E. Holland-Moritz

Neutron scattering on concentrated and diluted mixed-valent Tm-systems

Abstract In this paper recent measurements are presented on dilute systems Tm 0.05 Y 0.95 Se and Tm 0.05 La 0.95 Se in comparison to the concentrated systems TmSe and TmSe 0.85 Te 0.15 . In the high temperature regime there exists a nearly temperature independent QE-linewidth and at low temperatures an inelastic line arises. As these effects are found in diluted systems as well as in the concentrated ones, they are interpreted as a single ion effect. The results are discussed with respect to some theoretical models.

Spin dynamics of metallic Ce systems

Abstract Neutron-scattering experiments on CeCu2Si2, CeB6, CeAl2, and (Ce,M)Al2 with M = La, Y, Sc reveal a common temperature dependence of the reduced quasielastic magnetic linewidth for these substances, i.e. Γ/Γ(T→0)= const +( T 1K ) 1 2 . Our results strongly suggest that all these systems are of “Kondo” rather than “intermediate-valence” type.

Spin dynamics of TmSe studied by neutron scattering

Abstract We have measured the dynamical susceptibility of the intermediate valence compound TmSe in the temperature range from 2 K to 300 K. Our data can be consistently explained assuming a mixture of 50% Tm 2+ being in a magnetic ground state and of 50% Tm 3+ being in a singlet ground state. Both phases seem to be homogeneous mixed above 100 K and separated below 100 K.

Crystal field phenomena in rare earth cuprates

Abstract We present some results pertaining to the crystal field (CF) interactions in high T c rare earth (RE) cuprates and related layered compounds and manifestations of their impact on magnetic properties. We show that the widely disputed specific-heat and susceptibility data in PrBa 2 Cu 3 O 7 can be interpreted consistently in terms of the standard CF theory for Pr 3+ based on the CF parameters extracted from the inelastic neutron scattering spectra via the superposition model. The CF-induced electric quadrupoles are shown to lead to thermal expansion anomalies in Sm 2 CuO 4 and REBa 2 Cu 3 O 7 compounds. We examine general conditions for an Ising-like behaviour of the RE subsystem. We conclude that such a behaviour may possibly occur in cuprates containing Tb, Dy and Ho owing to the special nature of low-lying 4f states imprinted by the CF interaction.

Recent developments in studying intermediate valent systems by neutron scattering

Abstract This paper deals with the problem of extracting residual Crystal-Field (CF) and/or spin-orbit splittings or other types of inelastic excitations from the usually rather broad and featureless spectra of the magnetic fluctuation of RE intermediate valent systems as seen by inelastic neutron scattering. Deviations of the true power spectrum from the simple single line Lorentzian fits are detected by comparison with the static suceptibility and with the valence. Such deviations exist in the spectra of all intermediate valent compounds studied so far. In a second part of this paper the first measurement of relaxation spectra of an intermediate valent Eu-compound is reported.

Final-state effects in divalent Eu pnictides

From Mossbauer effect, lattice constant and susceptibility measurements we show that Eu is nearly divalent in Eu(Cu,Ag,Au)(P,As,Sb). However, the LIII X-ray absorption spectra consist of a pronounced double structure, suggesting a non-integral mean Eu valence. The high-energy structure in the LIII-edge spectra is interpreted as a final-state (shake-up) effect. This finding strongly supports the existence of final-state effects in the LIII X-ray absorption spectra of divalent Eu compounds as previously reported by Sampathkumaran et al (1985) in EuPd2P2.

Magnetic excitations and quasielastic linewidths in YbBe13 from neutron scattering

Abstract Inelastic magnetic neutron spectra were taken on polycrystalline YbBe 13 between 1.2 and 300 K. At low temperatures the formation of a magnon corroborates the existence of a magnetic phase transition observed also by static susceptibility. At higher temperatures two distinct CF-transition lines are observed, which lead to the cubic CF-parameters x = 0.911 and W = 0.1543 meV . The magnetic quasielastic linewidth increases linearly with temperature and is anomalous large compared to TbBe 13 but small everywhere compared to k B T .

Crystal-field phenomena in PrBa2Cu3O6/O7 compounds

Abstract We present results of the inelastic neutron scattering and the heat capacity measurements in PrBa2Cu3O6/O7 compounds. It is shown that these data correspond to the crystal-field splitting predicted theoretically for trivalent Pr. Our data for oxygen-deficient compound at low temperatures indicate the lowering of the symmetry at the Pr site, possibly of the Jahn-Teller origin.

Temperature induced valence instabilities in ternary Eu-pnictides: a comprehensive view

We report on measurements of the lattice constants, magnetic susceptibility, LIII X-ray absorption and Mössbauer-effect on EuNiP and EuPdP, which crystallize in the hexagonal layered Ni2In structure. In both compounds the Eu valence above 510 K is 2.33. With decreasing temperature they show one (EuPdP) or two (EuNiP) first order phase transitions with a valence increase of about 0.16. At the same time thec-axis shrinks while the a-axis even increases. From Mössbauer measurements we show that the nature of the valence mixing is static. In contrast, the valence mixing in isostructural EuPtP is static at low temperatures, too, but it becomes homogeneous valent above a first order phase transition at 235 K. The behaviour of these compounds (as well as that of EuPdAs) is explained in a new model of electrostatically charged layers. In this model we can explain the temperature dependence of the lattice constants, the static valence mixing and the occurrence of preferred valences of the order 2 6/n. Together with the compression shift model of Hirst we can also understand the mechanism of the phase transitions. A comparison with EuT2Si2 compounds in ThCr2Si2 structure shows that in EuTX compounds only the electronic structure of the transition elements is relevant for the occurrence of mixed valency.

Temperature dependence of the magnetic excitation in URu2Si2

Abstract We present a temperature dependent investigation of the inelastic magnetic line in URu 2 Si 2 at about 6 meV which appears below T ≈ 50 K.