Absence of Colossal Magnetoresistance in the Oxypnictide PrMnAsO0.95F0.05

Abstract

We have recently reported a new mechanism of colossal magnetoresistance in electron doped Mn oxypnictides NdMnAsO1-xFx. Magnetoresistances of up to -95 percent at 3 K have been observed. Here we show that upon replacing Nd for Pr, the CMR is surprisingly no longer present. Instead a sizeable negative magnetoresistance is observed for PrMnAsO0.95F0.05 below 35 K (MR7T (12 K) = -13.4 percent for PrMnAsO0.9F0.05. A detailed neutron and synchrotron X-ray diffraction study of PrMnAsO0.95F0.05 has been performed, which shows that a structural transition, Ts, occurs at 35 K from tetragonal P4/nmm to orthorhombic Pmmn symmetry. The structural transition is driven by the Pr 4f electrons degrees of freedom.