We discuss different physical effects which are caused by the crystalline electric field splitting of rare earth ions in metals. Thus, the rare earth ions may be impurities dissolved in a metallic matrix or they may form a regular lattice. In the former case we distinguish between the cases of a normal conducting and a superconducting matrix. The influence of the crystalline field splitting on the properties of the conduction electrons is calculated. In the case of a normal matrix anomalous behaviour of the thermoelectric power is found due to the impurity levels. If the matrix is superconducting large deviations result from the theory of Abrikosov and Gorkov which describes the influence of non-split magnetic impurities on superconductivity. A comparison of the theory with available experiments is presented. For the case that the rare earth ions form a regular lattice we discuss various aspects of the collective excitations in the paramagnetic state. Special attention is paid to the soft mode pr...

Some crystalline field effects in metals

A theory is developed for the line width of crystal-field excitations in metallic rare-earth systems were the damping is due to conduction electron-hole excitations. First the single ion or dilute alloy case is studied. As an example the theory is applied to Ce in LaAl2 and compared with recent experiments. Then the case of a regular lattice of rare-earth ions is considered. The theory is applied to theΓ
1 –Γ
4 system. Special attention is paid to the behaviour of the central peak near an induced-moment phase transition. It is shown that the dynamics of the conduction electrons leads to observable effects in the centralpeak intensity and can not be neglected as it is usually done. The theoretical predictions are in agreement with recent experimental findings on Pr3Tl.

Line width of crystal-field excitations in metallic rare-earth systems

Publisher Summary This chapter reviews a reasonable accounting of the magnetic and transport properties of rare earth metals and their alloys The rare earths, or lanthanides, are the trivalent 4f shell transition metals Their magnetic properties stem from unpaired electrons in the 4f shell 4f electron wave functions are confined close to the nucleus and that wave function overlap with neighboring atoms in a lattice is vanishingly small To account for the observed magnetic order in the rare earths, an indirect exchange mechanism via three 5d–6s conduction electrons is invoked Strong evidence to support this view comes from the observed spin polarization of the conduction electrons A wide variety of magnetic structures are displayed by the rare earth metals and their alloys These range from simple ferromagnetism to complex sinusoidal or helical ordering; the magnetic structure sometimes involves sublattices Because of the low magnetic moments of the light rare earths it is possible for electric crystal field effects to dominate the magnetic exchange interaction

Chapter 3 Rare earth metals and alloys

Collective excitations in the 1-D-ferromagnet CsFeCl3 with singlet ground state

The elastic constants of single crystals of double hcp allotrope of praseodymium have been measured over the temperature range 4.2–300 K. Maxima are observed near 100 K in the temperature dependences of C11, C33, and (C11 − C12)/2, and minima are observed near 30 K. The maxima correlate with the upper temperature limit of an anomalous contribution which has been reported in the heat capacity. The minima correlate with peculiar behavior which has been observed in other physical phenomena. Inference may be drawn from the elasticity data that the thermal expansion behavior of praseodymium at low temperatures is very highly anisotropic. Comparison of the elastic constants of praseodymium with available data for the other rare earths shows that the praseodymium data fit a general pattern. Evaluation from the elastic constants shows that the Debye temperature of praseodymium remains nearly constant throughout the temperature range of measurement within ± 2 K of 152 K.

Jens Christian Gylden Houmann

Papers

Magnetic Exciton Dispersion in Praseodymium