Theory of excitation behavior for Ce3+ systems with Coqblin-Schrieffer interaction

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Abstract
Following Siemann and Cooper, we consider the Ce3+ system with Coqblin‐Schrieffer‐type (CS) interaction, and examine the excitation behavior of the system. We first show that longer‐range antiferromagnetic CS interaction stabilizes the type IA ordering, and yields phase transitions in the applied field, in agreement with experiment. The excitation spectra for ferromagnetically ordered CS systems, including the field induced system, are then calculated in RPA. The spectra show anisotropic dispersion, and yield a low lying mode for q↘ along the direction of magnetic ordering. In the system which orders ferromagnetically in the zero field, this mode has zero energy at the zone center. In the field induced ferromagnet, the low lying mode shows finite gap, with a minimum at (0, 0,π/a), halfway to the zone boundary.