Structure and magnetism in Sr1-xAxTcO3 perovskites: Importance of the A-site cation

The Sr1-xBaxTcO3 (x = 0, 0.1, 0.2) oxides were prepared and their solid-state and magnetic structure studied as a function of temperature by x-ray and neutron powder diffraction. The refined Tc moments at room temperature and Neel temperatures for Ba0.1Sr0.9TcO3 and Ba0.2Sr0.8TcO3 were 2.32(14) mu(beta) and 2.11(13) mu(beta) and 714 degrees C and 702 degrees C, respectively. In contrast to expectations, the Neel temperature in the series Sr(1-x)A(x)TcO(3) decreases with increasing Ba content. This observation is consistent with previous experimental measurements for the two series AMO(3) (M = Ru, Mn; A = Ca, Sr, Ba) where the maximum magnetic ordering temperature was observed for A = Sr. Taken with these previous results the current work demonstrates the critical role of the A-site cation in the broadening of the pi(*) bandwidth and ultimately the magnetic ordering temperature.