Relationship between structural parameters and the Neel temperature in Sr1-xCaxMnO3 (0≤x≤1) and Sr1-yBayMnO3 (y≤0.2) -: art. no. 134412

The crystal and magnetic structures of newly synthesized Sr1-xCaMnO3 (0 less than or equal tox less than or equal to1) and Sr1-yBayMnO3 (y less than or equal to0.2) perovskite materials (of the ABO(3) type) were investigated using neutron and synchrotron x-ray powder diffraction at temperatures between 10 and 530 K. Upon decreasing the size of the A-site ion (or the unit-cell size) a series of structural transitions appears at room temperature from cubic Pm (3) over barm to tetragonal I4/mcm (at x similar to0.3) to orthorhombic Pbnm at x similar to0.4. In agreement with neutron-diffraction data, resistive and magnetic measurements show that the samples are antiferromagnetic with Neel temperatures T-N, varying from 233 to similar to 125 K and from 233 to 212 K by increasing the Ca and Ba contents, respectively. The observed variation of T-N cannot be solely explained by the changes of the unit-cell size or the average Mn-0-Mn bond angle theta. The behavior of T-N can be satisfactorily described as a function of [cos(2) theta] related to the superexchange interaction integral, and sigma (2), the A-site ionic size variance [L. M. Rodriguez-Martinez and J. P. Attfield, Phys. Rev. B 54, R 15 622 (1996)] regardless of the structural symmetry of the perovskite material.