Structural and magnetic properties of the perovskites Srn+1(Co0.5Nb0.5)nO3n+1 (n=, 2 and 1)

The perovskites Srn+1(Co0.5Nb0.5)nO3n+1 (n=, 2 and 1) have been prepared. The crystal structures are cubic Pm m for SrCo0.5Nb0.5O3 (n=) and tetragonal I4/mmm for Sr3(Co0.5Nb0.5)2O7 (n=2) and Sr2Co0.5Nb0.5O4 (n=1), respectively, with random occupation of the Co and Nb ions at the same site. DC magnetization-temperature (M-T) curves of SrCo0.5Nb0.5O3 reveal an antiferromagnetism-like transition at 19-20 K. Also the deviation from a Curie-Weiss (CW) law is observed between ~20 and ~250 K in inverse magnetization-temperature curves. For Sr3(Co0.5Nb0.5)2O7 and Sr2Co0.5Nb0.5O4, the CW law is well obeyed above ~100-160 K, and effective Co moments are considerably smaller than that of SrCo0.5Nb0.5O3. They exhibit no obvious magnetic order in their M-T curves, while magnetization-field (M-H) curves show hysteresis loops at 2 K.