain the persistent spin wave ridges previously reported by Lynn and Mook. We present our new polarized beam results on pure Fe and describe in some detail the special problems associated with the unpolarized beam studies of magnetic cross sections at high temperatures.
Neutron scattering study of the magnetic excitations in ferromagnetic iron at high energy transfers
Authors: Loong C.-K. , Carpenter J. M. , Lynn J. W. , Robinson R. A. , Mook H. A.
Published: February 2003

We have measured the spin-wave spectrum of iron by neutron inelastic scattering using the Low-Resolution Medium-Energy Chopper Spectrometer at the Intense Pulsed Neutron Source (IPNS) of the Argonne National Laboratory. Interest focuses on the magnetic excitations at high energy transfers where the spin-wave dispersion relation has not previously been determined. In measurements performed at 10 K using a 23-g single crystal of pure iron, we observed magnetic scattering around the (110) reciprocal lattice point with spin-wave energies from 40 to 160 meV. The spin waves over the entire range of energy are found to be consistent with an isotropic spin-wave dispersion relation. With the present experimental sensitivity we were unable to observe any band structure effects such as Stoner excitations or optical magnons in this range of wave vector and energy.
Neutron scattering study of MnSi proving no ‘‘exchange hole’’
Authors: Uemura Y. J. , Majkrzak C. F. , Shirane G. , Ishikawa Y.
Published: February 2003

Neutron scattering experiments have been performed on MnSi below TC with the double-axis powder scattering technique using unpolarized neutrons, and also with the polarization analysis technique. The magnetic scattering intensity has not shown any anomaly around q=0.5 Å−1, in contrast to the previous results of Ziebeck et al. who found a large intensity peak at this momentum transfer. Thus, the hypothesis of Ziebeck et al. of observing an ‘‘exchange hole’’ is excluded.
Phase diagram and critical points of Ce alloys (invited)
Authors: Fisk Z. , Thompson J. D. , Lawrence J. M. , Smith J. L. , Batlogg B.
Published: February 2003

The pressure-temperature phase diagram of Ce0.9−xLaxTh0.10 alloys is presented for 0.1≤x≤0.17. Two critical points are found in this range of compositions. The data are shown to be consistent with an analysis based on the known Fermi-liquid behavior of Ce in compounds and alloys. The possible appearance of β phase at intermediate pressures is noted.
Bistability and collective effects in the ground state of cerium and cerium based compounds (invited; abstract)
Authors: Schluter M. , Varma C. M.
Published: February 2003

The properties of rare earth solids are determined by strongly localized 4f electrons in the valence shell. In the limits of strong or weak binding of the 4f electrons this leads to Kondo—or mixed valence—behavior, respectively. The two limiting cases both exhibit ‘‘normal’’ spectral properties, i.e., one main UPS (XPS) photoemission peak and one BIS electron-addition peak separated from each other by U≊5–6 eV. Furthermore, for ‘‘normal’’ mixed valence materials the UPS—peak occurs at the Fermi level EF. In contrast to this, Ce and many of its compounds exhibit anomalous features.1 In addition to the UPS/BIS peaks around −2 and +4 eV there exists also structure near EF (in both UPS and BIS) with varying strength for different compounds. We have recently proposed a model which is designed to account for these findings.2 The model describes the groundstate of Ce as a boundstate of a localized 4f electron and a somewhat more delocalized f exciton. The new state is stabilized as a result of dynamic interactions induced by strong core charge polarizations which lead to a breakdown of the usual description of the groundstate in terms of one-electron states. As a result of the excitonic instability spectral strength appears in UPS experiments both at the Fermi level as well as 2 eV below it. Similar modifications occur in the BIS spectra. The modified groundstate should replace the usual simple localized moment picture in the Anderson Hamiltonian for the study of magnetic or mixed valence properties.
Hall effect and magnetization of amorphous FeZr alloys
Authors: Cochrane R. W. , Destry J. , Legault R. , Trudeau M.
Published: February 2003

We present measurements of the Hall coefficients of a series of amorphous Fe1−xZrx alloys (0.57≤x≤0.80, x=0.11) and correlate these with magnetization data on several samples. For x≤0.65 the alloys are ferromagnetic with large positive spontaneous Hall components. For x>0.71 the paramagnetic alloys exhibit small positive Hall coefficients. We suggest that this latter positive result arises from the spontaneous side jump contribution in the paramagnetic regime.
Magnetoresistance studies of melt-spun amorphous Fe1−xZrx ferromagnets
Authors: Dahlberg D. , Rao K. V. , Fukamichi K.
Published: February 2003

A remarkable feature in amorphous Fe1−xZrx alloys is that for Fe concentrations greater than 90 at %, the ferromagnetic transition temperature TC decreases with increasing Fe concentration. In addition, alloys containing 93–90 at % Fe are found to show a spin-glass-like behavior at low temperatures, i.e., below TC. The electrical resistivity of these alloys shows a minimum at roughly the Curie temperature. We have measured the transverse magnetoresistance of Fe91Zr9, and Fe90Zr10 alloys from 4 to 300 K in applied magnetic fields as large as 9 T. We find that (1) the field derivative of the magnetoresistance is positive at all temperatures in applied fields larger than 0.1 T; (2) a maximum occurs in the magnetoresistance at roughly the Curie temperature; (3) below the Curie temperature a small negative low-field magnetoresistance develops which increases with decreasing temperature. These results indicate that the resistance minimum which occurs around the Curie temperature for these alloys is due to the coherent exchange scattering by the Fe moments, and is not associated with a Kondo mechanism as previously proposed.
Magnetic and transport properties of Yb1−xTmxS
Authors: Suryanarayanan R. , Bach H. , Westerholt K. , Gorochov O.
Published: February 2003

With a view to studying the behavior of diluted Tm in a nonmagnetic matrix, we have prepared single crystals of Yb1−xTmxS (0≤x≤0.25). The lattice constant a0 decreases abruptly as x approaches 0.14, which is interpreted as a valence transition of Tm towards 3+. For 50<T<300, χ follows a Curie–Weiss law. The calculated μeff seems to indicate a valence change from 0.7 for x=0.03 to ∼3 as x approaches 0.22, the change following that of a0. The magnetic moment per Tm increases with x (up to x=0.14) for fields up to 150 kOe. For x=0.03, ρ decreases from RT, shows a minimum at 85 K, and increases as −log T. The number of carriers calculated from RH does not correspond to a one-electron contribution per Tm atom for x=0.03, 0.08, and 0.17. The data suggest an intermediate valence of Tm for x<0.14.
Magnetic properties of RNi4Fe alloys (R=La, Ce, or Y)
Authors: Pourarian F. , Pedziwiatr A. , Wallace W. E.
Published: February 2003

Magnetization of several RNi4Fe alloys (R=La, Ce, or Y) has been studied over the temperature region 4 to ∼300 K and in applied fields up to 21 kOe. Replacement of Ni by Fe in the RNi5 systems expands the lattice and produces a significant alteration in magnetic behavior. In contrast with the RNi5 systems which do not order magnetically, the RNi4Fe alloys develop ferromagnetic order at low temperatures with Curie temperatures ranging from 195 to 270 K. Saturation magnetizations (in μB per formula unit at 4 K) were 5.0, 3.3, and 4.0 for R=La, Ce, and Y, respectively. The low moment of CeNi4Fe together with its anomalously small unit cell volume strongly suggests that Ce in this alloy is quadripositive. The magnetic behavior of the RNi4Fe systems indicates that Fe induces moments on the neighboring Ni atoms, ∼0.9 μB/Ni atoms in the case of LaNi4Fe. Below the Curie temperature, magnetization-temperature plots obtained using low field (4 kOe) show broad maximum for the La system whose origin as yet is not completely clear. The maximum disappears at applied fields ∼20 kOe, and hence it may arise from increased magnetic hardness at low temperatures.
Magnetic characteristics of CeNi5−xCux (x=0, 1, 2, 2.5, 3, and 4) alloys and their hydrides
Authors: Pedziwiatr A. T. , Pourarian F. , Wallace W. E.
Published: February 2003

Susceptibilities were measured for the series of CeNi5−xCux (x=0, 1, 2, 2.5, 3, and 4) alloys and their hydrides over the temperature range 4.2–300 K in an applied field up to 20 kOe. All materials studied were found to crystallize in CaCu5-type crystal structure. A pronounced change in lattice parameters was observed for x=2.5. Materials with x=0, 1, and 2 exhibit Pauli paramagnetism, while for x>2 the total susceptibility can be regarded as a sum of Pauli paramagnetism and Curie–Weiss paramagnetism associated with the Ce3+ ions. The effective fraction of Ce3+ in all compounds was calculated. Hydrogenation increased the unit cell volume ∼15% without a change of crystal structure. It also caused an increase in effective moment for x=2.5 and x=3 alloys, but a small decrease was observed for x=4.
Saturation of resistivity in the La1−xCexRh2 mixed valent/Kondo system
Authors: Harrus A. , Mihalisin T. , Batlogg B.
Published: February 2003

We have measured the resistivity of mixed valent La1−xCexRh2 samples. Samples with 0.5<x<1 have essentially the same room temperature resistivities (∼80 μΩ cm even though their residual resistivities vary from 90 to 5 μΩ cm). Samples with x<0.5 do not show this ‘‘saturation’’ effect. Both resistivity and susceptibility measurements indicate that the valence of Ce in La1−xCexRh2 is decreasing with La substitution. The low-temperature resistivity of CeRh2 does not demonstrate the extreme sensitivity of impurities that have been observed in other mixed valent Ce-transition metal compounds like CePd3.
Small-angle neutron scattering of DyMo6S8 at low temperature
Authors: Lander G. H. , Pynn R. , Ishikawa M.
Published: February 2003

The Chevrel phase compound DyMo6S8 becomes superconducting at 2.05 K and is antiferromagnetic (AFM) below TM=0.4 K. Experiments with an applied magnetic field have shown that the AFM state is gradually suppressed and a ferromagnetic component seems to be induced before Hc2 (1200 Oe) is reached. The present experiments have been performed at the small-angle scattering facility D11 at the Institut Laue Langevin with a dilution refrigerator and applied fields of up to 2000 Oe. Neutron wavelengths of 6.25 and 10 Å have been used allowing a minimum wavevector Qmin≂0.005 Å−1 to be achieved. For increasing H we find a sudden increase in the small-angle scattering at H=180 Oe, which we identify as Hc1. With a position sensitive detector we have also investigated the scattering as a function of the relative orientation of Q and H. For a simple paramagnet we would expect more magnetic intensity with Q ⊥ H than with Q ∥ H, however, we find the exact reverse with somewhat more intensity for Q ∥ H. This is not understood, but we propose that the small-angle scattering is predominantly inelastic. Similar anisotropic effects have been found in other Chevrel phase systems.
Bulk superconductive behavior of EuMo6S8 under pressure
Authors: Decroux M. , Maple M. B.
Published: February 2003

The pressure dependence of the structural transition temperature TS of a high-quality melted EuMo6S8 sample was determined from electrical resistivity measurements under nearly hydrostatic pressure. Applied pressure depresses TS rapidly from 109 K at zero pressure to zero just below 13 kbar. The disappearance of the structural transition is accompanied by the sudden appearance of a superconducting transition with a critical temperature Tc=12.2 K at 13.2 kbar. Specific heat measurements demonstrate that the pressure-induced superconductivity of EuMo6S8 is a bulk phenomenon.
Magnetic transitions in Mn2−xMxSb (M=3d metals)
Authors: Kanomata T. , Ido H.
Published: February 2003

Magnetic and crystallographic measurements have been carried out for Mn2−xMxSb (M=Ti, V, Cr, Fe, and Co) in order to study the nature of the transition from ferrimagnetic (Fr) to antiferromagnetic (AF) states. The magnetic phase diagrams have been determined. In the cases of M=Ti and Fe, only the Fr phase is observed. In the case of M=Co, the transition between Fr and AF states is observed in the composition range of x<0.35, but for the specimens with x larger than 0.35 only the AF ordering is found. The phase diagrams obtained are discussed on the basis of the molecular field theory.
Magnetic and crystallographic properties of Cr1−xTixAs (0≤x≤1)
Authors: Suzuki T. , Ido H.
Published: February 2003

Magnetic and crystallographic measurements have been made in the temperature region from 77 to about 900 K for the compounds Cr1−xTixAs(0≤x≤1). The resulting phase diagram is composed mainly of three regions; (1) a low spin region with the crystal structure of the orthorhombic MnP type, where the chromium magnetic moment μCr takes the value of 1.7 μB; (2) a transition region with the MnP type structure, where the value of μCr changes gradually with temperature and composition; and (3) a high spin region with the hexagonal NiAs type structure, where μCr ≊3μB. Temperature dependence of the magnetic susceptibility is expressed by the Curie–Weiss law only in the region where the crystal is of the NiAs type.
Neutron diffuse scattering in β-manganese
Authors: Funahashi S. , Kohara T.
Published: February 2003

Neutron diffraction patterns of polycrystalline β-Mn samples containing 25% and 18% Co and 10% In have been measured. All the samples showed very wide diffuse scattering below about 100 K extending from angles lower than the 110 position to higher than the 200 position, while no diffuse scattering was observed in pure β-Mn in which no magnetic ordering takes place down to 1.1 K. The shape of the diffuse scattering of Mn0.9In0.1 is much broader than that of Mn0.82Co0.18 and Mn0.75Co0.25. The diffuse scattering shape of Mn0.82Co0.18 is apparently similar to that of γ-Mn alloys except for a slight but not negligible increase at high angles. The very wide magnetic diffuse scattering feature suggests the development of long period magnetic modulation which is locally fluctuating both in the period and in the direction of modulation. ON
Tin hyperfine fields in some cobalt-based Heusler alloys
Authors: Ritcey S. P. , Dunlap R. A.
Published: February 2003

The 119Sn Mössbauer effect has been used to measure Sn impurity hyperfine fields on the Z sites of some cobalt-based Heusler alloys of the composition Co2YZ0.98Sn0.02, with Y=Ti, V, and Cr, and Z=Al and Ga. Results are discussed in the context of current theoretical predictions of hyperfine fields at nonmagnetic sites in ferromagnetic alloys.
Site occupation of ternary elements in Sm2(CoTM)17 compounds
Authors: Krishnan K. M. , Rabenberg L. , Mishra R. K. , Thomas G.
Published: February 2003

The crystallographic positions of Fe and Mn atoms in a Sm2 (CoFe Mn)17 permanent magnet have been investigated using electron channeling/blocking techniques. Using the tilting and diffraction capabilities of an analytical transmission electron microscope, an electron beam was made to propagate along specific crystallographic directions in the magnet. By monitoring the characteristic x-ray spectrum as a function of incident electron beam orientation, it was possible to determine that 88.5% of the Mn and 85.1% of the Fe atoms occupy sites in the mixed planes in this compound.
Evidence from experimental nuclear magnetic resonance data concerning possible fundamental inadequacies of the conventional spin-wave theory (abstract)
Authors: Bykovetz N.
Published: February 2003

In the case of simple ferromagnets and antiferromagnets, the nuclear magnetic resonance data which had been used in the past to validate the applicability of conventional spin-wave theory, is shown to exhibit a simple pattern of functional forms, previously unrecognized. Special focus is given to the data of Narath et al. and deWijn et al. In all known cases (with minor qualifications) such data obey the equation ν=A(1−BT c) for the ‘‘low-temperature’’ region 0<ΔM≲10%. The experimentally found one-term power-law temperature dependences can be obtained in all cases from the first-term Heisenberg prediction, modified in a simple way: the exponent C=D/2d for ferromagnets and C=(D−1)/d for antiferromagnets, where d=1−( 1/2 )n, and n=1, 2, and 3 for 3D cases, and n=1 and 2 for 2D cases. (By contrast n=0, for conventional theory). In antiferromagnets the deviations from the simple power-law behaviors close to T=0 occur only below T≲Tgap, implying a far weaker influence of energy-gap effects than expected in conventional theory. The coefficients B (when T represents the reduced temperature) range between 0.3 and 0.5, clustering near the latter in most cases. A simple and coherent small-k spin-wave scheme can be constructed1 which reproduces the correct temperature dependences, if one assumes that the energies at the bottom of the spin-wave magnon spectrum are ‘‘renormalized’’ by a set of k-dependent (but temperature independent) renormalization factors in the following manner: for ferromagnets ωHeis(k), and for antiferromagnets ω2Heis(k) Tgap → 0), should be divided by k, k 1/2 , and k 1/4 for the 3D cases, and by k and k 1/2 for the 2D cases. Note in particular that such a renormalization gives a convergent result for ΔM for the 2D cases with no anisotropy forces, contrary to conventional theory (but in accord with experimental observations of 2D magnetic ordering). As is well known, non-integral exponents in the dispersion relations occur when the exchange interactions are long range. However, the above temperature dependences for the case of the antiferromagnets are inconsistent with such a possibility. Non-integral exponents in ω can also occur when there is a coupling of a long- and a short-range interaction (e.g., dipolar and exchange, for the 2D ferromagnet2). However, no known couplings reproduce the above effects correctly. Thus, the physical origins of the ‘‘renormalizations’’ still remain unidentified. Some difficulties may exist with regard to extending the above scheme to predict correctly the specific heats and susceptibilities of antiferromagnets, but the main difficulty so far has been in obtaining suitable data in numerical form.
Crystallization of FeB alloys with rare earths to produce hard magnetic materials (invited)
Authors: Koon N. C. , Das B. N.
Published: February 2003

Among the first crystallized melt quenched alloys to exhibit interesting hard magnetic properties was (Fe0.82B0.18)0.9Tb0.05La0.05. The high coercive force of this alloy results from a mixture of R6Fe23 and Fe3B phases with a very fine grained microstructure (∼300 Å). The hard magnetic state only exists over a narrow range of annealing temperatures due to phase decomposition and grain growth at higher temperatures. Recent results on alloys with compositions corresponding to varying ratios of R6Fe23 and Fe3B have suggested a new magnetically hard ternary phase near the composition R0.15Fe0.783B0.067. In contrast to earlier alloys, the hard magnetic state of this material remains essentially unchanged over a rather wide range of annealing temperatures up to at least 800 °C. When R is mostly Nd or Pr, isotropic magnets with energy products as high as 13 MGOe can be produced.
New material for permanent magnets on a base of Nd and Fe (invited)
Authors: Sagawa M. , Fujimura S. , Togawa N. , Yamamoto H. , Matsuura Y.
Published: February 2003

A new compound composed of Nd, Fe, and a small quantity of B (about 1 wt. %) has been found, which has a tetragonal structure with lattice constants a=0.880 nm and c=1.221 nm. This phase, which has the approximate composition, 12 at. % Nd, 6 at. % B and balance Fe, possesses remarkable magnetic properties. From the approach to saturation an anisotroy constant of about 3.5 MJ/m3 can be calculated, while saturation magnetization amounts to 1.35 T. The magnetization versus temperature curve shows a Curie temperature of 585 K, which is much higher than those of the Fe and light rare earth binary compounds. Based on the new compound, sintered permanent magnets have been developed which have a record high energy product. Permanent magnet properties and physical properties of a typical specimen which has the composition Nd15B8Fe77 are as follows: Br =1.23 T, HcB =880 kA/m, HcI =960 kA/m, (BH)max =290 kJ/m3, temperature coefficient of Br =−1260 ppm/K, density=7.4 Mg/m3, specific resistivity=1.4 μΩm, Vickers hardness=600, flexual strength=250 MPa.
Magnetic domains and reversal mechanisms in sintered ‘‘SmCo5’’ permanent magnets
Authors: Strnat K. J. , Li D. , Mildrum H. F.
Published: February 2003

Magneto-optic observations of magnetic domains and reversal processes in several SmCo5-type sintered magnets are reported. Patterns taken with variable applied fields on basal-plane and transverse sections are correlated with measured bulk magnetization curves. States studied included initial magnetization, points in second quadrant after saturation, and on recoil loops. It is seen that domain patterns on pole surfaces do not necessarily reflect the magnetization distribution and change mechanisms in the magnet interior. Observed processes also differ from those reported for low-coercivity SmCo5 samples.
Domain structures of two Sm-Co-Cu-Fe-Zr ‘‘2 : 17’’ magnets during magnetization reversal
Authors: Li D. , Strnat K. J.
Published: February 2003

Domain patterns during magnetization reversal were studied, using the Kerr magneto-optic effect, on sintered magnets of SmCo5Cu0.75Fe1.6Zr0.1 (MHc=6.5 kOe, (BH)m=28.8 MGOe) and SmCo5.36Cu0.64Fe1.76Zr0.24 (24.3 kOe, 23.6 MGOe). In the low-Hc magnet thin sheet reverse domains containing the [00.1] direction originate at grain boundaries. They grow in irreversible spurts along the edges, multiplying and branching, thus gradually filling all grains with dense, wavy patterns. Easy nucleation occurs on a grain boundary phase, while stronger uniform wall pinning by the dense 1–5 precipitate phase inside the 2 : 17 grains controls the coercivity. In the high-Hc magnet, similar grain boundary nucleation is seen in low fields. Additional nucleation inside grains may occur at higher H. Further growth shows ‘‘cloud-like’’ domains expanding fairly isotropically in all directions. Near the coercive field, local full reversal occurs in some large grains, while others remain completely unaffected. Pinning inside grains controls the magnetization reversal, but its strength is quite different for the two 2 : 17 major phase regions.
Properties of Mn-Al-C magnets prepared by spark erosion and other rapid solidification techniques
Authors: Berkowitz A. E. , Livingston J. D. , Walter J. L.
Published: February 2003

Mn–Al–C was prepared as fine powder by reactive spark erosion and by gas-water atomization, and in ribbon form by melt spinning. After optimum annealing, coercivities of spark-eroded particles were higher than those of commercial extruded magnets, but moments were lower. High-field moments of the atomized particles and melt-spun ribbons were comparable to those of the extruded magnets, but coercivities and remanences were lower. Differences in the microstructure and phase kinetics among the various Mn–Al–C materials were also substantial.
Performance of laser-scribed grain-oriented silicon steels in model stacked transformer cores
Authors: Von Holle Anthony L. , Schoen Jerry W.
Published: February 2003

Small laminations were prepared from laser-scribed and nonscribed 0.27-mm H-1 high-permeability and 0.23-mm M-3 conventional grain-oriented silicon steels. The 60-Hz core losses of the laminations were measured in a single-sheet fixture. Model single-phase and three-phase core-type stacked transformer cores were built from the laminations and were tested for their 60-Hz core losses. For either material, the laser scribing produced loss improvements in the model cores which closely approximated those indicated by the single-sheet tests. In both the scribed and nonscribed conditions, the 0.27-mm H-1 material exhibited higher destruction factors in the model cores than did the 0.23-mm M-3 material.
Effect of crystalline texture in grain oriented Si-Fe sheets on the building factor of transformers
Authors: Fukuda B. , Satoh K. , Shimizu Y. , Ito Y.
Published: February 2003

The core material dependency of the building factor in a three-phase transformer was clarified by a model transformer experiment. The building factor was found to be related to the B10 value (flux density at H=1000 A/m) of the core materials showing that it is dependent upon the degree of Goss texture. The dc simulation of the flux distribution at the instant when the total flux in center limb is zero during a magnetizing cycle showed that the increase in building factor proportional to the B10 value was caused by the increase in flux penetration into the center limb at that instant. The replacement of only the center limb sheets by those with lower B10 values reduced the building factor, as expected.
Roles of tin and copper in the 0.23-mm-thick high permeability grain-oriented silicon steel
Authors: Iwayama K. , Kuroki K. , Yoshitomi Y. , Homma K. , Wada T.
Published: February 2003

A study was made in order to make clear the roles of small amounts of tin and copper in the manufacturing process of 0.23-mm-thick steel with excellent magnetic properties. The precipitates in the steel containing 0.1 wt. % tin are smaller in size than those without tin, and provide a stronger inhibiting effect in secondary recrystallization. Such phenomena lead to lowering the secondary recrystallization temperature and improve the secondary grain size distribution. The addition of a small amount of copper improves the quality of a surface glass film.
Effects of thickness and resistivity on core loss and permeability of nonoriented semiprocessed steels
Authors: Stephenson E. T.
Published: February 2003

The effects of thickness t and resistivity ρ on the ac and dc core loss and permeability of six laboratory heats of nonoriented, semiprocessed, low-silicon (Si+Al<1.1%) steel were investigated at 10, 15, and 17 kG. The total ac core losses increased nearly linearly with t2/ρ at all three inductions, but none of the proportionality constants were predicted by classic theory. Hysteresis losses tend to increase with increasing oxygen (i.e., inclusions) and decreasing grain size in the steel, but they were not dependent on thickness or resistivity. ac permeability was a complex function of thickness, resistivity, and induction. dc permeability at 15 and 17 kG increased with thickness.
Enhanced domain imaging techniques
Authors: Rauch G. C. , Krause R. F. , Izzo C. P. , Foster K. , Bartlett W. O.
Published: February 2003

In this paper we present three techniques which provide improved permanent ferromagnetic-particle images of domain structures. A normal field, supplied by flexible permanent magnet strip, is used for all three. The first method employs a pigmented strippable coating which is peeled from the specimen after drying. The result is a high-resolution mirror image of the domain structure; the method can be used to study parts of large specimens nondestructively. In the second method, the coating is examined while still in place; its contrast can be increased by adding more white pigment and by painting the specimen white before application. The third method uses noncolloidal Fe3O4 powder in artist’s matte medium to provide domain images, on a white-painted specimen, with higher contrast but lower resolution.
Thermodynamic potential model for magnetization of textured polycrystalline materials
Authors: Jagusztyn W. , Szpunar J. A.
Published: February 2003

A general formula for the thermodynamic potential expressed using the magnetic phase theory is suggested as a description for the magnetization process in textured polycrystalline ferromagnets. The demagnetizing energy of the grain includes the simplified description of the domain structure. For a given value of magnetization the phase structure, which corresponds to the minimum value of the potential, is computed using a variation method. As an example the static permeability of texture Fe-Si steel is calculated as a function of the mean diameter of the grain and the specimen’s texture.
Half-metallic ferromagnets and their magneto-optical properties (invited)
Authors: de Groot R. A. , Mueller F. M. , van Engen P. G. , Buschow K. H. J.
Published: February 2003

We have calculated the electronic structure of PtMnSb in order to explain the very high magneto-optical Kerr effect (over 2.5° at 720 nm at room-temperature) of this compound. It is shown that this behavior is related to the unusual electronic properties of PtMnSb: it is a half-metallic ferromagnet like NiMnSb. The extreme asymmetry in the electronic structure of these compounds—metallic behavior for one spin direction and at the same time semiconducting behavior for the other spin direction—is responsible for the unusual magneto-optical properties.
First magneto-optical observation of an exchange-induced plasma edge splitting
Authors: Reim W. , Hüsser O. E. , Schoenes J. , Kaldis E. , Wachter P. , Seiler K.
Published: February 2003

The first magneto-optical data for the metallic thulium monochalcogenides TmS and TmSe in the 0.55–5.5-eV photon energy range is presented. The Kerr rotation and ellipticity spectra of both compounds display one pronounced structure with an ellipticity of up to 3.6 deg. It is demonstrated that the magneto-optical effect is related to a splitting of the conduction electron plasma edge which at 2-K and 4-T amounts to 30 and 60 meV for TmS and TmSe, respectively. In a skew scattering model, this splitting is shown to be approximately equal to the product of the exchange-induced conduction electron spin polarization with the spin-orbit energy. The d-spin polarization is estimated to be −20% and −40% at 2 K and 4 T for TmS and TmSe, respectively.
Magnetization and Faraday rotation of praseodymium-gallium substituted yttrium iron garnets
Authors: Leycuras C. , Le Gall H. , Guillot M. , Marchand A.
Published: February 2003

The saturation magnetization MS(T) and the Faraday rotation ΦF(T) of PrxY3−xGayFe5−yO12 single crystals have been measured for 4.2 K<T<300 K with a magnetic field applied along the [111] direction. The investigated samples have compositions: x∼1 and 0<y<1.32. From the experimental data, we extract the contribution m and φ of the Pr3+ ions assuming that the behavior of the Fe3+ ions is similar in PrxGay : YIG. The decrease of m and φ on increasing y can be assigned to the exchange perturbed wave functions of Pr3+ ions involved in these properties: ground state multiplet for induced magnetic moment, ground and excited states multiplets for induced Faraday rotation.
Magnetic susceptibility and Verdet constant in rare earth trifluorides
Authors: Leycuras C. , Le Gall H. , Guillot M. , Marchand A.
Published: February 2003

On three fluorides CeF3, NdF3, and PrF3 accurate susceptibilities measurements are reported from 2 up to 300 K under a magnetic field applied along the c axis. On the same samples, the optical Faraday rotation has been investigated in the temperature range 8–300 K at 0.6328 μm wavelength in a magnetic field up to 20 kOe. The reciprocal susceptibilities χ−1(T) follow a Curie Weiss law for T>100 K; the observed values of the paramagnetic Curie temperature are − 56 K (PrF3), − 114 K (CeF3), and − 26 K (NdF3). For T<100 K, strong crystalline field effects are evidenced: for example, a maximum of χ near 60 K has been found in PrF3. In the three fluorides negative Verdet constants have been obtained. The ratio V/χ appears as strongly temperature dependent, that is quite different from the theoretical prediction. Furthermore, the experimental results show an evidence of two behaviors of V/χ for T>77 K. (V and χ are expressed in deg cm−1 Oe−1 and in μB mol−1 Oe−1, respectively.) On one hand for NdF3 and PrF3, it has been found V/χ =A(1+αT) where A is a constant (−4320 in NdF3; −7241 in PrF3); in both samples, α is in the order of −6×10−4 K−1, note that Faraday rotation measurements performed at 0.4579 and at 0.5017 μm lead to an identical α value. On the other hand in CeF3, V/χ is a linear function of T−1 and is given by 13700(1+75.9/T).
Magneto-optical characteristics of double-layered amorphous RE-Fe films by rf sputtering
Authors: Takenouchi A. , Shichi E. , Kato T. , Tsunashima S. , Uchiyama S. , Imamura N.
Published: February 2003

Amorphous GdFe/TbFe double-layered films have been prepared by rf sputtering on glass substrates. GdFe films of about 300 A in thickness, TbFe films of about 500 A in thickness and SiOx films of about 900 A in thickness were successively deposited without breaking vacuum. The coercivity and polar Kerr rotation angle were measured as a function of rare-earth content. From these results, the optimum component of GdFe/TbFe double-layered films was determined. The coercivity of GdFe single-layered films and the GdFe layer in GdFe/TbFe double-layered films were also measured by polar Kerr hysteresis loops. It was found that the GdFe layer and the TbFe layer were exchange-coupled, since the coercivity of the GdFe layer in double-layered films was more than 10 times larger than that of GdFe single-layered films. Amorphous GdFe/TbFe double-layered media of the optimum component have been prepared on 200-mm-diam glass disks. A carrier-to-noise ratio (C/N) of 45 dB at 2.048 Mb/s (NRZ) was obtained, which is a few dB higher than that of TbFe single-layered films.
Control of birefringence in LPE-grown magnetic garnet films
Authors: Okuda T. , Koshizuka N. , Murata A. , Yokoyama Y. , Ando K.
Published: February 2003

Birefringence in LPE films of pure and substituted Y3Fe5O12 for magneto-optical waveguides was investigated by a guided-wave technique at the wavelength of 1.152 μm. In addition to the stress-induced birefringence Δnsf due to the lattice mismatch between film and substrate, we find another type of birefringence δn with negative sign of the order of 10−5 in (YNd)3Fe5O12 and (YSm)3Fe5O12 films. In the films containing Bi ions such as (YNdBi)3(FeGa)5O12 and (YbPrBi)3(FeGa)5O12, the signs of δn are positive and their magnitudes are of the order of 10−4. Correspondences of δn and the growth-induced magnetic anisotropy are pointed out, which suggest that δn is growth-induced birefringence.
3-D magnetic field computations by infinite elements
Authors: Jung Hyun-kyo , Lee Gi-shik , Hahn Song-yop
Published: February 2003

This paper describes an extended application of the infinite element method to three-dimensional magnetic field problems. First, the partial differential equations for the magnetic field region are expressed in terms of scalar potentials. The system stiffness matrix is then obtained using a variational method. To deal with the boundary conditions at the interfaces between finite element regions and infinite element regions, the collocation method is adopted. The new approach has been applied to a sample problem to verify the performance. The result shows that the infinite element method with some modifications can be applied to three-dimensional problems and provides good accuracy.
The iterative local 3-D finite element analysis method by modifying the machines from a simplified shape to a real one
Authors: Yamashita Hideo , Kawano Nobuyuki , Nakamae Eihachiro , Nomura Toshihide
Published: February 2003

The big problems in 3-D finite element analysis (FEA) are huge main memories required and long computation times. In this paper, the local FEA for 3-D fields is proposed as a method for breaking these bottlenecks. It is shown that by means of this proposed local method, the 3-D FEA can be executed by using a minicomputer and the results have high accuracy. The usefulness of this method is shown by applying this to a circular coil with an iorn core and a 3-phase reactor with air gaps.
Micromagnetics of domain walls in vertical recording
Authors: Soohoo R. F.
Published: February 2003

A detail micromagnetics calculation for a simplified model of domain walls in vertical recording is presented. From the resulting analytical expression for the wall magnetization distribution, wall energy density and wall width are determined for a single as well as for multiple walls. Whereas our simplified model presupposes a homogeneous medium, columnar structure is frequently observed in vertical recording media. Possible modifications to our results due to columnar formation is discussed. Finally, a comparison between the limiting recording densities of horizontal and vertical recording in the context of head field gradient and medium hysteresis loop squareness is given.
Self-consistent vector calculation of magnetic recording using the finite element method
Authors: Koehler T. R.
Published: February 2003

A two-dimensional finite element program has been developed for application to magnetic recording. It solves, as a boundary value problem, the system of a magnetic recording head with appropriate geometry, driven by a current carrying coil and interacting with a recording media whose properties are obtained from a new vector hysteresis model. Details of the program and the hysteresis model will be discussed.
Magnetics of small magnetoresistive sensors (invited)
Authors: Tsang Ching
Published: February 2003

In the application of magnetoresistive sensors to magnetic recording two basic magnetic issues must be addressed: namely, the suppression of domain effects and the linearization of the magnetoresistive (MR) response. In this paper, we examine past results of the Barkhausen noise problem in small MR sensors, as well as methods for their suppression. Furthermore, we shall also discuss various transverse bias schemes: their principles of operation, their advantages and limitations in terms of bias sensitivities, bias uniformity, as well as their impacts on the linear and track resolution of the MR sensor.
A thin film head for high density magnetic recording using CoZr amorphous films
Authors: Yamada K. , Maruyama T. , Tanaka H. , Kaneko H. , Kagaya I. , Ito S.
Published: February 2003

A thin film head using CoZr amorphous films has been developed for high density magnetic recording. The head has a single-layered 17-turn spiral copper coil, 0.2-μm head gap length, 15-μm track width, and 2-μm-thick CoZr films on an IBM 3370 type slider. The copper coil was electroplated through a photoresist pattern, which was fabricated by the oxygen ion milling to obtain a high aspect ratio (1.5 μm width, 3.4 μm thickness, 3.5 μm space). CoZr films used here have excellent magnetic properties, such as low coercive force (Hc≤0.05 Oe), high permeability ( μ≂3500 at 10 MHz), and high saturation magnetization (4πMs ≂14 000 G). These heads were evaluated using 8-in. Co-Ni-P plated disks which have a 300-Å-thick magnetic layer (Hc=600 Oe, Br =7200 G) and a 200-Å-thick protective layer. D50=36 KFRPI and overwrite=−34 dB (24 KFRPI on 8 KFRPI) were obtained at 19.7 m/sec relative velocity and 0.25 μm head-disk spacing. These values were superior to those for heads using Permalloy films (D50=25 KFRPI, overwrite=−20 dB). It was concluded that CoZr amorphous thin film heads have superior capabilities for high density magnetic recording.
Magneto-optic investigation of thin-film recording heads
Authors: Re Mark E. , Kryder Mark H.
Published: February 2003

A magneto-optic photometer system has been developed to study the magnetic characteristics of thin-film magnetic recording heads at frequencies up to 50 MHz, on spot sizes as small as 0.5 μm in diameter. The photometer system uses an argon laser as the light source to a Leitz MPV3 polarizing microscope. The changing magnetization of the head is detected by using the longitudinal Kerr magneto-optic effect. The signal is recovered with a photomultiplier tube and a lock-in amplifier detection scheme. Completed IBM 3380 thin-film heads have been analyzed by using the photometer system. The local frequency responses on the head have been measured while the head is being driven by its own coils. Different responses have been observed on different positions on the head. The differences in response are interpreted in terms of the domain structure of the yoke.