Spin fluctuations with two-dimensional XY behavior in a frustrated S = 1/2 square-lattice ferromagnet

TL;DR

This study reveals that the layered square-lattice vanadate Pb2VO(PO4)2 exhibits XY-like spin fluctuations driven by quantum effects, making it a unique frustrated 2D system with topological spin dynamics.

Contribution

It demonstrates that ESR measurements identify XY-type spin fluctuations in a frustrated square-lattice ferromagnet, highlighting the role of quantum fluctuations and anisotropy.

Findings

Linewidth divergence suggests low-dimensional quantum fluctuations.

Weak easy-plane anisotropy indicates XY-like exchange.

Pb2VO(PO4)2 is the first frustrated square lattice with XY-inherent topological spin fluctuations.

Abstract

The spin dynamics of the layered square-lattice vanadate Pb2VO(PO4)2 is investigated by electron spin resonance at various magnetic fields and at temperatures above magnetic ordering. The linewidth divergence towards low temperatures seems to agree with isotropic Heisenberg-type spin exchange suggesting that the spin relaxation in this quasi-two dimensional compound is governed by low-dimensional quantum fluctuations. However, a weak easy- plane anisotropy of the g factor points to the presence of a planar XY type of exchange. Indeed, we found that the linewidth divergence is described best by XY-like spin fluctuations which requires a single parameter only. Therefore, ESR-probed spin dynamics could establish Pb2VO(PO4)2 as the first frustrated square lattice system with XY-inherent spin topological fluctuations.