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

TL;DR

This neutron scattering study reveals magnetic ordering and spin fluctuations in Ce11B2C2, showing a long-range order at 7.3 K, broad quasielastic peaks in the paramagnetic phase, and electron dissociation below the transition.

Contribution

First neutron scattering analysis of Ce11B2C2 demonstrating magnetic order, spin fluctuations, and electron dissociation phenomena in this compound.

Findings

Long-range magnetic order confirmed at 7.3 K with sinusoidal modulation.

Broad quasielastic peaks indicate strong spin fluctuations in the paramagnetic phase.

Suppression of quasielastic fluctuations and growth of inelastic peaks below T_N suggest electron dissociation.

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 $T_{\rm N} = 7.3$ K, where a sinusoidally modulated structure is realized with the modulation vector ${\bm q} = [0.167(3), 0.167(3), 0.114(3)]$. Inelastic excitation spectra in the paramagnetic phase comprise significantly broad quasielastic and inelastic peaks centered at $\hbar \omega \approx 0, 8$ 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 $T_{\rm N}$. 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$_2$.