Study of magnetic microstructures of Nd-Fe-B casting strips by using magnetic force microscope

Dy-Al substituted Nd-Fe-B strips were produced by strip casting technique. The magnetic microstructures of the 2-14-1 and Nd2Fe17(B) phases in both as-cast strips and the strips heat-treated at 1050 deg. C in Ar atmosphere, and the domain structures of the final sintered magnets have been revealed by using magnetic force microscope. The existence of fine Nd2Fe17(B) crystals with 'plate-like' domains surrounded by 2-14-1 larger crystals with 'ripple' domains was found in the as-cast strips. After heat treatment, spheric or columnar crystals of Nd2Fe17(B) phase were formed and the crystals of 2-14-1 phase became larger. The sintered magnets made from the strips heat-treated at 1050oC possess better magnetic properties: the remanence Br∼1.42 T, the intrinsic coercivity Hcj∼995 kA/m, and energy density product (BH)max∼392 kJ/m3