Crystalline electric field excitations in Weyl semimetal \textit{R}AlSi (\textit{R} = Ce, Pr and Nd)

TL;DR

This study investigates the crystalline electric field excitations in RAlSi compounds with R = Ce, Pr, Nd, revealing their magnetic anisotropies and interactions using inelastic neutron scattering and other measurements.

Contribution

It provides detailed CEF parameters and ground state wave functions for Ce, Pr, and Nd in RAlSi, highlighting differences in magnetic anisotropy and interactions among these compounds.

Findings

CeAlSi shows CEF excitations at 19.2 and 24.9 meV.

PrAlSi exhibits a CEF excitation at 5.4 meV.

NdAlSi has CEF excitations at 2.5 and 4.2 meV.

Abstract

The rare earth intermetallic system \textit{R}Al\textit{X} (\textit{R} = rare earth elements, \textit{X} = Si and Ge) is known to be a promising candidate of magnetic Weyl semimetal. Due to the complex interactions between the rare earth elements and surrounding atoms, as well as hybridization with itinerant electrons, this family likely possesses highly intriguing and novel magnetic structures and thus exhibits dynamic behaviors. We systematically probe polycrystalline samples of \textit{R}AlSi (\textit{R} = La, Ce, Pr and Nd) combining inelastic neutron scattering (INS), heat capacity and magnetic susceptibility measurements. The INS measurements identify well-resolved crystalline electric field (CEF) excitations at 19.2 and 24.9 meV in CeAlSi, at 5.4 meV in PrAlSi, and at 2.5 and 4.2 meV in NdAlSi. We analyzed the INS data using the corresponding CEF models and determined the CEF parameters and ground state wave functions of \textit{R}AlSi (\textit{R} = Ce, Pr and Nd). Our results suggest strong single-ion anisotropy in their ground states: $|\pm3/2\rangle$ (94.5\%) in CeAlSi, $|\pm3\rangle$ (99.2\%) in PrAlSi, and $|\pm9/2\rangle$ (76.2\%) in NdAlSi. Notably, the weaker anisotropy and strong exchange interactions in NdAlSi promote competing magnetic orders and CEF splitting at low temperature, contrasting with the robust CEF levels in magnetic states of CeAlSi and PrAlSi.