Structure-property relationships in a series of mixed layer pnictide oxide compounds: A(2)Mn(3)Pn(2)O(2) (A=Sr, Ba; Pn=P, As, Sb)

Results of magnetic property measurements for the compounds A(2)Mn(3)Pn(2)O(2) (A = Sr, Ba; Pn = P, As, Sb) are reported and discussed in the light of structural trends in the series. The structure consists of a 1:1 intergrowth of metal oxide layers in which the metal coordination is square planar and metal pnictide layers in which the coordination is tetrahedral. With the exception of Sr2Mn3As2O2, magnetic susceptibility data reveal the presence of broad maxima that have been assigned to coupling of the MnO22- layers. The data have been fitted assuming a 2D Heisenberg antiferromagnet model and the intraplanar coupling constants obtained are observed to increase as the a parameter or metal oxygen bond length decreases. The same trend is observed for the relationship of transition temperatures, obtained from d(chi)T/dT plots, to the a axial parameters, The exception to the rule is Sr2Mn3As2O2, which has an anomalously low transition temperature and different magnetic behavior for field-cooled versus zero-field-cooled samples. The field-cooled data show a sharp antiferromagnetic transition whereas the zero-field-cooled data show no transition to 3D order between 5 and 300 K.