Introduction to Samarium Cobalt Magnet

Samarium cobalt magnets (SmCo) are high-performance energy products ranging to 32MGOe. SmCo magnets are better able to withstand higher temperatures than other rare earth magnets. Samarium cobalt magnet is a high performance, low-temperature coefficient permanent magnet made of samarium and cobalt and other rare-earth elements. Its biggest advantage is its high working temperature – 350 degrees centigrade. It needn’t be coated because it is difficult to be eroded and oxidized.

Typical forms and sizes of Samarium Colbalt Magnets

Magnetic Properties of Samarium Cobalt Magnets

Sintered SmCo
Material Code Remanence Coercivity Force Intrinsic Coercivity
Maximum Energy Curie Temperature Maximum
Br bHc iHc (BH)Max Tc TW
T KGs KA/m KOe KA/m KOe KJ/m3 MGOe °C °C
SR-18 0.85-0.9 8.5-9.0 620-648 7.8-8.2 1194-1513 15-19 127-143 16-18 750 250
SR-20 0.92-0.96 9.2-9.6 653-717 8.2-9.0 1194-1513 15-19 150-167 19-21 750 250
SR-24 0.96-1.0 9.6-10.2 730-770 9.2-9.7 1194-1513 15-19 175-190 22-24 750 250
SRG-24 0.95-1.02 9.5-10.2 637-732 8.0-9.2 1433-1990 18-25 175-190 22-24 800 350
SRG-26 1.02-1.05 10.2-10.5 748-796 9.4-10.0 1433-1990 18-25 195-215 24-26 800 350
SRG-28 1.05-1.08 10.5-10.8 756-796 9.5-10.0 1433-1990 18-25 205-220 26-28 800 350
SRG-30 1.08-1.10 10.8-11.0 788-835 9.8-10.5 1433-1990 18-25 220-240 28-30 800 350
SRG-32 1.10-1.15 11.0-11.5 812-860 10.2-10.8 1433-1990 18-25 231-255 29-32 800 350

Manufacturing of Samarium Cobalt Magnets

There are two types of samarium cobalt alloys – SmCo 1:5 and SmCo 2:17. Coded into SR and SRG at Essen Magnetics, the SmCo 1:5 series (SR) are composed with one part samarium to five parts cobalt as SmCo5 and the SmCo 2:17 series (SRG) are composed with two parts samarium to seventeen parts cobalt as Sm2Co17. Both of the alloys are produced by the powder metallurgical method.

SmCo 1:5 Series

The SR series has about 36% samarium by weight. The energy from this series ranges between 16 MGOe to 24 MGOe, with its maximum MGOe used in the code (i.e. SR-18 for a maximum of 18 MGOe). With a moderate magnetizing field, the magnet can achieve saturation magnetization.

When compared to the SmCo 2:17 series, the 1:5 series samarium cobalt magnet is easier to calibrate to a specific magnetic field.

As remanence of magnets is impacted by temperature, Essen can add gadolinium into the SmCo alloy to maintain the remanence of our SmCo magnets across a wide range of temperatures.

The 1:5 series magnets have high coercivity which is up to 9.7 KOe for resisting demagnitization. The magnets are manufactured by packing wide-grain lone-domain magnetic powders into a magnet, known as sinter manufacturing. The sinter manufacturing process made SmCo 1:5 magnets brittle but extremely hard.

The magnetization of SmCo5 magnets are easily impacted with impurities as they will form nuclei in the magnet. Nuclei and its lower anisotropy or misaligned axes could break the domain wall configuration of samarium cobalt magnets. Therefore, the quality control team at Essen Magnetics carefully monitor every step of the magnet manufacturing process to minimize any impurities being introduced into our magnets.

SmCo 2:17 Series

The SRG Sm2Co17 series is composed with 2 parts samarium to 13-17 parts of transition metals. While the transition metals are rich in cobalt, it may also contain other elements including iron and copper. For better heat treatment response, a trace amount of zirconium, hafnium or other elements might be added to the alloy. Samarium contributes about 25% to the weight of the alloy.

The energy of SRG series Sm2Co17 magnets ranges from 22 MGOe to 32 MGOe. Unlike the 1:5 series that requires high purity, impurities are intentionally added to the 2:17 series to increase coercivity due to its impediment to the domain wall motion.

Manufacturing process of Samarium Cobalt Magnets

Samarium cobalt alloys are machined in an unmagnitized state using wet grinding with diamond grinding wheels. This is due to the low ignition point of samarium-cobalt that wet can reduce the chance of ignition under sparks.

The manufacturing of samarium cobalt magnets can be done with the reduction/melt method and the reduction/diffusion method. Essen Magnetics uses the reduction/melt method for both SmCo5 and Sm2Co17 magnets. The raw materials are first melted in an induction furnace with noble gas. The melted mixture is then cast into a mold and cooled with water to form an ingot. The ingot is milled and reduced into particle size before being pressed into the desired shape. The pressing is done in a magnetic field to orient the particles. The resulting product then goes through sintering in 1,100 degrees celsius to 1,250 degrees celsius, solution treatment in 1,100 degrees celsius to 1,200 degrees celsius and tempering in 700 degrees celsius to 900 degrees celsius. The magnet is grounded and further magnetized before being tested and delivered.

Properties of Samarium Cobalt Magnets

Samarium cobalt magnets are hard but brittle as it is manufactured with pressing powder into a magnet. Similar to neodymium magnets, SmCo magnets are highly resistance to demagnetization. SmCo magnets are also highly stable under different temperatures and highly corrosion resistance.

However, due to the limited raw material supply, SmCo magnets are usually more costly. But the magnet is highly adopted for widely changing temperatures and corrosive environment.

Uses of Samarium Cobalt Magnets

The corrosion resistance and high operating temperature of samarium cobalt magnets make them ideal for corrosive or temperature environments. Its stability across different temperatures allows samarium cobalt magnets to be used in aircraft, marine, and spacecraft. Cylinder samarium magnets are hugely popular amongst industrial designers and manufacturers.

SmCo magnets are commonly made into cylinder, disc or block shapes for differnt applications, such as motors, accelerometers, and gyroscopes.

Samarium Cobalt Cylinders

Cylindrical samarium cobalt magnets are greatly used by industrial designers, tradespeople and manufacturers. And they are commonly used in downhold drilling operations and in precious control system.

Samarium Cobalt Discs

Disc shpaed samarium cobalt magnets are often used in specialist engineering applications, and also used in high performance motors with its temperature stability.

Samarium Cobalt Blocks

Block shaped samarium cobalt magnets are commonly used in sensors for measuring temperature and pressure in mining, refining, agriculture and other industries. Medical implants and computer disc drives also use samarium cobalt magnet blocks.