Detection of Neutron Scattering from Phase IV of Ce0.7La0.3B6: A Confirmation of the Octupole Order

TL;DR

This study used neutron scattering to confirm that the order parameter in phase IV of Ce0.7La0.3B6 is a magnetic octupole, providing microscopic evidence for complex multipolar order in f-electron systems.

Contribution

First direct neutron scattering evidence of octupole order in Ce0.7La0.3B6, confirming theoretical predictions about high-rank multipoles.

Findings

Detected superlattice reflections at (h/2,h/2,l/2) below 1.5 K.

Intensity variation suggests complex magnetization density.

Supports the octupole order hypothesis in phase IV.

Abstract

We have performed a single crystal neutron scattering experiment on Ce0.7La0.3B6 to investigate the order parameter of phase IV microscopically. Below the phase transition temperature 1.5 K of phase IV, weak but distinct superlattice reflections at the scattering vector (h/2,h/2,l/2) (h, l = odd number) have been observed by neutron scattering for the first time. The intensity of the superlattice reflections is stronger for high scattering vectors, which is quite different from the usual magnetic form factor of magnetic dipoles. This result directly evidences that the order parameter of phase IV has a complex magnetization density, consistent with the recent experimental and theoretical prediction in which the order parameter is the magnetic octupoles Tbeta with Gamma5 symmetry of point group Oh. Neutron scattering experiments using short wavelength neutrons, as done in this study, could become a general method to study the high-rank multipoles in f electron systems.