Nature of magnetocrystalline anisotropy in the basal plane of iron borate

Basal (hexagonal) magnetocrystalline anisotropy of iron borate FeBO 3 , including crystal field and dipole dipole contributions, is discussed in detail. Previously, the latter contribution had been ruled out on the basis of symmetry; indeed, considering the magnetic dipole dipole interaction in the approximation of point dipoles, only uniaxial magnetocrystalline anisotropy is accounted for. In the present work we con sider the dipole dipole interaction energy for extended dipoles and calculate the dipole dipole contribu tion to basal magnetocrystalline anisotropy for two different models of an extended dipole: a pair of fictitious magnetic charges and a circular current loop. A comparison between theoretical expressions developed and experimental results obtained by antiferromagnetic resonance allows estimating the effective size of magnetic dipoles and calculating the dipole dipole contribution to basal magnetocrys talline anisotropy constants of iron borate.