Large reversible magnetocaloric effect in high-entropy MnFeCoNiGeSi system with low-hysteresis magnetostructural transformation

High-entropy alloys have attracted tremendous research interest in recent years because of their special functional properties. However, the investigations on the high-entropy alloys with thermal- and magnetic-field-induced magnetostructural transformation are still lacking. In this work, we provide a basic strategy to design a six-component MnFeCoNiGeSi high-entropy system, exhibiting low-hysteresis magnetostructural transformation between ferromagnetic orthorhombic and paramagnetic hexagonal phases. An increase in the configurational entropy is helpful to make the alloy crystallize in the single hexagonal structure, which can almost completely transform into the orthorhombic structure during cooling. The thermal hysteresis in our high-entropy alloy is as low as about 4.3 K. This advantage guarantees reversible magnetic-field-induced magnetostructural transformation and is accompanying a large magnetocaloric effect. A reversible entropy change of −13.67 J K−1 kg−1 is realized under a magnetic field variation of 0–5 T. The obtained room-temperature magnetocaloric performance is comparable to that of some rare-earth-based high-entropy alloys and conventional first-order magnetocaloric materials. Moreover, the geometric nonlinear theory of martensitic transformation is adopted to explain the origin of low hysteresis in our high-entropy alloys.