bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetoresistance of amorphous alloys: Weak localization in three-dimensional metallic systems
Authors: Bieri J. B. , Fert A. , Creuzet G. , Ousset J. C.
Published: February 2003

We have observed an anomalous magnetoresistance at low temperature in amorphous CuZr alloys. This magnetoresistance can be accounted for in theoretical models of localization for three-dimensional metallic systems in the presence of strong spin-orbit interaction (with a significant additional contribution from the quenching of superconducting fluctuations at the lowest temperatures). We also report on similar results observed in CuTi and CuLu alloys.
Magnetic and transport properties of Co-Pt thin films
Authors: McGuire T. R. , Aboaf J. A. , Klokholm E.
Published: February 2003

Crystalline films of CoxPt1−x were prepared over the range of x=0.26 to 0.84 atomic fraction by rf sputtering. Magnetization measurements show a wide range of anisotropy conditions including perpendicular anisotropy at intermediate compositions. The magnetic moment per formula unit of Co-Pt increases with dilution which we attribute to a platinum moment of ≊0.3 μB over the entire range of compositions. The Hall effect and anisotropic magnetoresistance are both large at x≊0.4.
Anomalous behavior of the spin disorder resistivity of (La,RE)Sn3
Authors: Bautista G. , Klein R. B. , Crow J. E.
Published: February 2003

The temperature dependence of the spin disorder resistivity in dilute alloys of La1−xRExSn3 has been measured for RE=Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, and Er with x<0.10 and 1.5<T<300 K. The scaling of the high temperature incremental resistivity per rare-earth ion, Δρ/Δx, versus rare-earth atomic number is anomalous when compared to the variation typically seen in rare earth alloys and intermetallic systems. This quantity is larger for the lighter rare earths as compared to that measured for Gd and the heavier rare earths. For the lighter half of the RE series, the variation of the superconducting transition temperature depression rate ΔTs/Δx for (La,RE)Sn3 resembles the variation in Δρ/Δx. In addition, the temperature dependence of Δρ(T)/Δx for several rare-earth impurities is unusual. In particular, Δρ(T)/Δx for (La,Tb)Sn3 has a negative coefficient of resistivity at high temperatures with a maximum in the vicinity of 25 K. This anomalous temperature dependence can be accounted for by a first Born approximation calculation of the resistivity with the inclusion of both exchange and aspherical coulomb scattering in the presence of a crystalline electric field.
Resistivity and superconducting transition temperature dependence in the La1−xUxSn3 system
Authors: Lin C. L. , Zhou L. W. , Crow J. E.
Published: February 2003

It has been established that the magnetic character of U alloys and intermetallic compounds is strongly correlated with the average U–U separation. The electrical resistivity, superconducting transition temperature, and room-temperature lattice parameter have been measured for La1−xUxSn3 to examine manifestations of a changing U–U separation on the magnetic character of the U ion in this system. The properties were measured from 1.5 to 300 K for x=0 to 1. The temperature dependence of the total electrical resistivity minus the phonon contribution for x<0.3 has a negative temperature coefficient at high temperatures and passes through a maximum in the vicinity of 50 K. For x>0.3 and x<0.8, the maximum in this quantity is shifted to lower temperatures and for x=0.9 and 1.0, the resistivity minus phonon contributions decrease monotonically with decreasing temperatures and goes to zero at T2. The x dependence of the lattice parameter follows Vegard’s Law over the entire region. The x dependence of the superconducting transition temperature and the x and temperature dependence of the electrical resistivity are presented.
Magnetic and electrical properties of ilvaite
Authors: Coey J. M. D. , Allan Jacqueline , Xuemin Kan , Van Dang Nguyen , Ghose Subrata
Published: February 2003

Electrical conductivity, magnetization, magnetic susceptibility, and Mössbauer spectra are reported for three samples of ilvaite, a mixed-valence iron silicate with ideal composition CaFe2+2Fe3+Si2O8(OH). The Néel temperature is 118±3 K, but there is evidence from the susceptibility for competing antiferromagnetic and ferromagnetic exchange interactions. Analysis of the Mössbauer spectra at 4.2 K for Fe2+ at A and B sites, shows that e2qQ is positive and η∼0, indicating pseudotetragonal local symmetry and orbital singlet ground states for both ions. A peak found at 40 K in the susceptibility measured with the field perpendicular to the c axis may be related to the temperature dependence of the Fe2+ single-ion anisotropy.
L
III absorption studies of the mixed valence systems Ce(Rh1−xRux)2 and Ce(Rh1−yPty)2
Authors: Mihalisin T. , Harrus A. , Raaen S. , Parks R. D.
Published: February 2003

The valence of Ce in Ce(Rh1−xRux)2 and Ce(Rh1−yPty)2 has been measured by LIII absorption. The valence of Ce is constant at 3.0 for Ce(Rh1−yPty)2 samples from CePt2 to Ce(Rh0.5Pt0.5)2, then varies smoothly to 3.13 at CeRh2 and 3.20 at CeRu2. The lattice constants for this system have also been measured. Ce valences inferred from Vegard’s law are compared to the LIII determined values.
Resistivity, susceptibility, and superconductivity in mixed valent Ce(Rh1−xRux)2
Authors: Harrus A. , Timlin J. , Mihalisin T. , Batlogg B.
Published: February 2003

Resistivity, susceptibility, and superconducting transition temperatures Tc have been measured for the Ce(Rh1−xRux)2 system. Tc is depressed from ∼6 K for CeRu2 to zero at ∼Ce(Rh0.5Ru0.5)2. Striking violations of Nordheim’s and Matthiessen’s rules are observed for the resistivity in not only Ce(Rh1−xRux)2 but also La(Rh1−xRux)2 suggesting that large changes in d-electron spin fluctuations may be occurring. Striking variations in the susceptibility behavior are also observed across the Ce(Rh1−xRux)2 system.
Impurities in the heavy-fermion superconductor UBe13 (invited)
Authors: Smith J. L. , Fisk Z. , Willis J. O. , Batlogg B. , Ott H. R.
Published: February 2003

Small amounts of Sc, Lu, Gd, Np, Ce, Th, La, and Ba have been substituted for uranium in UBe13 to observe their effects on the superconducting and normal state properties. The thorium, which was the most complete study, resulted in an extremely unusual nonmonotonic depression of the transition temperature for a nonmagnetic impurity. This comes from an interplay that exists between the lowest temperature resistivity peak and the transition temperature, as the peak is depressed. These results suggest that heavy Fermion superconductivity is only one of the possible ground states for heavy mass electron systems. All of the impurities tested resulted in a transition temperature depression.
Magnetism and superconductivity in CeCu2Si2 single crystals
Authors: Batlogg B. , Remeika J. P. , Cooper A. S. , Fisk Z.
Published: February 2003

Single crystals of CeCu2Si2 were grown from metal solvents and their magnetic properties were systematically varied by partial substitution of Cu by Sn or In. The susceptibility χ is anisotropic and at high temperatures it is dominated by the crystal field split 4f state. At low temperatures the magnetic moments are drastically reduced. This reduction, as well as the Curie–Weiss temperature, depend sensitively upon the chemical composition. The observed variations both in the magnetic and the resistance behavior point to a Kondo-like coupling between local moments and conduction electrons. The strength of this interaction varies as the Fermi level is shifted by chemical means.
High field high pressure magnetic and superconducting properties of Y9Co7
Authors: Sarkissian B. V. B. , Beille J.
Published: February 2003

The effects of both high magnetic field and high pressure on the magnetic and superconducting properties of the compound Y9Co7 have been studied via magnetization and low field ac susceptibility measurements. The results imply that the magnetic state at ambient pressure is that of nearly ferromagnetic Fermi systems and most likely is quasi-low-dimensional in character. We find that the dependence of the magnetization on the field has the unusual form M(H)=M* exp−(H*/H),1/4 where M* and H* are temperature dependent parameters. Application of pressure rapidly suppresses the magnetic interactions whereas it enhances the superconducting transition temperature. This suggests coexistence of magnetism and superconductivity.
Effects of superconductivity on rare-earth ion dynamics in (HoxLu1−x)Rh4B4
Authors: Heffner R. H. , Cooke D. W. , Hutson R. L. , Leon M. , Schillaci M. E. , Smith J. L. , Yaouanc A. , Dodds S. A. , Gupta L. C. , MacLaughlin D. E. , Boekema C.
Published: February 2003

Zero-field muon spin-lattice relaxation rates have been measured in magnetically diluted HoxLu1−xRh4B4 ternary compounds, primarily for x=0.02. For temperatures below ∼11 K a characteristic two-component structure of the muon depolarization function is observed, which is consistent with slow (quasistatic) Ho3+-moment fluctuations. We have reported similar behavior for x=0.7, which indicates that the slow fluctuations are due to crystal-field isolation of the Ho3+ ground state. The observed relaxation rates in this temperature regime depend little on x, which is consistent with conduction-electron (Korringa) exchange scattering as the dominant mechanism for the fluctuations. The observed temperature dependence of muon spin-lattice relaxation in the superconducting state is not presently understood.
Magnetic susceptibility and superconductivity of single-crystal Ho-Mo-S Chevrel phase
Authors: Holtzberg F. , LaPlaca S. J. , McGuire T. R. , Webb R. A.
Published: February 2003

Single crystals of the Chevrel phase holmium molybdenum sulfide of approximately 0.15 mm on edge have been grown in sealed molybdenum crucibles. On the bases of microprobe and full x-ray structure analysis we find a large range of Ho concentration. Susceptibilities were measured on crystals oriented with the hexagonal c axis parallel to the applied magnetic field in the temperature range 5 to 200 K using a SHE SQUID magnetometer and a force balance. We observed a paramagnetic Curie Weiss behavior in this temperature interval with θ≊0 K and a molar Curie constant about a factor of 2 larger than the expected theoretical value of 14.1. The large value of CM suggests that the Ho spins are constrained by the crystal field to the c axis. The perpendicular susceptibility is extremely small. A superconducting transition at ∼2.4 K is measured in low fields by an ac SQUID technique.
Pressure induced superconductivity in Eu(Ho)Mo6S8
Authors: Capone D. W. , Lai Fook M. S. , Guertin R. P. , Foner S. , Hinks D. G.
Published: February 2003

The Chevrel phases EuMo6S8 and Eu-rich Eu1−xHoxMo6S8 (x=0.1 and x=0.2) are not superconducting at ambient pressure, but they become superconducting above 12 kbar, 7 and 5 kbar, respectively. The Tc maxima of Ho-doped pseudoternaries are below that of the undoped system (12 K), due to the smaller ionic radius of Ho3+ and to the pairbreaking of the large (10 μB) Ho ion moment. The superconducting-normal phase boundaries up to 20 kbar for several Eu(Ho)Mo6S8 samples are compared to those of EuMo6S8 and a La-doped sample. A Eu0.6Ho0.4Mo6S8 sample showed superconductivity at about 3 K and showed a weak maximum in Tc vs P, indicating a critical concentration of Eu (>0.7) is needed to bring about pressure induced superconductivity in EuMo6S8 based systems. The high field moment of Ho-doped EuMo6S8 at 9T is above that of fully saturated Eu2+ ions, but below that of the saturated (Eu2++Ho3+) ions together, because of crystalline electric field effects on the Ho ions. The results of this work are compared with pure EuMo6S8 and with EuMo6S8 samples having controlled oxygen content, and the data are contrasted with data for Eu(La)Mo6S8, La being a trivalent but nonmagnetic impurity.
Conduction electron spin resonance and relaxation in the superconducting state
Authors: Yafet Y. , Vier D. C. , Schultz S.
Published: February 2003

We report the first observation of conduction electron spin resonance (CESR) in both the normal and superconducting states of pure niobium. Surprisingly, the resonance displays a g value of 1.84±0.01 in both states. The linewidth narrows considerably in the superconducting state. We show that this narrowing is a consequence of the coherence factors which, in BCS theory, modify all scattering matrix elements. The relaxation linewidth for spin-orbit scattering off impurities is calculated as a function of temperature. It decreases, monotonically below Tc, in a qualitative agreement with the observed linewidth.
Low-temperature magnetic and superconducting behavior of some magnetic impurity substituted Y9Co7 compounds
Authors: Sarkissian B. V. B. , Tholence J. L.
Published: February 2003

The ac susceptibility and low-field magnetization measurements have been used to study the low-temperature (down to 70 mK) magnetic and superconducting properties of Y9Co7 substituted with 3% Ni, 0.72% Mn, and 0.5% Gd. In the Ni-substituted sample all results are indicative of itinerant weak ferromagnetism with TC =6.3 K; this sample appears to possess also some superconducting behavior below ∼0.5 K. A Mn-substituted specimen manifests significant magnetic character whereas a Gd-substituted sample shows long-range ferrimagnetic-like order at ∼8 K; neither of these specimens shows any sign of superconductivity down to 70 mK.
Magnetic structure of TbAuCu4
Authors: Kaneko T. , Abe S. , Kamigaki K. , Ohashi M. , Arai S.
Published: February 2003

The magnetic susceptibility of TbAuCu4 has been measured between 4.2 and 400 K. The results are: TN=8 K, θp=26 K, and μeff=10.1 μB. Neutron diffraction experiments were performed on powder specimen at temperatures, 4.2–20 K and 77 K. The magnetic spin structure was determined to be similar to that of MnO; the magnetic moments align ferromagnetically in sheets parallel to the (111) plane with adjacent sheets coupled antiferromagnetically. The magnetic moments are directed parallel to the (111) plane. The magnetic moment per Tb ion is obtained to be 8.9 μB.
Neutron diffraction measurement and the magnetic structure of the HoNi compound
Authors: Isikawa Y. , Mori K. , Sato K. , Ohashi M. , Yamaguchi Y.
Published: February 2003

In order to determine the magnetic structure of the HoNi intermetallic compound, a neutron diffraction measurement was carried out using a single crystal of HoNi in the temperature range from 4.2 to 78 K. At 78 K the Bragg reflections are only due to coherent nuclear scattering from the Ho and Ni atoms and the discrepancy factor R was 3%. Below 35 K the magnetic scatterings of the (102) and (201) lines increase rapidly with decreasing temperature. Below 15 K the intensity of (200) line increases rapidly with decreasing temperature, indicating that the ferromagnetic y component occurs in this temperature region. The intensity of the (100) line is zero at 78 K and very strong at 20 and 4.2 K, indicating that the antiferromagnetic z component exists at these temperatures. From these results, the magnetic structure of HoNi compound was determined.
Neutron diffraction study of the magnetic structure of the intermetallic compound DyRh2Si2
Authors: Melamud M. , Pinto H. , Felner I. , Shaked H.
Published: February 2003

A study of the magnetic structure of the intermetallic compound DyRh2Si2 (I4/mmm) was performed using neutron (2.459 Å) diffraction of a powder sample. Below 52 K the diffraction patterns reveal a type I antiferromagnetic structure on the Dy sublattice, with a magnetic moment of 9.9±1 μB per ion along c. The appearance of a weak 001 reflection below 18 K is interpreted as due to canting (∼19 °) of the Dy moment from the c axis.
Model of ferromagnetic behavior for dilute P
tFe alloys
Authors: González A. C. , Parra R. E.
Published: February 2003

A model is presented to describe the magnetization clouds of ferromagnetic dilute PtFe alloys. An expression is derived for the distribution of magnetic moments in the magnetization clouds indicating an exponential decay of the perturbation of the platinum moments due to the presence of an iron atom at the origin of the cloud. The model indicates that part of the magnetization resides in the platinum atoms, which carry moments proportional to the moments of its neighbors. The magnetization clouds are produced by first-neighbor interactions between localized moments. These interactions repeat themselves throughout the cloud producing the giant moments that have been detected by neutron and magnetization measurements.
Magnetic to nonmagnetic transition of Ce impurities in the La(Ce)(Pb1−ySny)3 system
Authors: Abou-Aly Aly I. , Teter J. , Crow J. E. , Mihalisin T.
Published: February 2003

The temperature dependence of the electrical resistivity for the La1−xCex(Pb1−ySny)3 system has been measured for x≤0.10, 0≤y≤1.0 and 1.5<T<300 K. The temperature dependence of the incremental resistivity i.e., Δρ(T), is Kondo-like for Pb-rich pseudobinary alloys and resembles the behavior predicted for localized spin fluctuations for the Sn-rich samples. The low temperature limit of Δρ(T)/x passes through a maximum in the vicinity of y=0.5. Both the temperature dependence of Δρ(T) and the y dependence of Δρ(0)/x is similar to the variation of the electrical resistivity reported for the concentrated system Ce(Pb1−ySny)3. The y-dependence of the superconducting transition temperature depression rate, ΔTs/Δx, for (La,Ce) (Pb,Sn)3 reported by Takeuchi and Masuda resembles the variation of Δρ(0)/x except that the maximum in ΔTs/Δx occurs at y=0.3.
Perturbed angular correlation studies of cold work on Heusler alloys Ni2MnGa and PdMnSb (abstract)
Authors: Jha S. , DeMarco M. , Seyoum H. M. , Julian Glenn M. , Matuson Michael , Blue James W.
Published: February 2003

Plastic deformation during cold work produces dislocations, lattice deformations, and defects in Heusler alloys. We report here the occurrence of such effects in L 21 Heusler alloy Ni2MnGa and in Clb Heusler PdMnSb. Perturbed angular correlation (PAC) study of In-111 probe substituted at the Ga site in Ni2MnGa gives B=160±1 kG, ΔB/B=0.15±0.02, and anisotropy A=0.044±0.002 for a sample annealed at 900 °C; B=157±4 kG, ΔB/B=0.22±0.12, and A=0.016±0.006 after grinding. Further annealing and grinding reproducibly restored then reduced the the anisotropy. Similar studies of In-111 at the Sb site in PdMnSb gave B=220±2 kG, ΔB/B=0.08±0.03, and A=0.052±0.009 for an annealed sample; B=222±4 kG, ΔB/B=0.26±0.06, A=0.010±0.001 after grinding. In addition, x-ray diffraction studies of both alloys showed symmetrical line broadening [by a factor of about 3 on (220) line] after grinding. Broadening of the field distribution and broadening of the x-ray lines are consistent with introduction of strain by cold work. The anisotropy may have been reduced by the introduction of new frequencies which have not yet been identified.
Rapidly quenched metals for permanent magnet materials (invited)
Authors: Becker Joseph J.
Published: February 2003

When magnetically soft amorphous metals are annealed until crystallization occurs, coercive forces sometimes arise that are high enough to suggest the possibility of permanent magnet materials. This paper begins with a brief review of results in alloys not containing rare earths. Then earlier results on rare-earth-modified Fe-B alloys and on Fe-R alloys quenched at intermediate rates are reviewed. Recent experiments indicate that intrinsic coercive forces of many kOe combined with high Ms and Mr are possible in rapidly quenched alloys containing only iron, light rare earths, and glass formers. Recent work and our current results in these alloys are presented and discussed, including effects of composition, quenching rate, annealing, and etching, as well as thermomagnetic effects and phase identification.
Cobalt-free permanent magnet materials based on iron-rare-earth alloys (invited)
Authors: Hadjipanayis G. C. , Hazelton R. C. , Lawless K. R.
Published: February 2003

The magnetic properties of rapidly quenched FeRM alloys where R=La,Y,Pr,Nd,Gd and M=B,Si,Al,Ga,Ge have been investigated over a wide range of chemical compositions. The samples are generally magnetically soft in the as-quenched state. Magnetic hardening is produced by annealing the samples around 700 °C. The best properties have been obtained in samples containing Pr and Nd together with B and Si. An energy product of 13 MGOe and a coercive field of 15 kOe have been obtained in a Fe76Pr16B5Si3 sample. The higher Fe content samples appear to be more promising with a potential energy product of 49 MGOe. Thermomagnetic data show that a structural transformation takes place upon heating the samples to 700 °C. The Curie temperature of the as-quenched phase is around 160 °C while that of the new phase is around 320 °C. Transmission electron microscope studies show fine precipitates (∼100 Å) dispersed in a matrix of different chemical composition. X-ray and electron diffraction data indicate that the precipitates have the Fe21R3B tetragonal structure. The high anisotropy of this phase together with its fine size and distribution give rise to the observed high coercive fields.
Magnetic hardening in Zr-substituted 2 : 17 rare-earth permanent magnets
Authors: Hadjipanayis G. C.
Published: February 2003

The effect of Zr on the hard magnetic properties of Sm(Co0.745−xFe0.200Cu0.055Zrx)7.5 permanent magnets has been examined by correlating the coercive field with the microstructure. Optical and transmission electron microscope studies show that Zr suppresses the precipitation of a SmCoCu phase and controls the size of the grains, the size of the cells, and the formation of the lamella phase. In the Zr-free samples large spherical precipitates of a SmCoCu phase have been observed to be uniformly distributed in the matrix. The microstructure of the matrix consists of very fine precipitates with a size below 60 Å. As the Zr concentration increases, the SmCoCu phase disappears, the cell size is increased, and the coercivity increases. At a Zr content around 1.5%, low density lamellae are observed to coexist with the cellular microstructure and coercivity is maximum. At higher Zr concentrations a CoZrFe phase is formed, the density of lamellae is increased, and the coercivity decreases.
Metallurgical behavior of Sm(Co,Fe,Cu,Zr)z alloys
Authors: Ray A. E.
Published: February 2003

A model, based on the Sm-Co system between SmCo5 (1:5) and Sm2Co17 (2:17 R and 2:17 H), is proposed to describe the metallurgical behavior of Sm(Co,Fe,Cu,Zr)z alloys between 6.8<z<8.5 in the development of hard magnetic properties. The same phases are encountered in both the binary and multicomponent alloys, but the stability ranges of the 1:5 and 2:17 phases are altered by the additive elements. The following points are made: (1) Cu, and Fe in combination with Cu, extend the high temperature stability of the 2:17 R phase to lower z values; (2) Cu stabilizes the 1:5 phase relative to the 2:7 and 2:17 R phases at low temperatures; (3) low concentrations of Fe (≂5 a/o) stabilize the 2:17 R phase relative to the 1:5 phase and Co-rich solid solutions in the presence of Cu; (4) high concentrations of Fe(>10 a/o) destabilize the 2:17 R phase due to Fe-Fe pairs which preferentially occupy the dumbbell sites (6c in R3̄m); (5) Zr-vacancy pairs stabilize the 2:17 R phase at high Fe concentrations by displacing Fe-Fe pairs at the dumbbell sites; (6) high coercivity permanent magnets of the type Sm(Co,Fe,Cu,Zr)z with 6.8<z<8.5 have a partially disordered 2:17 R structure at the solutionizing temperature, and this structure is retained on quenching to room temperature. On isothermal aging, Cu is rejected from the 2:17 R phase by the formation of the Cu:rich 1-5 boundary phase, and Zr is rejected by the formation of the Zr-rich 2:17 H platelet phase.
High-coercivity 2 : 17 cobalt rare-earth magnets
Authors: Leupold H. A. , Potenziani E. , Tauber A. , Mildrum H. F.
Published: February 2003

We have extracted the coercivities, remanences, and anisotropy fields from M-H loop measurements on four permanent magnets of composition Sm1−xErx(Co,Fe,Cu,Zr)7.3 with x=0, 0, 0.2, 0.4. Room-temperature coercivities iHc were observed which are higher than those of representative commercial 2 : 17 magnets by factors ranging from three to six. Room-temperature coercivity to anisotropy field ratios are extraordinarily high, ranging from 0.15 to 0.25. A pulsed magnetizing field of 60 kOe was insufficient to produce the latter result which was obtained only after exposure of the sample to 90 kOe. All of the specimens displayed demagnetization curves linear over the entire second quadrant, with slopes μr ranging from 1.1 to 1.4. Excellent temperature coefficients α with a good energy product (BH)max were obtained for x=0.4, with α=0.01%/K from 300 to 425 K and 0.005%/K from 225–300 K and (BH)max=16 MGOe.
Spinodal decomposition and magnetic hardening of Fe-23Cr-15Co-2Mo-0.5Ti permanent magnets
Authors: Run Wang , Jufang Chen , Shouzeng Zhou
Published: February 2003

Spinodal decomposition and magnetic hardening of Fe-23Cr-15Co-2Mo-0.5Ti alloy were studied by magnetic measurement, transmission electron microscopy (TEM), Mössbauer effect, and observation of magnetic domains after thermomagnetic treatment (TMT) and multiple step aging.
Microduplex Fe-Ni-Mo semihard magnet alloys
Authors: Tiefel T. H. , Jin S.
Published: February 2003

Cobalt-free, semihard magnet alloys based on the Fe-Ni-Mo system have been developed for potential substitution of Co-Fe base alloys such as Vicalloy I (52Co-38Fe-10V) for use in magnetic devices where ductility is required for processing into thin strips. Desirable magnetic properties for Fe-20Ni-4∼6 Mo alloys of Br∼4000–16 000 G, Hc∼20–220 Oe, Br/Bs∼0.8–0.99 can be achieved through processing which produces a microduplex, aligned and elongated multiphase structure. This structure is obtained by a combination of initial plastic deformation, two-phase decomposition in the (α+γ) region, final deformation, and final low temperature precipitation aging. The alloys are ductile and easy to process, and in the final aged condition have high strengths (0.2% yield strength=100∼200 ksi), which could be useful in applications where both magnetic and mechanical strength as well as ductility are required.
Theory of ferromagnetic hysteresis (invited)
Authors: Jiles D. C. , Atherton D. L.
Published: February 2003

A mathematical theory of hysteresis in ferromagnetic materials is presented based on existing ideas of domain wall motion and domain rotation. Hysteresis is shown to occur as a result of impedances to changes of magnetization such as when domain walls are pinned, while the mutual interactions of the magnetic moments are shown to be of secondary importance in this respect. An equation for the anhysteretic or ideal magnetization curve is derived based on a mean field approximation and this is shown to be dependent on the mutual interactions of the moments but independent of impedances such as pinning. The introduction of a term which measures the impedance to changes in magnetization leads to a simple differential equation of state for a ferromagnet which exhibits all the features of hysteresis. Some modifications of the simple model are necessary in order to bring the solution closer to the real situation. Results are presented which show all the features of hysteresis such as initial magnetization curve, major hysteresis loops, and minor hysteresis loops in excellent agreement with experimental results.
Effect of laser scribing on the magnetic properties and domain structure of high-permeability 3% Si-Fe
Authors: Krause R. F. , Rauch G. C. , Kasner W. H. , Miller R. A.
Published: February 2003

Localized laser heating was used to alter the magnetic characteristics and domain size of high-permeability grain-oriented silicon steel. A continuous-wave CO2 laser was used to scribe narrow transverse stripes on fully processed, Forsterite-coated strip. The laser power was maintained at 32 W, and the power density applied to the strip was controlled by varying the scan speed. The spacing of the scribe lines was varied between 3 and 13 mm. A decrease in core loss was observed at a scan speed of 169 mm/s and a scribe spacing of 6 mm. Losses decreased 9% at 1.7 T and 18% at 1.0 T. A maze domain structure, indicative of a compressive stress, was observed in the laser-affected regions. The average 180° domain size was reduced by scribing; as the scan speed was reduced and the scribe spacing decreased, the domain size decreased. Although the Forsterite coating was not visibly damaged by the laser heating, polishing and etching of the steel substrate revealed localized slip lines in the laser-affected zones. The hysteresis loss component was increased by laser scribing, and thus we attribute the observed loss reduction to a decrease in the eddy current loss component caused by the decrease in domain wall spacing.
Soft magnetic properties of a ferritic Fe-Ni-Cr alloy
Authors: Jin S. , Sherwood R. C. , Chin G. Y. , Wernick J. H. , Bordelon C. M.
Published: February 2003

Technologically important applications may exist for magnetically soft alloys that possess, in addition to the appropriate magnetic properties, relatively high mechanical strength and corrosion resistance. Such an alloy can be used, for example, for certain types of telephone receiver armature applications. In the present paper, we report the magnetic and mechanical properties of the ternary Fe-3Ni-5Cr alloy. The soft magnetic properties of the alloy are significantly improved by heat treatment within the (α+γ) two-phase region. Exemplary properties after heat treatment at ∼625 °C for 2 h are Hc∼1.2 Oe, μm∼4700, yield strength ∼59 ksi, and elongation ∼30%. The alloy exhibits reasonably good corrosion resistance. Magnetic, mechanical, and electrical properties of the alloy as well as the acoustic performance of telephone receivers using it, have been found to be comparable to those of the 2V-Permendur alloy.
Solid solutions of MnSb as recording media in optical memory applications
Authors: Seshu Bai V. , Rama Rao K. V. S.
Published: February 2003

We show in this paper that many of the difficulties, encountered in using the ferromagnetic MnSb films as storage media in memory devices employing the technique of laser Curie point writing and magneto-optic readout, can be overcome by forming solid solutions of MnSb with Fe, Co, In, and excess Mn, viz. Mn1−xFexSb, Mn1−xCoxSb, MnSb1−xInx and Mn1+xSb (0≤x≤0.25 or 0.3). Spins that are in basal plane of MnSb at 300 K are found to reorient to be along the film normal, from ferromagnetic resonance work, beyond a critical composition (xc=0.16, 0.21, 0.16, and 0.14 for the systems containing Co, Fe, In, and excess Mn, respectively) ensuring a large readout efficiency. Moreover, the lowering of Curie temperature for higher compositions can enable us to work with low power lasers which help to achieve sharper writing without diffusion of heat into neighboring domains. In addition, the absence of any crystallographic phase transformation in the temperature range of operation (unlike in MnBi) makes the MnSb alloys potentially more attractive for use as recording media.
Optical study of hydrogen diffusion in yttrium iron garnet
Authors: Milani E. , Paroli P.
Published: February 2003

Hydrogen diffusion in magnetic garnets is of interest in connection with both H+ ion implantation in bubble films and the proposed application to high-temperature chemical sensors. We have investigated hydrogen diffusion in several pure and doped YIG samples, using optical absorption and magnetic circular dichroism as probes. Differently from the previously reported cases of F− ions and oxygen vacancies, H+ ions are found to diffuse in YIG not obeying the classical diffusion equation. At constant temperature, simple exponential time behaviors are observed, and the time constants are much shorter for inward than for outward diffusion. These facts indicate that a major role is played by surface effects. H+ diffusion in YIG is accompanied by neither additional absorption nor dichroism at wavelengths λ>1.1 μm, so that charge compensation must involve centers of very different character, and more strongly bound, than Fe2+ induced by tetravalent ion dopings. In Ca2+- and Pb2+-doped YIG, besides the absorption peak due to the OH− stretching, a broad peak at λ=3.6 μm is found, similar to that previously reported for YIG(Na): the interaction of the OH− group with dodecahedral low valence ions is thus apparent. For T≤100 K, additional absorption structures arise at λ=3.15 μm indicating the formation of new equilibrium states for the H+ ion.
Finite element modeling of permanent magnet devices
Authors: Brauer J. R. , Larkin L. A. , Overbye V. D.
Published: February 2003

New techniques are presented for finite element modeling of permanent magnets in magnetic devices such as motors and generators. These techniques extend a previous sheet-current permanent magnet model that applies only for straight line B-H loops and rectangular-shaped magnets. Here Maxwell’s equations are used to derive the model of a permanent magnet having a general curved B-H loop and any geometric shape. The model enables a nonlinear magnetic finite element program to use Newton–Raphson iteration to solve for saturable magnetic fields in a wide variety of devices containing permanent magnets and steels. The techniques are applied to a brushless dc motor with irregular-shaped permanent magnets. The calculated motor torque agrees well with measured torque.
Calculation of the reversible part of the magnetization curves at any angle to the rolling direction for polycrystalline silicon steel
Authors: Del Vecchio R. M.
Published: February 2003

Polycrystalline Goss oriented electrical steel contains a distribution of grain orientations which has been shown, in previous work, to be characterized by one rms angle. Approximating the grains by long rods, theoretical single crystal reversible magnetization curves were averaged over the empirical grain directional distribution and the results compared with experimental curves above the knee where the magnetization is predominantly reversible. When the rms angle is chosen to give a best fit to the magnetization curve in the rolling direction, good fits are obtained for the family of magnetization curves at other angles to the rolling direction. The empirical relation between the induction at 10 Oe, B10, and rms angle is also reproduced. The methods described here may be used for electrical steel having any specified orientation.
Partially saturated ferromagnetic cylinders
Authors: Templeton T. L. , Arrott A. S. , Aharoni Amikam
Published: February 2003

The magnetostatics of a partially saturated ferromagnetic cylinder are calculated for the case where the susceptibility is infinite in the unsaturated region and Ms points along the direction of the internal field Hi for the saturated regions. The boundaries between the regions, the volume charge (∇⋅Ms) in the saturated regions and all the surface charges (n̂⋅M) are found by parameterization of the scalar potential, the surface charge distribution and the interfaces. The parameters are varied to minimize the deviation from Hi=0 in the unsaturated regions and the deviation from ∇⋅[H+4πMsH/‖H‖]=0 in the saturated region. Parameters, such as the distance between the interfaces, follow irrational powers of H0−Hs, where the saturation starts at the applied field H0=Hs. The results are found to explain the somewhat puzzling magnetic response of partially saturated iron whiskers.
Boundary Galerkin’s approach to the calculation of eddy currents in homogeneous conductors
Authors: Mayergoyz I. D.
Published: February 2003

This paper presents a new technique for the solution of 3-D eddy current problems. According to this technique, electric field E within conductors and scalar magnetic potential φ outside the conductors are used as state variables. Eddy current problems are formulated as boundary value problems with respect to E and φ which, in turn, are reduced to two coupled boundary Galerkin’s forms on conductor surfaces. A new quasifinite element discretization technique based on these coupled boundary Galerkin’s forms is discussed.
Hybrid finite element boundary element solutions using half-space Green’s functions
Authors: Peng J. P. , Salon S. J.
Published: February 2003

The hybrid boundary element-finite element method has been used with great success in problems of electrostatics, magnetostatics, and eddy currents.1,2 The present paper extends the method to problems which have nonhomogeneous exterior regions. The paper deals with the specific case in which the region of interest is represented by finite elements and the boundary of the problem by an integral equation. The exterior of the problem is composed of two materials: one in which the finite-element region is embedded and another material region which is an infinite half-space. These regions must be linear although they may contain sources. Examples are given and the results are compared to known solutions where possible.
A composite numerical model for the coercivity of soft magnetic materials (abstract)
Authors: Sukiennicki A. , Della Torre E.
Published: February 2003

In the analysis of soft magnetic materials, in particular for materials in which magnetization change is accomplished by domain wall motion, two models have been proposed recently for the calculation of the coercive force. Each of these is valid for a different range of material parameters. Since both models were numerical in nature and compatible with each other, it has been possible to merge them into a single model that is valid for a wide range of materials. In particular the NWE model is valid for low magnetization materials and the numerical dipole repulsion model, which we shall refer to as the NDR model, is valid for high magnetization materials. These two models are merged to form the composite numerical coercivity (CNC) model, which is the subject of this paper. In the two previous models, a domain wall was pinned by the effect of nonmagnetic inclusions in a magnetic material. In the NWE model, the pinning was caused by the decrease in wall energy that was experienced when the wall intersects the inclusion. On the other hand, in the NDR model, the wall was pinned in the region outside the holes by the repulsive action of the dipole moment induced at the location of the hole. Both of these effects are present in the CNC model; however, the role played by each of them depends upon the value of the material parameters.
Studies of spacing loss in longitudinal and perpendicular recording
Authors: Kugiya F. , Koizumi M. , Okuwaki T. , Shinagawa K. , Uesaka Y. , Tamura T. , Fujiwara H.
Published: February 2003

The effect of head-to-medium spacing on longitudinal and perpendicular magnetic recording with ring heads has been clarified. Media tested are a γ-Fe2O3 particulate disk and a Co–Ni–P plated disk for longitudinal recording, and single and double layer of Co–Cr sputtered disks for perpendicular recording. Experiments are performed utilizing Mn–Zn ferrite ring heads with 0.30, 0.56, and 0.78-μm gap lengths. In addition, self-consistent calculations by finite element method, which takes into consideration head-to-medium interaction, are applied to clarify the mechanism of read spacing loss.
Anhysteretic properties of interacting magnetic tape particles
Authors: Chantrell R. W. , Lyberatos A. , Wohlfarth E. P.
Published: February 2003

The anhysteretic properties of interacting tape particles are investigated using a model based on Monte-Carlo techniques. Anhysteretic remanent magnetization curves are calculated and the growth of the magnetization during the anhysteretic process is investigated. Predictions of the model are consistent with experimental data. Modifications are proposed which are expected to improve the range of applications of the model.
Magnetization dynamics of micron size thin Permalloy films
Authors: Ozimek E. J. , Paul D. I.
Published: February 2003

The magnetic properties of thin films of NiFe Permalloy of micron dimensions have been investigated both in the presence and absence of a titanium underlayer on silicon oxidized substrates. For those samples possessing a low aspect ratio, the domain walls remain fixed almost throughout the entire range of our external field capacity of 40 Oe—this stability increasing with increasing film thickness. Magnetic moment reversal appears to occur by magnetic moment rotation within the domains rather than by domain wall motion. As the sample length increases in size, we see edge domains at either end but a lack of domain structure through the sample length. The presence of the titanium underlayer increases the stability and produces a marked asymmetry in our domain wall structure as we cycled through the B-H hysteresis loop. All samples displayed a marked increase in the coercive force compared to Permalloy thin films of large size planar dimensions.
Magnetic properties of multilayered Fe-Si films
Authors: Kumasaka N. , Saito N. , Shiroishi Y. , Shiiki K. , Fujiwara H. , Kudo M.
Published: February 2003

The coercivity and permeability of Fe-Si films can be improved by laminating several layers with either nonmagnetic (SiO2, Al2O3, Al or Mo) or ferromagnetic (Ni, Fe, Co or 20-wt. % Fe–Ni) spacers. It is also found that films made with soft magnetic laminations have an advantage over nonmagnetic or hard magnetic ones. Such behavior is concluded to be attributed to the smaller grain size, and pinhole or exchange coupling of multilayered Fe-Si films by observing domain and grain structures.
Direct measurement of recording head fields using a high-resolution inductive loop (invited)
Authors: Hoyt R. F. , Heim D. E. , Best J. S. , Horng C. T. , Horne D. E.
Published: February 2003

A method is described for direct measurement of the magnetic microfield from a recording head. The method employs a thin film ‘‘microloop’’ as a transducer which by induction senses the recording head field. Measurements are presented on both a thin film and a ferrite head. Fits to the data allow the absolute efficiency to be determined. Data on the frequency dependence of head efficiency are also presented.
A new lubrication for high-density magnetic-coated disk
Authors: Hamada M. , Fukushima S. , Suenaga T. , Itoh K. , Ogawa S.
Published: February 2003

We have developed a new lubrication method to assure sufficient mechanical durability, which enabled us to produce low-noise, error-free magnetic-coated disks having a density as high as 30 000 FRPI. Improvement of SNR at high density requires reduction of alumina particles (the film hardening agent), and so the lubrication method is of great importance. So we first investigated the relationships between the film properties, head-to-disk adhesion, and the CSS (Contact Start & Stop) durability, and found that it was essential that the lubricant be absorbed into the film. For this purpose, we finally discovered a novel lubrication method, which is to put hydrophilic resin having an ether-bonded side chain as a component of the coating binder. By this method, the amount of absorbed lubricant increases with the resin content thus greatly improving durability. The resultant disk with a film thickness of 0.4 μm shows a durability of more than 100 000-CSS cycles, extremely low noise of 6 μV rms, and good bit-error characteristics at a density of 30 000 FRPI.
Muon spin rotation in magnetic oxides (invited)
Authors: Denison Arthur B.
Published: February 2003

Systematic measurements have been made using the technique of muon spin rotation (μSR) for a series of magnetic oxides. These measurements have been made as a function of temperature and externally applied field on α-Fe2O3, Cr2O3, magnetite (Fe3O4) and a set of rare-earth orthoferrites RFeO3 (R=Sm, Eu, Dy, Ho, Y, and Er). The muon behavior is found to exhibit common features for these materials with the muon forming a weak bond near the oxygen. Local motion or delocalization may occur at lower temperatures while global diffusion or hopping to similar sites occurs at higher temperatures (>400 K). As the behavior of the muon in its chemical environment becomes understood the μSR technique may be used to study other physical effects of interest.
Angular distribution of magnetization in coated magnetic films
Authors: Habbal F. , Vetterling W. T.
Published: February 2003

Recent Möessbauer studies of magnetic films have described the orientational distribution of spins in terms of a mean angle of orientation between the spin direction and the direction of γ-ray propagation. These studies have improperly interpreted the quantity 〈sin2 θ〉, and have failed to account for the effects of saturation. We present an improved analysis which describes the spin orientational distribution in terms of an expansion in spherical harmonics. Coefficients in the expansion are determined from line intensities in the Zeeman-split spectra. A similar description, using the same distribution function, is applied to the angular dependence of the squareness of the hysteresis loop. Mössbauer results rely most heavily on the l=2 coefficients in the expansion. The magnetization, however, depends also on coefficients describing the characteristics of individual particles. Examples of the application of these techniques to films with different distributions of acicular particles are given.
Bound magnetic polarons in dilute magnetic semiconductors (invited)
Authors: Wolff P. A. , Warnock J.
Published: February 2003

Optical experiments have been used to study bound magnetic polarons (BMP) in (Cd,Mn)S, (Cd,Mn)Se and (Cd,Mn)Te. This work is surveyed, and the theory of these complexes is discussed. BMP exhibit a remarkable, continuous transition from fluctuation dominated behavior at high temperatures, to a cooperative regime at low temperatures.
Neutron scattering studies of Cd1−xMnxTe (invited)
Authors: Giebultowicz T. , Lebech B. , Buras B. , Minor W. , Kepa H. , Galazka R. R.
Published: February 2003

The diluted magnetic (‘‘semimagnetic’’) semiconductor Cd1–xMnxTe reveals intriguing spin glass properties. In this paper, the results of neutron scattering studies of Cd1–xMnxTe are presented. The low-temperature spin correlations have been studied for several single crystal samples in the composition range 0.60<x<0.70 by neutron diffraction. For all the samples Lorentzian-shaped magnetic peaks were observed at low temperatures, indicating a strong tendency toward Type III fcc antiferromagnetic order, but no evidence has been seen of a phase transition to the long-range order suggested by other experiments. The temperature dependence of the intensity and the profiles of the magnetic maxima have been measured. Some measurements of inelastic scattering in Cd0.35Mn0.65Te have also been carried out, revealing broad magnon-like maxima in the scattered spectra. Computer calculations of the elastic neutron scattering cross section and some other quantities characterizing the system have been performed using the Monte Carlo modelling method, and the accepted data for exchange interactions in Cd1–xMnxTe. The results of these calculations are discussed in the light of the experimental results.
Spin wave spectra in doped ferromagnetic semiconductors
Authors: Mauger A. , Mills D. L.
Published: February 2003

We present a theory of the magnetic excitation spectrum of ferromagnetic semiconductors and semimetals. The calculations are performed up to second order in the exchange coupling between the localized spin array Si and the free carrier spin density s(ri), using the functional differentiation technique and Green functions. A high frequency spin wave mode is found, in addition to the usual low frequency spin wave branch. The damping of both modes is found to be small at low temperatures when the free carriers are spin polarized, in which case the bottleneck limit is applicable. At high temperature where 〈sz〉→0, the spin dynamics is described by the Hasegawa equations and the Korringa relaxation term which governs the width of the magnetic resonance is recovered.