Magnetization reversal process for Nd₂Fe₁₄B crystal covered by an α-Fe surface layer

The magnetization reversal process for an Nd₂Fe₁₄B grain of volume 20 × 20 × (20-t) nm³ covered by an α-Fe layer of volume 20 × 20 × t nm³ (t = 0-12 nm) was studied by the use of finite element technique of the micromagnetics. It was found that μ_0iH_c decreases with the increase of the angle θ_c between the c-axis of the Nd₂Fe₁₄B grain and the applied field direction. μ_0iH_c also decreases with increase of t such that when t increases from 0 to 6 nm μ_0iH_c decreases from ∼7 to ∼3.5 T for θ_c = 0.5° and from ∼4 to ∼1.5 T for θ(c) = 30° and 60°. The effect is only slightly affected by the angle between the α-Fe layer and the field direction.