RESISTIVITY AND MAGNETISM OF AMN2P2 (A=SR, BA) - THE EFFECT OF STRUCTURE TYPE ON PHYSICAL-PROPERTIES

AMn2P2(A = Sr, Ba) is an example of a composition that can assume a di fferent structure type depending on the identity of the cation. BaMn2P 2 crystallizes in the ThCr2Si2 structure type (I4/mmm), and SrMn2P2 cr ystallizes in the CaAl2Si2 structure type (P3BARm1). Temperature-depen dent magnetic susceptibility, neutron diffraction, and resistivity mea surements were obtained for the two compounds. Neutron diffraction sho ws that BaMn2P2 exhibits long-range antiferromagnetic ordering at room temperature. Mn(II) is high spin, with ordered moment 4.2 (1) mu(B), and the magnetic structure is type G. Magnetic susceptibility measurem ents show no maxima up to 750 K, indicating that the transition temper ature, T(c), is very high. SrMn2P2 is antiferromagnetic below T(c) = 5 3(1) K, as determined from the temperature dependence of the magnetic reflections. There are two distinct sets of magnetic reflections disti nguished by different temperature dependencies and indexing schemes. T he magnetic structure is evidently complex, but was not determined. Bo th compounds exhibit semiconducting resistivity behavior with E(a) = 0 .073(1) eV (BaMn2P2) and 0.0129(2) eV (SrMn2P2). The properties of BaM n2P2 and SrMn2P2 are discussed in light of their structures and previo us theoretical investigations by Zheng and Hoffmann. (C) 1994 Academic Press, Inc.