Spin-orbit transitions

The supposition that the spin-orbit coupling is relatively insensitive to the local ionic environment (see sect. 2.1.2) is amply confirmed by neutron measurements on metallic systems. The observed spin-orbit splittings are all very close in energy to those previously measured in optically transparent compounds. The only exceptions to this rule so far are in the intermediate valent compounds EuPd2Si2 (Holland-Moritz et al. 1987) and Smp 25S (Holland-Moritz et al. 1988), in which the transition energies are nearly 20% lower than in the free ion (Martin et al. 1978). 

This section is divided into two parts. In sect. 4.2 experiments on normal lanthanides, i.e. those in which the 4f configuration is believed to be stable, are reviewed. Except in the case of neodymium and thulium, the transitions so far observed are J J l. This is because the J J 2 transitions, which are not 

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The available recoil kinetic energy of 22,585 cm for the formation of S( P) from process 43 is much higher than the spin-orbit splitting Pi) = 377 cm [61,147]. The translational adiabaticity parameter for spin-orbit transition is given as (t = where a is the... 

The atomic form factor of Sm ions has a maximum at non-zero k as a consequence of the antiparallel alignment of L and S. The orbital contribution to the form factor is more extended in K-space than the spin contribution, and the partial cancellation of the two components produces a minimum at k = 0. By contrast, the structure factor of the spin-orbit transition is calcu-... 

Osborn et al. (1990) have observed the spin-orbit transition in... 

Coulomb repulsion between the electrons in the f shell and are much more sensitive to changes in the local environment than the spin-orbit transitions. They are therefore a useful probe of the way intra-atomic correlations are affected by the metallic state, particularly in the actinides. Nevertheless, there are relatively few investigations of Coulomb transitions in metals since their energies all exceed 500 meV and most exceed 1 eV, as can be seen in fig. 1. The lowest energies are found in Pr, Sm " and Tm, all of which have now been studied by neutrons (Taylor et al. 1988, Needham 1989, Osborn et al. 1990). Although Coulomb transitions are non-dipolar, they can have appreciable cross-sections at intermediate values of momentum transfer, and are, in many cases, stronger than the dipolar (i.e., J—>J 1) cross-sections at the same k. 

Fig. 44. Spin-orbit transition in CeSna-jIn t measured at 7 =20K with (, = 600meV on the HET spectrometer (redrawn from Murani et al. 1990b).

Preliminary experiments on the F7/2-> F5/2 spin-orbit transition by Osborn and Goremychkin (1991) locate this transition at (1374 12) meV and find an unusually large FWHM of 340 meV. The large width is taken as evidence for the strong hybridization of the f-shell with the conduction band. 

In both lanthanides and actinides the levels may be characterized by the notation Spin-orbit transitions are those between levels with the same value of L and S but different values of J. Since the neutron couples directly to the J quantum number, dipole transitions correspond to AJ = 1. The cross section is finite at Q = 0, but for increasing Q falls i jo) — in intensity, where the (70) and (72) functions are Bessel transforms... 

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