Antiferromagnetic order in the ternary phosphides LnNi(2)P(2) (Ln=Tb, Dy, Ho, Er)

The magnetic structures of the ThCr2Si2 type compounds LnNi(2)P(2) (Ln = Tb , Dy, Ho, Er) were investigated by neutron powder diffraction. In agreement with the previously determined magnetic susceptibility data only the lanth anoid atoms were found to carry magnetic moments. They order antiferromagne tically at T-N = 10.2(4) K (TbNi2P2), 5.0(4) K (DyNi2P2), 2.5(4) K (HoNi2P2 ) and 1.9(3) K (ErNi2P2), respectively. The magnetic unit cell of these com pounds can be described with the propagation vector k = (1/2, 0, 1/2). The magnetic moments of the terbium, dysprosium and holmium atoms are aligned p arallel to the doubled c axis of the tetragonal nuclear cell, whereas the m oments of the erbium atoms are ordered perpendicular to this axis and the ( one) doubled a axis. Magnetization measurements carried out with a SQUID ma gnetometer at 2 K show metamagnetic transitions for TbNi2P2 and DyNi2P2. (C ) 1999 Elsevier Science S.A. All rights reserved.