Crystal-field anisotropy

For lanthanides other than Gd(III), the magnetic anisotropy still depends on the the local coordination environment it determines which crystal field anisotropy terms in Equation 7.2 are allowed by symmetry, the rest simply vanish. However,... 

Besides the isomer shift, the experimental linewidth and the electric field gradient, information about the crystal-field anisotropy can also be obtained from Yb Mossbauer spectroscopy, as shown by Bonville et al. (1990) and Bonville and Hodges (1985) for YbCuAl. Furthermore, YbCuAl was investigated by Yb Mossbauer spectroscopy at pressures up to ISOkbar. The data give strong evidence for a valence transition towards the 4f (Yb ) configuration. At 4.2 K the transition is completed at about SOkbar (Schdppner et al. 1986). This behavior is paralleled by the pressure-dependent susceptibility measurements (Klaasse et al. 1977). 

The form of the interaction of 4f moments in the lanthanides is further modified by both the crystal-field anisotropy and magnetostriction. The former is predominantly a single-ion interaction in the lanthanides and arises from the Coulomb coupling of the local spin moment (via the spin-orbit interaction) to the hexagonally symmetric charge cloud of the neighboring ions. Stevens (1952) was instrumental in providing the definitive description of this interaction via a series of operator equivalents of the spherical harmonics which describe in effect the quad-... 

All f 2Cu2ln indides order ferromagnetically with Curie temperatures between 26.7 and 85.5 K. Strong crystal field anisotropies result in Tc values that do not scale with the de Getmes frmction of the rare earth elements (Fisher et al., 1999). Dy2Cu2ln shows a second phase transition to an antiferromagnetic ground state at 7n = 22 K. 

X -I- 2x l) are shown in fig, 63. In this model the two broad inelastic peaks observed in the neutron scattering experiments are not related to crystal field transitions but to electronic transitions due to the assumed large characteristic energy (temperature) of this VF system. The crystal field anisotropy is reflected in the different position of the broad peak for xf(m) and xl(< )- This model, however, does not explain the low-energy response (<6meV, see fig. 61) and the presence of two broad inelastic peaks in the single crystal spectra for all g-vectors (see fig. 62). 

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