YAFET-KITTEL ANGLES IN ZINC-NICKEL FERRITES

The chemical and magnetic structures of the ZnxNi1-xFe2O4 system have been determined using neutron diffraction for x=0, 0.25, 0.50, and 0.75. The data yield a cation distribution (Znx2+Fe1-x3+) [Ni1-x2+Fe1+x3+]. All the mixed ferrites show a noncollinear, Yafet-Kittel (YK) type of magnetic ordering. The YK angles increase with the zinc content and for a given composition decrease with increasing temperature. For x=0.25 and 0.50, there is a transition from the YK to Néel type of ordering prior to the paramagnetic transition. The Néel region decreases with increasing x; thus, for x=0.75, there is no Néel region, while NiFe2O4 has the Néel type of ordering at all temperatures. The YK angle can be analytically related to x, using the molecular-field theory. The angles predicted in this manner are consistent with a three-sub-lattice molecular-field analysis of the paramagnetic susceptibility data of Néel and Brochet. © 1969 The American Physical Society.