Lattice dynamics of tetragonal R2BaCuO5 (R = La,Nd) oxides in the P4/mbm structure

A short‐range force constant model (SRFCM) has been applied to investigate the Raman and the infrared wavenumbers in R₂BaCuO₅ (R = La, Nd) in their tetragonal phase of space group P4/mbm. Calculations of zone‐center phonons are made with six stretching and five bending force constants. All the Raman and infrared values are then assigned to their corresponding modes. The force constants were evaluated by fitting ten Raman and eight infrared modes. The calculated Raman and infrared modes show good agreement with the observed values. Copyright © 2007 John Wiley & Sons, Ltd.     

Infrared spectroscopy of the Nd3+ ion in Nd2BaCuO5 and Nd2BaZnO5

Absorption spectra of the Nd³⁺ ion in the Nd₂BaCuO₅ and Nd₂BaZnO₅ ternary oxides were measured within broad spectral (1500–17000 cm^?1) and temperature (4.2–200 K) intervals. The positions and widths of the Stark sublevels were determined. The exchange splittings of the Nd³⁺ Kramers doublets in several multiplets were found for the magnetically ordered state of Nd₂BaCuO₅ (T _N =7.5 K).     

IR active phonons in single crystals RFe3(BO3)4 (R = Pr,Nd, and Sm)

We have studied the reflection and transmission spectra of multiferroics RFe₃(BO₃)₄ (R = Pr, Nd, and Sm) at room temperature. Simulation of reflection spectra by the dispersion-analysis method have allowed us to determine the frequencies and oscillator strengths of the majority of IR active A ₂ and E vibrational modes.     

Electronic structure and magnetism of RPdIn compounds (R=La, Ce, Pr, Nd)

RPdIn (R = La-Nd) compounds were studied by means of magnetic susceptibility, specific heat and photoelectron spectroscopy measurements. The results prove that CePdIn is an antiferromagnetic Kondo lattice with T_N below 1.7 K. The Pr-based indide remains paramagnetic down to 1.7 K, and the lack of any magnetic ordering may be due to the presence of a singlet as the crystalline electric field ground state or/and strong hybridization between Pr 4f states and Pd 4d states. In turn, NdPdIn exhibits ferromagnetism below about 26 K. In contrast to CePdIn, for the Pr- and Nd-based compounds any significant enhancement of the electronic specific heat coefficient was observed.     

Structural properties and charge ordered states in RMnO3 (R=La, Pr, Nd, Ca, Sr) and (La, Sr)2NiO4

Structural distortions arising from the condensations of two essential kinds of phonon modes: the triply degenerate rotational modes (phix, phiy, phiz) of MnO(6) and the doubly degenerate Jahn-Teller active modes (Q1, Q2) have been systematically investigated in the perovskite manganites. Microstructural features associated with certain types of distortions have been observed by transmission electron microscopy (TEM). In RMnO(3) and La(Sr)(2)NiO(4), we characterize the local structure, charge ordered states and orbital ordering by means of low-temperature TEM. We present direct evidence that the stripe modulation in La(Sr)(2)NiO(4) is indeed one-dimensional within each NiO(2) plane. Several typical kinds of defect structures, including antiphase boundaries and the 90 degrees -twin domains, appear commonly in the charge-ordered states.     

Optical properties of the charge-density-wave polychalcogenide compounds R 2Te 5 (R=Nd, Sm and Gd)

We investigate the rare-earth polychalcogenide R₂Te₅ (R=Nd, Sm and Gd) charge-density-wave (CDW) compounds by optical reflectivity measurements. We obtain the optical conductivity through Kramers-Kronig transformation of the reflectivity spectra. From the real part of the optical conductivity we then extract the excitation energy of the CDW gap and estimate the fraction of the Fermi surface which is gapped by the formation of the CDW condensate. In analogy to previous findings on the related RTe_n (n=2 and 3) families, we establish the progressive closing of the CDW gap and the moderate enhancement of the metallic component upon chemically compressing the lattice.     

Enhanced susceptibility in LNiO3 perovskites ( L = La,Pr,Nd,Nd0.5Sm0. 5)

The temperature dependence of the resistivity rho(T) and of the dc magnetic susceptibility chi(T) were measured on high-quality LNiO3 (L = La,Pr,Nd,Nd0.5Sm0.5) samples synthesized under high oxygen pressure. Subtraction of the rare-earth contribution to chi(T) allows the presentation of the evolution of the susceptibility of the NiO3 array from Pauli to Curie-Weiss paramagnetism with decreasing bandwidth. A metal-insulator transition occurring at a temperature T(t) = T(N) is first order for L = Pr and Nd; it becomes second order and produces no anomaly in chi(-1)(T) at a T(t)>T(N) for L = Nd0.5Sm0.5. In the antiferromagnetic domain T相似文献   

119Sn Mössbauer spectra of RMnSn2 intermetallics (R = La,Ce, Pr,Nd, Sm)

The ternary stannide series of RMnSn₂ compounds crystallize in the defect orthorhombic CeNiSi₂-type structure. They order magnetically close to room temperature. Isomer shifts are approximately 1.9 and 2.8 mm/s at the two tin sites, and there are transferred hyperfine fields of 3–6 T at 15 K, which depend on the rare-earth partner, especially at Sn₂ sites. The magnitude of the transferred hyperfine field per manganese neighbour is 4T.     

First-principles investigations of the physical properties of RCd (R=Ce,La, Pr,Nd)

The crystal structural, electronic, elastic and the thermodynamic properties of RCd are investigated by using the first-principles plane-wave pseudopotential density function theory within the generalized gradient approximation (GGA). The calculated equilibrium lattice parameters for RCd are in good agreement with the available experimental data. Furthermore, the optical properties, namely the dielectric function, refractive index and electron energy loss are reported for radiation up to 30 eV. Finally, the elastic properties, the bulk modulus and the Debye temperature of RCd are given for reference.     

Superconductivity in self-flux-synthesized single crystalline R_2Pt_3Ge_5(R=La,Ce,Pr)

In order to study the basic superconductivity properties of R_2Pt_3Ge_5, we synthesized the single crystalline samples by the Pt–Ge self-flux method. R_2Pt_3Ge_5(R = La, Ce) were also grown for a systematic study. Zero-resistivity was observed in both the La-and Pr-based samples below the reported superconducting transition temperatures. However, magnetic susceptibility measurements showed low superconductivity volume fractions in both La_2Pt_3Ge_5 and R_2Pt_3Ge_5(less than2%). Ce_2Pt_3Ge_5 did not show any signature of superconductivity. From the specific heat measurements, we did not observe a superconducting transition peak in R_2Pt_3Ge_5, suggesting that it is not a bulk superconductor. The magnetic susceptibility and heat capacity measurements revealed two antiferromagnetic(AFM) orders in R_2Pt_3Ge_5 at T_(N1)= 4.2 K and T_(N2)= 3.5K, as well as a single AFM transition at TN= 3.8 K in Ce_2Pt_3Ge_5.     

Thermal vibrations and the structure of quasi-two-dimensional R 2CuO4 crystals (R=La, Pr, Nd, Sm, Eu, and Gd)

Thermal vibrations of ions in R ₂CuO₄ crystals (R=La, Pr, Nd, Sm, Eu, Gd) were studied by x-ray diffractometry. A comparative analysis of thermal displacements of the copper and rare-earth ions permitted a conclusion as to the main interactions responsible for the structural state of the CuO₂ sheets and of a crystal as a whole. The structural properties were found to correlate with the magnitude of the ionic radius and with the ground state of the rare-earth ions.