On the anisotropy of the exchange interactions in the rare earth orthoferrites

This paper presents some new results on orthoferrite magnetic properties. We have measured the temperature dependence of the spontaneous magnetization for neodim, samarium, and thulium orthoferrites having compensation temperatures. The measurement of the magnetic permeabilities near these temperatures makes it possible to find the effective fields of exchange interactions between the iron and rare earth ions and to prove that these interactions have strong anisotropy. For example, the exchange interactions for TuFeO
3
have opposite signs along the
a
and
c
axes, so that the spin reorientation results in the change of the orthoferrite spontaneous magnetization. The different mechanisms of the anisotropy of the iron and rare earth ion exchange interactions are discussed.