Micromagnetic simulation of the ground states of Ce-Fe-B amorphous nanodisks

Using 3D micromagnetics package OOMMF, the ground states of Ce2Fe14B amorphous nanodisks with different dimensions, initial magnetization states and magnetocrystalline anisotropy constants (K) in zero external field were investigated. The simulations indicate that the disk size is the decisive factor in determining magnetic configurations. A diagram is constructed to bring out the dependence of the different equilibrium states on the disk thickness and diameter. When the ratio of thickness (T) to diameter (D) is smaller than 1, the vortex state is energetically more favorable than other states and the eigenfrequency of vortex approximately proportional to (T/D)1/2. A variety of magnetization distributions of ground states for different anisotropy strengths is obtained. The result shows the magnetocrystalline anisotropy not only shrinks or broadens the vortex core but also induces an out-of-plane magnetization component both at the edge and the center of disks. When the K strength reaches a threshold value, there is a transition from vortex state to Bloch-type Skyrmion state which suggests the possibility of Skyrmion in rare-earth materials. In addition, in the system with specific aspect ratio and low intrinsic anisotropy, the vortex domain can always be sustained under various initial conditions. Meanwhile, the existence of stable vortex domain is found by experimentation in amorphous Ce-Fe-B ribbons which is in good agreement with the simulation result.