  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)
BM). 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) BM and mab,Nd = 1.94(1) BM. The electrical
resistivity is characterized by a broad maximum at 250 K, below which it has a
metallic temperature dependence but semiconducting magnitude (rho250K = 50 Ohm
cm, residual resistivity ratio = 2), and a slight upturn at the SR transition.
