A viable compound for magnetic refrigeration at ambient temperature must present a large change in magnetic entropy, with minimum hysteresis and should be composed of earth abundant and non-toxic elements. 1 Recently a computational proxy was developed to identify new magnetocaloric materials whereby first principle structure relaxation is carried out with and without spin polarization to ascertain the degree of magnetic deformation. 2
By applying this method to ferromagnets in the PbFCl family we found magnetic deformation of around 2% which is similar to other magnetocaloric compounds. We therefore have focussed our experimental study on MnZnSb, which is reported to be an itinerant ferromagnet with a second order phase transition and Curie temperature about room temperature. 3 Detailed magnetization measurements were carried out and Arrott analysis (Fig 1. a)) yields a Curie temperature of 304K, with the system being described as one universality class across all order parameters and identified as ‘2-dimensional long-range.’ We find a reasonably large magnetic entropy change of 4.5 Jkg^-1K^-1 with a relative cooling power of 153 Jkg^-1. Temperature dependant powder neutron diffraction was used to investigate the origin of the significant magnetic entropy change around the magnetic transition which is attributed to the release of crystallographic strain through the magnetic transition. We identify the c/a parameter as an accurate crystallographic proxy to control the magnetic transition (Fig. 1 b)). Using this concept, chemical substitution on the square-net allows to experimentally tune the Curie temperature over a broad temperature span between 252-322 K (Fig. 1 c)). A predictive machine learning model for the c/a parameter is developed to guide future exploratory synthesis.