Nd-induced Mn spin-reorientation transition in NdMnAsO

A combination of synchrotron x-ray, neutron powder-diffraction, magnetization, heat-capacity, and electrical-resistivity measurements reveals that NdMnAsO is an antiferromagnetic semiconductor with large Neel temperature [TN=359(2) K]. At room temperature the magnetic propagation vector k=0 and the Mn moments are directed along the crystallographic c axis [mMn=2.41(6) μB]. Upon cooling a spin-reorientation (SR) transition of the Mn moments into the $ab$ plane occurs (TSR=23 K). This coincides with the long-range ordering of the Nd moments, which are restricted to the basal plane. The magnetic propagation vector remains k=0. At base temperature (1.6 K) the fitted moments are mab,Mn=3.72(1) μB and mab,Nd=1.94(1) μB. The electrical resistivity is characterized by a broad maximum at 250 K, below which it has a metallic temperature dependence but semiconducting magnitude (ρ250 K=50 Ω cm, residual resistivity ratio=2), and a slight upturn at the SR transition.