Magnetic ordering of PrCoAl4 a neutron diffraction study

The magnetic ordering of the orthorhombic (Pmma space group) PrCoAl4 compou nd has been studied by neutron diffraction. Only the Pr moments order. Belo w TN = 17 K they adopt a longitudinal amplitude modulated structure. The ma gnetic moments are confined to the c direction with the wave vector q = (0, 0, q,) with an almost temperature independent length. At 1.5 K the amplitu de of the wave is 2.24(4) mu (B)/Pr atom and the wave vector q(z) = 0.437(2 ) can be approximated within error limits by a rational fraction (11)/(25) which alternatively gives the possibility to consider the structure as a co mmensurate phase. (C) 2001 Elsevier Science B.V. All rights reserved.