Hybrid magnon-phonon localization enhances caloric response near ferroic glassy states in a magnetic shape memory alloy

The field of solid-state cooling is attracting more interest in recent years owing to the development of better materials [1] and devices [2]. Nevertheless, the advancement in comprehending the intricate physics governing the highest-performing materials, many of which exhibit disorder, has not kept pace. While improvements in functional properties have been observed in materials nearing ferroic glassy states, the underlying mechanisms behind such enhancements are not well understood. Using a suite of neutron scattering instruments at multiple facilities we discovered a novel hybrid magnon-phonon localization within a magnetic shape memory alloy that explains why its caloric and magnetic shape memory function are enhanced near ferroic glassy states [3]. The localized hybrid modes emerge from short-range correlations associated with glassiness and bridge the magnon and phonon dispersion curves over a broad part of the spectrum, leading to substantial shifts in the phonons under applied fields that alter phase stability and triple the release/absorption of thermal energy – thereby elevating caloric response. Since interplay between short- and long-range correlations is common near ferroic glassy states, our work provides general insight on how glassiness can enhance function.

[1] Hou et al. Nature Rev. Mater. 7, 633 (2022).

[2] Qian et al. Science 380, 722 (2023).

[3] Manley et al. Science Adv. 10, eadn2840 (2024).