SAMARIUM COBALT

There are two families of Sm-Co magnets — SmCo5 and Sm2Co17. SmCo5 was developed in the 1960s and further development produced Sm2Co17 in the 1970s.

SmCo5 has a hexagonal crystal structure that consists of five atoms of cobalt for each samarium atom. SmCo5 magnets are also known as Sm-Co 1:5, samarium-cobalt 1:5 magnets, SmCo series 1:5 magnets, or sometimes as 1:5 magnets.

Sm2Co17 has a rhombohedral crystal structure, which is obtained by replacing Sm atoms in the SmCo5 hexagonal structure with a pair of Co atoms. Other elements are added to improve properties such as intrinsic coercivity or reversible temperature coefficient. Elements such as iron, copper, hafnium, gadolinium, terbium, erbium and zirconium are commonly used. Sm2Co17 is also known as samarium-cobalt 2:17, SmCo Series 2:17, Sm(Co,Fe,Cu,Zr)z or sometimes as 2:17 magnets.

1:5 has a maximum energy product, (BH)max, around 20 MGOe. The reversible temperature coefficient of residual induction of SmCo5 is about -0.04%/°C. 2:17 has a maximum energy product (BH)max as high as 35 MGOe. The reversible temperature coefficient of residual induction is about -0.035%/oC.

Both SmCo5 and Sm2Co17 have very high intrinsic coercivity, Hci, a measurement of resistance to demagnetization. They also have very good corrosion resistance, thermal stability and resistance to radiation. Although brittle, they do not require a surface coating and can be used at temperatures up to 300℃.