In the 1960’s while a civilian researcher at the Wright-Patterson Air Force Base Materials Laboratory in Dayton, OH, Dr. Karl Strnat was attempting to better understand the origins of magnetic properties. Between 1946 and 1952 the study of rare earth metals had been greatly accelerated by advances in chemical separation techniques developed in association with the US Army Corps of Engineers’ Manhattan Project. Methods for producing pure rare earth metals in quantity were developed. This, in turn, stimulated interest in the use of rare earth metals as alloying additions.
Dr. Strnat’s critical contribution was to realize that the entire rare earth element family presented an opportunity for developing powerful new magnetic compounds. He started trying many possible compounds, and in 1966, he discovered SmCo5 (Samarium Cobalt five) which had an energy product that turned out to be much higher than any previous permanent magnets. The discovery of this class of magnets known as rare earth permanent magnets prompted a renaissance in research into new magnet materials. It is the direct precessor to sintered NdFeB and their manufacturing processes are very similar.
Of course, with this new high coercivity alloy, further research spread on many fronts. Samarium is not the cheapest rare earth element, so efforts to replace some began. Cobalt is one of the more expensive transition metals and came from unstable sources, so efforts were also made to replace it. But the never-ending effort to; raise (BH)max, Hcj, and Tc, and to lower the temperature coefficient and to make the manufacturing process faster and less costly was, and still is, paramount. Through this research, the Sm2Co17 magnet materials were developed. He, Dr. Allen Ray, and their team developed the 2nd generation Sm2Co17 in 1972 while at the University of Dayton. This material has higher magnetization and uses less Sm.
The low temperature coefficients of induction and coercivity reflect the material’s stability over a large temperature range. By switching some lanthanide series metals, low temperature coefficient and even zero temperature coefficient (over a limited temperature range) magnets can be purchased. SmCo materials stand up well against oxidation and corrosion.
In production, the SmCo material is crushed, then milled down to the size of one magnetic domain. That fine (pyrophoric) powder is loaded into a press. There the powder is aligned with a magnetic field and compressed. The resulting green compact is then sintered, annealed in a vacuum furnace, and ground. Sm2Co17 has more ingredients than its name suggests. One, of many, more detailed chemistries is: Sm2(Co, Cu, Fe, (Ti or Zn), C)17.
SmCo magnet-containing motors are extensively used in aerospace & military motors and actuators. They do not rust or corrode, are very magnetically stable, have high energy and low temperature coefficients for induction and coercivity. SmCo can withstand cryogenic temperatures and radiation bombardment well. When you require a low temperature coefficient magnet with high energy in a small package, you will consider SmCo material.
|Advantages||High energy, high coercivity, low temperature coefficient, high resistance to corrosion, magnetically stable, many different grades with many different properties, operates in cryogenic temperatures better than other high energy magnets, can withstand neutron radiation better than other materials.|
|Disadvantages||Raw materials come from limited sources, high cost, fragile, finish grinding required, requires a large magnetizing field.|
|Major applications||Military, Aerospace, motors, generators, sensors. When a high-energy, low temperature coefficient magnet is required in a small package, SmCo should be considered.|
|Item||Grade||Remanence||Coercivity||Max Energy Product||Max Working Temperature|