Mala N. Rao

Inelastic neutron scattering in ferromagnetic Kondo lattice compounds

An inelastic neutron scattering investigation of the ferromagnetic Kondo lattice compounds belonging to the system that have x = 0.7, 1.0, and 1.3 is reported. In these compounds, the ground state is expected to be split by a crystalline electric field. Using the experimental results, we have calculated the crystal-field parameters for all three compounds studied here.

Magnetic spectral response of cerium based Kondo systems

Abstract Inelastic neutron scattering studies on two cerium Kondo systems, CeSiGa and CeSn 2 In are reported. In CeSiGa the thermal evolution of the quasielastic line width indicates a strong competition between Kondo and RKKY interaction and the spectral response shows only one inelastic peak, the possible reasons for this behaviour are discussed. In the case of CeSn 2 In our results agree well with those of previous workers.

Spin dynamics of CeSi2-xGax, 0.7 ≤ x ≤ 1.3

Abstract In this paper we report inelastic neutron scattering experiments performed on CeSi 2− x Ga x , 0.7⩽ x ⩽1.3. The thermal evolution of quasielastic linewidth indicates a crossover from a magnetic 4f metal type state of Ce ion to a dense ferromagnetic Kondo system in these compounds.

Inelastic neutron scattering investigations of negative thermal expansion behavior in semiconductors and framework solids

Volume 25 • Number 1 • 2014 Neutron News 34 Negative thermal expansion (NTE) is known in simple compounds like ZnSe as well as framework compounds like Zn(CN)2 [1] and Cu2O [2]. In Cu2O, the Cu atoms are linearly coordinated by two oxygen atoms, while oxygen is tetrahedrally coordinated by four Cu atoms. EXAFS data [3] on intranetwork and internetwork Cu-Cu distances suggest different thermal expansion of these bonds above 100 K, which is not possible in the cubic structure; no structural changes have been reported from diffraction experiments too. Zn(CN)2 is reported [4] to have an isotropic NTE coeffi cient (αV = –51 × 10 -6 K-1). The ordered structure of Zn(CN)2 consists of a ZnC4 tetrahedron (at the centre of the cell) linked to four neighbouring ZnN4 tetrahedra (at the corners of the cell) with CN groups along four of the body diagonals. Low energy (large-amplitude) transverse modes have been identifi ed as the principal cause of anomalous thermal expansion in framework compounds. At ambient pressure, ZnSe, Zn(CN)2 as well as Cu2O crystallize in the cubic structure. ZnSe has a transition [5] to a rocksalt phase at about 13.7 GPa. Theoretical studies [6] predicted that ZnSe could transform from zincblende to SC16 (simple cubic with 16-atom basis) phase, and then to rocksalt. But the SC16 phase has not been observed experimentally in this material, upon either pressure increase or decrease. For the semiconductor alloy ZnS1-xSex, infrared and Raman spectra [7] reveal a two-mode behavior (corresponding to ZnSe-like vibrations and ZnS-like ones). Two additional modes were also observed in the region of the ZnS-like modes. In all the four materials, inelastic neutron scattering measurements were carried out to determine the phonon density of states and interpreted with lattice dynamics computations, for the calculation of the phonon frequencies, their pressure dependence, and to estimate their anharmonicity, thus leading to an insight to the phonon modes responsible for the NTE, the phase transitions and the nature of these modes.

Phonon Dynamics of Multiferroics: (Er, Tm) MnO3

The phonon dynamics of orthorhombic multiferroic perovskite RMnO3 (R = Er, Tm) using a shell model with pairwise interionic interaction potential has been investigated. The present work includes the computation of the structural parameters, phonon frequencies and the specific heat curves. The symmetry vectors obtained through detailed group‐theoretical analysis for Pnma space group at the zone center point were employed to classify the phonon frequencies obtained into their irreducible representations. The evaluated phonon dynamical properties are in good agreement with the available experimental data.