Giant Magnetocaloric Effect in a Honeycomb Spiral Spin-Liquid Candidate

TL;DR

This study reports a giant magnetocaloric effect in a honeycomb-lattice spiral spin liquid candidate, GdZnPO, demonstrating its potential for low-temperature magnetic refrigeration with enhanced cooling performance near a critical magnetic field.

Contribution

It provides the first experimental evidence of a giant magnetocaloric effect in a spiral spin liquid, linking the effect to the frustrated honeycomb spin model and low-temperature stability.

Findings

GdZnPO exhibits a giant magnetocaloric effect near the critical field.

The effect surpasses that of other known magnetocaloric materials.

Magnetic cooling is effective down to approximately 36 mK.

Abstract

Unlike conventional magnetic states, which lack degeneracy, the spiral spin liquid (SSL) fluctuates among degenerate spiral configurations, with ground-state wave vectors forming a continuous contour or surface in reciprocal space. At low temperatures, the field-induced crossover from the polarized ferromagnetic state to the SSL results in a large entropy increase and decalescence, indicating its potential for magnetic cooling. However, magnetic cooling using a SSL has yet to be reported. Here, we investigate the magnetocaloric effect and cooling performance of single-crystal GdZnPO, a spin-7/2 honeycomb-lattice SSL candidate, under a magnetic field $H$ $<$ $H_\mathrm{c}$ ($\mu_0H_\mathrm{c}$ $\sim$ 12 T) applied perpendicular to the honeycomb plane and below the crossover temperature ($\sim$2 K). For $H$ $\geq$ $H_\mathrm{c}$, GdZnPO enters a polarized non-degenerate ferromagnetic state. Our results demonstrate that GdZnPO exhibits a giant low-temperature magnetocaloric effect near $H_\mathrm{c}$, surpassing other magnetocaloric materials. This giant magnetocaloric effect is well-explained by the frustrated honeycomb spin model of GdZnPO, suggesting the stability of the SSL below $H_\mathrm{c}$ down to very low temperatures. Additionally, its magnetic cooling performance remains robust up to at least 4.5 K, making GdZnPO a promising candidate for magnetic refrigeration down to $\sim$36 mK through cycling the applied magnetic field within a narrow range.