Yafet-Kittel angles in Zinc-Nickel ferrites

Abstract

The chemical and magnetic structures of the Zn_xNi_1-xFe₂O₄ system have been determined using neutron diffraction for x=0, 0.25, 0.50, and 0.75. The data yield a cation distribution (Zn_x²⁺Fe_1-x³⁺) [Ni_1-x²⁺Fe_1+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.