Structural tuning of ferromagnetism in a 3D cuprate perovskite

The perovskite SeCuO3- is unusual for possessing (i) a very small A-site (Se4+) radius, (ii) highly distorted Cu-O-Cu bond angles (alpha), and (iii) a ferromagnetic (FM) ground state. Negative chemical pressure is applied by replacing Se with Te in solid solution, causing a continuous transformation between the FM state and an antiferromagnetic (AFM) state. This is the first FM-AFM transformation to be controlled by a single microscopic parameter, the in-plane cu, allowing a precise determination of the crossover angle (alpha(c) = 127 degrees +/- 0.5 degrees) between FM and AFM superexchange.{[}S0031-9007(99)08402-1].