Realisation of magnetostructural coupling and a large magnetocaloric effect in the MnCoGe1+x system

•The increase of Ge-content can reduce the structural transformation temperature.•A stable Curie-temperature window of 70K is obtained.•The magnetostructural transformation is accompanied by large magnetocaloric effect. Magnetic field-induced magnetostructural transformations taking place in MnCoGe-based alloys attract considerable attention due to their associated multi-magnetoresponsive effects. The key to maximising these effects across a wide working temperature range is to increase the magnetisation difference during the transformation and simultaneously sustain the Curie temperatures of the Ni2In and TiNiSi phases. In this work, we achieve the above goals by importing additional Ge atoms into the MnCoGe alloy, as the increase in Ge content sharply decreases the transformation temperature but does not influence the Curie temperatures in the system. As a result, magnetostructural transformation between paramagnetic Ni2In and ferromagnetic TiNiSi phases is realised within a Curie-temperature window of 70K. The magnetostructural transformation can be induced by the magnetic field, bringing about considerable entropy change.