Showing papers on "Spin wave published in 1998"
TL;DR: In this article, the Bogoliubov theory is extended to a Bose-Einstein condensation with internal degrees of freedom, realized recently in 23 Na gases where several hyperfine states are simultaneously cooled optically.
Abstract: The Bogoliubov theory is extended to a Bose-Einstein condensation with internal degrees of freedom, realized recently in 23 Na gases where several hyperfine states are simultaneously cooled optically. Starting with a Hamiltonian constructed from general gauge and spin rotation symmetry principles, fundamental equations for condensate are derived. The ground state where time reversal symmetry is broken in some cases and low-lying collective modes, e.g. spin and density wave modes, are discussed. Novel vortex as a topological defect can be created experimentally.
711 citations
TL;DR: In this article, the authors show that the decrease of the junction magnetoresistance with increasing dc bias is intrinsic to ferromagnetic junctions, and that the strong disagreement with recent theories in the low dc bias region can be attributed to magnetic excitations in these junctions.
Abstract: Careful tunneling studies in high quality $\mathrm{Co}/{\mathrm{Al}}_{2}{\mathrm{O}}_{3}/{\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}$ junctions show a junction magnetoresistance (JMR) of 20.2% and 27.1% at 295 and 77 K, respectively, where the latter is in agreement with Julliere's model. The temperature dependence of the JMR can be explained by the temperature dependence of surface magnetization. The decrease of the JMR with increasing dc bias is intrinsic to ferromagnetic junctions. The strong disagreement with recent theories in the low dc bias region can be attributed to magnetic excitations in these junctions, as seen in inelastic tunneling measurements.
350 citations
TL;DR: In this paper, the exact low energy spectra of the spin 1/2 Heisenberg antiferromagnet on small samples of the kagome lattice of up to N=36 sites were studied.
Abstract: We study the exact low energy spectra of the spin 1/2 Heisenberg antiferromagnet on small samples of the kagome lattice of up to N=36 sites. In agreement with the conclusions of previous authors, we find that these low energy spectra contradict the hypothesis of Neel type long range order. Certainly, the ground state of this system is a spin liquid, but its properties are rather unusual. The magnetic (
$$(\Delta S = 1)$$
) excitations are separated from the ground state by a gap. However, this gap is filled with nonmagnetic (
$$(\Delta S = 0)$$
) excitations. In the thermodynamic limit the spectrum of these nonmagnetic excitations will presumably develop into a gapless continuum adjacent to the ground state. Surprisingly, the eigenstates of samples with an odd number of sites, i.e. samples with an unsaturated spin, exhibit symmetries which could support long range chiral order. We do not know if these states will be true thermodynamic states or only metastable ones. In any case, the low energy properties of the spin 1/2 Heisenberg antiferromagnet on the kagome lattice clearly distinguish this system from either a short range RVB spin liquid or a standard chiral spin liquid. Presumably they are facets of a generically new state of frustrated two-dimensional quantum antiferromagnets.
276 citations
TL;DR: In this article, the wave-number-dependent exchange constant matrix is obtained from spin-density-functional calculations with constrained moment directions, and the central assumption considers a fast electronic and a slow magnetic time scale, and postulates negligible correlation of fast motion between different ionic sites.
Abstract: The adiabatic theory of spin-density waves is developed on the basis of spin-density-functional theory. The wave-number-dependent exchange constant matrix is obtained from spin-density-functional calculations with constrained moment directions. The central assumption considers a fast electronic and a slow magnetic time scale, and postulates negligible correlation of the fast motion between different ionic sites. The parameter-free calculated magnon spectra for Fe, Co, and Ni are in excellent agreement with available experimental data. In the case of Fe, they show strong Kohn anomalies. Using Planck statistics at low temperature, the temperature dependence of the magnetization is well described up to half the Curie temperature. It is conjectured that correlated local-moment clusters survive the Curie transition. On this basis, calculated Curie temperatures are obtained within $10%$ deviation from experiment for Fe and Co, but $30%$ to low for Ni.
217 citations
TL;DR: In this paper, two-dimensional neutron-scattering imaging of YBa2Cu3O6.6 was presented, which revealed that the low-frequency magnetic excitations are virtually identical to those of similarly doped La2−xSrxCuO4.
Abstract: An important feature of the high-transition-temperature (high-Tc) copper oxide superconductors is the magnetism that results from the spins associated with the incomplete outer electronic shells (3d9) of the copper ions. Fluctuations of these spins give rise to magnetic excitations of the material, and might mediate the electron pairing that leads to superconductivity. If the mechanism for high-Tc superconductivity is the same for all copper oxide systems, their spin fluctuations should be universal. But so far, theopposite has seemed to be the case: neutron scattering data reveal clear differences between the spin fluctuations for two major classes of high-Tc materials, La2−xSrxCuO4 (1-3) and YBa2Cu3O7−x (4-6), whose respective building blocks are CuO2 layers and bilayers. Here we report two-dimensional neutron-scattering imaging of YBa2Cu3O6.6, which reveals that the low-frequency magnetic excitations are virtually identical to those of similarly doped La2−xSrxCuO4. Thus, the high-temperature (Tc ≲ 92 K) superconductivity of the former materials may be related to spatially coherent low-frequency spin excitations that were previously thought to be unique to the lower-Tc (<40 K) single-layer La2−xSrxCuO4 family.
211 citations
TL;DR: In this paper, the low-energy magnetic excitations of nanographite ribbons with zigzag edges were investigated by a random phase approximation of the corresponding Hubbard model, which was used to derive an effective Heisenberg model with ladder structure.
Abstract: We consider the low-energy magnetic excitations of nanographite ribbons with zigzag edges. The zigzag ribbons possess almost flat bands at the Fermi level which cause a ferrimagnetic spin polarization localized at the edge sites. The spin wave mode of this magnetic state is investigated by a random phase approximation of the corresponding Hubbard model. This result is used to derive an effective Heisenberg model with ladder structure. Although this system has a spin gap (Haldane type), our analysis shows that the gap is small and the tendency towards ferrimagnetic correlation at the edges is strong.
202 citations
TL;DR: In this paper, the results obtained on nondeuterated samples provide the first direct measurement of the zero-field splitting in a large cluster nanomagnet, and a reliable and accurate determination of the composition of the cluster's spin wave functions and the spin-Hamiltonian parameters are deduced from the experimental observations, giving crucial information for the study of macroscopic quantum tunneling process.
Abstract: Neutron spectroscopy has been used to observe transitions between the energy levels for the 21 different orientations of the $S\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}10$ spin ground state of an octanuclear iron molecular cluster $({\mathrm{Fe}}_{8})$ exhibiting quantum tunneling of the magnetization. The results obtained on nondeuterated samples provide the first direct measurement of the zero-field splitting in a large cluster nanomagnet. A reliable and accurate determination of the composition of the cluster's spin wave functions and the spin-Hamiltonian parameters are deduced from the experimental observations, giving crucial information for the study of the macroscopic quantum tunneling process.
176 citations
TL;DR: In this paper, the effects of basic dissipative mechanisms involved in the dynamics of the magnetization field in terms of the spatial average of that field were analyzed, and two illustrative examples of these categories are treated; direct relaxation via magnetostriction into a lattice of known elastic constant, and indirect relaxation via excitation of many magnetic modes.
Abstract: The aim of this paper is to express the effects of basic dissipative mechanisms involved in the dynamics of the magnetization field in terms of the one most commonly observed quantity: the spatial average of that field. The mechanisms may be roughly divided into direct relaxation to the lattice, and indirect relaxation via excitation of many magnetic modes. Two illustrative examples of these categories are treated; direct relaxation via magnetostriction into a lattice of known elastic constant, and relaxation into synchronous spin waves brought about by imperfections. Finally, a somewhat speculative account is presented of time constants to be expected in magnetization reversal.
172 citations
TL;DR: In this article, Brillouin light scattering spectroscopy was used to observe quantized surface spin waves in periodic arrays of magnetic Ni81Fe19 wires by means of Brilloustime Spectroscopy.
Abstract: We report on the observation of quantized surface spin waves in periodic arrays of magnetic Ni81Fe19 wires by means of Brillouin light scattering spectroscopy. At small wavevectors (q_1 = 0 - 0.9*100000 cm^-1 ) several discrete, dispersionless modes with a frequency splitting of up to 0.9 GHz were observed for the wavevector oriented perpendicular to the wires. From the frequencies of the modes and the wavevector interval, where each mode is observed, the modes are identified as dipole-exchange surface spin wave modes of the film with quantized wavevector values determined by the boundary conditions at the lateral edges of the wires. With increasing wavevector the separation of the modes becomes smaller, and the frequencies of the discrete modes converge to the dispersion of the dipole-exchange surface mode of a continuous film.
167 citations
TL;DR: A detailed analysis of the two magnon scattering contribution to the microwave relaxation and ferromagnetic resonance linewidth in isotropic and anisotropic films and disks has been made in this paper.
Abstract: A detailed analysis of the two magnon scattering contribution to the microwave relaxation and ferromagnetic resonance linewidth in isotropic and anisotropic films and disks has been made. The analysis is based on the Sparks, Loudon, and Kittel (SLK) theory for the scattering of uniform mode magnons into degenerate spin wave states for isotropic spherical samples in the presence of magnetic inhomogeneities in the form of spherical voids or pores. The SLK theory has been extended to include: (i) thin film and thick film samples magnetized in an oblique out-of-plane direction; (ii) uniaxially anisotropic materials with either easy-axis or easy-plane anisotropy and an anisotropy axis perpendicular to the disk plane; (iii) a modified density of degenerate states to account for the nonzero relaxation rate of the scattered spin waves; and (iv) two limiting cases of the scattering interaction: (a) the original SLK case where the inhomogeneities are modeled as spherical voids and the coupling to the degenerate spi...
166 citations
TL;DR: In this article, the authors compare the behavior of ferromagnetic and antiferromagnetic Ising-type spin models on the cubic pyrochlore lattice, and show that the up-down spin models map onto the in-out spin models with the opposite sign of the exchange coupling.
Abstract: We compare the behaviour of ferromagnetic and antiferromagnetic Ising-type spin models on the cubic pyrochlore lattice. With simple `up - down' Ising spins, the antiferromagnet is highly frustrated and the ferromagnet is not. However, such spin symmetry cannot be realized on the pyrochlore lattice, since it requires a unique symmetry axis, which is incompatible with the cubic symmetry. The only two-state spin symmetry which is compatible is that with four local anisotropy axes, which direct the spins to point in or out of the tetrahedral plaquettes of the pyrochlore lattice. We show how the local `in - out' magnetic anisotropy reverses the roles of the ferro- and antiferromagnetic exchange couplings with regard to frustration, such that the ferromagnet is highly frustrated and the antiferromagnet is not. The in - out ferromagnet is a magnetic analogue of the ice model, which we have termed the `spin ice model'. It is realized in the material . The up - down antiferromagnet is also an analogue of the ice model, albeit a less direct one, as originally shown by Anderson. Combining these results shows that the up - down spin models map onto the in - out spin models with the opposite sign of the exchange coupling. We present Monte Carlo simulations of the susceptibility for each model, and discuss their relevance to experimental systems.
TL;DR: Inelastic neutron scattering from a single crystal of the quasi-two-dimensional antiferromagnet has been used to measure the spin wave dispersion curve at 4 K and the exchange integrals were subsequently calculated from linear spin wave theory as discussed by the authors.
Abstract: Inelastic neutron scattering from a single crystal of the quasi-two-dimensional antiferromagnet has been used to measure the spin wave dispersion curve at 4 K. The exchange integrals were subsequently calculated from linear spin wave theory. The values meV, meV, meV and meV are within stability conditions calculated from mean-field theory. In addition, the critical behaviour of the gap in the spin wave energy at the Brillouin zone centre has been measured, and compared to the critical behaviour of the magnetization from neutron scattering data of the magnetic (020) Bragg peak. The gap varies with magnetization for , and with the square of the magnetization for . Two possible explanations are proposed: a competition between single-ion and dipolar anisotropies; or a crossover to XY-like excitations.
TL;DR: In this article, the spin spin of an electron tunneling in a junction made up of magnetic electrodes is studied and it is found that magnetic impurities give a contribution which increases the resistance and lowers the magnetoresistance, which saturates at low temperatures.
Abstract: Processes which flip the spin of an electron tunneling in a junction made up of magnetic electrodes are studied. It is found that (i) magnetic impurities give a contribution which increases the resistance and lowers the magnetoresistance, which saturates at low temperatures. The conductance increases at high fields. (ii) Magnon assisted tunneling reduces the magnetoresistance as ${T}^{3/2}$ and leads to a nonohmic contribution to the resistance which goes as ${V}^{3/2}.$ (iii) Surface antiferromagnetic magnons, which may appear if the interface has different magnetic properties from the bulk, gives rise to ${T}^{2}$ and ${V}^{2}$ contributions to the magnetoresistance and resistance, respectively. (iv) Coulomb blockade effects may enhance the magnetoresistance, when transport is dominated by cotunneling processes.
TL;DR: In this article, the authors considered a Landau theory of coupled charge and spin-density wave order parameters as a simple model for the ordering that has been observed experimentally in the La{sub 2}NiO{sub 4} and La³ 2³CuO³³ ³µ families of doped antiferromagnets.
Abstract: We consider a Landau theory of coupled charge and spin-density-wave order parameters as a simple model for the ordering that has been observed experimentally in the La{sub 2}NiO{sub 4} and La{sub 2}CuO{sub 4} families of doped antiferromagnets. The period of the charge-density wave is generically half that of the spin-density wave, or equivalently the charges form antiphase domain walls in the antiferromagnetic order. A sharp distinction exists between the case in which the ordering is primarily charge driven (which produces a sequence of transitions in qualitative agreement with experiment) or spin driven (which does not). We also find that stripes with noncollinear spin order (i.e., spiral phases) are possible in a region of the phase diagram where the transition is spin driven; the spiral is circular only when there is no charge order, and is otherwise elliptical with an eccentricity proportional to the magnitude of the charge order. {copyright} {ital 1998} {ital The American Physical Society}
TL;DR: In this article, the attenuation of the echo amplitudes as a function of evolution time is presented for cymantrene and ferrocene polycrystalline samples, involving one and two five spin rings per molecule, respectively.
Abstract: The reversal of the time evolution of the local polarization in an interacting spin system involves a sign change of the effective dipolar Hamiltonian which refocuses the “spin diffusion” process generating a polarization echo. Here, the attenuation of these echo amplitudes as a function of evolution time is presented for cymantrene and ferrocene polycrystalline samples, involving one and two five spin rings per molecule, respectively. We calculate the fraction of polarization which is not refocused because only the secular part of the dipolar Hamiltonian is inverted. The results indicate that, as long as the spin dynamics is restricted to a single ring, the non-inverted part of the Hamiltonian is not able by itself to explain the whole decay of the polarization echoes. A crossover from exponential (cymantrene) to Gaussian (ferrocene) attenuation is experimentally observed. This is attributed to an increase of the relative importance of the spin dynamics, as compared with irreversible interactions, which favors dynamical irreversibility.
TL;DR: In this article, different mechanisms of spin-dependent tunneling are analyzed with respect to their role in tunnel magnetoresistance (TMR), and it is found that tunneling via resonant defect states in the barrier radically decreases the TMR by order of magnitude.
Abstract: Different mechanisms of spin-dependent tunneling are analyzed with respect to their role in tunnel magnetoresistance (TMR). Microscopic calculation within a realistic model shows that direct tunneling in iron group systems leads to about a 30% change in resistance, which is close but lower than experimentally observed values. The larger observed values of the TMR might be a result of tunneling involving surface polarized states. It is found that tunneling via resonant defect states in the barrier radically decreases the TMR by order of magnitude. One-magnon emission is shown to reduce the TMR, whereas phonons increase the effect. The inclusion of both magnons and phonons reasonably explains an unusual bias dependence of the TMR. The model presented here is applied qualitatively to half metallics with 100% spin polarization, where one-magnon processes are suppressed and the change in resistance in the absence of spin mixing on impurities may be arbitrarily large. Even in the case of imperfect magnetic configurations, the resistance change can be a few 1000%. Examples of half-metallic systems are CrO2/TiO2 and CrO2/RuO2.
TL;DR: In this article, the out-of-plane angular dependence of the ferromagnetic resonance linewidth, ΔH, has been measured for thin magnetic films coupled to NiO and for uncoupled control films.
Abstract: The out-of-plane angular dependence of the ferromagnetic resonance linewidth, ΔH, has been measured for thin magnetic films coupled to NiO and for uncoupled control films. In the control films, ΔH is described by nearly angle-independent damping parameters. In the NiO-coupled films, however, the damping was found to depend strongly on magnetization orientation, with linewidth values comparable to the control samples at normal orientation, but several times larger when the magnetization lies in plane. The additional linewidth in the NiO-coupled films follows the angular dependence of the number of nearly degenerate spin wave modes, in agreement with the predictions of a two-magnon scattering model of damping which incorporates a spin wave dispersion relation suitable for ultrathin films.
TL;DR: In this paper, the authors numerically investigate elementary excitations of the Heisenberg alternating-spin chains with two kinds of spins, 1 and $1/2,$ antiferromagnetic coupled to each other.
Abstract: We numerically investigate elementary excitations of the Heisenberg alternating-spin chains with two kinds of spins, 1 and $1/2,$ antiferromagnetically coupled to each other. Employing a recently developed efficient Monte Carlo technique as well as an exact-diagonalization method, we verify the spin-wave argument that the model exhibits two distinct excitations from the ground state which are gapless and gapped. The gapless branch shows a quadratic dispersion in the small-momentum region, which is of the ferromagnetic type. With the intention of elucidating the physical mechanism of both excitations, we make a perturbation approach from the decoupled-dimer limit. The gapless branch is directly related to spin 1's, while the gapped branch originates from cooperation of the two kinds of spins.
TL;DR: In this paper, the phase transition of the three-dimensional Ising spin glass with Gaussian couplings and of the low-temperature phase were characterized numerically. But they were not shown to be off-equilibrium.
Abstract: We characterize numerically the properties of the phase transition of the three-dimensional Ising spin glass with Gaussian couplings and of the low-temperature phase. We compute critical exponents on large lattices. We study in detail the overlap probability distribution and the equilibrium overlap-overlap correlation functions. We find a clear agreement with off-equilibrium results from previous work. These results strongly support the existence of a continuous spontaneous replica symmetry breaking in three-dimensional spin glasses.
TL;DR: In this paper, the generalized local force theorem for small nonuniform rotations of the spin magnetic moments near equilibrium has been applied to investigate abilities of several different first-principles techniques: local density approximation, LDA plus Hubbard $U$'' $(\mathrm{LDA}+U)$ and optimized effective potential (OEP).
Abstract: It is shown that the fundamental gauge-symmetry constraints superimposed on the admissible form of the exchange-correlation energy functional lead to the generalized local force theorem for small nonuniform rotations of the spin magnetic moments near equilibrium. The theorem suggests that the magnetic interactions responsible for the low-energy spin-wave excitations near the ground state can be expressed in terms of the effective single-particle potential designed for the ground-state spin-magnetization density. The theorem allows us to obtain an empirical effective potential for MnO by fitting the experimental low-temperature spin-wave dispersion curve. The theorem is further applied to investigate abilities of several different first-principles techniques: local-(spin)-density approximation, LDA plus ``Hubbard $U$'' $(\mathrm{LDA}+U)$ and optimized effective potential (OEP). None of these approaches treats the magnetic interactions in MnO properly. Limitations of the one-electron band picture underlying the failure are elucidated in each case. As one of the perspective techniques to deal with the electronic structure of narrow-band materials, we propose to combine the $\mathrm{LDA}+U$ form of the single-particle equations with the variational principles of the OEP approach. Several possible approximations along this line are discussed.
TL;DR: In this paper, high-resolution neutron scattering experiments have been carried out in order to study the interplay between magnetism and superconductivity in the heavy fermion superconductor.
Abstract: High resolution neutron scattering experiments have been carried out in order to study the interplay between magnetism and superconductivity in the heavy fermion superconductor ${\mathrm{UPd}}_{2}{\mathrm{Al}}_{3}$. We found direct evidence for a magnetic excitation gap associated with superconductivity. We observed $1%$ suppression of the antiferromagnetic Bragg intensities below the superconducting transition temperature ${T}_{c}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1.9\mathrm{K}$. We also observed the increases of the spin wave excitation energy and its linewidth in the superconducting state. These results indicate a strong coupling between magnetism and superconductivity in this compound.
TL;DR: In this article, the specific heat and magnetic susceptibility of the one-dimensional Heisenberg ferrimagnet with antiferromagnetically exchange-coupled spins of two kinds were calculated using a modified spinwave theory as well as a quantum Monte Carlo method.
Abstract: We study thermodynamic properties of the one-dimensional Heisenberg ferrimagnet with antiferromagnetically exchange-coupled spins of two kinds. The specific heat and the magnetic susceptibility are calculated employing a modified spin-wave theory as well as a quantum Monte Carlo method. The specific heat is proportional to ${T}^{1/2}$ at low enough temperatures but shows a Schottky-like peak at mid temperatures. The susceptibility diverges as ${T}^{\ensuremath{-}2}$. We reveal that at low temperatures the model acts as a ferromagnet, while at mid temperatures it behaves like a gapped antiferromagnet.
TL;DR: In this paper, the first observation of spatiotemporal self-focusing of spin waves is reported, and the experimental results are obtained for dipolar spin waves in yttrium-iron-garnet films by means of a newly developed space and time-resolved Brillouin light scattering technique.
Abstract: The first observation of spatiotemporal self-focusing of spin waves is reported. The experimental results are obtained for dipolar spin waves in yttrium-iron-garnet films by means of a newly developed space- and time-resolved Brillouin light scattering technique. They demonstrate self-focusing of a moving wave pulse in two spatial dimensions, and formation of localized two-dimensional wave packets, the collapse of which is stopped by dissipation. The experimental results are in good qualitative agreement with numerical simulations.
TL;DR: In this article, a non-perturbative method is presented for the calculation of spin Hamiltonian parameters of d″ ions, 1 ≤ n ≤ 9, which is based on a direct comparison of the spin Hamiltonians energies with the ligand field energies including spin-orbit coupling and Zeeman interaction of all-order perturbation.
TL;DR: In this article, specific heat measurements from 45 to 300 K were reported on a series of polycrystalline La1−xCaxMnO3−δ samples, with x=010, 033 and 062, using electrical transport, magnetic measurements and low temperature NMR.
TL;DR: In this article, the two hydrogen nuclei remain magnetically equivalent and therefore in a singlet state, despite this equivalence, an enhanced longitudinal magnetization is observed to decrease toward thermal equilibrium.
Abstract: Os3(CO)10(NCCH3)2 has been hydrogenated with para-hydrogen to yield H2Os3(CO)10 where the two hydrogen nuclei remain magnetically equivalent and therefore in a singlet state. Despite this equivalence, an enhanced longitudinal magnetization is observed to decrease toward thermal equilibrium. It is postulated that this enhanced magnetization is created through a nuclear relaxation interference mechanism (cross-correlation between dipolar interaction and chemical shift anisotropy); decay curves are then successfully analyzed by means of a spin relaxation theory adapted to this situation.
TL;DR: In this article, the authors present theoretical studies of the spin dynamics of bulk Fe and of ultrathin Fe(1.0) films, within an empirical tight binding description of the one electron energies.
TL;DR: In this paper, the authors studied bifurcations of localized stationary solutions of the externally driven, damped nonlinear Schrodinger equation iC t1Cxx12uCuC52igC2he in the region of large g.
Abstract: We study bifurcations of localized stationary solutions of the externally driven, damped nonlinear Schrodinger equation iC t1Cxx12uCuC52igC2he in the region of large g (g.1/2). For each pair of h and g , there are two coexisting solitons C1 and C2 . As the driver’s strength h increases for the fixed g , the C1 soliton merges with the flat background while the C2 forms a stationary collective state with two ‘‘C pluses’’: C2→C (121) . We obtain other stationary solutions and identify them as multisoliton complexes C (11) ,C (22) ,C (21) ,C (222) ,C (212) , etc. @S1063-651X~98!06002-4#
TL;DR: In this paper, the authors used time-of-flight spectrometers on an polycrystal to detect magnetic excitations and a gap at around 14.5 meV.
Abstract: Neutron scattering measurements have been performed with time-of-flight spectrometers on an polycrystal. The spectra show clearly the presence of magnetic excitations and a gap at around 14 meV. At low temperature, two broad signals , one asymmetric, the other one of Lorentzian shape, are well defined. After subtracting the phonon contribution, the former signal is further decomposed into a sharp 15.5 meV peak and a broader 20 meV peak. The 15.5 meV peak behaves similarly to that of the exciton at 14.5 meV for as regards both the Q- and T-dependencies. The 20 meV peak was identified as manifesting a transition from a localized Kondo singlet with a gap to a magnetic state. With decreasing temperature, the gap disappears and the scattering becomes quasi-elastic, like for the metallic Kondo system. The second signal, centred at 37 meV, was assigned previously to a crystal-field excitation. However, the observed behaviour is anomalous, indicating a shift of the intensity from the lower peaks to the higher peak, suggesting a change in the -value due to lattice distortion.