Magnetic Gd Research Articles

Magnetic isolation of Gd in superconducting GdBa2Cu3O7- delta.

The electronic and magnetic structures of Gd in superconducting GdBa/sub 2/Cu/sub 3/O/sub 7-//sub delta/ have been probed using the 86.5-keV Moessbauer resonance transition in /sup 155/Gd. The values of the hyperfine interaction parameters provide direct evidence for an absence of conduction electrons at the Gd site in this lattice and hence no exchange coupling of the Gd ion with the conduction electrons. The results explain why the superconducting transition temperature of YBa/sub 2/Cu/sub 3/O/sub 7-//sub delta/ is not suppressed by the substitution of Y atoms by magnetic Gd atoms.

Optimal properties of semimagnetic compound Pb 1− xGd xTe with x=0.01 and 0.025

Reflectivity and transmission spectra of a new semimagnetic compound Pb 1− x Gd x Te with x=0.01 in the 300-77K temperature range are reported. From reflectivity data the high dielectric constant ϵ(∞) is deduced. Lyddane-Sachs-Teller relation gives the static dielectric constant ϵ(0). The conductivity effective mass m ∗ c measured from the plasma frequency agrees well with the one deduced from absorption measurements α vs the wavelength in the short wavelength range. The energy gap as well as its temperature dependence is given by absorption data. The introduction of low concentration magnetic ion Gd does not affect drastically the optical properties of the material comparatively to the optical PbTe ones.

Weak localisation in metallic glasses. I. Magnetoresistance

The authors present magnetoresistance measurements at low temperature on a series of metallic glasses: Mg80Cu20, Cu50Lu50, Pd80Si20, Cu50Y50, Y80Si20, Cu57Zr43, CuYGd and CuLuGd. The magnetoresistance clearly exhibits three-dimensional localisation effects with a strong influence of the spin-orbit scattering: the magnetoresistance is negative for weak spin-orbit scattering (Mg80Cu20) and positive for strong spin-orbit scattering (Cu50Lu50, Pd80Si20), and changes from positive at low field to negative at high field for intermediate spin-orbit scattering (Cu50Y50, Cu57Zr43). The magnetoresistance curves can be accounted for by only localisation terms for most alloys and interaction effects are significant only for Y80Si20. An additional contribution from superconducting fluctuations is observed for the superconducting alloy Cu57Zr43. The analysis of the magnetoresistance yields the spin-orbit and inelastic scattering rates. The inelastic scattering rate of the alloys varies as T2 at high enough temperature and departs from T2 below about 5K. The measurements in a dilution refrigerator on Cu50Y50 and Y80Si20 have shown a variation as T1/2 below 1K. They discuss the possible origin of such a variation. They finally present measurements on Cu50Y50 and Y80Si20 doped with Gd. Surprisingly the addition of magnetic Gd impurities does not depress strongly the localisation effects, as would be expected from the existing theories.

De Haas-van Alphen scattering measurements on the reentrant superconductor La1-xCexAl2.

de Haas--van Alphen quantum oscillations have been seen for the first time in single crystals of ${\mathrm{LaAl}}_{2}$ heavily doped with the magnetic impurities Ce and Gd. Spin-split zeros have been detected on the \ensuremath{\Gamma}-centered sheet of the Fermi surface in pure ${\mathrm{LaAl}}_{2}$. These change to spin-split minima in the doped crystals. From these observations, along with orbitally averaged effective-mass measurements, estimates have been made of the g-value shift and the spin-dependent scattering due to the presence of the rare-earth impurities. Measurements of the scattering rate were made, as a function of temperature, in the 0.5 at. % Ce and the 0.5 at. % Gd impurity-doped crystals, for two orbits. An orbit selected for high s-p--wave character showed no temperature dependence for either impurity, whereas an orbit selected for high d-f character showed Kondo-like behavior for both the Ce- and the Gd-doped crystals. This is in contrast to the resistivity, which has a Kondo-like behavior for Ce but not for Gd doping. Dingle-temperature anisotropy has been studied on the \ensuremath{\Gamma}-centered sheet of the Fermi surface for the 0.3 at. % Ce and the 0.5 at. % Gd impurity-doped crystals, with use of three orbits of qualitatively different symmetry character. Data from the Ce-doped sample indicate the presence of extreme spin-dependent scattering for the orbit passing through four 〈100〉 directions in k space, which include a strong f-wave component. This behavior is consistent with the spin-split-minimum rotation diagrams, which show increased spin-dependent scattering as one proceeds in the direction of increasing f-wave character from 〈111〉 to 〈100〉 in the (110) plane.

Properties of rare-earth metal superlattice grown by molecular-beam epitaxy (abstract)

Metal superlattices are predicted to exhibit novel properties such as zone-folding effects of electronic bands and phonon dispersions. Heterostructures consisting of rare-earth magnetic metals Gd, Tm, and nonmagnetic elements Y, Lu with nearly perfect lattice match provide the unique opportunity of studying on the atomic scale the RKKY interaction, and the resultant magnetic ordering spin phases. However, such study would be fruitful only if the layer modulation direction coincides with the crystallographic C axis and a compositionwise sharp interface is achieved. Furthermore, because of the strong reactiveness of rare-earth metals with gas impurities, these stringent film growth requirements can be best met by molecular-beam-epitaxial technique in a UHV environment. We have grown the rare-earth metal single and multilayer films in a versatile UHV deposition system equipped with effusion cells and e-beam evaporators. The typical growth rate is 1 monolayer/s, and the typical background pressure during growth is 1.0×10−10 Torr. With the in situ RHEED characterization, the preferred film growth direction, namely C axis, is controlled by optimizing the substrate temperature, and growth planes of substrates including sapphire, mica, and single crystal yttrium. Magnetic properties including anisotropy and moments versus temperature are studied by vibrating sample magnetometry on these multilayers with modulation wavelength varying from 20 to 200 Å. Results of x-ray structure analysis, Rutherford backscattering depth profile, and the resistivity measurements will also be reported.

Emission lines in the magnetic white dwarf GD 356

GD 356 est l'unique naine blanche montrant des triplets de Zeeman resolus pour les raies d'emission Hα et Hβ

The metal-insulator transition in magnetic semiconductors: Transport in Gd−xvxS4

This note reviews magnetotransport data on the magnetic semiconductor Gd−xvxS4 (v = vacancy). New data on the metallic side of the transition are presented. The results for two samples may be summarized as follows: 1) At low temperatures (T ∼ 10 mK) the conductivity, σ(0) ∝ (H - Hc), where Hc is a critical field below which the material is an insulator; 2) for the sample with the larger critical field, the data are not consistent with variable range hopping: 3) for H/Hc ≳ 1, the temperature dependence deviates only little from a √T law.

Ferromagnetic pinning of superconducting fluxoids at the contact between Sn and Gd films

To investigate of the magnetic interaction of superconducting fluxoid with magnetic substances, coaxial multilayer samples are prepared by alternate deposition of two or three superconducting Sn or Pb (Tl) films of 2–3×10 3 Å and magnetic Gd or Y of (4±1)×10 2 Å. The measured superconducting critical current with perpendicular magnetic field H was enhanced more than ten times by the magnetic contact, and attained a value of 1.4×10 5 Acm -2 at H = 0.5 kOe, T = 4.2 K for Pb (Tl). However, no significant difference in the effect between Gd and Y was observed.

Observations of phase transitions in the mixed crystal system Dy pGd 1-pVO 4

The low temperature crystallographic and magnetic phase transitions in the mixed crystal system Dy p Gd 1- p VO 4 (0 ⩽ p ⩽ 1) have been studied using thermal expansion measurements and Mössbauer spectroscopy. The introduction of magnetic Gd 3+ ions into the DyVO 4 host causes an anomalous dip in the Néel temperature T N ( p), and a rapid reduction of the distortion temperature T D ( p) which differs from results on similar mixed systems. A number of pseudo-spin Hamiltonians that model these observations are discussed.

Magnetic moments at backbending and spectroscopy of 134Ce

Employing the static hyperfine fields at cerium nuclei in magnetized Fe and Gd hosts, the g-factor of the 134Ce(10 +) state at backbending ( E x = 3719.3 keV) has been determined as g = − 0.30 (25). The coexistence of this neutron-dominated state with the ( v h 11 2 ) n 10 + isomer ( E x = 3208.5 keV, g = −0.19(1)) is unexpected. A comprehensive spectroscopic study following the 122Sn( 16O, 4n) reaction, including γ-angular distributions, prompt and delayed γ coincidence and recoil-distance measurements has yielded new information on quasi-collective bands of both parities. The properties of the low-lying positive-parity states are well described by the interacting boson model.

Scaling of the transient magnetic field with the polarization density of the host

The transient magnetic field strength has been determined accurately for 28Si(2~) at an initial recoil velocity of vi = 1.7 vo (vo = c/137) in magnetized Fe, Co, Ni and Gd. The first-excited state of 28Si was produced with the 28Si(~,~') reaction at E~ = 7.50 MeV. Time-integral rotations of the ~-u angular correlation were measured, which led to transient-field strengths for 2esi in the four ferromagnetic hosts. These strengths were found to scale with the polarization density of the host rather than with the number of polarized electrons per host atom.

THE ULTRAVIOLET SPECTRUM OF THE MAGNETIC DEGENERATE STAR GD 229.

ABSTRACT The ultraviolet spectrum obtained with the IUE satellite of the magnetic degenerate white dwarf star GD 229 is presented. The ultraviolet energy distribution measured by the short- and long-wavelength cameras covering the range 1170-3200 A, when combined with optical data, indicates a best fit blackbody temperature of 16,000 K, which is significantly lower than previous estimates. A broad absorption trough in the 2000-3000 A region is observed which may be produced by opacity in the fundamental cyclotron frequency for surface magnetic fields from 3.2 to 5 x 10 to the 8th gauss. The absence of a strong Lyman-alpha sigma + component suggests that the primary atmospheric constituent is not hydrogen, with various absorption features probably attributable to Zeeman components of neutral helium, or possibly Mg II, C II and other metal lines. The superposition of many strong Zeeman features is also an alternative interpretation of the absorption in the 2000-3000 A interval.

Electron spin resonance ofGdxLa1−xPd3intermetallic compounds

We have extended our ESR study of Gd in the intermetallic compound ${\mathrm{Gd}}_{x}{\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Pd}}_{3}$ to samples annealed at 940\ifmmode^\circ\else\textdegree\fi{}C and cooled rapidly to room temperature. We have measured the ESR linewidths and $g$ shifts as a function of temperature and concentration of Gd. They were found to exhibit Korringa-like thermal broadening between 6 and 40\ifmmode^\circ\else\textdegree\fi{}K. We have deduced the average value of ${J}_{\mathrm{eff}}$ for the effective-exchange integral to be 0.24 \ifmmode\pm\else\textpm\fi{} 0.03 eV. We have calculated also the magnitudes of the conduction-electron relaxation rates to the lattice, (i) due to the undisturbed host lattice, (ii) by spin-flip scattering due to the magnetic impurity Gd, and (iii) by spin-flip scattering due to the nonmagnetic impurity Th.

Observations of the magnetic white dwarf GD 90

view Abstract Citations (6) References (17) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Observations of the magnetic white dwarf GD 90. Brown, D. N. ; Rich, A. ; Williams, W. L. ; Vauclair, G. Abstract The white dwarf GD 90 has been found to manifest Zeeman structure in H beta and H gamma. This indicates the existence of a magnetic field of approximately 5 x 10 to the 6th gauss. GD 90 has been observed for broadband circularly polarized radiation in the 3500-5500 A wavelength region. The value of broadband circular polarization is found to be -0.15 plus or minus 0.09%. The value of the magnetic field, expected on the basis of a magnetoabsorption version of Kemp's model, is estimated to be -0.58 plus or minus 0.15%, or, including Balmer edge effects, -0.4 plus or minus 0.2%. This shows that the upper limit on broadband circular polarization set by observation is consistent with magnetoabsorption calculations based on a field derived from Zeeman splitting only when the Balmer edge is invoked. A spectroscopic observation of GD 90 has been found to be consistent with previous work, eliminating any possibility that the magnetic field, as detected by the Zeeman components of H beta, is variable. Publication: The Astrophysical Journal Pub Date: November 1977 DOI: 10.1086/155674 Bibcode: 1977ApJ...218..227B Keywords: H Beta Line; H Gamma Line; Magnetic Stars; Stellar Models; White Dwarf Stars; Zeeman Effect; Astronomical Models; Balmer Series; Circular Polarization; Gravitational Effects; Magnetic Effects; Magnetic Flux; Astronomy full text sources ADS |

Gadolinium as a ferromagnetic host for IMPAC experiments

The properties of ferromagnetic Gd as a host for IMPAC measurements have been investigated. The transient and internal magnetic fields at Cd, Nd, Sm, Dy, Er, Yb and Hf nuclei recoil implanted into polarized Gd at 80 K have been studied by the IMPAC technique. All available experimental transient field data for Gd have been analysed in the framework of the Lindhard-Winther theory. Empirical values of the parametersv p andC ion C atom have been deduced which give good agreement between experiments and theory. Internal magnetic fields at rare-earth nuclei in magnetized Gd at 80 K have been deduced. The results areH h.f. (NdGd)=−1370±440 kG,H h.f.(SmGd)=−1440±120 kG,H h.f.(DyGd)=1410±400 kG,H h.f.(ErGd)=2310±420 kG andH h.f.(YbGd)=−216±32 kG. The signs of these fields are, except for Yb which is in a 2+ ionic state, consistent with a ferromagnetic coupling between the 4f spins of the implanted ion and the Gd host. The deduced internal field at Hf in Gd is −440±90 kG. The observed time-dependent interactions for rare-earth nuclei in ferromagnetic Gd are consistent with the Abragam-Pound theory. For the Cd isotopes,g-factors of the first 2+ states were deduced from the experiments. The results areg(110Cd)=0.49±0.11,g(114Cd)=0.34±0.09 andg(116Cd)=0.41±0.11. The use of transient magnetic fields forg-factor measurements on high-spin rotational states is discussed.

GFactor Measurements of High-Spin (Iπ≤10+) Rotational States

The ion implantation perturbed angular correlation (IMPAC) technique was used to measure the precession angles of the ${4}^{+}$, ${6}^{+}$, ${8}^{+}$, and ${10}^{+}$ rotational states of $^{158,160,162}\mathrm{Dy}$ nuclei recoil implanted into magnetized Gd ($T=77$ \ifmmode^\circ\else\textdegree\fi{}K). The $\mathrm{Gd}(\ensuremath{\alpha},2n)\mathrm{Dy}$ reaction (${E}_{\ensuremath{\alpha}}=27$ MeV) on natural Gd was used to populate the levels studied. By comparing the precession results obtained from the ($\ensuremath{\alpha},2n$) experiments for the ${4}^{+}$ and ${6}^{+}$ states to those obtained from Coulomb excitation IMPAC measurements one can conclude the following: (i) $g(^{158}\mathrm{Dy})=0.36\ifmmode\pm\else\textpm\fi{}0.06$ for ${I}^{\ensuremath{\pi}}={4}^{+},{6}^{+}, \mathrm{and} {8}^{+}$; (ii) no effect due to final feeding times into the g.s. rotational band can be observed; and (iii) the deduced $g$ factors are constant for members of the g.s. bands of $^{158,160,162}\mathrm{Dy}$ up to ${I}^{\ensuremath{\pi}}\ensuremath{\le}{8}^{+}$ but a possible drop in $g$ for the ${10}^{+}$ states may be indicated by the data. A reduction in the $g$ factors is theoretically expected to accompany the "back bending" in the energy levels which was recently observed for high-spin rotational states in some deformed nuclei.

Dispersion of the Magnon and Optical-Exciton States of GdCl3and Gd(OH)3and Their Effect upon the Single-Ion-Induced Absorption Line Shapes

The high-resolution optical-absorption spectra of the magnetic insulators Gd${\mathrm{Cl}}_{3}$ and Gd${(\mathrm{OH})}_{3}$ in a 35-kG magnetic field are used to demonstrate, for the first time, the influence of the magnon dispersion on the line shapes of single-ion-induced optical transitions. The absorption line shapes for transitions from the first thermally populated spin state to several single-ion states of the $^{6}P_{\frac{7}{2}}$ and $^{6}P_{\frac{5}{2}}$ manifolds of the ${\mathrm{Gd}}^{+3}$ ion are calculated. The initial and final states are properly treated as a magnon and exciton, respectively, including the dispersion of both states. The single-ion transition-moment operator is transformed to a basis in the crystal eigenstates and the resulting absorption line shape is shown to depend on a $\stackrel{\ensuremath{\rightarrow}}{\mathrm{k}}$-dependent transition-moment operator weighted by a combined exciton-magnon density of states and the magnon occupation number. The magnon dispersion is calculated from the known ground-state exchange interactions while the exciton dispersion is varied to give a best fit to the observed line shapes. The resulting excited-state exchange parameters are shown to be reasonable. The exciton dispersion is found to be quite significant (up to 2 ${\mathrm{cm}}^{\ensuremath{-}1}$) for one of the excited states. These two materials thus represent the first examples for which the exciton dispersion of the electronically excited states of a rare-earth salt have been directly observed.

Superconductivity in Pure La and La-Gd

Superconducting La doped with the magnetic impurity Gd has been investigated to determine whether the thermodynamic properties show evidence for "gapless" superconductivity. The measurements show that the specific heat of pure hcp La closely follows the predictions of the BCS theory. The addition of small amounts of Gd does not appreciably change the normal-state electronic specific heat, but it drastically alters the superconducting characteristics. An increase in the Gd content decreases the rate at which the normalized superconducting specific heat $\frac{{C}_{\mathrm{es}}}{\ensuremath{\gamma}{T}_{c}}$ approaches zero. This may be due to a diminishing ratio of the energy of the energy gap to the critical temperature, or it may be due to ordering of the Gd ions. The measurements do not extend to low enough temperatures to distinguish between these two possibilities. The magnitude of the specific-heat jump at ${T}_{c}$ is depressed by the Gd somewhat more rapidly than $1.43\ensuremath{\gamma}{T}_{c}$, but less rapidly than is suggested by the electron-tunneling energy-gap measurements. These alloys can support current densities greater than 5\ifmmode\times\else\texttimes\fi{}${10}^{4}$ A/${\mathrm{cm}}^{2}$, and they show no latent heat at the transition in a magnetic field. The latter two characteristics are qualitatively similar to behavior of type II superconductors.