Interplay of itinerant electrons and Ising moments in a hybrid honeycomb quantum magnet TmNi$_3$Al$_9$

TL;DR

This study investigates the magnetic behavior of TmNi$_3$Al$_9$, revealing how Ising-like moments and itinerant electrons interact, leading to complex magnetic phases and enhanced quantum fluctuations near a critical magnetic field.

Contribution

It provides the first comprehensive experimental analysis of the magnetic phase diagram and quantum fluctuations in a honeycomb lattice magnet with Ising moments coupled to itinerant electrons.

Findings

Antiferromagnetic order below 2.97 K in zero field.

Suppression of antiferromagnetism and emergence of ferromagnetism above 0.92 T.

Enhanced quantum spin fluctuations near the critical field.

Abstract

The interplay between itinerant electrons and local magnetic moments in quantum materials brings about rich and fascinating phenomena and stimulates various developments in the theoretical framework. In this work, thermodynamic, electric transport, and neutron diffraction measurements were performed on a newly synthesized honeycomb lattice magnet TmNi$_3$Al$_9$. Based on the experimental data, a magnetic field temperature phase diagram was constructed, exhibiting three essentially different magnetic regions. Below ${T_{\rm N}=2.97 \pm 0.02}\ \rm K$ Tm$^{3+}$ moments order antiferromagnetically in zero field. We found that the Tm$^{3+}$ ions form a pseudo-doublet ground state with the Ising-like moments lying normal to the two-dimensional honeycomb layers. Application of a magnetic field along the easy axis gradually suppresses the antiferromagnetic order in favor of an induced ferromagnetic state above the critical field ${B_c=0.92 \pm 0.05}\ \rm T$. In the vicinity of $B_c$, a strong enhancement of the quantum spin fluctuations was observed. The quantum Ising nature of the local moments and the coupling to itinerant electrons are discussed.