A High Pressure Neutron Study of Colossal Magnetoresistant NdMnAsO0.95F0.05

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A high pressure neutron diffraction study of the oxypnictide NdMnAsO0.95F0.05 has been performed at temperatures of 290 K - 383 K and pressures up to 8.59 GPa. The results demonstrate that the antiferromagnetic order of the Mn spins is robust to pressures of up to 8.59 GPa. TN is enhanced from 360 K to 383 K upon applying an external pressure of 4.97 GPa, a rate of 4.63 K/GPa. NdMnAsO0.95F0.05 is shown to violate Bloch's rule which would suggest that NdMnAsO0.95F0.05 is on the verge of a localised to itinerant transition. There is no evidence of a structural transition but applied pressure tends to result in more regular As-Mn-As and Nd-O-Nd tetrahedra. The unit cell is significantly more compressible along the c-axis than the a-axis, as the inter-layer coupling is weaker than the intrinsic bonds contained within NdO and MnAs slabs.