The origin of Chinese chess2018-07-24
In 1932, Bloch first analyzed the domain walls of large magnets from the energy point of view, called the Bloch wall. 180. In the domain wall, if the atomic magnetic moment suddenly reverses between two adjacent atoms, the change in exchange energy is 4Aa2; if it is gradually and evenly rotated between the eccentrically equidistant faces, at n +1 turn In the turning of the magnetic moment, 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 rotated.
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 in the domain walls, the magnetocrystalline anisotropy energy and the magnetoelastic energy can be higher than those in the domains. The higher part of the energy is called the domain wall energy and is represented by E. The energy per unit area of a domain wall is called the domain wall energy density, expressed in y, in units of J / cm 2 .
If only the exchange energy is considered, the thicker the domain walls, the smaller the exchange energy, and the Jυ exchange enables the domain walls to be infinitely widened. In fact, this is impossible. Since 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 energy map makes the domain wall thin. Considering the above two factors, 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. The above is an explanation of the relationship between NdFeB and domain wall energy.