What are rare earth magnets - NdFeb magnet and SmCo magnet uses?

NdFeb magnet and SmCo magnet are both rare-earth magnets They are called rare earths because samarium and neodymium are found in the lanthanide group of metals in the periodic table of the elements, and so the properties and crystal structures of these magnets are very similar.

Samarium forms alloys with the transition metal cobalt. Neodymium forms an alloy with the transition metal iron. So each magnet is the result of combining a rare earth metal with a transition metal. Neodymium magnets also contain a very small amount of boron, which makes them different from SmCo magnets because NdFeB uses three major alloying elements, while SmCo uses only two. How Rare Earth Magnets are Made Samarium Cobalt magnets are similar to neodymium magnets in many ways, with process steps including mining, powder production, milling, pressing, annealing, cutting, grinding, and surface treatment.

Corrosion Resistance

Samarium Cobalt and Neodymium SmCo magnets are composed of about 65% cobalt. Cobalt is a major component of stainless steel, so it is easy to see that cobalt is a major reason why Samarium Cobalt magnets have very good corrosion resistance. Cobalt is one of the three naturally occurring ferromagnetic elements other than iron and nickel. Neodymium-iron-boron magnets contain about 65% iron (as noted above, iron is ferromagnetic). 

Iron has poor corrosion resistance unless corrosion-resistant metals are added. NdFeB usually has about 1.5% cobalt added to slightly improve corrosion resistance, but this is a very small percentage of cobalt compared to the cobalt in SmCo magnets. NdFeB magnets can be plated, epoxied and otherwise coated to give them excellent corrosion resistance even in very challenging environments.

Samarium Cobalt Magnet Temperature 

Coefficient The (Br) temperature coefficient of samarium cobalt magnets is only -0.03-05%/°C. It is much smaller than the -0.11%/°C value of NdFeB. It is much smaller than the -0.11%/°C value of NdFeB. This means that SmCo loses less field strength per degree of temperature increase than NdFeB. This makes it easier for engineers to adjust for temperature effects because these effects are smaller over a wider temperature range. smCo has a temperature coefficient of about 0.20-0.30 %/°C. NdFeB has a temperature coefficient of 0.45-0.60 %/°C. The two things that lead to magnet demagnetization are high temperatures and high antimagnetic fields. 

By this measure, SmCo magnets are vastly superior to NdFeB magnets - especially at high temperatures. Both Samarium Cobalt and Neodymium Iron Boron make very strong magnets. The big difference is the optimum temperature for each magnet. NdFeB magnets are the strongest permanent magnets available at room temperature and up to about 180 degrees Celsius - measured by their remanent magnetism (Br). However, their strength decreases rapidly as the temperature increases. 

As the operating temperature begins to approach the 180 degree Celsius region, samarium cobalt magnets begin to outperform neodymium iron boron. The difference in performance can be seen in the table below. There is a lot of overlap between the two materials, but it is clear that NdFeB performs better at lower temperatures while SmCo performs better at higher temperatures. Each of the two materials has its own characteristics, and I hope you find this helpful after listening to my explanation!