Commensurate ferrimagnetic and incommensurate antiferromagnetic order in the ThCr2Si2-type phosphide PrFe2P2

The nuclear and the magnetic structures of PrFe2P2 have been investigated b y neutron powder diffraction. Complementary studies of the magnetic order w ere carried out on single crystals of PrFe2P2 using a SQUID magnetometer. T he nuclear structure of this phosphide was confirmed to be isotypic with Th Cr2Si2 (space group I4/mmm, Z = 2). No magnetic order could be found for th e iron atoms down to 1.6K. The order of the praseodymium moments is antifer romagnetic with a most likely incommensurate sine-wave modulated magnetic s tructure from the Neel temperature T-N = 28(1)K down to 16 K. The propagati on vector is k = (0, 0, 0.799(3)) and the moment direction is parallel to t he tetragonal c-axis. Below 16 K the magnetic structure changes to a corres ponding square-wave modulated structure. The presence of a net ferromagneti c component mu (exp) = 0 600(6) mu (B) along the c-axis indicates a commens urate ferrimagnetic structure with k = (0, 0, 4/5) and a magnetic unit cell of a x b x 5c, where the Pr moments have the spin sequence + - + + - + - + -, + - ... along the tetragonal axis. The magnetic moment mu (exp) = 3.0 0(3)mu (B), is close to the theoretical moment of the free Pr3+ ion mu (eff ) = 3.20 mu (B). From the SQUID data a second-order crystal field parameter of B-2(0) = - 5.8( +/- 0.2)K was deduced. (C) 2000 Elsevier Science B.V. A ll rights reserved.