Coercivity calculation of Sm2(Co,Fe,Cu,Zr)17 magnets

The coercivity of Sm2(Co,Fe,Cu,Zr)17 is calculated on the basis of a two dimensional model. To find local minima of the sum of the domain wall energy and the magnetostatic energy, the domain wall is divided into 1 nm long segments which are allowed to fluctuate randomly. With increasing field strength the domain wall is heavily bowed, forming the well known zig–zag domains. At higher field strengths, the domain wall is depinned first, from the edges of the 2/17 cells and later, from the intersection lines of the Z phase with the 1/5 boundary phase. For these two sites, the widths and the heights of the energy barriers for the movement of the domain walls are calculated in dependence of the applied magnetic field and compared with the thermal activation energy. As a result, the stronger pinning site is stable up to a local field strength of about 40 kA/cm. Since the domain wall generates a demagnetizing field of about 11 kA/cm at the critical position, the coercivity correlated to the stronger pinning site is reduced to 29 kA/cm at room temperature.