Plastic crystal neopentylglycol (NPG, C5H12O2) has become an important candidate material in the future solid-state refrigeration field due to its huge colossal barocaloric effects near room temperature. However, NPG encounters significant shortcomings in practical cooling process that hinders its further application. Here, we systematically investigate the effect of defects and substituting a small amount of additional alien molecules on the barocaloric performance of NPG plastic crystals. It is found that low concentration of defects and substitution moderately affect the isothermal entropy, adiabatic temperature, and thermal hysteresis of NPG. Importantly, the substituted carbon nanotubes significantly enhance the thermal conductivity by more than one order of magnitude, arising from structural-modification enhanced acoustic phonons. Using dimensionless variable, we define the comprehensive cooling performance that represents the most promising working materials for barocaloric refrigeration. The present work provides important guidance on improving the barocaloric performance of NPG as prototypical plastic crystals for practical cooling applications.

Using the ab initio-based training database, we trained the potential function for ammonium iodide (NH4I) based on a deep neural network-based model. On the basis of this potential function, we simulated the temperature-driven β ⇒ α-phase transition of NH4I with isobaric isothermal ensemble via molecular dynamics simulations, the results of which are in good agreement with recent experimental results. As it increases near the phase transition temperature, a quarter of ionic bonds of NH4+-I− break so that NH4+ starts to rotate randomly in a disorderly manner, being able to store thermal energy without a temperature rise. It is found that NH4I possesses a giant isothermal entropy change (∼93 J K−1 kg−1) and adiabatic temperature (∼27 K) at low driving pressure (∼10 MPa). In addition, through partial substitution of I by Br in NH4I, it is found that the thermal conductivity can be remarkably improved, ascribed to the enhancement of lifetime of low frequency phonons contributed by bromine and iodine. The present work provides a method and important guidance for the future exploration and design of barocaloric material for practical applications.

The creation of a high-pressure rhombohedral phase leads to a colossal barocaloric effect in KPF6.

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The magnetic flux noise caused by surface spin fluctuations in superconducting quantum interference devices (SQUIDs) limits their development. In this work, we report that different adsorbents such as H, O2, NO, and NO2 that adsorb on the surfaces of Mg-based and Pb-based SQUIDs, respectively, producing large local magnetic moments ranging from 0.7–1.6 μ B, with energy barriers for thermal spin fluctuation as low as 10–30 mK. Moreover, we observe that the presence of H atoms on the surface of MgO can cause the coadsorption of other molecules, which generates additional spin sources. Monte Carlo simulations of the weakly coupled spin on a two-dimensional square lattice produce a low-frequency flux noise spectrum. We suggest eliminating the surface magnetism by coating the surface with monolayer indium phosphide or protecting the surface from other molecules by nonmagnetic preoccupants with a larger adsorption energy. The work provides important physical insights and feasible strategies for reducing magnetic noise sources in superconducting circuits.