CeRuPO, a ferromagnetic Kondo lattice, undergoes two novel pressure-induced structural phase transitions. CeRuPO undergoes an isostructural transition to a collapsed tetragonal structure near 7.5 GPa. Since pressure suppresses the initial ferromagnetic ordering of Ce3+, our observation suggests a quantum critical point for CeRuPO near this pressure. The collapsed tetragonal phase transforms into an orthorhombic Cmma structure. This phase is isostructural with the low temperature phase of LaFeAsO, which is superconducting under high pressure. Since CeRuPO exhibits a similar relationship between the two phases of LaFeAsO, the collapsed tetragonal and orthorhombic phases of CeRuPO may adopt a novel magnetic ground state.
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