MICROMAGNETIC STUDIES OF COHERENT ROTATION WITH QUARTIC CRYSTALLINE ANISOTROPY

The nucleation fields under coherent rotation for uniaxial ferromagnets are rigorously determined including the second anisotropy constant K2. Theoretical studies cover the whole range of the relationships between K1 and K2. We show that the reversal processes can be classified into eight types depending on the parameters characterizing the magnetic materials. The results show that the value of K2 affects both the hysteresis loop and nucleation field significantly. The nucleation field along the c-axis is not always equal to 2K1/M(s). For certain values of second anisotropy, the easy axes may be oblique to the c-axis. When the ratio of K2 and K1 is large, the easy cone or hard cone will form at a certain oblique angle. The effects of K2 on the saturation field of hard axis loops have also been investigated. It is suggested that the values of K1 and K2 can be determined independently from the slope and saturation field of hard axis loops.