Large Enhancement of Magnetocaloric and Barocaloric Effects by Hydrostatic Pressure in La(Fe_0.92Co_0.08)_11.9Si_1.1 with a NaZn₁₃-Type Structure

Abstract

Solid-state refrigeration based on caloric effect has been regarded as an attractive alternative to the conventional gas compression technique. Boosting the caloric effect of a system to its optimum is a long-term pursuit. Here, we report enhanced magnetocaloric effect (MCE) and barocaloric effect (BCE) by hydrostatic pressure in La(Fe0.92Co0.08)11.9Si1.1 with a NaZn13-type structure. The entropy change ΔSMCE is almost doubled under 11.31 kbar, while the ΔSBCE is more than tripled under 9 kbar. To disclose the essence from the atomic level, neutron powder diffraction studies were performed. The results revealed that hydrostatic pressure sharpens the magnetoelastic transition and enlarges the volume change, ΔV/V, during the transition through altering the intra-icosahedral Fe–Fe bonds rather than the inter-icosahedral distances in the NaZn13-type structure. First-principles calculations were performed, which offers a theoretical support for the enlarged caloric effect related to the evolution of phase transition nature. Moreover, the enhanced lattice entropy change was calculated by Debye approximation, and a reliable way to evaluate BCE is demonstrated under a high pressure that DSC cannot reach. The present study proves that remarkable caloric effect enhancement can be achieved through tackling specific atomic environments by physical pressure, which may also be used to tailor other pressure-related effects, such as controllable negative thermal expansion.