Measurement of local susceptibility at100Rh in some metallic hosts

The local susceptibilities (T) of isolated Rh impurities in Pb, Ru, Au, Pd, Pt andYb hosts have been measured as a function of temperature. The results show close to unity for Rh in Pb, Ru, Au andYb indicating nonmagnetic behaviour. In contrast, the magnetic response in exchange enhanced d band metal hosts, e.g. Pd andPt, shows Curie-Weiss-like local susceptibility andreflects a large quasi stable 4d magnetic moment on Rh.     

Local magnetism of Rh in Ni-Rh alloys near the critical composition for ferromagnetism

Local magnetic behaviour of Rh implanted into Ni-Rh alloys near the critical Rh compositionx=0.37 has been studied using the TDPAC method. The observed Curie-Weiss type local susceptibility reflects the presence of large d spin polarization around Rh yielding a total moment of 4.7 _B. Our results show that the magnetism of Rh in the alloys depends strongly on the number of Ni near neighbour atoms.     

Magnetic Properties of Np2Ir2In Investigated by 237Np Mössbauer Spectroscopy

The present study of Np₂Ir₂In completes the ²³⁷Np Mössbauer spectroscopy investigations of Np₂T₂X (T = Co, Rh, Ir, Ni, Pd, Pt; X = In, Sn) compounds. Np₂Ir₂In is found to order at T _ord30 K and the complex Mössbauer spectra suggest the occurrence of a noncollinear modulated magnetic structure with an average magnetic moment on the neptunium _Np0.76 _B. The magnetic properties of Np₂Ir₂In are consistent with the general trends observed in the An₂T₂X (An =U, Np) isostructural family.     

Superconductivity and resistance behaviour of σ-phase alloys: Nb−Rh and Ta−Rh

Superconductivity, structure and electrical resistance behaviour of -phase alloys of Nb–Rh and Ta–Rh are investigated. The Ta–Rh alloys do not become superconducting above 1.2 K. The andH _c2 (0) values of a homogeneous alloy with the composition Nb_65.2Rh_34.8 are 2.95 K, 13.9 kG/K and 23 kG, respectively, whereas for an inhomogeneous alloy with the composition Nb_63.7Rh_36.3 these values are 4.24 K, 5.5 kG/K and 14 kG, respectively. Splat quenching results in a substantial increase in the andH _c2 (0) values of the Rh-rich sample. Annealing (900°C, 100 h) of the Rh-rich sample leads only to small changes in the superconducting properties but a small amount of Nb–Rh solid solution has been formed. The electrical resistance of Nb_65.2Rh_34.8 decreases with decreasing temperature and varies asT ^0.5 between 150 and 240 K and asT between 60 and 140 K. For Ta_70.0Rh_30.0 the temperature coefficient changes to negative values below 170K. values are calculated for Nb–Rh using McMillan's formula. An estimatedT _c value of Ta–Rh is 0.2 K. TheH _c2 (0) values of Nb–Rh are in good agreement with the theoreticalH _c ^2** (0) values.Dedicated to Prof. Dr. W. Buckel on the occasion of his 60th birthday     

Magnetism in UPtAl Under High Pressure

UPtAl exhibits ferromagnetic ordering (T _C = 42.5 K) of uranium 5f-electron moments. The magnetic ordering transition is accompanied by an electrical-resistivity () anomaly at Curie temperature (T _C). We report on resistivity measurements performed in a wide temperature range on a UPtAl single crystal under hydrostatic pressures p 8 GPa. The initial increase of T _C with p becomes gradually reduced for p > 2 GPa. The maximum T _C value is reached between 4 and 6 GPa that is followed by a decrease of T _C beyond 6 GPa. The latter result is attributed to the approaching collapse of U 5f moment ferromagnetism.     

Possible manifestation of spin fluctuations in the temperature behavior of the resistivity of Sm<Subscript>1.85</Subscript>Ce<Subscript>0.15</Subscript>CuO<Subscript>4</Subscript> thin films

A pronounced step-like (kink) behavior in the temperature dependence of resistivity ρ(T) is observed in the optimally doped Sm_1.85Ce_0.15CuO₄ thin films around T _sf = 87 K and attributed to the manifestation of strong-spin fluctuations induced by Sm³⁺ moments with the energy ħω_sf = k _B T _sf ≃ 7 meV. The experimental data are found to be well fitted by the residual (zero-temperature) ρ_res, electron-phonon ρ_e-ph(T) = AT, and electron-electron ρ_e-e(T) = BT ² contributions in addition to the fluctuation-induced contribution ρ_sf(T) due to thermal broadening effects (of the width ω_sf). According to the best fit, the plasmon frequency, impurity scattering rate, electron-phonon coupling constant, and Fermi energy are estimated as ω_p = 2.1 meV, τ ₀ ⁻¹ = 9.5 × 10⁻¹⁴ s⁻¹, λ = 1.2, and E _F = 0.2 eV, respectively. The text was submitted by the authors in English.     

On the universal linear in-layer resistivity ϱ∝T 1of high-T c superconductors

Based on the Boltzmann equation an inversion formula for the resistivity is deduced which for a general coupling between two carrier bands yields, in dimensionD, T ^D–1. While being well known inD=3, this is a new result inD=2. It is then shown that in a 2-band model of strongly anisotropic masses as are found in the cuprate layer structures, the in-layer resistivity follows the law forD=2, T ¹, in agreement with the majority of experiments. Exceptions to the linear law and to the 2-band assumption are also discussed. Assuming the spin-flip term of the interaction to be dominant, the spin-flip relaxation time _sf is estimated by using the data on · _sf is found to be orders of magnitude shorter than the EPR period thus explaining the complete absence of intrinsic EPR signals in the cuprates. It is also shown that the spin-flip interaction gives rise to pairing, preferentially of the heavier carriers.     

Magnetic properties of amorphous Bi2DyFe5O12

Amorphous Bi₂DyFe₅O₁₂ films have been prepared by rf sputtering technique. The magnetic properties, structure and effect of annealing have been investigated. The magnetization increases with increasing magnetic field and is not saturated at a high magnetic field of 65 kOe. In the temperature range 20 K<T<200 K the susceptibility can be described by a Curie-Weiss law with a Weiss constant of =–15 K. The effective paramagnetic moment for the iron ion (4.1 _B ) is much smaller than the theoretical moment (5.9 _B ). Above 200 K the slope in ^–1 vsT curve changes. The Weiss constant and effective paramagnetic moment for the iron ion increase. After annealing above 600°C the amorphous samples crystallize to a single garnet phase with the magnetization of 21 emu/g at 1.5 K and 7.2 emu/g at 300 K, which are the same as those of the bulk Bi₂DyFe₅O₁₂ garnet ferrites.     

Über die Supraleitung von Hf-Rh-Legierungen

The transition temperaturesT _c of quenched Hf- Rh alloys are strongly increased in the hexagonal phase by Rh, similar to the homologous systems Ti-Rh and Zr-Rh. On the other hand a stabilization of the cubic high-temperature phase by Rh has not been possible. At higher amounts of Rh(>6 at%) the intermetallic compound Hf₂Rh with aT _c of 1.98 °K is formed. Moreover a transition temperature of 1.73 °K is found which is probably due to the intermetallic compound HfRh. The results above are interpreted with the help of X-ray diffraction and metallurgic techniques.     

Polarized fluorescence and absorption spectroscopy of 1,32-dihydroxy-dotriacontane-bis-rhodamine 101 ester. A new and lipid bilayer-spanning probe

We report on the properties of 1,32-dihydroxy-dotriacontane-bis-rhodamine 101 ester (Rh101C₃₂Rh101) in lipid bilayers of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and in liquid solvents. The results are compared with those of rhodamine 101 octadecanyl ester (Rh101C₁₈). Both molecules are solubilized in the lipid bilayer and the Rh101 moieties are anchored in the lipid-water interface, so that the electronic transition dipole moments (S ₀ S ₁) are oriented preferentially in the plane of the bilayer. At low concentrations of the dyes in lipid bilayers of DOPC, the fluorescence relaxation is single exponential with a lifetime of =4.9±0.2 ns. The relative fluorescence quantum yield of _C32/_C18 0.95 in DOPC vesicles. These results strongly suggest that only a small fraction of the Rh101C₃₂Rh101 molecules are quenched, by, for example, intra- or intermolecular dimers in the ground state at mole fractions of less than 0.1% in the lipid bilayers. For Rh101C₃₂Rh101 in lipid vesicles, the steady-state and time-resolved fluorescence anisotropies are compatible with efficient intramolecular electronic energy transfer. It is concluded that nearly every Rh101C₃₂Rh101 molecule is spanning across the lipid bilayer of DOPC.     

Magnetic order in a Kondo lattice: A neutron scattering study of CeCu2Ge2

Elastic and inelastic neutron scattering studies of the Kondo lattice CeCu₂Ge₂ were performed. AtT _N=4.1 K an incommensurate magnetic order develops with an ordering wave vectorq ₀=(0.28, 0.28, 0.54) and an ordered moment µ _s =0.74 µB. The crystalline electric field splits the 4f ¹-J-multiplet of the Ce ion into a ground state doublet and a quartet at 191 K. The wave function of the ground state yields an ordered moment of 1.54µB. Thus, due to the onset of the formation of a Kondo singlet the magnetic moment is considerably reduced. The magnetic relaxation rate was investigated via quasielastic neutron scattering. The temperature dependence of (T) is characteristic of heavy-fermion systems with a high temperature square root dependence and a limiting low temperature value, yielding a Kondo temperatureT _K10K. The quasielastic component of the scattered neutron intensities persists down to the lowest temperatures, well belowT _N. This quasielastic line is regarded as a characteristic feature of heavy-fermion systems and corresponds to the enhanced value of the linear term of the specific heat.     

Strain Hardening and Fracture of Austenitic Steel Single Crystals with High Concentration of Interstitial Atoms

Stages in the flow curves, mechanisms of deformation (slip or twinning), evolution of the dislocation structure and fracture are studied in austenitic stainless steel single crystals alloyed with nitrogen (C _N = 0–0.7 wt. %) and Hadfield steel in relation to the orientation of the crystal axis of tension, test temperature, and atomic concentrations of nitrogen and carbon. The dislocation-structure pattern (cellular or planar) and deformation mechanisms (slip or twinning) are shown to depend on the matrix stacking-fault energy _sf, friction forces due to solid-solution hardening by interstitial atoms, and crystal orientation. An interrelation between the stages in the flow curves and the type of dislocation structure is found. The contribution of mechanical twinning to the plastic flow of steel crystals is shown to increase with increase in nitrogen and carbon concentrations. The mechanical twinning develops in the early stages of deformation and determines the strain-hardening coefficient and fracture of crystals in high-strength states for interstitial atomic concentration C 0.5–0.7 wt. %. High deforming stresses due to solid-solution strain hardening by interstitial atoms of nitrogen and carbon in combination with low _sf are found to result in twinning in the <001> orientations. The values of _sf in Hadfield steel single crystals and in austenitic stainless steel single crystals are found experimentally depending on the concentration of nitrogen atoms and test temperature.     

Ferromagnetism in the thermodynamically stable monolayer Fe(110) on W(110), coated by Ag

Ferromagnetic order in the thermodynamically stable, pseudomorphic monolayer Fe(110) on W(110), coated by Ag, was studied in situ in UHV using Conversion Electron Mössbauer Spectroscopy (CEMS) and Torsion Oscillation Magnetometry (TOM). Films near the monolayer coverage, prepared at 475 K, consist of nearly independent monolayer and double-layer patches. The properties of monolayer patches are nearly independent of the mean film thickness resulting in excellent conditions to determine the true monolayer properties. The Curie temperature is reduced toT _{c, mono}= 282 K = 0.27 T_c,bulk, the ground state hyperfine field is reduced toB _hf(0)=11.9 T = 0.35B _hf,bulk(0) and the magnetic moment per atom is enhanced to(0) = 2.53 _B=1.14(0)_bulk. Remanent magnetization is detected forT 260 K=0.92T _{c, mono}, square loop magnetization forT 230 K=0.82T _{c, mono}. Unusual properties of the phase transition are detected by the combination of both experimental techniques.     

Temperature dependence of the contribution to the transport coefficients of nearly ferromagnetic metals from electron-paramagnon scattering

We present calculations of the temperature dependence of the contribution from electron-paramagnon scattering to the electrical and thermal resistivity of a simple model of a nearly ferromagnetic metal. The purpose of the work is to explore the behavior of these quantities when the temperature is the order of or greater than the spin fluctuation temperature T_sf. As the temperature T is raised from zero through T_sf, the electrical resistivity varies more slowly with temperature than the T² law characteristic of the regime T?T_sf. When T?T_sf, the electrical resistivity becomes proportional to T, although this asymptotic behavior is approached very slowly. The Lorenz number rises monotonically with temperature, and appears to approach the ideal Sommerfeld value when T?T_sf, although this limit is also approached slowly.     

Antiferromagnetic Ordering in TmCu2

Intermetallic compound TmCu₂ crystalizes in the orthorhombic structure, orders antiferromagnetically (AF) and exhibits four different AF phases below T _N = 6.5 K. In all these phases the Tm magnetic moment is parallel to the b-axis. The ground-state AF1 (T < 3.4 K) corresponds to the squared-up AF structure with propagation vector ₀₁ = (5/8, 0, 0) and magnetic unit cell 8a × b × c. Narrow phases AF2 and AF3 (3.3 K < T < 3.7 K and 3.6 K < T < 4.6 K) are 'spin-slip'-derivatives from the AF1 structure, yielding propagation vectors ₀₂ = (0.633, 0, 0.02) and ₀₃ = (0.618, 0, 0), respectively. The phase AF4 (4.4 K < T < T _N) is then incommensurate transversal spin-wave with the propagation ₀₄ = (0.64, 0, 0). The co-existence of AF phases indicates the first-order transitions between them.     

Giant quadrupole moment andproton halo discovered in8B

The nuclear quadrupole moment of⁸B(I =2⁺,T _1/2=769 ms) has been determined by use of a modified -NMR detection as |Q(⁸B)|=68.3±2.1 mb, which is twice the prediction of the Cohen-Kurath shell model calculation. The anomalous quadrupole moment which is carried mainly by the protons in the nucleus, has been accounted for by the proton halo effect.     

Kondo effect in spin glasses: Electrical resistivity

We investigate the influence of the Kondo effect on the electrical resistivity of spin glasses. Our approximation reduces in the limit of vanishing impurity concentrations to the Suhl-Nagaoka theory for the Kondo effect. The magnetic impurity interactions are taken into account in the form of time dependent two-spin correlation functions which can be measured by neutron scattering. The dynamics of the impurity spins leads to a partial destruction of the Kondo effect. For the resistivity this can be described by a temperature dependent effective spinS _eff ² (T) withS _eff ² 0 forT0 andS _eff ² S(S+1) forT, and by a reduction of the Kondo temperatureT _K. Sufficiently strong interactions lead toT _K=0. We obtain a resistivity maximum at a temperatureT _m due to the interplay of the Kondo effect and the spin dynamics;T _m depends onT _K and on the excitation spectrum, and therefore on parameters such as impurity concentration or pressure. The ratioT _m/T_f (T _f is the freezing temperature) is calculated for a single relaxation time and for a square density of relaxation modes and is compared with experimental data forAuCr,AuMn,AgMn, andCuMn. The influence of other possible modes on various spin glass properties is discussed.SFB 125 Aachen-Jülich-Köln     

Singlet-groundstate magnetism in TbP

Elastic neutron scattering and magnetic susceptibility data are reported for temperatures around the Neél-point,T _N=7.3 K, and for zero magnetic field. AboveT _N, the temperature dependence of the magnetic central peak intensity can adequately be described within the RPA assuming isotropic exchange between nearest and next-nearest neighbours as the only parameters. This two-parameter model is quantitatively confirmed by the susceptibility data. AtT _N, magnetic Bragg-intensities arise almost discontinuously (reaching 70% of the saturation within 0.1 K) accompanied by thermal hysteresis. For all temperatures belowT _N the sublattice magnetic moment is explained by solutions of meanfield equations, if an effective quadrupole-quadrupole interaction is included. The quadrupolar coupling parameter is fully consistent with a value determined recently from the softening of thec ₄₄-mode. These results show, that earlier suggestions of renormalization group results upon the origin of the first order phase transition in TbP are not needed.A project of the Sonderforschungsbereich 65 Festkörperspektroskopie Darmstadt-Frankfurt, supported by the Deutsche Forschungsgemeinschaft     

Experimental characterization of temperature‐dependent electron transport in single‐wall multi‐tube carbon nanotube transistors

Current–voltage, radio‐frequency (RF) and noise characteristics of single‐wall multi‐tube carbon nanotube (CNT) transistors were measured at cryogenic temperatures. Compared to an ambient temperature (T_a) of 300 K, only a slight drain current increase at T_a = 77 K was observed. In addition, a weak dependence of the maximum value of the current gain cut‐off frequency (f_T) on T_a was obtained, indicating that f_T is rather limited by the device intrinsic quantum and extrinsic capacitances than by an improved mobility due to reduced optical phonon scattering at low T_a. A noise analysis of the devices at T_a = 10 K reveals that the noise factor (NF) improvement at very low temperatures is related to the reduced Nyquist noise of all resistive transistor noise contributors. Since the main noise source in CNTFETs is the shot noise, NF remains comparatively high even at T_a = 10 K.

     

Susceptibility of the rectangular Ising ferromagnet

The critical index values= 7/4 for the susceptibility and=15 for the critical isotherm are derived rigorously for the rectangular Ising ferromagnet with nearest neighbor interactions. The critical indices associated with the Fisher moment definition of the correlation length are obtained asTT _c+. The index of the fluctuation sum definition of critical correlations is obtained.Partially supported by grant PHY 76 17191.