Magnetization Plateau Observed by Ultra-High Field Faraday Rotation in a Kagom\'e Antiferromagnet Herbertsmithite

TL;DR

This study used ultra-high field Faraday rotation to observe a magnetization plateau in herbertsmithite, revealing insights into its quantum spin liquid state and magnetic behavior at extremely high fields.

Contribution

First direct observation of the 1/3 magnetization plateau in herbertsmithite using Faraday rotation at ultra-high magnetic fields.

Findings

Magnetization saturation above 150 T indicating a 1/3 plateau.

Behavior consistent with nearest-neighbor Heisenberg model.

Superlinear magnetization increase suggests reduced free spin contribution.

Abstract

To capture the high-field magnetization process of herbertsmithite (ZnCu3(OH)6Cl2), Faraday rotation (FR) measurements were carried out on a single crystal in magnetic fields of up to 190 T. The magnetization data evaluated from the FR angle exhibited a saturation behavior above 150 T at low temperatures, which was attributed to the 1/3 magnetization plateau. The overall behavior of the magnetization process was reproduced by theoretical models based on the nearest-neighbor Heisenberg model. This suggests that herbertsmithite is a proximate kagome antiferromagnet hosting an ideal quantum spin liquid in the ground state. A distinguishing feature is the superlinear magnetization increase, which is in contrast to the Brillouin function-type increase observed by conventional magnetization measurements and indicates a reduced contribution from free spins located at the Zn sites to the FR signal.