J. K. Kjems

Singlet ground state magnetism: II. magnetic excitons in paramagnetic TbP

The magneticΓ1 –Γ4 exciton of the singlet ground state system TbP has been studied by inelastic neutron scattering above the antiferromagnetic ordering temperature. Considerable dispersion and a pronounced splitting was found in the [100] and [110] directions. Both the band width and the splitting increased rapidly as the transition temperature was approached in accordance with the predictions of the RPA-theory. The dispersion is analysed in terms of a phenomenological model using interactions up to the fourth nearest neighbour.

Elastic properties of CsCN

The temperature dependence of the elastic constants of CsCN exhibiting the CsCl structure was measured with ultrasonic and neutron techniques. The room temperature values were found to bec11=18.8,c12=10.7 andc44=2.95 1010 dyn/cm2. The sound waves inT2g andEg symmetries exhibit anomalous temperature effects which are similar but definitively weaker than those in the NaCl type cyanides. In addition we measured the acoustic phonon dispersion along [100] and [110]. These results are compared with recent molecular dynamics calculations.

Statics and dynamics of a glassy crystal: a NMR- and neutron scattering investigation of (NaCl)0.35(NaCN)0.65

The statics and the dynamics of the glass transition in (NaCl)0.35(NaCN)0.65 have been investigated by inelastic neutron scattering and are directly compared to NMR results. Insight into the relaxation dynamics is gained via the temperature dependence of the transverse acoustic phonon modes and via the spin relaxation time T1. The statics of the system is reflected by the growth of a central peak and by the distribution of electric-field gradients. Both quantities are directly related to the glass order parameter. The temperature dependence of the order parameter provides experimental evidence that in NaCl:NaCN mixed crystals the glass transition is dominated by random fields rather than by frustration effects.

Anisotropic exchange in PrSn3

Abstract The intermetallic rare earth compound PrSn 3 has been investigated by neutron scattering. The wave vector dependence of the quasielastic paramagnetic scattering, the dispersion of the excitations of the antiferromagnetic phase and the temperature dependence of the sublattice magnetization indicate that the exchange coupling is highly anisotropic.

Singlet ground state magnetism: III. Magnetic excitons in antiferromagnetic TbP

The dispersion of the lowest magnetic excitations of the singlet ground state system TbP has been studied in the antiferromagnetic phase by inelastic neutron scattering. The magnetic exchange interaction and the magnetic and the rhombohedral molecular fields have been determined.

A neutron scattering study of the magnetic properties of PrSn3

The intermetallic compound PrSn3 has been studied by elastic and inelastic neutron scattering. The paramagnetic phase shows overdamped crystal field excitations and an anisotropic distribution of the diffuse magnetic intensity. The dispersion relation of the excitations of the antiferromagnetic phase has been determined. The results are analyzed in terms of an anisotropic exchange coupling.

Soft Modes and Mode Splitting in Paramagnetic TbP

In contrast to spin-only systems the paramagnetic phases of systems with crystal field split ground multiplets exhibit magnetic excitations of finite energy. In the presence of a magnetic exchange coupling the excitons will propagate through the lattice. A measurement of the dispersion allows in principle an insight into the exchange interaction, which is of fundamental importance for the understanding of the magnetic phenomena. Unfortunately the evolution of the dispersion at low temperatures is in most cases interrupted by the onset of magnetic order due to an alignment of the magnetic moments of the crystal field ground state. A noticeable dispersion of well-defined excitons is only expected in systems with non-magnetic ground states if in addition the exchange is about equal to the crystal field energies1. This criterion is very restrictive and only a few systems are known in the literature which meet the condition.

Magnetic excitations in TbP

Abstract The magnetic Г 1 - Г 4 exciton of the singlet ground state system TbP has been studied by inelastic neutron scattering above the antiferromagnetic ordering temperature. It showed considerable dispersion and a pronounced splitting in the [001] and the [110] directions which increased as the transition temperature was approached in accordance with the predictions of the RPA-theory.