Relationship between NdFeB and magnetic domain walls2018-07-07
In 1932, Bloch first analyzed the domain wall of a large magnet body from the energy point of view, called the Bloch wall. At 180. In the domain wall, if the atomic magnetic moment suddenly reverses between two adjacent atoms, as shown in Figure 2-13a, the change in exchange energy is 4Aa2; if it is gradually and evenly turned between the eccentric equidistant faces, as shown in Figure 2 136, in the turn of n +1 spin magnetic moments, the energy E is exchanged. The total change in x is AEex = Ad02 /n. It can be seen that the larger the knife, the lower the exchange energy. Therefore, the atomic magnetic moment in the domain wall must be gradually turned.
The domain wall is a transition region in which the atomic magnetic moment is gradually shifted from the direction of one magnetic domain to the direction of an adjacent magnetic domain. The exchange energy, magnetocrystalline anisotropy energy and magnetoelastic energy in the domain wall can be higher than those in the domain. The higher part of the energy is called the domain wall energy and is represented by E. The energy per unit area of the domain wall is called the domain wall energy density, expressed in y, and the unit is J/cm2.
If only the exchange energy is considered, the thicker the domain wall, the smaller the exchange energy, and the J卩 exchange enables the domain walls to be infinitely widened. In fact, this is impossible. Because the ridge is large, more atomic magnetic moments deviate from the easy magnetization direction, which increases the magnetocrystalline anisotropy energy, that is, the magnetocrystalline anisotropy ability map makes the domain wall thin. Considering the above two factors comprehensively, in order to minimize the total energy, the domain wall energy density Y can be obtained, and the expression of the domain wall thickness J is 7TM=2 redundancy/stone tile, respectively. The above is the explanation of the relationship between NdFeB and domain wall energy.