Commensurate ferrimagnetic and incommensurate antiferromagnetic order in the ThCr 2Si 2-type phosphide PrFe 2P 2

Abstract

The nuclear and the magnetic structures of PrFe 2P 2 have been investigated by neutron powder diffraction. Complementary studies of the magnetic order were carried out on single crystals of PrFe 2P 2 using a SQUID magnetometer. The nuclear structure of this phosphide was confirmed to be isotypic with ThCr 2Si 2 (space group I4/mmm, Z=2). No magnetic order could be found for the iron atoms down to 1.6 K. The order of the praseodymium moments is antiferromagnetic with a most likely incommensurate sine-wave modulated magnetic structure from the Néel temperature T N=28(1) K down to 16 K. The propagation vector is k =(0, 0, 0.799(3)) and the moment direction is parallel to the tetragonal c -axis. Below 16 K the magnetic structure changes to a corresponding square-wave modulated structure. The presence of a net ferromagnetic component μ exp=0.600(6) μ B along the c-axis indicates a commensurate ferrimagnetic structure with k =(0, 0, 4 5 ) and a magnetic unit cell of a× b×5 c, where the Pr moments have the spin sequence +−++−+−++−, +−… along the tetragonal axis. The magnetic moment μ exp=3.00(3) μ B is close to the theoretical moment of the free Pr 3+ ion μ eff=3.20 μ B. From the SQUID data a second-order crystal field parameter of B 2 0=−5.8(±0.2) K was deduced.