THEORY OF ANISOTROPIC HYBRIDIZATION-BROADENED MAGNETIC RESPONSE IN CERIUM AND ACTINIDE SYSTEMS

Inelastic-neutron-scattering measurements on cerium and plutonium mono pnictides, thought to have moderately delocalized f electrons, yield m agnetic-excitation spectra with anisotropic dispersion; while reasonab ly sharp excitations have been observed only for USb and UTe among pre sumably more-delocalized uranium monopnictides and monochalcogenides. For UTe the broadening as well as the dispersion is quite anisotropic. We have now extended our previous theory for the magnetic behavior of hybridizing partially delocalized f-electron systems to include hybri dization-induced relaxation effects in the magnetic response, and this work and results are reported in the present paper. Each partially de localized f-electron ion is coupled by hybridization to the band sea; and this both leads to a hybridization-mediated anisotropic two-ion in teraction giving magnetic ordering and also gives a damping mechanism, via the coupling to the band sea, for the excitations of the magnetic ally ordered lattice. This coupling also provides a strong renormaliza tion of the magnetic-excitation energies obtained for the ionic lattic e coupled by the two-ion interaction. To treat these effects on the ma gnetic response we have developed a formalism for calculating the dyna mic susceptibility based on the projection-operator method developed b y Mori and others. We have applied our model and theory to the behavio r of CeSb, CeBi, PuSb, UP, UAs, and UTe; and excellent overall agreeme nt with the wide range of unusual experimentally observed anisotropic magnetic-excitation behavior is obtained.