Strongly Quenched Kramers Doublet Magnetism in SmMgAl11O19

TL;DR

This study investigates SmMgAl11O19, revealing it as a weak-exchange, nearly single-ion Kramers doublet magnet on a triangular lattice with significant single-ion physics and no long-range magnetic order down to very low temperatures.

Contribution

It provides the first detailed characterization of SmMgAl11O19 as a strongly quenched Kramers doublet system dominated by single-ion effects rather than collective exchange.

Findings

Weak exchange interactions with a strongly quenched Kramers doublet.

Absence of long-range magnetic order down to 0.35 K.

Confirmation of an effective S=1/2 doublet ground state.

Abstract

We report magnetic susceptibility, isothermal magnetization, and specific-heat measurements on the rare-earth hexaaluminate SmMgAl$_{11}$O$_{19}$, where Sm$^{3+}$ realizes a strongly quenched Kramers doublet on a triangular lattice with an exceptionally weak net exchange scale. The Curie--Weiss analysis yields strongly reduced ground-doublet $g$ factors, $g_{ab}\simeq 0.65$ and $g_{c}\simeq 0.70$. This indicates that the low-temperature response is governed primarily by single-ion physics, with crystal-field splitting and $J$-multiplet mixing jointly renormalizing the Sm$^{3+}$ moment, rather than collective exchange. For $H \parallel c$, the specific heat shows no $\lambda$-type anomaly down to 0.35~K but evolves into a well-defined two-level Schottky peak whose gap grows linearly with field, yielding $g_c\simeq0.62$ and recovering nearly all of $R\ln2$ at high fields, thereby confirming an effective $S_{\mathrm{eff}}=\tfrac12$ Kramers doublet description for $T\lesssim10$~K. Together, these results establish SmMgAl$_{11}$O$_{19}$ as a weak-exchange, nearly single-ion triangular Kramers magnet in which frustration produce an anisotropic low-field correlated regime without inducing long-range order.