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RESEARCH PRODUCT

Crystal Field Excitations in CeAgl−xInx Compounds

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The substitution of the monovalent Ag for the trivalent In in LaAgl−xInx and CeAgl−xInx offers the possibility of influencing the conduction electron system in these compounds. The strong dependence of the spin susceptibility of La-systems on the In-concentration1 was interpreted by band calculations which suggest that the Fermi level is pushed into a region of a high 5d-eg-band density of states2. Furthermore, CeAgl−xInx is one of the rare 4f systems where a structural phase transition (from cubic to tetragonal) occurs prior to magnetic ordering. The ferromagnetic Curie temperature TC is roughly independent of x whereas the structural transition temperature Ts rises from 15 K for CeAg to about 120 K for GeAg0.8In0.2 3,4. The simple fact that the dependence of Ts on x is almost identical for the Ce- and La-compounds shows that the early view put forward by Ray and Sivardiere5 that the structural transition is driven by the interacting electric quadrupoles of the 4f states is incorrect. Nevertheless, the reduced lattice symmetry should affect the magnetic properties below Ts via the crystal field (CEF).