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 1 c / K 1 u < 5 ( K 1 c and K 1 u are the first constants of the crystallographic and uniaxial anisotropies), the value of K 1 u 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 1 c / K 1 u 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 3 d alloys and γ-Fe 2 O 3 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.