The magneto-structural transition in magnetocaloric Mn1-xFexCoGe

Abstract

Magnetic refrigeration techniques based on the magnetocaloric effect are considered an increasingly viable alternative to conventional gas-compression refrigerant, particularly with energy-saving and environmental aspects in mind. Following the discovery of a large magnetocaloric effect in Gd5Si2Ge2, researchers have shifted their attention to investigation of materials exhibiting magneto-structural transitions where large magnetic entropy changes are expected. MnCoGe-based compounds are promising materials for the exploration of large magnetocaloric effects. They are relatively cheap (no rare earth elements) and, importantly, allow an appropriate temperature window (275 – 345 K) around room temperature in which the magneto-structural transition may be positioned. It has been established that Fe is a suitable substitute for Mn to ‘tune’ the structural transition temperature and hence obtain a magneto-structural transition. Here we present the results of a detailed investigation of the structural and magnetic properties and magnetocaloric effect for a range of as-prepared Mn1-xFexCoGe alloys (x = 0.01, 0.02, 0.03 and 0.04) using temperature variable x-ray diffraction (20 – 310 K), neutron diffraction (5 – 450 K) and physical properties measurement system (PPMS, 5 – 300 K). Particular attention will focus on analysis of neutron diffraction data for Mn0.98Fe0.02CoGe and the nature of the magnetic phase transition in Mn0.98Fe0.02CoGe.