Samarium Cobalt: High Temperature Rare Earth Magnet
SmCo5 and Sm2Co17 magnets are respectively the 1st and 2nd generations of rare earth permanent magnets. SmCo5 was discovered as a rare earth magnet alloy in 1966 and Sm2Co17 in 1972 by Karl J. Strnat at the U.S. Air Force Materials Laboratory at Wright-Patterson Air Force Base. Sm2Co17 has improved magnetic properties compared to SmCo5, but is more difficult to produce. In the 1970s, Samarium-Cobalt was the material with the highest magnetic energy density until neodymium-iron-boron was discovered.
Magnetic Properties of Samarium Cobalt 2:17
| Grade | Remanence (Br) | Intrinsic Coercivity (Hcj) | Coercivity (Hcb) | Maximum Energy Product (BH)max | ||
| kGs | kOe | kOe | MGOe | |||
| Max | Min | Range | Range | Max | Min | |
| YXG20L | 9.20 | 8.60 | 5-18 | 4.5-8.8 | 22 | 18 |
| YXG22L | 9.50 | 9.00 | 5-18 | 4.5-9.2 | 24 | 20 |
| YXG24L | 10.00 | 9.50 | 5-18 | 4.5-9.7 | 26 | 22 |
| YXG26L | 10.40 | 10.00 | 5-18 | 4.5-10 | 27 | 24 |
| YXG28L | 10.80 | 10.40 | 5-18 | 4.5-10.5 | 28 | 26 |
| YXG30L | 11.10 | 10.80 | 5-18 | 4.5-10.6 | 30 | 28 |
| YXG32L | 11.40 | 11.10 | 5-18 | 4.5-10.8 | 31 | 30 |
| YXG33L | 11.60 | 11.40 | 5-18 | 4.5-11.0 | 32 | 31 |
| YXG34L | 11.80 | 11.60 | 5-18 | 4.5-11.2 | 33 | 32 |
| YXG35L | 12.20 | 11.70 | 5-18 | 4.5-11.2 | 35 | 33 |
| YXG20 | 9.20 | 8.60 | 18-25 | 7.8-8.8 | 22 | 18 |
| YXG22 | 9.50 | 9.00 | 18-25 | 8.2-9.2 | 24 | 20 |
| YXG24 | 10.00 | 9.50 | 18-25 | 8.6-9.7 | 26 | 22 |
| YXG26 | 10.40 | 10.00 | 18-25 | 9.0-10.0 | 27 | 24 |
| YXG28 | 11.10 | 10.40 | 18-25 | 9.5-10.5 | 28 | 26 |
| YXG30 | 11.10 | 10.80 | 18-25 | 9.8-10.6 | 30 | 28 |
| YXG32 | 11.60 | 11.10 | 18-25 | 10.1-10.8 | 31 | 30 |
| YXG33 | 11.60 | 11.40 | 18-25 | 10.4-11.0 | 32 | 31 |
| YXG34 | 11.80 | 11.60 | 18-25 | 10.6-11.2 | 33 | 32 |
| YXG35 | 12.20 | 11.70 | 18-25 | 10.8-11.5 | 35 | 33 |
| YXG20H | 9.20 | 8.60 | ＞25 | 7.8-8.8 | 22 | 18 |
| YXG22H | 9.50 | 9.00 | ＞25 | 8.2-9.2 | 24 | 20 |
| YXG24H | 10.00 | 9.50 | ＞25 | 8.6-9.7 | 26 | 22 |
| YXG26H | 10.40 | 10.00 | ＞25 | 9.0-10.0 | 27 | 24 |
| YXG28H | 10.80 | 10.40 | ＞25 | 9.5-10.5 | 28 | 26 |
| YXG30H | 11.10 | 10.80 | ＞25 | 9.8-10.6 | 30 | 28 |
| YXG32H | 11.40 | 11.10 | ＞25 | 10.1-10.8 | 31 | 30 |
| YXG33H | 11.60 | 11.40 | ＞25 | 10.4-11.0 | 33 | 31 |
| YXG34H | 11.80 | 11.60 | ＞25 | 10.6-11.2 | 33 | 32 |
| YXG35H | 12.20 | 11.70 | ＞25 | 10.8-11.5 | 35 | 33 |
Samarium Cobalt of Low Temp. Coefficient and High Temp. Resistance
| Grade Sm2Co17 | Br | Hcj | Hcb | (BH)max | Max. Working Temp. | Temperature Coefficient | ||
| kGs | kOe | kOe | MGOe | αBr (20℃-150℃) | ||||
| Max | Min | Range | Range | Max | Min | ℃ | %/℃ | |
| YXG20LT | 9.2 | 8.6 | ＞20 | 7.8-8.8 | 22 | 18 | 350 | ±0.005 |
| YXG22LT | 9.5 | 9.0 | ＞20 | 8.2-9.2 | 24 | 20 | 350 | -0.0100 |
| YXG24G | 10.0 | 9.5 | ＞20 | 8.6-9.7 | 26 | 22 | 500 | -0.0350 |
| YXG22G | 9.5 | 9.0 | ＞20 | 8.2-9.2 | 24 | 24 | 550 | -0.0350 |
Manufacture and Applications of Samarium Cobalt
SmCo magnets are usually manufactured using powder metallurgy. The alloying elements are first melted in a vacuum induction furnace, quickly cooled and then ground to a particle size of less than 10 µm, at which point only monocrystalline powder is present. The alloy powder is then aligned in a magnetic field and, depending on the process, pressed into a green compact at the same time. This is then followed by a dense sintering process in a vacuum or under protective gas. The magnets obtain their coercive field strength during heat treatment.
From around 150 to 180°C, SmCo has a higher energy product than neodymium-iron-boron, which is why it is mainly used at higher application temperatures. But the better corrosion resistance, the lower reversible temperature coefficient or the better resistance to ionizing radiation can also make the use of SmCo worthwhile. By alloying the antiferromagnetically behaving gadolinium, the reversible temperature coefficient of the remanence can be reduced to zero or even reversed to positive values.
Due to the higher production costs of SmCo, the economic importance is lower than that of neodymium magnets. The material is used, among other things, in rotating electrical machines with permanent excitation, sensors in automobile construction or in chemical pumps.
