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 aOE (c) 111 > or aOE (c) 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 gamma-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.