Crystal electric field

The pressure-dependent electrical resistivity of the heavy-fermion compound YbNi2B2C (see also Section 4.12) could be explained by competing contributions from crystal-electric-field splitting and Kondo effect (Oomi et al., 2006). The pressure-dependent room-temperature thermoelectric power of YNi2B2C exhibits a peak around 2 GPa, which was explained by changes in the Fermi-surface topology (Meenakshi et al., 1998). A possible correlation with a small peak in the temperature-dependent thermopower around 200 K (Fisher et al., 1995 Section 3.4.3) needs further investigation. 

The resonance frequency vNQR is very sensitive to the squared wavefunc-tion at the nucleus i// is(r = 0) 2, to the local crystal electric field, and also to temperature changes (Table 11.16). 

In the case of an unfilled 4f shell with more than one 4f electron, the potential energy of the ion in the crystal electric field may be written as... 

The crystal electric field Hamiltonian for some commonly encountered situations are as follows. 

Some information on crystal electric field levels can be obtained from the measurement of temperature-dependent Van Vleck susceptibility which can be described by the relationship... 

Mixing of configurations with opposite parity can occur if the contributions from V to the Hamiltonian contain terms with odd parity. The contribution from V arises due to the interaction of electrons of the ion with the crystal electric field which may be written as... 

Considering the crystal electric field as a first-order perturbation, the mixing of states with higher energy and opposite parity, nla"[S"l"]J"M") may be represented by iff") with A) and Z ) defined as... 

Gignoux, D., Givord, F., Lemaire, R. Paper No. L4, Second International Conf. on Crystal Electric Field Effects in Metals and Alloys, Zurich (1976). 

Crystal field theory A theory of bonding in transition metal complexes in which ligands and metal ions are treated as point charges a purely ionic model. Ligand point charges represent the crystal (electric) field perturbing the metal s d orbitals that contain nonbonding electrons. 

The specific resistivity of ferromagnetic YbNiSn was investigated for a single crystal (Bonville et al. 1992). From these measurements it is evident that the specific resistivity is the highest in the c-direction (fig. 15), where the ferromagnetie moments lie. Also the Kondo minimum and the crystal electric field effects are pronounced in this direetion. 

Crystal electric field parameters for YbPtBi have been derived from neutron scattering data (Robinson et al. 1993, 1995) and are interpreted in terms of strongly broadened crystal-field levels. The ground state is six-fold degenerate, consisting of a doublet (F7) and a quartet (Fg). Integration of the levels is in agreement with the experimentally derived linear specific-heat coefficient within an accuracy of 20%. Furthermore, ° Bi NMR... 

Luthi, B., 1974, Proc. 1st Conf. Crystal Electric Field Effects in Metals and Alloys, ed. R.A.B. Devine (Universite de Montreal). 

Luthi, B., M. Niksch, R. Takke, W. Assmus and W. Grill, 1982, in Crystal Electric Field Effects in f-Electron Magnetism, eds Guer-... 

CF crystal electric field NCW non-Curie-Weiss behavior... 

The electrical resistivities of the dense Kondo systems CeNiln, CePdln, and CePtln have been measured under hydrostatic pressures up to 19 kbar (Kurisu et al., 1990). The Kondo temperature of CeNiln and CePtln shifts linearly with pressure to higher temperatures at rates of 2.3 and 1.5 K/kbar, respectively. For CePdIn, the pressures were not high enough to reach the CePtln or CeNiln state. Measurements of the elastic properties of CePdln reveal that all elastic constants exhibit softening at low temperatures due to the crystal electric field effect and the antiferromagnetic ordering (Suzuki et al., 1990). 

Just as with liquid crystals, electric fields could be used to study defect mobility. For such a study one would want to begin with a well-defined and simple system. For example, two sections with uniformly aligned lamellae could be annealed together with an orthogonal lamellar orientation, thus forming a wall defect. Movement of the wall defect in response to an electric field would reveal the mobility of the wall, because the alignment force can be calculated and the velocity measured. 

AalAx static lattice expansion (due to H) CF crystal electric field... 

---