Doping-induced redistribution of magnetic spectral weight in the substituted hexaborides Ce_1-xLa_xB₆ and Ce_1-xNd_xB₆

We investigate the doping-induced changes in the electronic structure of CeB6 on a series of substituted Ce1-xRxB6 samples (R = La, Nd) using diffuse neutron scattering. We observe a redistribution of magnetic spectral weight across the Brillouin zone, which we associate with the changes in the Fermi-surface nesting properties related to the modified charge carrier concentration. In particular, a strong diffuse peak at the corner of the Brillouin zone (R point), which coincides with the propagation vector of the elusive antiferroquadrupolar (AFQ) order in CeB6, is rapidly suppressed by both La and Nd doping, like the AFQ order itself. The corresponding spectral weight is transferred to the X(001/2) point, ultimately stabilizing a long-range AFM order at this wave vector at the Nd-rich side of the phase diagram. At an intermediate Nd concentration, a broad diffuse peak with multiple local maxima of intensity is observed around the X point, evidencing itinerant frustration that gives rise to multiple ordered phases for which Ce1-xNdxB6 is known. On the La-rich side of the phase diagram, however, dilution of the magnetic moments prevents the formation of a similar (001/2)-type order despite the presence of nesting. Our results demonstrate how diffuse neutron scattering can be used to probe the nesting vectors in complex f-electron systems directly, without reference to the single-particle band structure, and emphasize the role of Fermi surface geometry in stabilizing magnetic order in rare-earth hexaborides