EFFECT OF \alpha-Fe SURFACE LAYER ON THE MAGNETIC REVERSION PROCESS FOR Nd₂Fe₁₄B CRYSTAL

The demagnetization process for a Nd₂Fe₁₄B grain covered by an \alpha-Fe layer was studied by use of the finite element technique of micromagnetics. \mu_0iH_c decreases with the increase of \alpha-Fe layer thickness t. With the increase of t from 0 to 6nm, \mu_0iH_c decreases from ～7 T to ～3.5 T when the angle between the applied field and the c-axis of the Nd₂Fe₁₄B grain is 0.5° and from ～4 T to ～1.5 T when the angle is 30° or 60°. The effect is only slightly affected by the angle between the \alpha-Fe layer and the field direction.