# Long-range magnetic order in the ${\tilde S}=1/2$ triangular lattice antiferromagnet KCeS$_2$

### Submission summary

 As Contributors: Gaël Bastien · Jeroen van den Brink Arxiv Link: https://arxiv.org/abs/2005.06300v3 (pdf) Date accepted: 2020-08-26 Date submitted: 2020-07-23 13:55 Submitted by: Bastien, Gaël Submitted to: SciPost Physics Academic field: Physics Specialties: Condensed Matter Physics - Experiment Condensed Matter Physics - Computational Inorganic Chemistry Approaches: Experimental, Computational

### Abstract

Recently, several putative quantum spin liquid (QSL) states were discovered in ${\tilde S} = 1/2$ rare-earth based triangular-lattice antiferromagnets (TLAF) with the delafossite structure. A way to clarify the origin of the QSL state in these systems is to identify ways to tune them from the putative QSL state towards long-range magnetic order. Here, we introduce the Ce-based TLAF KCeS$_2$ and show via low-temperature specific heat and $\mu$SR investigations that it yields magnetic order below $T_{\mathrm N} = 0.38$ K despite the same delafossite structure. We identify a well separated ${\tilde S} = 1/2$ ground state for KCeS$_2$ from inelastic neutron scattering and embedded-cluster quantum chemical calculations. Magnetization and electron spin resonance measurements on single crystals indicate a strong easy-plane $g$~factor anisotropy, in agreement with the ab initio calculations. Finally, our specific-heat studies reveal an in-plane anisotropy of the magnetic field-temperature phase diagram which may indicate anisotropic magnetic interactions in KCeS$_2$.

Published as SciPost Phys. 9, 041 (2020)

### Submission & Refereeing History

Resubmission 2005.06300v3 on 23 July 2020
Submission 2005.06300v2 on 5 June 2020

## Reports on this Submission

### Report

The small changes requested in the previous report are implemented.
The paper should be accepted as is.

• validity: -
• significance: -
• originality: -
• clarity: -
• formatting: -
• grammar: -

### Anonymous Report 1 on 2020-7-23 (Invited Report)

• Cite as: Anonymous, Report on arXiv:2005.06300v3, delivered 2020-07-23, doi: 10.21468/SciPost.Report.1853

### Strengths

1- extensive study of new triangular lattice antiferromagnet, KCeS2, member of a group of interesting materials for spin liquid physics

2- range of experimental and theoretical tools used is very large

### Weaknesses

1- authors cannot derive firm conclusions on controlling element of spin liquid vs. magnetic ground state

### Report

In the present work the authors present an extensive study of a new triangular lattice antiferromagnet, KCeS2, member of a group of interesting materials studied intensively for spin liquid physics. From a thermodynamic and microscopic study they firmly establish the ground state of the f-electron carrying element Ce, which is in a well-defined S=1/2 state. Moreover, again from a (different) thermodynamic and microscopic study they also establish that the material undergoes a transition into some kind of antiferromagnetic order at low temperatures and establish the basic features of the magnetic phase diagram. Taking all data together, the authors conclude that the material is a triangular frustrated magnet, which different from closely related materials does not have a quantum spin liquid ground state, but rather the mentioned antiferromagnetic one. Unfortunately, the authors are not able to derive firm conclusions as to the controlling element driving some of these triangular magnets into a spin liquid, others into a magnetic ground state. One might argue, the authors found just "another magnet".

All in all, the paper is well-written and represents a very thorough experimental and theoretical characterization of the studied material. It contributes to the present discussions of these types of materials and meets the criterion of a novel and inclusive approach from different research areas to understand new materials. I therefore recommend the paper for publication.

• validity: high
• significance: good
• originality: good
• clarity: high
• formatting: good
• grammar: good