Experimental Approach to the Thermodynamics of the Pure Two-Dimensional Spin-1/2 Triangular Lattice Antiferromagnet in Ba8CoNb6O24

TL;DR

This study investigates the thermodynamics of a nearly ideal two-dimensional spin-1/2 triangular lattice antiferromagnet using Ba8CoNb6O24, revealing no magnetic order down to very low temperatures and supporting Mermin-Wagner physics.

Contribution

It provides experimental evidence of 2D quantum magnetism effects in a highly isolated triangular lattice antiferromagnet, bridging theory and real materials.

Findings

No magnetic ordering observed down to 0.028 K

Strong low-energy spin fluctuations detected

Correlation length diverges at low temperatures

Abstract

Frustrated quantum magnets pose well-defined questions concerning quantum fluctuation effects and the nature of the many-body wavefunction, which challenge theory, numerics, experiment and materials synthesis. The S = 1/2 triangular-lattice antiferromagnet (TLAF) presents a case where classical order is strongly suppressed by quantum fluctuations, leading to extensive renormalization of physical properties at all energy scales. However, purely two-dimensional (2D) models are difficult to realise in the 3D world and their physics is controlled by the Mermin-Wagner theorem, which describes the dominant effects of additional thermal fluctuations. Here we report the magnetic properties Ba8CoNb6O24, whose Co2+ions have an effective spin 1/2 and construct a regular TLAF with very large interlayer spacing. We find no magnetic ordering down to 0.028 K, strong low-energy spin fluctuations in qualitative agreement with theoretical analysis and a diverging correlation length, all indicating a Mermin-Wagner trend towards zero-temperature ordering in this ideal 2D system.