“…For example, antisite disorder has been shown to be responsible for spin-glass behavior for different double perovskites, i.e., Sr 2 FeTeO 6 [13], Sr 2 Mn 0.7 Fe 0.3 O 6 [14], Sr 2 FeMoO 6 [15] among others. The double perovskites La 3 Co 2 NbO 9 and La 3 Co 2 TaO 9 were prepared by our group [16,17] by sol-gel and solid state methods and the correlation between the B order-disorder and magnetic behavior was reported. Samples prepared by solid state showed spontaneous magnetization bellow 72 K for La 3 Co 2 TaO 9 and 62 K for La 3 Co 2 NbO 9 and positive y values, showing prevalence of ferromagnetic interactions, while those prepared by sol-gel present low spontaneous magnetization (below 40 and 20 K, respectively) and negative y values, showing prevalence of antiferromagnetic interactions.…”