STRUCTURE AND MAGNETIC-PROPERTIES OF THE PHOSPHIDES CACO2P2 AND LNT2P2 WITH THCR2SI2 STRUCTURE AND LANTHANOIDS FEP, LANTHANOIDS COP, LANTHANOIDS NIP WITH PBFC1 STRUCTURE

The structures of the ThCr2Si2-type phosphides PrFe2P2 (a new compound) and EuFe2P2 were refined from single-crystal X-ray data to residuals of R = 0.011 (246F-values) and R = 0.027 (215 Fs). As was previously reported for the Ni atoms of the ThCr2Si2-type phosphides LnNi2P2, the Fe atoms in the series LnFe2P2 do not carry magnetic moments. In contrast, the magnetic behaviour of the corresponding Co-containing phosphides is frequently complex, due to the possibility for magnetic order in both the Ln and the Co sublattices. Antiferromagnetic order can be inferred for the Co sublattices of CeCo2P2 (TN = 440 K), PrCo2P2 (TN = 304 K), NdCo2P2 (TN = 309 K) and SmCo2P2 (TN = 302 K). At about 15-30 K the 1 χ vs T plots of PrFe2P2, PrCo2P2 and NdCo2P2 suggest a variety of different ordering phenomena for the magnetic moments of the lanthanoid atoms. The magnetic properties of CeFe2P2 and CeCo2P2 indicate valence fluctuations of the Ce atoms. At lower temperatures the magnetic susceptibility of SmCo2P2 reflects the Van Vleck paramagnetism of the Sm3+ species, while the magnetic behaviour of CaCo2P2 is suggestive of the itinerant exchange of a Fermi liquid. In the closely related (anti-) PbFCl-type structure of the new compound SmCoP the Co sublattice also shows antiferromagnetic order with a magnetic moment of μexp = 1.36 μB per Co atom. The isotypic compounds SmFeP, PrCoP and NdCoP are reported for the first time. The compounds LaFe2P2, CeFe2P2, CaNi2P2, LaNi2P2 and CeNi2P2 do not become superconducting down to 1.8 K. © 1990.