Crystal structural transformation accompanied by magnetic transition in MnCo1−xFexGe alloys

• Fe substitution for Co atoms in MnCoGe alloy can improve the stability of parent phase and lower the MT temperature.
• The magnetostructural transition from PM austenite to FM martensite was realized in a temperature window of about 50 K.
• A large magnetization difference of 75 emu/g was found in MnCo0.78Fe0.22Ge alloy under a magnetic field of 50 kOe.
• A structural and magnetic phase diagram of MnCo1−xFexGe alloys was established.

The effects of Fe-doping on the crystal structure and martensitic transformation (MT) temperature in MnCoGe alloy have been investigated by using x-ray diffraction, calorimetry and magnetic measurements. Substitution of Fe for Co atoms can stabilize the parent phase and significantly lower the MT temperature of the MnCoGe alloy. By tuning the Fe content, the magnetostructural transition from paramagnetic parent phase (i.e. austenite) with a Ni2In-type hexagonal structure to ferromagnetic TiNiSi-type martensite can be realized in a temperature window determined by the Curie temperature of the austenite and that of the martensite. A large difference in magnetization between the austenite and martensite, accompanied by the magnetostructural coupling, gives rise to the magnetic-field-induced temperature shift of MT, which makes the MnCo1−xFexGe alloys being a new kind of potential magnetic functional materials used as the magnetic-field-driven actuator or magnetic refrigeration material.