Magnetic properties of YbNi5 from 170Yb Mössbauer and magnetisation measurements

From Yb¹⁷⁰ M?ssbauer measurements on YbNi₅, we establish: the Yb³⁺ ground state Kramers doublet is well isolated and has uniaxial anisotropy, the compound magnetically orders at 0.55 K, the Yb³⁺ moments are aligned along the hexagonal axis, they have a saturated value of 3.9μ_B and a thermal variation close to a mean field S = 1/2 law. We obtain the strength of the Yb³⁺–Yb³⁺ coupling which we find is considerably smaller than that between the rare earths (R³⁺) in the other RNi₅. From a study of the spin dynamics, we find that dynamic short range order is present just above the ordering temperature and that above 2 K, the relaxation rate of the paramagnetic Yb³⁺ spins follows a T-linear Korringa law with a relatively pronounced slope which we link to a high density of states at the Fermi level. Magnetic susceptibility and magnetisation measurements establish the ferromagnetic nature of the Yb³⁺–Yb³⁺ coupling. We comment on the Yb³⁺ crystal field properties.     

Transport,magnetic, and thermal properties of non-centrosymmetric Yb2Co12P7

We report magnetization and specific heat measurements down to 2?K and electrical resistivity down to millikelvin temperatures on polycrystalline samples of the non-centrosymmetric compound Yb₂Co₁₂P₇. In addition to the previously reported ferromagnetic ordering of the cobalt sub-lattice at T _C ?=?136?K we find a magnetic transition below T _M ?=?5?K that is likely associated with ordering of the Yb ions. The broad nature of the specific heat anomaly suggests disordered magnetism and possible short-range correlations well above T_M .     

Correlation between transport properties and quasielastic linewidths of Ce and Yb compounds with unstable 4f-shell

From an analysis of available data it is shown that there is experimental evidence for a rather general correlation of electrical resistivity, ϱ, and thermopower with the quasielastic linewidth of the neutron spectra, Γ_QE, for intermetallic Ce- and Yb-compounds with an unstable 4f-shell. At high temperatures, k_BT > Γ_QE, the 4f-contribution to the resistivity, Δϱ, scales with Γ⁻¹_QE. For Ce-compounds, which show a resistivity maximum, the measured strong temperature dependence of Γ_QE corresponds to the temperature dependence of the resistivity above the resistivity maximum over a few hundred K. Empirical expressions for resistivity and thermopower are presented, which not only yield the observed correlation for k_BT > Γ_QE, but which also describe the low temperature decrease of the two quantities: Fits for the resistivities and the thermopowers of a large number of Ce- and Yb-compounds are is very good agreement with the data over a large range of temperatures. The correlation as well as the empirical expressions for resistivity and thermopower are discussed within a model of M. Weger, which has recently been proposed to account for the so called “resistivity saturation” observed in materials with narrow bands.     

Structural and magnetic properties of layer compounds: CoGaInS4

XPS spectra of the layer compound CoGaInS₄ show that CO²⁺ ions are distributed within the sheets of a ZnIn₂S₄-type structure. The magnetic properties are explained in terms of antiferromagnetic uncompensated clusters.     

Transport and magnetic properties of cobalt doped CeNiAl4

Electrical resistivity and thermoelectric power (TEP) have been measured in polycrystalline sample of CeNi_0.75Co_0.25Al₄. The magnetization measurements have been performed in oriented powder with a-axis of the crystallites parallel to the external magnetic field. All the data have been compared with its parent compound CeNiAl₄. In the range 120-300 K, the Seebeck coefficient is significantly higher for alloy than for the parent material and exhibits a peak at ∼150 K. R(T)/R(300) follows a logarithmic temperature dependence for all samples above 100 K, and rapidly decreases as the temperature is lowered. The decrement is much faster in the cobalt doped samples than in the parent compound, suggesting stronger electronic correlations in the former. Inverse magnetic susceptibility in oriented powder follows a Curie-Weiss law above 100 K and shows p_eff=2.7 slightly higher than that of the free Ce³⁺ ion value of 2.5.     

Electrical and magnetic properties of CeNi4In with Ce in saturated valence state

Measurements of the electrical resistance, thermopower, and magnetic susceptibility of CeNi₄In have been carried out within the 4.2–400 K range, with Ce in saturated valence state. It is shown that this state of Ce in metallic compounds is characterized by formation of a fine structure in the density of states near the Fermi level, which is qualitatively different from the case of usual intermediate-valence state. Fiz. Tverd. Tela (St. Petersburg) 40, 7–9 (January 1998)     

Transport properties of CsHSO4 investigated by impedance spectroscopy and nuclear magnetic resonance

Transport properties of the superprotonic conductor, CsHSO₄, have been investigated by impedance spectroscopy and nuclear magnetic resonance (NMR). It has been found that both, conductivity (σ) and NMR diffusion (D _NMR) are practically isotropic in the high-conductive (superprotonic) phase (above 414 K). The NMR diffusion coefficient, D _NMR , increases rapidly and discontinuously at the melting point (~490 K). The temperature change of D _NMR in the superprotonic phase is characterized by a smaller activation energy compared to that in the liquid state. The values calculated from the Nernst-Einstein relation practically coincide with D _NMR in the superprotonic phase, i.e., the Haven ratio is close to unity. This indicates that in this phase the proton motion is rather uncorrelated.     

Transport properties of dilute magnetic alloys

The electrical resistivity, thermopower, and the electronic part of the thermal resistivity of dilute magnetic alloys are calculated in the framework of the Suhl-Nagoaka theory. Using Bloomfield's and Hamann's solution of the Nagaoka equations, we derive expressions for the transport quantities in the limitT? ¯ T_K andT?¯ T_K to order (In ¯T _K /T)^?4 where ¯T _K is the Kondo temperature which may depend on the spin independent scattering. We find that the thermopower and deviations from the Wiedemann-Franz law in this limit decrease as ¦In ¯T_K/T¦^?3 if one neglects a trivial temperature dependence of the thermopower due to the electron-phonon interaction.     

Preparation and properties of Er and Yb doped InP-based semiconductor compounds

In this paper we pursue the effect of the erbium and ytterium addition during the liquid phase epitaxial (LPE) growth on physical properties of thin InP layers. Series of InP layer samples were prepared by LPE from the melts containing 0–0.3 wt.% of Er and Yb. The grown layers were examined by the Hall effect andC-V measurements, photoluminescence spectroscopy and Rutherford backscattering spectrometry (RBS). We have found that only Yb impurity was incorporated into the lattice of InP layer. With increasing Yb content in the growth melt the layer’s conductivity smoothly changed from n to p type when Yb admixture exceeded certain limit. On the basis of these results we prepared p-n junctions in the InP layers directly doped by Yb, and tested then byC-V measurements. Presented at the 1st Czech-Chinese Workshop “Advanced Materials for Optoelectronics”, Prague, Czech Republic, June 13–17, 1998. This work has been supported by the Grant Agency of the Czech Republic, project No. 102/99/0341.     

Transport properties of alkali metal-graphite intercalation compounds

Basal resistivity ?_a has been measured $\text{in situ}$ on MC₈ compounds (M=K, Rb, Cs) from 5–300K. We find ?_a(T) = A+BT+CT², in agreement with Suematsu et. al., except our value of A is ～200 times smaller implying fewer defects. In MC₈ compounds R_H at 5K is positive and increases linearly with magnetic field, suggesting a complex Fermi surface. On the other hand, R_H for RbC₂₄ is negative and field-independent but the magnitude is inconsistent with a simple one-carrier model (assuming one free electron per Rb).     

High magnetic field properties and ESR of the compounds

compounds have a layered structure made of alternating Ni-O and Li-O slabs. An amount z of extra divalent Ni ions is always present in the Li-O layers. We show, using high field magnetisation, static and dynamic susceptibility and high frequency ESR, that the magnetic properties are driven by the z parameter. The compounds can be described as ferromagnetic Ni-O layers, bridged by clusters possessing a net ferromagnetic moment. Received: 24 July 1998 / Revised and Accepted: 23 September 1998     

Transport properties of PbSnI4

PbSnI₄ has been prepared from equimolar amounts of PbI₂ and SnI₂. X-ray and DSC measurements show the material to be uniphase in the temperature range 30 to 400°C; it has a tetragonal structure and melts at 379°C. The electrical conductivity is mainly ionic with an ionic transport number greater than 0.99 at 200°C. Conductivity at room temperature is 2.56 × 10⁻⁸ Ω⁻¹ cm⁻¹ while the value at 200°C is 1.25 × 10⁻⁶ Ω⁻¹ cm⁻¹.     

Transport properties and electronic structure of nonmagnetic REAg compounds

The temperature dependence of the electrical and the thermal resistivity of the three nonmagnetic compounds REAg (RE=Y, La, Lu) is investigated. As with other physical properties LaAg shows a remarkable different behaviour in its transport properties compared to the YAg and LuAg compounds. To understand this anomalous behaviour of LaAg we have performed selfconsistent ASW bandstructure calculations for all three compounds. A comparison of these results shows a much higher density of states for LaAg at the Fermi energy. Flat bands near the Fermi level in LaAg together with a stronger electron-phonon coupling can explain the mentioned differences. A stronger electron-phonon coupling in LaAg is in coincidence with other physical properties.     

Transport and magnetic properties of layered rare earth disilicides

The layered rare earth (RE) disilicides RE₃Si₅ with RE = Y, Er, Tm, YbandLu have been studied by means of ac magnetic susceptibility and ac electrical resistance measurements. Evidence for magnetic orderings have been found at 4.4K, 3.1K and 1.7K for Er₃Si₅ and at 2.1K for Tm₃Si₅. The resistance of Lu₃Si₅ was observed to drop abruptly below 7K, possibly indicating the presence of a superconducting phase. An apparent correlation was noted between the value of the room temperature resistivity and the amount of negative curvature observed in the resistivity above ～ 50K in these materials.     

Systematic investigations on the magnetic properties of Gd3Ni2In4 compound

We have investigated the structural, magnetic, magnetocaloric, thermodynamic and transport properties of polycrystalline Gd₃Ni₂In₄ compound. X-ray powder diffraction pattern shows that Gd₃Ni₂In₄ crystallizes in hexagonal Lu₃Co₂In₄ – type structure. Magnetization studies reveal the presence of two magnetic transitions, T_N and T_C at 21 K and 55.5 K, respectively. The maximal value of magnetic entropy change, -ΔS_M, computed from isothermal magnetization data in a magnetic field of 9 T is 4.57 J/kg K, which is spread over a wide temperature (ΔT = 61.5 K) and hence yields a relative cooling power (RCP) of 281 J/kg. In addition, the compound shows a significant positive magnetoresistance, MR (T = 2 K) = 44% in B = 9 T. These results on Gd₃Ni₂In₄ compound signify that such materials exhibiting successive reversible magnetic transitions may comprise a distinct class of magnetocaloric materials as they work in a wider temperature range than conventional refrigerant materials.     

Transport properties of graphene under periodic and quasiperiodic magnetic superlattices

We study the transmission of Dirac electrons through the one-dimensional periodic, Fibonacci, and Thue–Morse magnetic superlattices (MS), which can be realized by two different magnetic blocks arranged in certain sequences in graphene. The numerical results show that the transmission as a function of incident energy presents regular resonance splitting effect in periodic MS due to the split energy spectrum. For the quasiperiodic MS with more layers, they exhibit rich transmission patterns. In particular, the transmission in Fibonacci MS presents scaling property and fragmented behavior with self-similarity, while the transmission in Thue–Morse MS presents more perfect resonant peaks which are related to the completely transparent states. Furthermore, these interesting properties are robust against the profile of MS, but dependent on the magnetic structure parameters and the transverse wave vector.     

Note on the magnetic properties of Y-Mn compounds and their hydrides

The lattice constants and the magnetic properties of YMn₂ and Y₆Mn₂₃ were studied before and after hydrogen absorption. The compound YMn₂ is an exchange-enhanced Pauli paramagnet. Upon hydrogen absorption it becomes a magnetically ordered compound with an ordering temperature of 285 K. Conversely, the compound Y₆Mn₂₃ is a ferromagnet (T_c=498), in which hydrogen absorption leads to a loss of magnetic moment of the Mn atoms.     

Transport properties of the LaSrNiO4 ± δ ceramics

The temperature dependence of electrical resistivity in LaSrNiO_{4 ± δ} ceramics synthesized using various techniques and subjected to heat treatment is studied. The occurrence of a metal-semiconductor transition is shown to be accounted for by the Anderson carrier localization originating from the random arrangement of oxygen vacancies.     

Investigations of crystal and magnetic properties of Dy-Fe intermetallic compounds

The crystal and magnetic properties of Dy₂Fe₁₇, Dy₆Fe₂₃, DyFe₃ and DyFe₂ intermetallic compounds are investigated with X-ray, magnetometric, ⁵⁷Fe and ¹⁶¹Dy Mössbauer effect methods. The X-ray analysis shows that investigated compounds are single phases with Th₂Ni₁₇, Th₆Mn₂₃, PuNi₃ and NgCu₂ type crystal structures, respectively. The magnetometric measurements prove their ferrimagnetic behaviour, localization of Fe magnetic moments and long range Fe-Fe exchange magnetic interactions. The crystal field effects induce magnetic anisotropy which results in local magnetic symmetry or iron atoms lower than the crystal one. This is observed by the Mössbauer effect method. The values of ¹⁶¹Dy hyperfine magnetic fields measured for investigated compounds exceed that found in metallic dysprosium due to polarization of conduction electrons by 3d-electrons of iron atoms. The weighted average value of ⁵⁷Fe hyperfine magnetic field decreases with the increase of Dy content in the compounds.