Magnetic properties of triangular lattice antiferromagnets Ba3RB9O18 (R = Yb, Er)

TL;DR

This study investigates the magnetic properties of Ba3RB9O18 (R=Yb, Er), revealing no long-range order down to very low temperatures, and elucidates the crystal electric field effects and magnetic interactions in these triangular lattice antiferromagnets.

Contribution

It provides detailed experimental and theoretical analysis of the magnetic behavior and crystal electric field effects in Ba3RB9O18, a rare-earth triangular lattice antiferromagnet, highlighting the absence of magnetic order and the nature of magnetic interactions.

Findings

Yb variant shows pseudospin Jeff=1/2 with weak antiferromagnetic interaction.

Er variant exhibits strong antiferromagnetic interaction and no long-range order down to 500 mK.

Crystal electric field calculations match experimental susceptibility and specific heat data.

Abstract

Frustration, spin correlations and interplay between competing degrees of freedom are some of the key ingredients that underlie exotic states with fractional excitations in quantum materials. Rare-earth based two dimensional magnetic lattice wherein crystal electric field, spin-orbit coupling, anisotropy and electron correlation between rare-earth moments offer a new paradigm in this context. Herein, we present crystal structure, magnetic susceptibility and specific heat accompanied by crystal electric field calculations on the polycrystalline sample of Ba3RB9O18 (R = Yb, Er) in which R3+ ions form a perfect triangular lattice without anti-site disorder. The localized R3+ spins show neither long-range order nor spin-glass state down to 1.9 K in Ba3RB9O18. Magnetization data reveal a pseudospin Jeff = 1/2 ( Yb3+) in the Kramers doublet state and a weak antiferromagnetic interaction between Jeff = 1/2 moments in the Yb variant. On the other hand, the effective moment {\mu}eff = 8.8 {\mu}B was obtained from the Curie-Weiss fit of the low-temperature susceptibility data of Er variant suggests the admixture of higher crystal electric field states with the ground state. The Curie-Weiss fit of low-temperature susceptibility data for Er system unveils the presence of a relatively strong antiferromagnetic interaction between Er3+ moments compared to its Yb3+ analog. Ba3ErB9O18 does not show long-range magnetic ordering down to 500 mK. Furthermore, our crystal electric field calculations based on magnetization data of Ba3ErB9O18 suggest the presence of a small gap between the ground and first excited Kramers doublets. The broad maximum around 4 K in magnetic specific heat in zero-field is attributed to the thermal population of the first CEF excited state in Ba3ErB9O18, which is consistent with our CEF calculations.