Based on the specific microstructure of HDDR (hydrogenation, disproportionation,
desorption, recombination) grains, that the bivariate model concerning the anisotropy
constant K'_1 and exchange integral A'_1 in defect region, which was put forward.
Subsequently, the dependence of magnet coercivity on the intergranular phase thickness
d and structure defect thickness r_0 was studied. The results showed that the coercivity,
H_c, increases with increasing d, for the r_0, the anisotropy constant K_1(0) and exchange
integral constant A_1(0) at the grain surface taking different values. While K_1(0) and
A_1(0) are fixed, H_c enhances with increasing r_0 for the same d. On the contrary,
for the fixed r_0 and d, H_c decreases with increasing K_1(0) or A_1(0). The calculated
coercivity is in good agreement with experimental results given by others when d takes 1 nm,
r_0 is in the rang of 2--5 nm, A_1(0) and K_1(0) change in the range of (0.6--0.7) of A_1
and K_1, respectively.