Effects of La substitution on the crystal structure and intrinsic magnetic properties of MM-Fe-B alloy (MM = La, Ce, Pr, Nd)

Since the discovery of NdFeB in 1983 by Sagawa, permanent-magnet materials developed rapidly and have become the heart of modern technology. Misch metal (MM) is mined as raw ore with a composition of La25Ce55Pr5Nd15, but Pr and Nd are overused which causes idle of La and Ce. Sintered magnets made using of MM can greatly reduce costs. It has been reported that the MM
₃₃
Fe
₆₆
B alloys yield M
_s
of 11.3 kG, H
_A
of 48.4 kOe, and Tc of 502.9 K. The intrinsic magnetic properties of MM-Fe-B are not very low, but it has a lower price. In some researches, CeFe
₂
phase exists in the magnet as harmful phases and decreases the magnetic properties. In our study, alloy ingot with nominal composition of (La
_x
MM
_1-x
)
₃₃
Fe
₆₆
B were prepared, the effects of La substitution on the crystal structure and intrinsic magnetic properties of MM-Fe-B alloy were investigated. It is found that the addition of La could suppress the CeFe
₂
phase.