Neutron scattering study of magnetic ordering and excitations in the ternary rare-earth diborocarbide Ce^{11}B_2C_2

Abstract

Neutron scattering experiments have been performed on the ternary rare-earth diborocarbide Ce${}^{11}$B${}_2$C${}_2$. The powder diffraction experiment confirms formation of a long-range magnetic order at $T_{\mathrm{N}}=7.3$ K, where a sinusoidally modulated structure is realized with the modulation vector $\mathbf{q}=[0.167(3),0.167(3),0.114(3)]$. Inelastic excitation spectra in the paramagnetic phase comprise significantly broad quasielastic and inelastic peaks centered at $\hslash \omega \approx 0,8$ and 65 meV. Crystalline-electric-field (CEF) analysis satisfactorily reproduces the observed spectra, confirming their CEF origin. The broadness of the quasielastic peak indicates strong spin fluctuations due to coupling between localized $4f$ spins and conduction electrons in the paramagnetic phase. A prominent feature is suppression of the quasielastic fluctuations, and concomitant growth of a sharp inelastic peak in a low energy region below $T_{\mathrm{N}}$. This suggests dissociation of the conduction and localized $4f$ electrons on ordering, and contrasts the presently observed incommensurate phase with spin-density-wave order frequently seen in heavy fermion compounds, such as Ce(Ru${}_{1-x}$La${}_x$)${}_2$Si${}_2$.

accepted for publication in Phys. Rev. B