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 different structure type depending on the identity of the cation. BaMn₂P₂ crystallizes in the ThCr₂Si₂ structure type (I4/mmm), and SrMn₂P₂ crystallizes in the CaAl₂Si₂ structure type (P3̄m1). Temperature-dependent magnetic susceptibility, neutron diffraction, and resistivity measurements were obtained for the two compounds. Neutron diffraction shows that BaMn₂P₂ exhibits long-range antiferromagnetic ordering at room temperature. Mn(II) is high spin, with ordered moment 4.2 (1) μ_B, and the magnetic structure is type G. Magnetic susceptibility measurements show no maxima up to 750 K, indicating that the transition temperature, T_c, is very high. SrMn₂P₂ is antiferromagnetic below T_c = 53(1) K, as determined from the temperature dependence of the magnetic reflections. There are two distinct sets of magnetic reflections distinguished by different temperature dependencies and indexing schemes. The magnetic structure is evidently complex, but was not determined. Both compounds exhibit semiconducting resistivity behavior with E_a = 0.073(1) eV (BaMn₂P₂) and 0.0129(2) eV (SrMn₂P₂). The properties of BaMn₂P₂ and SrMn₂P₂ are discussed in light of their structures and previous theoretical investigations by Zheng and Hoffmann.