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The application of chemical pressure by P substitution in CeFeAsO does not introduce a superconducting state, but ferromagnetic ordering of the local Ce moments. This behavior of CeFeAsO is in sharp contrast to the observations in other iron-pnictide superconductors, where P substitution generally introduces a superconducting phase. We present a combined pressure and P-substitution study on CeFeAsO to elucidate its phase diagram. On applying external pressure or P substitution the iron ordering temperature TN,Fe is suppressed but levels off at about 25 K before we loose its signature in our data. In the same P substitution range the type of order of the local 4f moments of the Ce changes from antiferromagnetic to ferromagnetic suggesting a subtle relation between the iron and cerium ordering. We will discuss this connection in details and further elucidate the possibility of the occurrence of superconductivity in this region of the phase diagram. |
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