Magnetic order and excitations in Ce$_3$TiBi$_5$ and Ce$_3$ZrBi$_5$

TL;DR

This study uses neutron scattering to explore the magnetic structure, excitations, and crystal electric field effects in Ce3TiBi5 and Ce3ZrBi5, revealing incommensurate antiferromagnetic order, Kondo hybridization, and unconventional magnetic behavior.

Contribution

It provides the first detailed neutron scattering analysis of Ce3TiBi5 and Ce3ZrBi5, highlighting their complex magnetic order and the interplay of Kondo effects and RKKY interactions.

Findings

Incommensurate cycloidal antiferromagnetic order in Ce3TiBi5 and Ce3ZrBi5.

Well-separated crystal electric field excitations indicating a Kramers doublet ground state.

Presence of sizable Kondo hybridization influencing magnetic order.

Abstract

The R3MBi5 rare-earth intermetallics (R = rare earth, M = Ti, Zr, Sc) provide a versatile platform to explore how Kondo hybridization, RKKY exchange, magnetic frustration, and broken inversion symmetry may cooperate to generate unusual magnetic behavior. We present a comprehensive neutron scattering investigation of the magnetic structure, crystal electric field (CEF), and low-energy excitations in the locally noncentrosymmetric Kondo-lattice compounds Ce3TiBi5 and Ce3ZrBi5. Powder and single-crystal neutron diffraction reveals incommensurate cycloidal antiferromagnetic order in Ce3TiBi5 with propagation vector k = (0, 0, 0.388) and a reduced ordered moment of m = 0.53(3)$\mu_{B}$. Ce3ZrBi5 exhibits a qualitatively similar magnetic diffraction profile, with k $\simeq$ (0, 0, 0.37). Inelastic neutron scattering measurements resolve two clear, well-separated CEF excitations in both compounds with nearly the same profile, confirming a well-isolated Kramers doublet ground state. At low energies, a broad, quasi-elastic magnetic response is observed at T $\simeq$ TN, whose momentum-dependence is inconsistent with that expected from conventional collective excitations of localized moments. This discrepancy, along with a Kondo temperature estimate TK ~ 3--5 K -- comparable to TN -- indicates sizable Kondo hybridization, which accounts for the moment reduction and the spiral magnetic order that appears to involve the magnetic hard direction. Our results place these compounds in a regime where local inversion symmetry breaking, anisotropic CEF effects, and competing Kondo and RKKY interactions collectively give rise to unconventional magnetic order.