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 ferromagnetism in the mixed-valence systems is not continuous. In a range of about 5%-15% of Mn4+ (x similar to 0.05-0.15), canted magnetic arrangements of the A(y)F(z) type are observed. The interlayer coupling is changed gradually from theta = 180 degrees for x = 0-0.05 to theta similar to 90 degrees for x = 0.15. For about x = 0.15-0.20, the canted phase with 90 degrees coupling coexists with a purely ferromagnetic arrangement of the F-y type. The observed behavior is related to an interplay of the magnetic superexchange and the double exchange. (C) 1997 American Institute of Physics.