bluuebunny/crossref_metadata_2025 huggingface dataset:
What is the Harris criterion telling us about spin glass?
Authors: Fisch Ronald
Published: February 2003

A TAP-like diagrammatic analysis of the magnetic susceptibility of spin glass is presented, with careful attention to the thermodynamic limit. This leads to a heuristic understanding of why naive linear response theory fails for T<Tg, and why the lower critical dimension for long range order in spin glass is dc = 4. The Harris criterion is used to argue that there is a Griffiths singularity in the Ising spin glass for 2<d<4.
The temperature dependence of the order parameter in a dilute AgMn spin glass
Authors: Roshko R. M. , Symko O. G.
Published: February 2003

The magnetization of a dilute AgMn spin glass containing 150 ppm Mn has been measured over the temperature range from 20 mK to 2 K in an applied field of 0.9 Oe, using a SQUID magnetometer. A comparison of the measured magnetization with numerical calculations of the magnetization based on the Mean Random Field (MRF) theory of a 3-D Heisenberg spin glass with an internal field distribution P(h) = Δ/[π2(Δ2+h2)2] yields the temperature dependence of the internal field parameter Δ and hence of the MRF order parameter.
Magnetic anisotropy constants of Fe and Ni at 77, 4.2, and 1.09 K: Interdomain configuration transitions in Ni
Authors: Tung C. J. , Said I. , Everett Glen E.
Published: February 2003

The magnetocrystalline anisotropy constants of Ni and Fe have been determined at 77, 4.2, and 1.09 K from M⊥(ϑ) measurements above technical saturation. At 4.2 K and below the X2↓ hole band contribution is observed for H↘0 rotation in the (100) and (110) planes. Anisotropy constants, K1, K2, K3, and K4 determined for Ni and K1, K2, and K3 for Fe are compared with previous values from torque measurements. Second-order interdomain configurations transitions in M∥ versus H have been measured for H↘0 in a (100) plane of Ni. The angular dependence of the transition fields is in good agreement with the theory of Lawton and Stewart extended to include higher-order contributing anisotropy constants.
Abstract: Magnetovolume effects in transition metal alloys including the Invar anomalies: A molecular orbital study
Authors: Salahub D. R. , Kaspar J.
Published: February 2003

As a result of SCF-Xα-SW molecular orbital calculations on pure and mixed fcc Fe-Ni clusters we have recently proposed [Phys. Rev. Lett. 47, 54 (1981)] an explanation of the Invar anomalies including, among others, the maximum in the lattice constant, the maximum in the magnetization, and the minimum in the thermal expansion coefficient for the concentration range around 40% Ni. Our model attributes these to the existence, at the Fermi level for this concentration range, of highly antibonding majority-spin levels and nonbonding minority-spin levels. As the nickel concentration varies there is a fairly complex, but understandable, interplay between the occupation of the levels, the magnetization and its concommitant exchange splitting, and the chemical effects due to the occupation of different types of orbitals that leads to a coherent explanation of the set of anomalies. Similar, though less dramatic, effects have been observed, among others, for the bcc Fe-Ni and Fe-Co alloys. Examination of our existing calculations for bcc Fe15 and hcp Co13 indicates the probability of a similar explanation, and we are currently verifying this through further calculations on mixed clusters.      a)Supported by the NSERC-Canada.
Abstract: de Haas-van Alphen effect and band structure of Ni3Al
Authors: Lonzarich G. G. , Sigfusson T. I. , Buiting J. J. M. , Kübler J. , Mueller F. M.
Published: February 2003

The intermetallic compound Ni3Al orders in the simple cubic (Cu3Au) crystal structure and becomes ferromagnetic below about 40 K with a spontaneous magnetization extrapolation to absolute zero corresponding to approximately 0.075 μB/Ni atom. An investigation of parts of the Fermi surface has been carried out in stoichiometric single crystals by means of the de Haas-van Alphen effect in the magnetic field and temperature ranges 20⩽H⩽95 kG and 0.35⩽T⩽8 K, respectively. The results have been interpreted in terms of a band structure model including both the effects of the exchange spin-splitting of the energy bands and the spin-orbit interaction. Our combined experimental and theoretical findings will be discussed in relation to current microscopic models of very weak itinerant electron ferromagnetism.
Transport properties of CeSb1−xTex for x<0.05
Authors: Escorne M. , Ravot D. , Achard J. C. , Mauger A.
Published: February 2003

Magnetic and transport properties of x = 0, 0.02, and x = 0.05 single crystals have been investigated in the range 3<T<300 K. A decrease of the number of magnetic phases of the Néel temperature TN as a function of x is observed. Elastic plus inelastic magnetic scattering of the carriers by spin fluctuations have been computed, and the electron phonon interaction satisfies the Grüneisen-Bloch law. A fairly good agreement between theory and experiments is observed in the whole range TN<T<300 K, precluding the hypothesis of any significant Kondo effect in this range of temperatures. However, Kondo effects may explain anomalies in the resistivity below 10 K in the x≠0 samples. The crystal field splittings are larger or equal to 50 K in the x≠0 samples compared with 28.5 K in CeSb. These variations of Δ and TN are discussed with respect to the models of the anisotropic exchange interactions in such materials.
Identification of a low spin state associated with conformational equilibria in methemoglobin
Authors: Levy A. , Walker J. C. , Rifkind J. M.
Published: February 2003

Low-temperature Mössbauer and Electron Spin Resonance (ESR) studies on paramagnetic horse methemoglobin demonstrate the existence of a low spin state of hemoglobin which is not identical to the typical Hb+-OH low spin state. The amount of this species was found to increase when samples were gradually cooled instead of being quenched into liquid nitrogen. This state is found in the pH range from 6.0 to 8.9, although an increase of the relative population of this state is found below pH 6.9. This species is formed from Hb+-H2O and Hb+-OH. Temperature studies indicate that this species can be reversibly formed from the usual high spin and low spin species even at 210 K, where water is already completely frozen, ruling out a direct perturbation due to the freezing process. These results are interesting in terms of conformational equilibrium in the region of the heme pocket. The relative intensity of the various species is explained in terms of energy barriers between the different conformations which limit the rate at which the usual high spin and low spin states are converted to this state.
Proton NMR in the paramagnetic and magnetically ordered phases of SmH2+x and NdH2+x
Authors: Bohn H. G. , Arons R. R.
Published: February 2003

The deuteron Knight shift K of SmD2+x and NdD2+x has been measured for various x between −0.15 and +0.15. In the paramagnetic state, K is found to be independent of the deuterium concentration and can be described by a modified Curie-Weiss law: K = K0+λ/(T−ϑ). On the other hand, the temperature dependence of the line width in SmD2+x is strongly affected by the D concentration, indicating a strong magnetic short-range order to be present for x?0. For NdD2+x the hyperfine field at the deuteron site could be determined in the ferromagnetic state. It is found to be +0.21 T for x?0 and +0.15 T for x = 0.1. For the first time a zero-field resonance at the proton site has been measured, the frequency being 16.1 MHz at 1.2 K.
Dipolar surface spin waves in ferromagnetic films
Authors: Rahman T. S. , Mills D. L.
Published: February 2003

Recent light scattering experiments probe surface spin waves in ferromagnetic films under conditions where the dominant contribution to the excitation energy comes from the Zeeman and dipolar interactions. We explore the dispersion relation of these modes for the case where the magnetic field is rotated out of the plane of the film toward the normal. We find that as the field is rotated the surface- and bulk-mode frequencies decrease, and, under certain conditions, the surface mode can lie below the Larmour frequency and distinct from the bulk manifold. Several examples of dispersion curves will be presented, with attention to the possibility that the surface spin wave may couple to the conduction spin resonance in a layered structure with nearly free electron metal as a constituent.
Density of states for the asymmetric Anderson model
Authors: Lacroix C.
Published: February 2003

The Anderson model is studied using a procedure of Green’s function decoupling, as a function of the parameters U (intra-atomic Coulomb interaction), E0-EF (position of the d-level compared to the Fermi level), Δ (width of the virtual d-level), and the temperature T. In the case of a Kondo impurity, i.e., U→∞ and ‖E0-EF‖≫Δ, the density of states consists in three peaks: the two resonances at E0 and E0+U and a very narrow peak around the Fermi level. We discuss the temperature dependence of the density of states using the approximate Green’s functions: the peak at the Fermi level has a width of the order of the Kondo temperature TK at T = 0 K and it disappears gradually at higher temperature. In the case of a mixed valence impurity we show, using the same decoupling procedure, that the peak at the Fermi level disappears when ‖E0-EF‖ becomes of the order of Δ.
Electronic structure of CePd3 from resonant photoemission and optical reflectivity spectra
Authors: Allen J. W. , Nemanich R. J. , Oh S.-J.
Published: February 2003

Optical reflectivity and resonant photoemission measurements on CePd3 yield a 4f binding energy Ef between 0.7 and 1.0 eV and set an upper limit of 0.3 eV on a surface shift of Ef. The 4f halfwidth at half maximum δ is between 0.5 and 0.8 eV. The spin fluctuation energy Γ = 20 meV is successfully related to Ef and δ by the Kondo impurity Ansatz.
Conduction electron lattice relaxation due to the cerium ion in GdxCe1−xBe13 and GdxR1−x−yCeyBe13 (R = La, Y, or Lu)
Authors: Heinrich G. , Kappler J. P. , Meyer A.
Published: February 2003

EPR measurements in the bottleneck regime permit estimation of the conduction electron lattice relaxation rates due to the several components of an intermetallic compound. We first recall the values obtained for the Gd3+ g value or g shift and linewidth slope in some intermediate valence compounds with cerium. We then present the relaxation rates deduced from the bottleneck regime in GdxCe1−xBe13 and GdxR1−x−yCeyBe13 (R = La, Y, or Lu). The values obtained for the cerium ion are two to three orders larger than those resulting from only nonmagnetic elements like La, Y, or Th in the same compounds and are also higher than those given by a magnetic impurity like Nd3+. We show that these results, δeL∼1014 s−1, can be compared with those deduced from neutron scattering or NMR measurements and also with that calculated by the theory of Kuramoto and Müller-Hartmann employing the extrapolated Curie temperature and the cerium valence in the compound.
Conductivity of some mixed-valence oxides below Tv
Authors: Hurd C. M. , McAlister S. P. , Savvides N. , Shiozaki I. , McKinnon W. R. , Strobel P.
Published: February 2003

We show from existing data that the electrical conductivity σ of Fe3O4 in the range Tv≳T≳Tv/2 can be described by log σ∝T. To check whether this behavior is more widespread, we have made new measurements of the conductance G(T) in Fe3O4 (40–340 K), Ti3O5 (64–364 K), and Ti4O7 (80–272 K). The log σ∝T behavior is most striking for Ti4O7. We refer to a mechanism that can account for the behavior in terms of incoherent electron tunneling between cation sites.
Details of the electronic superstructure of Fe3O4
Authors: Iida S. , Mizushima K. , Mizoguchi M. , Kose K. , Kato K. , Yanai K. , Goto N. , Yumoto S.
Published: February 2003

After introducing briefly the derived electronic superstructure of Fe304, recent advances in the model are explained. The transition may be described as the ordered microsegregation of the linked molecular pseudo-metallic units. Mössbauer results predicted that the population ratio of Fe2+−II to Fe2+−I is 3:5 in contrast to 4:4 of the previous understanding and all the results are consistently understood by assuming that all the Fe2+ ions have a Jahn-Teller stabilized dεξη orbital for the additional electron. We observed ferroelectric hysteresis curves at 4.2 K with the saturation polarization of about 0.8 μC/cm2 along the c axis. The importance of strains in the metal-insulator electronic transition in general is pointed out and the term ’’releasing the microscopic strain by antiphases’’ is emphasized, which may replace the term ’’incommensurable charge density wave’’ in many cases.
Abstract: Magnetic interactions in Yb1−xEux alloys
Authors: Oestreich V. , Czjzek G. , Schmidt H. , Götz F. , Harmon B. , Wienand K. H.
Published: February 2003

We have studied the magnetic properties of face centered cubic Yb1−xEux alloys with x = 0.05, 0.10, 0.30, and 0.40 by 151Eu Mössbauer spectroscopy, magnetization, and resistivity measurements in the temperature range from 1.5 to 300 K. At 1.5 K, the Mössbauer spectra of all samples show a well-defined magnetic hyperfine field. For x = 0.30 and 0.40 the temperature dependence of the hyperfine fields follows a Brillouin function (TM = 11.2 and 14.4 K, respectively). The magnetization versus temperature curves for these samples show broad maxima which are shifted to higher temperatures with decreasing external fields. An extrapolation to zero external field yields ordering temperatures close to those found from Mössbauer spectroscopy. The specific resistivity of these samples is quite high with a negative temperature coefficient, obeying the Mooij correlation, but no indication of the magnetic transition occurs near the ordering temperature. The Mössbauer spectra for x = 0.05 and 0.20 at temperatures above 3 K can be described only by the assumption of at least two different Eu sites distinguished by different hyperfine fields. The transition temperatures (26 and 22 K, respectively) are in good agreement with those found from resistivity and magnetization measurements. The latter show that the alloys with low Eu concentration are ferromagnetic. The concentration dependent magnetic ordering suggests a competition between short-range antiferromagnetic and long-range ferromagnetic coupling while the resistivity data indicate increased d-band occupation as Eu is added.      a)Permanent address: Ames Laboratory, Iowa State University, Ames, Iowa 50011.
Origin of anisotropy in transition metal spin glass alloys (invited)
Authors: Levy P. M. , Morgan-Pond C. , Fert A.
Published: February 2003

The strong enhancement of anisotropy produced in CuMn by the addition of impurities with strong spin-orbit coupling is explained by Dzyaloshinsky-Moriya interactions. Estimates of the anisotropy have been obtained by approximate analytic methods as well as Monte Carlo studies. Although D-M interactions seem to be dominant, we discuss some other sources of anisotropy, e.g., pseudo-dipole and crystal-field-like terms.
Further evidence for a spin-glass phase transition in amorphous Fe-Mn-P-B-Al alloys
Authors: Goldfarb R. B. , Rao K. V. , Chen H. S. , Patton C. E.
Published: February 2003

Low field dc susceptibility, thermoremanent magnetization, and hysteresis studies are presented for two amorphous Fe-Mn-P-B-Al alloys of concentrations close to, and on either side of, the multicritical point in the magnetic phase diagram. They exhibit spin-glass and para-ferro-spin-glass transitions, respectively. For the spin-glass alloy, the Edwards–Anderson-type order parameter deduced from the dc susceptibility is found to yield a mean-field-valued critical exponent. In the alloy with two magnetic transitions, the temperature dependence of the thermoremanence and hysteresis indicate a ferro-spin-glass transition temperature consistent with that deduced from a scaling approach for the same alloy system.
Ferromagnetic-spin glass transition in Fe-Zr amorphous alloy system
Authors: Hiroyoshi H. , Fukamichi K.
Published: February 2003

Several kinds of Fe-Zr amorphous ribbons have been prepared from the melt in an argon atmosphere, and the spin-glass-like behaviors have been investigated. The thermomagnetic history has been observed, and the freezing temperature monotonously decreases, in contrast to the Curie temperature, which increases and then goes through a maximum with increasing Zr content. Asymmetric hysteresis loops and the relaxation of remanence have also been found. The coercive force of Fe92Zr8 amorphous alloy drastically increases below 30 K, and the high-field susceptibility of the present alloys are extremely large. These behaviors are explained in terms of the coexistence of ferromagnetic and antiferromagnetic states.
Frequency dependence of the ac susceptibility of EuxSr1−xS
Authors: Holtzberg F. , Francavilla T. L. , Huang C. Y. , Tholence J. L.
Published: February 2003

The ac susceptibility of Eu0.44Sr0.56S and Eu0.48Sr0.52 has been measured at low frequency (17 Hz<ν<2100 Hz) and at 9×109 Hz. A strong frequency dependence of the real part of the susceptibility is observed below the spin-glass transition temperature Tf. Moreover, the increase of Tf with frequency ν can be described with a Fulcher law ν = ν0 exp[−Ea/k(Tf−T0)], with ν0 = 1013 s−1 and T0 = 1.3 and 1.65 K, respectively, for x = 0.44 and 0.48. These data, compared to a similar analysis of other ac measurements indicate that [Tf(ν)−T0] and Ea/k remain almost constant for x between 0.15 and 0.48. Both Tf(ν) and T0 increase linearly with x in the same concentration range. This confirms that the spin-glass transition becomes less time dependent for an increasing fraction of interacting impurities (the ferromagnetism is observed for x≳0.5 in this system).
A new magnetic amorphous alloy system: (Fe,Co)-bismuth
Authors: Forester D. W. , Schelleng J. H. , Lubitz P. , D’Antonio P. , George C.
Published: February 2003

We have synthesized, for the first time, amorphous alloy films of (Fe,Co)1–xBix. The amorphous alloys are most stable in a narrow composition range near x = 0.20, while above or below this composition (for 0.10⩽x⩽0.30), a predominant amorphous alloy along with Fe or Co and Bi metal is observed. The alloys are ferromagnetic and magnetization data indicate that the Fe or Co moments are little affected by the Bi content near x = 0.20 and are at least 95% of that for the pure magnetic metals. For the Fe-Bi alloys, a detailed characterization was made using x-ray, magnetization, Mössbauer, FMR, and differential scanning calorimetry (DSC) techniques. The DSC measurements show irreversible exothermic or combined exothermic-endothermic transitions over narrow temperature ranges up to 830 K. Their magnetization versus temperature plots exhibit discontinuous changes associated with the DSC transitions and Curie temperatures near 1020 K. The films display large uniaxial anisotropies perpendicular to the film planes. They are highly resistant to oxidation or tarnishing at room temperature.
Preparation and properties of coevaporated amorphous Co-Zr thin films
Authors: Krishnan R. , Tarhouni M. , Tessier M. , Gangulee A.
Published: February 2003

Co1–xZrx thin films (5<x<35) were prepared by coevaporation in a two E-beam source system on glass substrates held at 30 °C. The crystallinity of all films were monitored by x-ray diffraction techniques; the films in the composition range x⩾7.4 were found to be amorphous. Magnetization, hysteresis loop, and FMR measurements were carried out with these Co-Zr films. The saturation magnetization as a function of composition shows similar trends as in the Co-Ti thin films. The FMR spectra were rather complex with four to six modes for perpendicular resonance; the most intense mode gives a value for 4πMs close to the static data. The other modes at higher resonance fields may be caused by preferential oxidation of Zr or a large negative anisotropy induced by oxidation. Auger and ion probe profile analysis of the Co-Zr films indicated the presence of oxygen throughout the bulk of these films. SEM examination of some of these Co-Zr films showed the existence of a columnar structure, and it is possible that oxygen transport is enhanced along the column boundaries. Regions with varying degrees of oxidation are thought to be responsible for the multiple FMR modes.
Pressure effect on the Curie temperature and high-field susceptibility of FeCrB amorphous Invar alloy
Authors: Fukamichi K. , Shirakawa K. , Kaneko T. , Masumoto T.
Published: February 2003

FeCrB amorphous alloys were prepared by rapid quenching from the melt. The spontaneous volume magnetostriction ωs of amorphous Fe74Cr11B15 is very large. The value of ωs(T) vs (T/Tc)2 exhibits a linear relationship over a wide temperature range. The measured high-field susceptibility and the estimated forced volume magnetostriction are remarkably large, suggesting a high density of states at the Fermi level. The pressure effect on the Curie temperature is remarkably large, being −3.6 K/kbar and the decrease of the Curie temperature with applied hydrostatic pressure is linear. This result is in agreement with Wohlfarth’s theory of itinerant ferromagnetism. The magnetovolume coupling constants determined from the spontaneous volume magnetostriction and the pressure effect on the Curie temperature are large.
Magnetization of small amorphous particles
Authors: Aharoni Amikam
Published: February 2003

Amorphous ferromagnetic particles are approximated by a theory which assigns, at random, exchange interactions between various parts of a ferromagnetic sphere. These interactions are randomly selected from a gaussian distribution with a standard deviation of 0.3, and include negative exchange values for the lower end of the distribution. The magnetization versus applied field curve is calculated with a specific Ritz model for such a sphere which has a radius of 200 Å and no anisotropy. The result is that the magnetization curve for such a sphere is essentially the same as that of a regular ferromagnet, with a somewhat smaller but constant exchange interaction.
Thermal and magnetic properties of amorphous Prx(Fe0.8B0.2)1−x
Authors: Kabacoff L. , Dallek S. , Modzelewski C. , Krull W.
Published: February 2003

Amorphous ribbons of the composition Prx(Fe0.8B0.2)1–, 0?x?0.30, have been produced by meltspinning onto a copper wheel under argon atmosphere. The alloys were characterized thermally using a DuPont 1090 Thermal Analysis System. The crystallization onset temperature Tx, measured at a heating rate of 20 K/min, has a maximum of 899 K at x = 0.10. Tx equals 696 and 729 K for x = 0 and x = 0.30, respectively. The activation energy of crystallization of 5.4 eV for x = 0.05, dropping to 4.3 eV at x = 0.10, remaining approximately constant betwen x = 0.10 and 0.20, then dropping to 2.7 eV for x = 0.30. There is evidence that the alloys phase-separate slowly at room temperature, rapidly at elevated temperature. The magnetic moment was measured as a function of applied field at room temperature and at 4.2 K. The saturation moment decreased from 142 to 50.2 emu/gm at room temperature, and from 171.5 to 93.5 emu/gm at 4.2 K. The low temperature moments were strongly time dependent. The room temperature coercive force was too small to measure (<5 Oe).
Electrical magnetoresistivity of amorphous (Fe-Ni)80B20, (Fe-Ni)80P14B6, (Fe-W)80B14Si6, and (Fe-Cr)80B14Si6 alloys
Authors: Yao Y. D. , Arajs Sigurds , Lin S. T.
Published: February 2003

The electrical magnetoresistivity of amorphous Fe80–xNixB20 (x = 0, 10, 20, 30, 40, 50), Fe80–xNixP14B6 (x = 0, 10, 20, 30, 40, 50, 60, 70), Fe80–xWxB14Si6(x = 0, 2, 4, 6, 8), and Fe80–xCrxB14Si6 (x = 0, 2, 4, 6, 10, 14, 16, 20) alloys has been measured at both 77 and 300 K in applied magnetic fields up to 6 kG. The ferromagnetic anisotropy of electrical resistivity (FAR) decreases much faster with increasing concentration of Cr or W than Ni. Our experimental data suggest that FAR is closely related to the magnetic saturation moment (μ̄) per transition metal atom at 0 K, i.e., FAR = Aμ̄m, where A and m are temperature-dependent parameters.
Pressure effect on the Curie temperature of cobalt based amorphous alloys
Authors: Shirakawa K. , Ohnuma S. , Kaneko T. , Masumoto T. , Kanehira J.
Published: February 2003

Pressure effect on the Curie temperature was studied for Co-TM-Zr (TM = Cr and Mo), Co-TM-B (TM = Ti, Mo, and Mn), Co-B and Co-Si-B amorphous alloys under pressure up to about 10 kbar. The Curie temperature of all prepared specimens decreased linearly with applied pressure. It was found that Co rich Co-Mo-Zr alloys have strong pressure dependence of the Curie temperature. Thermal expansion was also measured for some specimens of the alloys mentioned above. It was found that while the Curie temperature of Co-Cr-Zr and Co-Mo-Zr amorphous alloys have strong pressure dependence, the magnetic thermal expansion anomalies are undetectably small.
Crystallization and domain properties of thinned amorphous FeBSi ribbon
Authors: Grundy P. J. , Jones G. A. , Parker S. F. H. , Tebble R. S.
Published: February 2003

A transmission electron microscope study has been made of the crystallization and associated domain behavior of an amorphous Fe82B15Si3 alloy. The first obvious signs of crystallization in microscope-annealed foils occur at a temperature of about 345 °C with the appearance of α-iron nuclei. These crystallites grow with annealing time but the grain size at complete crystallization is still small (∼0.1 μm). At a temperature of 500 °C a bct Fe2B phase is formed. Furnace annealed specimens differ in that the iron nuclei have a dendritic morphology. The as-quenched material shows an isotropic domain structure with no magnetization ripple. The onset of crystallization is accompanied by the formation of this magnetization dispersion and, in some cases, stripe domains which reflect a perpendicular anisotropy. The results of in-situ magnetization observations of the domain structure clearly indicate the perturbing effects of the crystallization products.
High-temperature magnetic and microstructure studies of transition-metal-metalloid glasses containing Cr
Authors: Hadjipanayis G. C. , Yadlowsky E. J. , Wollins S. H. , Sellmyer D. J.
Published: February 2003

The magnetic properties of splat-cooled (Fe1−xNix)78–yCrySi10B12 Metglasses have been measured over the temperature range of 300–1000 K and the results correlated with measurements of sample microstructure. Thermomagnetic data indicate the presence of two magnetic phases with different Curie temperatures in the samples containing Cr. Transmission electron microscopy studies indicate that both phases are amorphous with different Fe concentrations. X-ray studies reveal that crystallization of the amorphous samples occurs at temperatures around 720 K with the formation of a bct Fe3B and a fcc FeNi phase. The high coercive fields which exist from liquid helium temperatures to above the Curie point of the amorphous sample have been attributed to the heterogeneous magnetic structure. The increase of the coercive field (150 Oe) after crystallization has been attributed to the coexistence of two crystalline phases.
Phenomenological theory of magnetostriction in amorphous ferromagnets
Authors: Fähnle M. , Egami T.
Published: February 2003

A single-ion anisotropy mechanism is considered to discuss the volume average of magnetostriction in macroscopically isotropic amorphous ferromagnetic alloys. Within the framework of our phenomenological theory, the macroscopic magnetostrictive strain vanishes only if the volume average of the local anisotropy coefficients vanishes. In contrast, in crystalline materials magnetostriction vanishes if the strain derivative of the anisotropy coefficient vanishes. In transition metal base amorphous ferromagnets the theory satisfactorily explains the observed value of magnetostriction.
Abstract: Quadrupole energy shifts of low temperature iron Mössbauer lines in amorphous magnets
Authors: Eibschütz M. , Lines M. E.
Published: February 2003

The 57Fe Mössbauer effect has been used to study the hyperfine Zeeman pattern below the spin ordering or spin freezing temperature in amorphous magnets. At very low temperatures, for which the electronic magnet moments approach their saturation values, it is a common dictum of the amorphous Mössbauer literature that the effects of quadrupole energy are now contained only in the linewidths and line shapes of the six Mössbauer lines and not in their positions.1,2 A previously unsuspected quadrupole shift of the nuclear Zeeman lines in amorphous magnets has been observed by 57Fe Mössbauer spectroscopy in speromagnetic amorphous yttrium iron garnet of 4.2 K. The distinctive shift pattern, with the symmetry −3, +1, −1, +1, −1, +3, is shown to arise theoretically as a second-order perturbation of the Zeeman levels by the distribution of electric field gradients in the amorphous state. It is observed to have a magnitude which conforms quantitatively with the theoretical expectation.      1T. E. Sharon and C. C. Tsuei, Phys. Rev. B 5, 1047, (1972).  2C. L. Chien and R. Hasegawa, Phys. Rev. B 16, 3024 (1977).
Giant coercivities and chemical short-range order in Pr-Ga-Fe metallic glasses
Authors: Cornelison S. G. , Sellmyer D. J. , Zhao J. G. , Chen Z. D.
Published: February 2003

Results of magnetic, Mössbauer, and structural studies are presented for (Pr80Ga20)100−xFex metallic glasses, where 0⩽x⩽30. For x⩾20 two magnetic transitions are observed and the structural studies indicate the presence of a phase separation into at least two glassy phases, one being Fe-rich and the other Fe-deficient. Coercivities above 60 kOe are observed and the results are discussed in terms of a model involving the magnetic properties of the two phases.
Rare-earth transition metal exchange interactions in amorphous (Fe0.82B0.18)0.9RxLa0.1−x alloys
Authors: Koon N. C. , Das B. N. , Geohegan J. A. , Forester D. W.
Published: February 2003

We have estimated the rare-earth subnetwork magnetization near room temperature for a series of amorphous melt-quenched alloys having the compositions (Fe0.82B0.18)0.9RxLa0.1−x, where R = Pr, Nd, Sm, Gd, Tb, Dy, Ho, and Er, by using a combination of bulk magnetization and Mössbauer measurements. To a good approximation the magnetization of the rare earths can be described by a molecular field which is proportional both to the iron subnetwork magnetization and the spin part of the rare-earth moment. The Curie temperatures exhibit small but systematic variations which are also in good qualitative agreement with mean field theory.
Crystal electric field and local symmetry in rare-earth amorphous alloys
Authors: Bieri J. B. , Sanchez J. , Fert A. , Bertrand D. , Fert A. R.
Published: February 2003

Amorphous alloys containing small concentrations of rare earths exhibit very different magnetic properties for Pr (strong singlet ground state effects), Tm (smaller singlet effects), and Dy or Er (small deviations from the free ion behavior). All the experimental results for different rare earths in a given host can be accounted for by a unique distribution of nonuniaxial quadratic crystal fields. The distribution of local symmetries is not consistent with random dense packing of hard spheres and suggests well defined local angular correlations.
A comparison of random anisotropy and spin glass properties in several amorphous rare-earth alloys
Authors: von Molnar S. , Barbara B. , McGuire T. R. , Gambino R.
Published: February 2003

We report magnetic measurements on the amorphous (a) alloys a-Dy0.52Cu0.48, a-Gd0.52Ag0.48, and a-Gd0.37 Al0.63. We compare the first two alloys to a recent theory for random anisotropy systems and conclude that both alloys display some but not all aspects of the theory. We also show that their magnetic properties contrast with those of the spin glass a-Gd0.37Al0.63.
Time and field dependence of the magnetization in AuFe, AgMn, and ThGd spin glasses
Authors: Oseroff S. , Mesa M. , Tovar M. , Arce R.
Published: February 2003

We report time dependence measurements of the zero field cooled magnetization (MZFC) and the thermoremanent magnetization (TRM) for AuFe (2 and 4 at.%), AgMn (1 and 4 at.%), and Th1−xGdx (3⩽x⩽20 at.%) as a function of the magnetic field. The time effect behavior was similar in the three systems. The time dependence can be fitted with a log (t) law when the temperature T is not too close to the reversible temperature TR at which the magnetization becomes reversible. The rate of the TRM decay increased with H, presented a maximum with T, and extrapolated to zero when T→TR.
Powder metallurgy processing of CrCoFe permanent magnet alloys containing 5–25 wt. % Co
Authors: Green M. L. , Sherwood R. C. , Wong C. C.
Published: February 2003

Permanent magnet alloys in the CrCoFe family and containing 5–25 wt. % Co and 18–31 wt. % Cr have been prepared by a variety of powder metallurgical techniques. Dense (relative density generally greater than 95%) samples of these alloys were prepared by solid-state or liquid-phase sintering of elemental or prealloyed powder compacts, followed by magnetic-field aging to develop magnetic properties. The residual porosity in the alloys gave rise to lower flux density and maximum energy product as compared to cast alloys; however, the coercive force is generally higher. By maximizing alloy density, excellent magnetic properties may be obtained: 5Co-31Cr-64Fe, Br = 12.3 kG, Hc = 500 Oe, (BH)max = 4.4 MG Oe; 12Co-25Cr-63Fe, Br = 14.0 kG, Hc = 551 Oe, (BH)max = 5.2 MG Oe; 25Co-29.5Cr-3Mo-42.5Fe, Br = 11.1 kG, Hc = 782 Oe, (BH)max = 4.4 MG Oe.
Melt-spun R0.4Fe0.6 alloys: Dependence of coercivity on quench rate
Authors: Croat J. J. , Herbst J. F.
Published: February 2003

We report the hard magnetic properties and crystallization behavior of several R0.4Fe0.6 alloys (R = Pr, Sm, Gd, Tb, Er) prepared by the melt-spinning technique. In particular, we find that the coercivity of each alloy exhibits a maximum as a function of quench rate, which was controlled by varying the surface velocity of the rotating substrate. Pr0.4Fe0.6 develops an intrinsic room-temperature coercivity maximum of 7.5 kOe. The corresponding value for Sm0.4Fe0.6, whose properties change dramatically with cooling rate, is 24 kOe.
Laser processing for reducing core loss of grain oriented silicon steel
Authors: Iuchi T. , Yamaguchi S. , Ichiyama T. , Nakamura M. , Ishimoto T. , Kuroki K.
Published: February 2003

A nonconstact technique for reducing the core loss of a grain oriented silicon steel has been developed by the use of Q-switched laser irradiation. Vaporization of the surface layer of the silicon steel by the laser irradiation induced a stress which resulted in a refinement of 180° domain wall spacing. This phenomenon reduced the core loss of the steel. It was found that the laser irradiation was more effective in a specimen with a higher magnetic induction and the core loss reduced by more than 10% under the optimum condition of the laser irradiation. Since the laser processing is a noncontact technique, it is easily applicable to the production line of the silicon steel.
Effect of tensile stress on magnetic properties of oriented alloys with residual sulfur
Authors: Foster K.
Published: February 2003

Applied tensile stress was shown to reduce core loss in two types of experimetal (110) [001] oriented alloys with residual sulfur contents: continuously strip annealed 3% Si-Fe and iron-base alloys containing less than 2% Si textured by a primary recrystallization and normal grain growth mechanism. Application of 700 psi (5 MPa) to a 3% Si-Fe sample containing 0.018% S resulted in a decrease of Hc from 0.17 to 0.13 Oe and a decrease in 60 Hz, 15 kG core loss from 1.40 to 1.26 W/kg. Similar reductions in Hc and loss were obtained by the application of a ’’high stress’’ glass coating to the same sample. Reductions of Hc and core loss were observed in primary textured iron-base alloys with additions of 0.005% S. In highly textured material, loss decreases with tension included both reductions in hysteresis loss and domain loss.
Properties of grain oriented 3% silicon steel for transformers with minimum cost of ownership
Authors: Littmann Martin F.
Published: February 2003

The dependence of total loss on thickness at inductions of 1.0–1.7 T is shown for commerical regular grain oriented and high-permeability 3% silicon-iron with nearly constant grain size and permeability at 800 A/m. As energy evaluations increase, minimum cost of transformer ownership may be attained with regular grain oriented material less than 0.27 mm thick operated at inductions of 1.5 T or less.
The influence of annealing conditions on the internal oxidation and magnetic properties of silicon-aluminum bearing electrical steels
Authors: Lyudkovsky G. , Preban A. G. , Shapiro J. M.
Published: February 2003

Internal oxidation often occurs in electrical steels during decarburization anneals of sufficiently long time and high oxygen potential, resulting in deterioration of magnetic properties. Relationships between subscale thickness, anneal time, and effective oxygen potential of the anneal atmosphere were established for a Si-Al-bearing electrical steel. These kinetics are described by a Rhines diffusion equation modified to accommodate the oxygen potential. Electron microprobe and Auger spectroscopy confirmed the significance of solute element diffusion. Permeability at 1.5 T was found to decrease about 50 units for each micron of subscale thickness, while core loss remained essentially constant. SEM observations of the fine structure were used to estimate that the coercivity of the subscale is sufficiently high that this region is barely magnetized. Thus, the induction of the clean interior metal must be higher than the measured average value, resulting in reduced apparent permeability. Good agreement with observation was obtained.
Magnetic properties of lithium zinc ferrite
Authors: Patton C. E. , Edmondson C. A. , Liu Y. H.
Published: February 2003

The magnetization of Li-Zn ferrite, Li0.5−x/2ZnxFe2.5−x/2O4, with x = 0 to x = 1.0 Zn at./f.u. has been examined over the temperature range 4–950 K and for fields up to 90 kOe. Magnetization M and high-field incremental susceptibility χinc were compared with a calculation based on a localized canting model. A qualitative fit was found for M versus x for an exchange ratio JAB/JBB = 3–4, but the experimental and theoretical χinc versus x results were completely different. On the other hand, a good correlation was found between χinc and the probability of a B-site Fe having only one A-site Fe neighbor. The data also reveal low-temperature maxima in M in the 30–80 K range for x = 0.4 up to 1.0; the effect is most pronounced for x = 0.7. Weak mictomagnetic behavior is found for x = 0.5 and 0.6. Samples with x = 0.9 and 1.0 show no spontaneous moment down to 4 K, but exhibit initial susceptibility maxima at about 15 K with extrapolated Curie temperatures of 10 K and 4 K, respectively. For x = 0.8, a Curie temperature of 238 K is obtained. These are considerably lower than literature values.
Iron losses in turbogenerator teeth
Authors: Young F. J. , Schenk H. L.
Published: February 2003

The flux density was measured in a typical tooth of a 500-MV A synchronous generator. Peak flux densities of 14.3, 16.9, and 21.2 kG were observed in an open circuit test at 80%, 100%, and 125% of rated voltage. The search coil voltage waveforms were rich in odd harmonics tending toward a square wave. These voltages were reproduced in an Epstein test frame for the purpose of measuring the core loss in the generator material (M-14), a singly oriented and a cube-textured material. When the turbogenerator tooth flux density waveform was reproduced in the Epstein frame, the measured losses were less than the loss under sinusoidal conditions at all values of induction for all three materials. The less oriented the test material, the greater the relative decrease in losses under the observed tooth flux density wave form. These results are in agreement with an earlier work which established that a square waveform of rate of change of induction produces a minimum core loss.1
Magnetic aftereffect in zero magnetostriction amorphous alloys
Authors: Jagielinski T.
Published: February 2003

The magnetic aftereffect and its dependence on annealing have been measured in a zero magnetostrictive Fe4.7Co70.3Si15B10 amorphous alloy. The relaxation strength depends sensitively on the magnetizing ac field amplitude. It also depends on annealing temperature and time in a complex manner. There is a critical field at which the permeability changes abruptly. This field corresponds to the unpinning (stabilization) field of domain walls. The observed behavior can be explained in terms of two main processes: the irreversible stress relaxation and the reversible changes in short range order associated with the local induced anisotropy.
Magnetization and crystallization of transition metal-boron metallic glasses
Authors: Chattopadhyay S.
Published: February 2003

Magnetic properties of amorphous (Fe1–xNix)75B25 (for 0⩽x⩽0.7) alloys prepared by chill block melt spinning have been studied with a vibrating sample magnetometer in the temperature range 4.2–300 °K. The average magnetic moment/transition metal atom at 0 °K decreases linearly with increasing nickel concentration. The temperature dependence of magnetization is in good agreement with the Bloch law Ms(T) = Ms (0) (1−BT3/2) with values of B ranging from 1.3×10−5 to 6×10−5 K−3/2 (for 0⩽x⩽0.7). The ratio (D/Tc), which is a measure of the exchange interaction, remains practically independent of the nickel concentration. The crystallization of these alloys were studied by differential scanning calorimetry, x-ray diffraction, and transmission electron microscopy. All of the results indicate that the crystallization temperature of the ternary glasses is somewhat increased compared to that of the binaries. The effect of composition on the thermal stability of the amorphous alloys and the structure of the stable and metastable crystalline phases is reported.
Anisotropy of the Faraday rotation in erbium-yttrium iron garnet below the compensation temperature
Authors: Feldmann P. , Le Gall H. , Guillot M. , Marchand A.
Published: February 2003

Faraday rotation has been measured in (Er2.2Y0.8)Fe5O12 crystals in the 11–300-K temperature range in a magnetic field along the three main crystallographic directions. A strong anisotropy is observed below the compensation temperature, which vanishes at the compensation. The origin of this anisotropy is discussed and it is shown that the magnetization cannot account for the whole Faraday rotation anisotropy and that the magneto-optical coefficient Ce of electric dipole type transitions is anisotropic. A comparison between (Er2.2Y0.8)IG and pure ErIG results is given. The strong anisotropy is tentatively related to the noncollinear magnetic structure observed below the compensation.
Damage evaluation for ion-implanted garnet layer by Monte Carlo technique
Authors: Matsutera H. , Esho S. , Hidaka Y.
Published: February 2003

A Monte Carlo simulation technique has been developed to investigate damage generation mechanisms in H+ and Ne+ implanted garnet layers. Calculation of ion scattering process and energy loss process reveals that less than 10% of H+ ion collisions with garnet nuclei generate damage, which is caused by relatively small displacement of knocked-on oxygen nuclei in the garnet layer. On the other hand, more than 80% of Ne+ ion collisions with garnet nuclei generate damage, which is mainly caused by not only relatively large displacement of knocked-out oxygen nuclei but by displacement of secondarily knocked-on oxygen nuclei generated by the knocked-out oxygen nuclei. This implies marked differences in magnetic properties between H+ and Ne+ implanted layers.
Annealing effects on the crystalline and magnetic properties of neon implanted garnet layers
Authors: de Roode W. H. , Algra H. A.
Published: February 2003

A study has been made of the annealing effects on the magnetic and crystalline properties of neon implanted garnet layers by means of ferromagnetic resonance and X-ray double-crystal diffraction measurements. Epitaxially grown films of Tm,Ca,Ge:YIG (implanted with neon at 300 keV and doses of 5×1013, 1×1014, and 1×1016 ions/cm2) were annealed in air at temperatures between 150 °C and 900 °C. Nondestructive determination of the strain profiles, by means of computer simulations of the observed fringe patterns in the X-ray double-crystal spectra, show that upon annealing after implantation doses up to 1×1014 ions/cm2 only the maximum strain decreases, while both the thickness and the shape of the strain profile of the implanted layer remain unchanged. The strain relief observed on annealing is assigned to three different processes: (i) restoration of the oxygen-cation geometry; (ii) restoration of the garnet lattice geometry; and (iii) annealing of formed dislocations. The effective anisotropy field (Keffu/M) as deduced from the FMR measurements, showed upon annealing a behavior similar to that shown by the maximum strain values. In fact, it appears that, except for the sample implanted with a dose of 1×1016 ions/cm2, Keffu/M is linearly dependent on the maximum strain.
Angular dependence of GdFe and GdCo FMR spectra
Authors: Ng W. , Soohoo R. F. , Taylor R. C.
Published: February 2003

The ferromagnetic resonance spectra of a series of GdFe and GdCo amorphous bubble films have been measured with the static magnetic field H↘s applied at various angles to the film normal. A typical spectrum exhibits two or more peaks. The relative position of these peaks changes as the direction of H↘s is changed in such a way that at some field angles, the peaks may be widely separated, while at others they strongly overlap. To analyze these results, a computer program was developed to find the best fit to these spectra by adjusting the effective anisotropy field Hk′ = Hk-4πMs and gyromagnetic ratio γ. The effective g-values obtained agree very well with the Wangness formula, especially if the spectra for H↘s nearly normal to the film are excluded from the computer analysis. In these cases, spin wave excitation renders the determination of the uniform peak position difficult. The multiple-peak spectra obtained indicate the existence of sample inhomogeneities and the Hk′ and γ values deduced from our analysis throw some light on the nature of these inhomogeneities.
Magnetic anisotropy of Ho2Co17 and Ho2Fe17
Authors: Sarkis Angie , Callen Earl
Published: February 2003

The magnetic anisotropy energy K1, the energy to rotate the magnetization from the easy basal plane to the unique axis, has been measured in Ho2Co17 and Ho2Fe17, both by the magnetization curve and by neutron diffraction. Neutron diffraction studies have been taken to imply a K1 for Ho2Co17 a factor eleven times larger than that measured by magnetization measurements. For Ho2Fe17 the discrepancy may be as large, if one also takes K2 into account. We show that the two sets of measurements are compatible; what has obscured the interpretation of the measurements is the canting of the rare earth and transition metal moments, induced by the field and by the anisotropy torques.
Magnetic anisotropy of R2[Co1−xFex]17
Authors: Callen Earl
Published: February 2003

The magnetic anisotropy (temperature-composition) phase diagram of the rare-earth compounds R2[Co1−xFex]17 can be rationalized by taking account of the magnetic anisotropy of the background Co-Fe, the shape of the rare-earth 4f charge cloud, the dependence of TC on x, and therefore, the strong composition dependence, at fixed temperature, of the rare-earth magnetic anisotropy. This suggests two phase diagrams, one for oblate and one for prolate ions. For the first set (Pr, Nd, Tb, Dy, Ho), the easy direction should be in the plane except within a U-shaped region above a spin reorientation boundary extending roughly from x = 0.05 to x = 0.5. For the prolate ions (Sm, Er, Tm, Yb), there should be two isolated easy plane regions: one at temperatures above Tsr and for 0⩽x<0.05, the other above Tsr and for 0.5<x⩽1, or so. The rest of the (T, x) plane should be easy axis.