Giant Magnetocaloric Effect in a High-Spin Shastry-Sutherland Dipolar Magnet

TL;DR

This paper reports a giant magnetocaloric effect in a high-spin Eu-based Shastry-Sutherland magnet, enabling efficient sub-Kelvin cooling and introducing a minimal dipolar model to explain its magnetic behavior.

Contribution

It demonstrates a significantly enhanced magnetocaloric effect in Eu2MgSi2O7 and introduces a dipolar Shastry-Sutherland model explaining its unique magnetic properties.

Findings

Entropy change peak of 55.0 J kg-1 K-1 under 0-4 T field change

Achieved lowest temperature of 151 mK via adiabatic demagnetization

Persistent cooling effect below 1 T due to dipolar couplings

Abstract

The Shastry-Sutherland lattice is a prototypical frustrated quantum magnet. It is notable for its exactly solvable dimer-singlet ground state and hosts a wealth of magnetic phenomena under external fields. Here, this work investigates the high-spin (S = 7/2) Eu-based magnet Eu2MgSi2O7 (EMSO) using low-temperature magnetothermal measurements and Monte Carlo simulations, revealing a giant magnetocaloric effect (MCE) in this Shastry-Sutherland compound. The entropy change peak value is found to be 55.0 J kg-1 K-1 under a field change of B = 0-4 T, approximately 1.5 times larger than the commercial Gd3Ga5O12 (GGG). Adiabatic demagnetization refrigeration achieves a lowest temperature of 151 mK, deeply into the sub-Kelvin regime. Furthermore, a distinctive cooling effect persists below about 1 T, a characteristic absent for conventional magnetic coolants. A dipolar Shastry-Sutherland model is introduced as a minimal model to describe this system; in particular, the experimentally revealed 1/3 magnetization pseudo-plateau can be ascribed to the presence of dipolar couplings between Eu2+ ions, further stabilized by the thermal fluctuations, explaining the persistent cooling effect. This work establishes EMSO as a novel platform for exploring the dipolar Shastry-Sutherland system and for sub-Kelvin adiabatic demagnetization refrigeration.