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 [T-N=359(2) K]. At room temperature the magnetic propagation vector k=0 and the Mn moments are directed along the crystallographic c axis [m(Mn)=2.41(6) mu(B)]. Upon cooling a spin-reorientation (SR) transition of the Mn moments into the ab plane occurs (T-SR=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 m(ab,Mn)=3.72(1) mu(B) and m(ab,Nd)=1.94(1) mu(B). The electrical resistivity is characterized by a broad maximum at 250 K, below which it has a metallic temperature dependence but semiconducting magnitude (rho(250) (K)=50 Omega cm, residual resistivity ratio=2), and a slight upturn at the SR transition.