Neutron-diffraction study of the magnetic structure of PrCoAl4

The magnetic structure of PrCoAl 4 has been studied by neutron diffraction from a single crystal. The Pr moments order at a temperature near to 20 K with a sine-wave longitudinal amplitude-modulated structure. The length of the wave vector q = ( 0 0 q z ) is almost temperature independent with q z = 0.4087 ( 5 ) , and only the first harmonic was observed down to 2 K. The amplitude of the wave, 2.05(3) μ B /Pr atom at 2 K, is reduced compared to the Pr 3+ free-ion moment value g J μ B = 3.2 μ B , due to strong crystal-field effects. One difference between the present and previously reported neutron powder-diffraction results concerns the wave vector length. The reason for this may lie in the different magnetic microstructure (stacking faults) of the material depending on the thermochemical history of each sample.