Adiabatic physics of an exchange-coupled spin-dimer system: magnetocaloric effect, zero-point fluctuations, and possible two-dimensional universal behavior

TL;DR

This study investigates the magnetic and thermal behavior of a spin-dimer system, revealing a significant magnetocaloric effect across all fields at low temperatures, zero-point fluctuation contributions, and potential two-dimensional universal critical behavior.

Contribution

It demonstrates the widespread magnetocaloric effect in a spin-dimer system and suggests universal critical behavior with two-dimensional characteristics, challenging previous confined predictions.

Findings

Magnetocaloric effect occurs for all fields > 0 at low temperatures.

Zero-point fluctuations significantly influence heat capacity.

Evidence suggests two-dimensional universal critical behavior.

Abstract

We present the magnetic and thermal properties of the bosonic-superfluid phase in a spin-dimer network using both quasistatic and rapidly-changing pulsed magnetic fields. The entropy derived from a heat-capacity study reveals that the pulsed-field measurements are strongly adiabatic in nature and are responsible for the onset of a significant magnetocaloric effect (MCE). In contrast to previous predictions we show that the MCE is not just confined to the critical regions, but occurs for all fields greater than zero at sufficiently low temperatures. We explain the MCE using a model of the thermal occupation of exchange-coupled dimer spin-states and highlight that failure to take this effect into account inevitably leads to incorrect interpretations of experimental results. In addition, the heat capacity in our material is suggestive of an extraordinary contribution from zero-point fluctuations and appears to indicate universal behavior with different critical exponents at the two field-induced critical points. The data are consistent with a two-dimensional nature of spin excitations in the system.