The plumbide CeZnPb - Structure, magnetism, and chemical bonding

The plumbide CeZnPb was synthesized from the elements in a sealed tantalum ampoule. Its YPtAs-type structure was refined on the basis of single-crystal X-ray diffraction data: P6(3)/mmc, a = 463.7(2) and c = 1669.6(6) pm, wR2 = 0.1161, 189 F-2 values, and 12 variables. CeZnPb crystallizes with a superstructure of AlB2. The zinc and lead atoms form puckered [Zn3Pb3] hexagons, which are stacked in a sequence ABB'A'. The Zn-Pb distances within the layers are 278 pm. The shortest interlayer distance occurs between the zinc atoms of adjacent layers (305 pm). Susceptibility measurements of CeZnPb show Curie-Weiss behavior with an experimental magnetic moment of 2.47(1) mu(B)/mol CeZnPb. CeZnPb shows two antiferromagnetic transitions at T-N1 = 3.8 K and T-N2 = 2.6 K. Magnetization measurements at 2 K show two metamagnetic transitions at critical fields of approximately 1.1 and 7.0 kOe, underlining the antiparallel spin alignment at zero field. The electronic and magnetic structure is discussed based on scalar relativistic computations using the augmented spherical wave (ASW) method within density functional theory (DFT). As a result, our calculations employing the generalized gradient approximation (GGA) reveal a delicate competition of ferro and antiferromagnetic interactions. Only after properly taking into account the electronic correlations present in CeZnPb via a GGA + U treatment we are able to correctly describe the antiferromagnetic ground state. In addition, our calculations give a clue to the metamagnetic transitions as being due to the inherent geometric frustration of the cerium spin system. (C) 2010 Elsevier Masson SAS. All rights reserved.