CANTED STRUCTURES IN THE MN3+ MN4+ PEROVSKITES/

Neutron diffraction and magnetization measurements have been performed on numerous systems with the divalent and monovalent substitution, Pr (1-x)A(x)(2+)Mn(1-x)(3+)Mn(x)(4+)O(3) (A=Ca, Sr, Ba) and Pr(1-x/2)A(x/ 2)(+)Mn(x)(4+)O(3) (A=Na, K). The study shows that the transition from the Ay-type (layer) antiferromagnetism in pure PrMnO3 to the ferromag netism in the mixed-valence systems is not continuous. In a range of a bout 5%-15% of Mn4+ (x similar to 0.05-0.15), canted magnetic arrangem ents of the A(y)F(z) type are observed. The interlayer coupling is cha nged gradually from theta = 180 degrees for x = 0-0.05 to theta simila r to 90 degrees for x = 0.15. For about x = 0.15-0.20, the canted phas e with 90 degrees coupling coexists with a purely ferromagnetic arrang ement of the F-y type. The observed behavior is related to an interpla y of the magnetic superexchange and the double exchange. (C) 1997 Amer ican Institute of Physics.