Canted-ferrimagnetic structure

Defects in ferrimagnetic structures often lead to noncollinear (canted) spin structures. For example, a diamagnetic substitution or a cation vacancy can result in magnetic frustration which leads to spin-canting such that a spin may form an angle 6c with the collinear spins in the sample [80, 81]. Similarly, the reduced number of neighbor ions at the surface can also lead to spin-canting [80-83]. 

Spin-only moments would give /z = l/z5 and 0hb, respectively. Since the spins are in the (111) plane (303), a contribution to the ferrimagnetic moment should come from a canted-spin configuration. Orbital contributions to the g factor must also be playing a role, especially in the case of Co2+. It was pointed out in the discussion on rock salt structures that Co2+ in CoO carries an atomic moment of 3.7hb rather than the spin-only value of 3.0/z, and that this moment can be accounted for quantitatively if orbital considerations are included. 

Neutron diffraction, magnetization and Mossbauer data by Bazela et al. (1981a) show a transition to a ferrimagnet with canted moments. The angle between the magnetic moment direction and the c-axis of the Ni2In-type structure is 34° 4°. 

The orthoferrites, RFeOa, where R is yttrium or a rare-earth element have a structure based on a distorted perovskite lattice with only one iron environment. Most of them possess weak ferrimagnetic character as a result of spin canting from the ideal two-sublattice antiferromagnetic ordering. 

Fig. 4.8. Schematic representation of some magnetic structures (a) ferromagnetic (b) antiferromagnetic, (c) ferrimagnetic (d) triangular or canted and (e) helical.

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