The charge-density-wave transition in Lu5Ir4Si10 under uniaxial pressure

Abstract

An uniaxial pressure cell for low temperature use is described in detail. Then we present data of the electrical resistance of single crystals of Lu₅Ir₄Si₁₀, which is known to show a charge-density-wave transition around 83 K and to become superconducting near 3.8 K, both phenomena being anticorrelated under pressure. Since the CDW in Lu₅Ir₄Si₁₀ is a quasi one-dimensional phenomenon because of a chain-like structure, it responds to uniaxial pressure in a specific way.     

Suppression of the charge density waves in 1T-TaS2 by 70 MeV16O6+ bombardment

We report on the measurement of the nuclear quadrupole interaction by TDPAC on a single crystal of 1T-TaS₂ before and after bombardment with 70 MeV¹⁶O⁶⁺ ions. In 1T-TaS₂, two groups of inequivalent Ta-sites are observed at 298 K due to the presence of a nearly commensurate charge density wave (CDW) Upon¹⁶O⁶⁺ bombardment a single slightly broadened line is observed which resembles closely the incommensurate CDW state.     

Magnetic and related properties of U4Rh13Si9 and U4Ir13Si9

The compounds U₄Rh₁₃Si₉ and U₄Ir₁₃Si₉ crystallize with the orthorhombic Er₄Ir₁₃Si₉-type structure that contains three non-equivalent positions of uranium atoms. Their magnetic, electrical transport and thermal properties were studied down to liquid helium temperature in magnetic fields up to 9 T. Both compounds have been found to order antiferromagnetically at low temperatures and to exhibit complex magnetic behavior in the ordered state. Some features characteristic of spin fluctuators (U₄Rh₁₃Si₉) and Kondo lattices (U₄Ir₁₃Si₉) indicate that the two ternaries studied are novel strongly correlated electron systems.     

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.     

Charge-density-wave transitions in the local-moment magnet Er5Ir4Si10

We report the observation of a new type of charge-density wave (CDW) in the large magnetic-moment rare-earth intermetallic compound, Er5Ir4Si10, which then orders magnetically at low temperatures. Single crystal x-ray diffraction shows the development of a 1D incommensurate CDW at 155 K, which then locks into a purely commensurate state below 55 K. The well-localized Er3+ moments are antiferromagnetically ordered below 2.8 K. We observe very sharp anomalies in the specific heat at 145 and 2.8 K, signifying the bulk nature of these transitions. Our data suggest the coexistence of strongly coupled CDW with local-moment antiferromagnetism in Er5Ir4Si10.     

Electron spin resonance study of a CuIr2S4 single crystal

A spinel sulphide CuIr₂S₄ single crystal, which exhibits an orbitally induced Peierls phase transition at ～230?K, is investigated by electron spin resonance (ESR) spectroscopy. The phase transition is clearly manifested on the ESR spectra. It is suggested that the ESR signals are produced by a few non-dimerized Ir⁴⁺ ions. Moreover, an extra ESR spectrum appears at low temperature in addition to the paramagnetic ESR signals of Ir⁴⁺ ions, which is suggested to be caused by the Jahn–Teller effect of the non-dimerized Ir⁴⁺ ions. From the ESR results, it is found that the Jahn–Teller splitting energy ΔE _JT is much smaller than the spin-dimerization gap.     

Infrared study on the formation of charge density waves in (TMTSF) 2X (X = Reo4− and PF6− at atmospheric pressure

The temperature dependence of the infrared absorption spectra (4000–200 cm^?) of (TMTSF) ₂Reo₄ and (TMTSF) ₂PF₆ are investigated with the aim at using the appearance of vibronic absorptions originated by electron-molecular vibration interactions to monitor the formation of charge density waves (CDW) on the donor stacks. The presence of vibronic bands at ≈1400, 436 and 264 cm^?1 in (TMTSF) ₂Re0₄ below 180 K shows that the anion ordering transition in this salt induces the formation of commensurate CDW. The absence of vibronic bands in the PF₆^? salt at 8K indicates that no CDW formation nor an underlying 2K_f lattice distortion takes place at the metal-insulator (MI) phase transition. These results show that, at atmospheric pressure both salts do not undergo a conventional Peierls type MI transition.     

Influence of Si and Co substitutions on magnetoelastic properties of R2Fe17 (R=Y, Er and Tm) intermetallic compounds

The magnetostriction of the off-stoichiometric R₂Fe₁₇-type intermetallic compounds based on R₂Fe_14−xCo_xSi₂ (R=Y, Er, Tm and x=0, 4) was measured, using the strain gauge method in the temperature range 77-460 K under applied magnetic fields up to 1.5 T. All compounds show sign change and reduction in magnetostriction values compared to the R₂Fe₁₇ compounds by Si substitution. For Y₂Fe₁₄Si₂ and Er₂Fe₁₄Si₂, saturation behaviour is observed near magnetic ordering temperature (T_C), whereas for Tm₂Fe₁₄Si₂, saturation starts from T>143 K. Also, Co substitution has different effects on the magnetostriction of R₂Fe₁₄Si₂ compounds. In Er₂Fe₁₀Co₄Si₂ and Tm₂Fe₁₀Co₄Si₂, saturation occurs below the spin reorientation temperature (T_SR). In addition, in Er₂Fe₁₄Si₂, a sign change occurs in the anisotropic magnetostriction (Δλ) as well as the volume magnetostriction (ΔV/V) at their T_SR values. The volume magnetostrictions of the Tm-containing compounds show an anomaly around their T_SR. In R₂Fe₁₄Si₂ compounds, parastrictive behaviour is also observed in ΔV/V near their T_C values. In addition, the magnetostriction of the sublattices is investigated. Results show that in R₂Fe₁₄Si₂ compounds, the rare-earth sublattice contribution to magnetostriction is negative and comparable to the iron sublattice, whereas, in R₂Fe₁₀Co₄Si₂ compounds, the rare-earth sublattice contribution is positive and larger than Fe sublattice. These results are discussed based on the effect of Si and Co substitutions on the anisotropy field of these compounds. Influence of the spin reorientation transition on the magnetostriction of these compounds is discussed in terms of the anisotropic sublattice interactions.     

Neutron diffraction study of the CeFeSi-type RTiGe compounds (R=Pr,Nd, Tb–Er)

Neutron diffraction experiments were carried out on polycrystalline RTiGe (R=Pr, Nd, Tb–Er) samples. These compounds crystallise with the tetragonal CeFeSi-type structure (space group P4/nmm). This structure is closely related to the ThCr₂Si₂-type and can be described as “BaAl₄ blocks” connected via R–R contacts (“W blocks”). All the compounds are antiferromagnetic. PrTiGe and NdTiGe are characterised by an easy-plane sine-modulated structure characterised by a wave vector k=0,0,q_z=0.242 and 0.334 below 62 and 128 K, respectively. Below 80 K, NdTiGe exhibits a commensurate arrangement, which consists on ferromagnetic (0 0 1) Nd layers coupled antiferromagnetically along the c direction with the sequence ++−−. This commensurate magnetic ordering also occurs in TbTiGe, DyTiGe, HoTiGe and ErTiGe below 312, 185, 124 and 36 K, respectively. In the first three compounds (R=Tb−Ho), the magnetic moment is aligned along the c-axis whereas it is localised in the basal plane in ErTiGe. In all the RTiGe compounds, the magnitude of the ordered moments at 2 K amounts nearly to the free ion magnetic moment (gJ) values for the respective R³⁺ ions.     

Thermal expansion measurements of the quasi-one-dimensional conductor K0.30MoO3

The charge density wave (CDW) dynamics of the quasi-one-dimensional conductor K_0.30MoO₃ shows two different regimes depending on the temperature: a strongly damped CDW motion above ∼50 K and CDW motion with almost no damping below ∼50 K. In a search for a characterization of this CDW behaviour, we performed thermal expansion measurements on K_0.30MoO₃ single crystals in the temperature range 4-250 K. In addition to the anomaly observed at the Peierls transition at 180 K along the [102] direction, an anomaly is observed at ∼50 K along the [−201] and [102] directions. The results are discussed in relation with the change in the CDW rigidity at ∼50 K.     

Charge density wave transport in NbSe<Subscript>3</Subscript> at low temperatures under high magnetic field

Charge density wave (CDW) depinning and sliding regimes have been studied in NbSe₃ at low temperatures down to 1.5 K under magnetic field of 19 T oriented along the c-axis. We found that the threshold field for CDW depinning becomes temperature independent below T ₀ ≈ 15 K. Also CDW current to frequency ratio characterizing CDW sliding regime increases by factor 1.7 below this temperature. The results are discussed as a crossover from thermal fluctuation to tunneling CDW depinning at T < T ₀. Besides, we found that CDW sliding strongly suppresses the amplitude of Shubnikov-de Haas oscillations of magnetoresistance.     

Magnetic order in RCr\mathsf{_{2}}Si\mathsf{_{2}} intermetallics

The magnetic structure and ordering temperatures of three intermetallic compounds which crystallize in the tetragonal ThCr₂Si₂ structure, TbCr₂Si₂, HoCr₂Si₂ and ErCr₂Si₂, have been determined by neutron diffraction, differential scanning calorimetry and magnetization measurements. The Cr-sublattice orders anti-ferromagnetically with Néel temperatures of 758 K for TbCr₂Si₂, 718 K for HoCr₂Si₂ and 692 K for ErCr₂Si₂. Chromium atoms located at 4d crystallographic sites are aligned anti-parallel along the c-axis, with G_ZCr magnetic modes. In contrast with metallic bcc Cr, the refined room temperature value of the ordered Cr moment is anomalously large for all three compounds. No long range magnetic order of the R sublattice in TbCr₂Si₂ and HoCr₂Si₂ is observed, whilst the Er sublattice in ErCr₂Si₂ orders independently of the Cr sublattice below 2.4 K with moments ferromagnetically aligned in the basal plane.Received: 4 November 2003, Published online: 30 January 2004PACS: 75.25. + z Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source X-ray scattering, etc.) - 75.30.Cr Saturation moments and magnetic susceptibilities - 75.50.Ee Antiferromagnetics     

Paramagnetic hyperfine structure of193Ir in K2IrCl6 diluted into K2PtCl6

The paramagnetic hyperfine splitting of Ir⁴⁺ (5d⁵) in K₂IrCl₆ diluted into diamagnetic K₂PtCl₆ has been observed at 4.2 K and Ir∶Pt ratios of 1∶10 and 1∶25. In the latter case a narrow paramagnetic pattern with a hyperfine coupling constant ofA=−13.1(2) mm/s was observed, but both samples also exhibit a single Ir⁴⁺ line typical for fast relaxation, either because of macroscopic inhomogeneities in the Ir distribution or because part of the Ir spins are still coupled to nearest Ir neighbours.     

Hysteresis in the electrical properties of orthorhombic tantalum trisulphide: Evidence for an incommensurate-commensurate charge-density wave transition?

A study of electrical conduction in orthorhombic TaS₃ has revealed the existence of thermal hysteresis throughout the temperature range 55 K < T < 205 K. This is attributed to variability in the wavevector q of the charge-density wave (CDW) which develops below T_p = 215 K, and confirms the recent finding, from electron diffraction, that at temperatures not too far below T_p the CDW is incommensurate with the underlying lattice. Evidence that q becomes commensurate, at least along the chain direction at 55 K is provided by the vanishing of hysteresis at that temperature, and also by a rise in the threshold field for continuous motion of the CDW.From its dependence on temperature it is concluded that between T_p and 55 K the conduction in the linear regime is better described as that of a Peierls semi-metal, rather than that of a Peierls intrinsic semiconductor. At most temperatures within that range electrical hysteresis also is observed, and a detailed study of this leads to the tentative conclusion that translation of the CDW conveys negative charge, carried presumably by negatively-charged discommensurations. The mechanisms of conduction below 55 K remain uncertain.     

Charge-density-wave instabilities and quantum transport in the monophosphate tungsten bronzes with m = 5 alternate structure

Resistivity, thermoelectric power and magnetotransport measurements have been performed on single crystals of the quasi two-dimensional monophosphate tungsten bronzes (PO₂)₄(WO₃)_2m for m =5 with alternate structure, between 0.4 K and 500 K, in magnetic fields of up to 36 T. These compounds show one charge density instability (CDW) at 160 K and a possible second one at 30 K. Large positive magnetoresistance in the CDW state is observed. The anisotropic Shubnikov-de Haas and de Haas-van Alphen oscillations detected at low temperatures are attributed to the existence of small electron and hole pockets left by the CDW gap openings. Angular dependent magnetoresistance oscillations (AMRO) have been found at temperatures below 30 K. The results are discussed in terms of a weakly corrugated cylindrical Fermi surface. They are shown to be consistent with a change of the Fermi surface below 30 K. Received 23 November 1999 and Received in final form 23 March 2000     

Crystal structure and magnetic properties of pseudoternary TbRh2−xMxSi2(M = Ru,Ir) compounds

The structural and magnetic characteristics of the pseudoternary TbRh_2−xM_xSi₂(M = Ru, Ir) compounds were studied. The compounds crystallize in the tetragonal ThCr₂Si₂-type structure. The magnetic data were collected in the temperature range 70–300 K. Their magnetic susceptibilities satisfy the Curie-Weiss law in the temperatures higher than 130 K. The magnetic moment of the rare earth atom is larger than of the free Tb³⁺ ion. A modified RKKY theory with included interaction between the conduction electrons was applied to explain the variation of properties of the compounds.     

Crystal structure and magnetic ordering of RNi Si compounds

The element distributions and the magnetic ordering behaviour of compounds RNi₁₀Si₂ (R = Tb, Dy, Ho, Er, Tm) have been studied by neutron powder diffraction down to temperatures of 1.6 K. The compounds crystallize in an ordered variant of the ThMn₁₂ structure type in the tetragonal space group P4/nmm. An ordered 1:1 distribution of Ni and Si on sites 4d and 4e, respectively, corresponds to a modulation vector [0, 0, 1] with respect to the space group I4/mmm of the ThMn₁₂ structure. TbNi₁₀Si₂ orders antiferromagnetically below T _N = 4.5 K with a magnetic propagation vector of [0, 0, 1/2]. The magnetic Tb moments, 8.97(2) /Tb atom at 1.6 K, are aligned along the c-axis. The Ni sites in TbNi₁₀Si₂ do not carry any ordered magnetic moments. The compounds with R = Dy, Ho, Er, and Tm are paramagnetic down to 1.6 K and 3.0 K, respectively. Received 10 July 2002 / Received in final form 12 September 2002 Published online 29 October 2002     

Polarized spectral properties of Er<Superscript>3+</Superscript> ions in NaGd(WO<Subscript>4</Subscript>)<Subscript>2</Subscript> crystal

Polarized spectral properties of Er³⁺:NaGd(WO₄)₂ single crystal are reported. The crystal was grown by the Czochralski method. The Judd–Ofelt theory was applied to analyze the polarized absorption spectra and then calculate the spontaneous emission probabilities, radiative lifetimes, and branching ratios. Fluorescence decay curves of the ⁴ I _13/2, ⁴ I _11/2, and ⁴ S _3/2 multiplets for the Er³⁺ ions were measured. Stimulated emission cross-sections of the ⁴ I _13/2→⁴ I _15/2 transition obtained by the Fuchtbauer–Ladenberg formula and the reciprocity method were compared. Multi-phonon relaxation rates of the crystal were estimated. Green up-conversion fluorescence around 531 and 552 nm was observed, and the possible up-conversion mechanisms were proposed. PACS 78.20.-e; 42.70.Hj     

Multi-range high-frequency EPR spectroscopy of LiYF<Subscript>4</Subscript> and LiLuF<Subscript>4</Subscript> crystals doped by rare-earth ions

EPR spectra of isostructural LiYF₄ and LiLuF₄ crystals doped by Dy³⁺, Er³⁺, and Ho³⁺ ions are measured at 4.2 K in the frequency range 40–800 GHz. The effects caused by isotopic disorder in the lithium sublattice, the random crystal field, and the interaction between paramagnetic impurity ions are detected and studied. The results of the measurements are used to determine the spectral characteristics of the compounds and the crystal field parameters. It is demonstrated that the formation of the isotope structure of the EPR signal is dominated by local deformations of the crystal lattice induced by mass defects.     

Interaction of both charge density waves in NbSe3 from interlayer tunneling experiments

An interlayer tunneling technique has been used for spectroscopy of charge density wave (CDW) energy gaps (Δ_1,2) in NbSe₃ subsequently opened at the Fermi surface on decreasing temperature at T _p1 = 145 K (CDW1) and at T _p2 = 60 K (CDW2). We found that the CDW2 formation is accompanied by an increase of the CDW1 gap below T _p2. The maximum enhancement of Δ₁, δΔ₁ is about 10%. The effect observed has been predicted theoretically as resulting from the joint phase locking of both CDWs with the underlying crystalline lattice below T _p2. The text was submitted by the authors in English.