Neutron scattering investigation of the novel itinerant-electron frustration

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The stella quadrangula lattice, which is a cornner-shared netwark of stella quadrangula units consisting of two nested tetrahedra with same center of gravity, is a novel frustrated lattice. In the eta-carbide compounds, the magnetic 3d atoms form the stella quadrangula lattice, and hence, new phenomena caused by the new geometric magnetic frustration are expected. We investigated two eta-carbide compounds, Fe3Mo3N and Fe6W6C, by means of magnetization, electrical resistivity, thermal conductivity, thermal expansion, magetostriction, and muSR experiments, and discovered intriguing phenomena.Fe3Mo3N shows a ferromagnetic quantum critical behavior as well as a random spin freezing, indicating the ferromagnetic order is suppressed by the geometric frustration. Fe6W6C shows a successive spin freezing caused by the geometric frustration originating from two tetrahedra in the stella quadrangula. These results are caused by the inherent frustration of the stella quadrangula lattice.