Magnetic anisotropy of single-domain particles

The competition between uniaxial and cubic magnetic anisotropies of single-domain particles is analyzed theoretically. As long as K _1c /K _1u < 5 (K _1c and K _1u are the first constants of the crystallographic and uniaxial anisotropies), the value of K _1u noticeably affects coercive force H _c and relative residual magnetization j _r of particle ensembles. If the uniaxial anisotropy direction coincides with crystallographic axis 〈111〉 or 〈100〉, the dependences of H _c and j _r on ratio K _1c /K _1u have a minimum. The competition between the induced uniaxial anisotropy and cubic anisotropy was detected experimentally when the effect of temperature T on the H _c (T) and j _r (T) dependences for single-domain spherical particles of magnetic 3d alloys and γ-Fe₂O₃ oxide was investigated. For all single-domain particles studied here, the effect of crystallographic anisotropy on H _c and j _r is manifested at low temperatures, while uniaxial anisotropy plays a decisive role in the temperature range T > 250 K. The effect of second constant K ₂ on H _c and j _r of ensembles of single-domain particles with uniaxial and cubic anisotropies is investigated theoretically. It is shown that the value of K ₂ may substantially change the value of H _c for a particle ensemble, preserving the value of j _r unchanged.