Qingyong Ren, University of New South Wales
Room 616,Physics Building
Magnetic refrigeration based on the magnetocaloric effect (MCE) is considered as an alternative to conventional gas compression-expansion refrigeration for both energy efficiency and environmental reasons. Large MCE occurs generally around a magnetic transition, especially around a first-order magnetic transition, such as magneto-structural transition. Therefore, tuning the crystal and magnetic structures is an important issue for exploring large MCE. Neutron diffraction and magnetisation measurements indicated that substitution of Fe or Ni for Mn or Co in MnCoGe can bring about magneto-structural transition and ferromagnetism/spiral-antiferromagnetism transition. These two transitions lead to direct and inverse MCE, respectively. Analysis of Mӧssbauer, high-pressure x-ray diffraction and neutron diffraction measurements indicated that chemical pressure plays an important role in the adjustments of crystal and magnetic structures in the samples with low doping concentration while redistribution of valence electrons is the key factor in the samples with high doping concentration. We also observed that the substitution of Si for Ge in TbMn2Ge2 can also bring two magnetic transitions.