Thermal expansion of lT-TaS2 and 2H-NbSe2

The thermal expansion of the a and c axes of lT-TaS₂ and of the a axis of 2H-NbSe₂ have been measured between 4 K and 360 K. Discontinuities in the lattice parameters of TaS₂ were observed at the known charge density wave phase transitions near 200 K and 352 K, and a new transition was found near 283 K. These results are used to estimate the entropy changes occurring at the phase transitions. At the charge density wave onset temperature in NbSe₂ we find an upper limit to any discontinuity in the a axis of 2 × 10^-7 and to any discontinuity in the expansion coefficient of 3 × 10^-7 K^-1.     

Transverse energy gap in 2H-NbSe2

The transverse energy gap in 2H-NbSe₂ has been measured using a Nb flat “point” contact tunneling technique. Its value of 1.15±0.07 milivolt yields a value of 3.78 for the ratio 2Δ(0)/kT_c.     

Anomalous resistivity of iodine-free 2H-NbSe2

Resistance ratios of crystals of 2H-NbSe₂ grown with and without iodine were measured over the temperature range 6K–40K. Iodine-free crystals had higher ratios than any NbSe₂ previously reported and exhibited an abrupt anomaly at the onset of the charge density wave phase. All crystals displayed a cubic temperature dependence of their resistivities below 18K.     

Angle-resolved photoemission spectra of 2H-NbSe2

Angle-resolved photoemission measurements have been made on the metallic layer compound 2H-NbSe₂. From the results, E vs k_∥ dispersion curves have been obtained along two principal symmetry directions in the Brillouin zone. The experimental energy bands are found to be in good agreement with the results predicted by one-dimensional density of initial states along k_⊥.     

Magnetostriction measurements of CoS2 single crystal

The magnetorestriction constants of CoS₂ single crystal were measured by a capacitance method in a temperature range from liquid N₂ to the Curie temperatures.The constants γ₁₀₀ and γ₁₁₁ are ?1.9 × 10^?6 and 5.7 × 10^?6 at liquid N₂ temperature respectively, and the absolute values of the constants decrease monotonically with the increase of the temperature. The volume magnetorestriction constant δω/δH at 110 K in the ferromagnetic state is 6 × 10^?10 Oe^?1.     

Magnetic behavior of HoAl2 single crystal

Heat capacity measurements recently reported on the compound HoAl₂ show an unexplained peak at 20 K. Magnetic measurements on a single crystal of HoAl₂ reveal the existence, at this temperature, of a first order reorientation of the holmium moment.     

Intensity variations of angle-resolved photoemission spectra of 2H-NbSe2

Angle-resolved photoemission spectra of 2H-NbSe₂ are calculated on the one-step model with a single plane wave final state and within the constant matrix element approximation. The results are compared with the experimental spectra obtained for ?ω = 21.2 eV. It is found that the intensities of the observed peaks are predicted reasonably well by this model (especially by one-dimensional density of initial states along k_?).     

Free induction decay in single crystal CaF2

The free induction decay in CaF₂ has been calculated with the help of the simple model. The method allows to clarify the physical nature and to compute some parameters of the nuclear magnetic resonance spectra.     

Electron diffraction study of the charge-density wave superlattice in 2H-NbSe2

In addition to the well-known 3a₀ CDW superlattice, we have observed in 2H-NbSe₂ a 2a₀ superlattice and a well-defined elliptical contour of diffuse intensity between the 3a₀ CDW spots. The 2a₀ superlattice is indicative of a CDW formation through the saddle-point nesting on the Fermi-surface.     

Infrared reflectance of single crystal tetragonal GeO2

The transverse and longitudinal optical phonon frequencies of tetragonal GeO₂ have been determined by standard i.r. reflectance measurements employing classical dispersion theory to fit the experimental data. The static and high-frequency dielectric constants, as derived from the data, are also presented.     

Magnetic properties of A DyNi2 single crystal

Magnetic measurements have been performed on a single crystal of DyNi₂ in applied fields up to 135 kOe. In the ferromagnetic range (T_c = 25 K), the easy magnetization direction is [100] and the hardest one is [111]. Crystal field parameters have been determined from the field and temperature dependence of the magnetization measured along the three principal axes. A two-dimensional model has been used to take into account the rotation of magnetization towards the field. The deduced parameters are W = -0.8 K and x = 0.49. The corresponding anisotropy is very large: especially even a field of 135 kOe applied along a difficult magnetization axis cannot rotate the magnetization along this direction.     

Magnetic properties of Y2Fe15Cr2 single crystal

A Y₂Fe₁₅Cr₂ single crystal with the Th₂Ni₁₇-type structure has been prepared by the Czochralski method and investigated by means of Laue back-reflection, metallographic observation, X-ray diffraction, the singular point detection technique and magnetic measurements. A magnetohistory effect has been observed at a low temperature. Magnetization curves have been measured along the easy and hard directions in fields up to 6.5 T. The saturation magnetization and magnetocrystalline anisotropy field decrease with increasing temperature. The experimental magnetocrystalline anisotropy constant is in good agreement with the calculation results on first approximation.     

Electrical conduction and critical magnetic field for superconductivity of a Nb3Se4 single crystal

With respect to the quasi-one dimensionality of single crystals of Nb₃Se₄, the electrical resistivity from 1.3 to 320 K and the critical magnetic field for superconductivity are measured. The resistivity along the Nb-chain direction is represented as a sum of a temperature independent and an intrinsic temperature dependent term. The temperature dependence of the intrinsic resistivity subjects to T³ form between 10 and 80 K above which it tends to a T linear form. The critical magnetic field is proportional to the temperature difference from the transition temperature. Its dependence is well fitted by the elliptical fluxoid model of Ginzburg-Landau theory. The ratio of the parallel and the perpendicular to the c-axis is 5.7.     

NMR in single crystal metallic ferromagnets: GdAl2

Necessary conditions to observe NMR in wall-free metallic single crystal ferromagnets are formulated. ²⁷Al NMR study in a magnetized single crystal GdAl₂ confirms the validity of the preconditions. Improved resolution and control over orientation, both inherent to single crystal study, enable for the first time an angular dependent NMR measurement of hyperfine interaction in metallic ferromagnetic system. The significance of the measured hyperfine tensor $\text{A}\text{?}\text{(A}{}_{\mathrm{\chi \chi }}\text{/λ}\text{h}\text{?}\text{= A}{}_{\mathrm{yy}}\text{/λ}\text{h}\text{?}\text{= - 14.825}\text{kG}$; $\text{A}{}_{\mathrm{zz}}\text{/gl}\text{h}\text{?}\text{= - 15.313}\text{kG}$) is briefly discussed.     

Metamagnetism in ErGa2 studied on a single crystal

Magnetization measurements and neutron difrraction experiments were performed on a single crystal of ErGa₂. Because of the strong crystal field effects a huge uniaxial anisotropy imposes the Er moments to be parallel to the c-axis of the hexagonal structure. We have shown that the transition from the antiferromagnetic structure to the ferromagnetic one, when the field is applied along c, occurs through an intermediate phase. Such a behaviour is very well accounted for using a simple Ising-like model which takes into account first and second nearest neighbours exchange interactions in the hexagonal layers. A quantitative determination of the crystalline electric field effects is also presented.     

Structural determination of CoIn2S4 single crystal spinel

Single crystals of the spinel CoIn₂S₄ were grown by iodine vapor transport. The structural determination leads to Fd3m space group with Co²⁺ ions distribution between O_h (63%) and T_d (37%) sites of the spinel structure.     

Bi2ZnOB2O6单晶偏振拉曼光谱

本文通过分析不同几何配置下的偏振拉曼光谱对非线性光学晶体的晶格振动模式进行了研究. 首先根据因子群分析,将晶体的振动模按晶体对称群的不可约表示进行分类,其次测量了晶体在10–1600 cm^-1范围内,不同几何配置下的偏振拉曼光谱,并在此基础上指认了晶体的晶格振动模式. 300 cm^-1以下的振动峰,归结为晶体的外振动,来自[BiO₆],[ZnO₄],[BO₄]和[BO₃]原子基团的平动和转动;300cm^-1以上为晶体的内振动,主要与Bi-O,和Zn-O键振动有关. 晶体拉曼光谱中最高振动频率达到1407 cm^-1,被指认为[BO₃]三角形中B-O键的伸缩振动,体现了[BO₃]基团中高的电子非局域化程度. 关键词： 2ZnOB₂O₆单晶')" href="#">Bi₂ZnOB₂O₆单晶 偏振拉曼光谱 振动模式     

An electron diffraction evidence of charge density wave instability in 2H-NbSe2

A superlattice is observed by electron diffraction in 2H-NbSe₂ below the onset of charge density wave instability at 33.5 K.     

High-resolution heat capacity of SnCl2·2H2O single crystal

The heat capacity of SnCl₂·2H₂O single crystal was measured in the close vicinity of the phase transition temperature, T_c = 217.994 ± 0.01 K. Its anomalous part ΔC could be expressed as ΔC = A_± ⊥ (T ? T_c)/T_c⊥^-α_±, where α₊ = 0.492 ± 0.02, α_- = 0.492 ± 0.02, A₊ = 1.148 JK^?mol^?, and A_- = 1.155 JK^?mol^?. A quasi-isothermal absorption of the enthalpy amounting to 34 J mol^? was observed at T_c.     

Optical spectroscopy of Yb in the Cs2NaYF6 single crystal

Results of the optical spectroscopy investigation of the cubic paramagnetic center Yb³⁺ ion in the Cs₂NaYF₆ single crystal are presented. The Stark level energies of the Yb³⁺ multiplets are established from absorption, luminescence and excitation luminescence spectra and the crystal field parameters are calculated. Information about the phonon spectra of Cs₂NaYF₆ crystals is obtained from the electron-vibrational structure of the optical absorption and luminescence spectra.