One-Third Magnetization Plateau with a Preceding Novel Phase in Volborthite

TL;DR

This study reports the discovery of a wide 1/3 magnetization plateau and a novel intermediate phase in volborthite, a kagome antiferromagnet, through high-field magnetization and NMR measurements, revealing complex magnetic ordering.

Contribution

First high-field magnetization and NMR study on volborthite showing a wide 1/3 plateau and a new intermediate phase, highlighting complex magnetic behavior in this frustrated system.

Findings

Observation of a wide 1/3 magnetization plateau above 28 T

Identification of an incommensurate order below 22 T

Discovery of a novel intermediate phase with linear magnetization variation

Abstract

We have synthesized high-quality single crystals of volborthite, a seemingly distorted kagome antiferromagnet, and carried out high-field magnetization measurements up to 74 T and 51V NMR measurements up to 30 T. An extremely wide 1/3 magnetization plateau appears above 28 T and continues over 74 T at 1.4 K, which has not been observed in previous study using polycrystalline samples. NMR spectra reveal an incommensurate order (most likely a spin-density wave order) below 22 T and a simple spin structure in the plateau phase. Moreover, a novel intermediate phase is found between 23 and 26 T, where the magnetization varies linearly with magnetic field and the NMR spectra indicate an inhomogeneous distribution of the internal magnetic field. This sequence of phases in volborthite bear a striking similarity to those of frustrated spin chains with a ferromagnetic nearest-neighbor coupling J1 competing with an antiferromagnetic next-nearest-neighbor coupling J2.