What Are SmCo Magnets, and How are They Made?

Introduction

SmCo magnets are strong permanent magnets. They are one of the two common rare-earth magnets. These permanent magnets are made from two rare-earth elements – samarium and cobalt. It is important to note that when producing SmCo magnets, the cobalt portion can be replaced by transition metals, while the samarium portion can be replaced by cerium and gadolinium. SmCo magnets were invented by Alden Ray and Karl Strnat in the ’70s. Alnico magnets were the most widely used magnet in industries until SmCo magnets were discovered. At the time, SmCo magnets were the most popular commercial permanent magnet until neodymium magnets were discovered. 

Production of SmCo Magnets

There are two different methods of producing samarium cobalt magnets. One of the methods is called bonding, while the other is called sintering.

Bonding Method

In the bonding method, a bonding chemical is used. An example of a bonding chemical is epoxy resin. The first step in this process is forming an alloy of the raw materials needed in making SmCo magnets. The alloy is formed by heating the raw materials in an induction furnace containing argon gas. In the second step, the alloy previously formed is poured into molds and allowed to cool with water. The product formed after cooling is ground and milled into a powdery state. After this, the powder is combined with a binding chemical and heated. An external magnetic field is usually present while heating the alloy powder with the binding chemical. The external magnetic field determines the magnetization direction. The final step in this process involves the magnetization of the magnet. In some cases, the magnet is also coated.

Sintering Method

The first and second steps of the sintering method are very similar to the first two steps of the bonding method. The main difference between the two methods can be found in step three. In the third step, the powder formed in step two is compacted into a solid mass by passing it through a temperature of 1523 K. At this temperature, the material undergoes solution treatment before it is cooled. The material is cooled in the presence of an external magnetic field. In the final step, the cooled material is ground using a diamond-coated grinding machine. After this, the magnet can be magnetized. Occasionally, the magnet is also coated.

Types of Samarium Cobalt Magnets

Samarium cobalt magnets are classified into two types based on the ratio of samarium to cobalt used during production.

SmCo₅

In this type of samarium cobalt magnet, the ratio of samarium to cobalt is 1:5. This implies that for every atom of samarium used, five atoms of cobalt are used. This type of samarium cobalt magnet is highly resistant to corrosion. It was discovered before the other type. However, it is not used frequently anymore because the second type of samarium cobalt magnet has overtaken it. Its maximum energy product is 15 to 24 MGOe.

Sm₂Co₇

In this type of samarium cobalt magnet, the ratio of samarium to cobalt is 2:7. This means that two samarium atoms are added per seven atoms of cobalt. Although this type of samarium cobalt magnet was discovered after SmCo₅, it has gained wider popularity for being stronger. Its maximum energy product is 20 to 32 MGOe. The downside of using this type of samarium cobalt magnet is that it is susceptible to corrosion when it comes in contact with water because it contains traces of iron.

Features of Samarium Cobalt Magnets

SmCo magnets are powerful permanent magnets. They are resistant to high temperatures, being most efficient at temperatures between 523 K and 853 K. They are also resistant to corrosion, oxidation, and demagnetization. Another notable property of samarium cobalt magnets is their electrical resistivity. Their electrical resistivity is 0.8 × 10^-6 Ωm. Also, their bending strength is 1.2 × 10³ kg/m^2, and their compressive strength is 9.1 × 10³ kg/m^2.  This rare-earth magnet is brittle and can easily break or crack when stressed. Due to the external magnetic field present during production, samarium cobalt magnets are anisotropic. This means they have a preferred magnetization direction. Outside their magnetization direction, they cannot be magnetized.

Samarium Cobalt Magnets vs. Neodymium Magnets

Although SmCo magnets and neodymium iron boron magnets have some properties in common because they are rare-earth magnets, they also have properties that make them distinct from each other. Samarium cobalt magnets are more resistant to corrosion than neodymium magnets. However, neodymium magnets are significantly stronger and cheaper than samarium cobalt magnets.

Further Reading: SmCo Magnets vs Neodymium Magnets

Conclusion

SmCo magnets are important magnets in many industries. Production of these magnets is by the bonding and sintering methods. However, their high cost and relative weakness compared to neodymium magnets threaten their popularity. Thank you for reading our article and we hope it can help you to have a better understanding of SmCo magnets. If you want to find out more about permanent magnets, we would like to recommend you to visit Stanford Magents for more information.