Samarium-cobalt magnet

A samarium–cobalt (SmCo) magnet, a type of rare earth magnet, is a strong permanent magnet made of an alloy of samarium and cobalt. They were developed in the early 1960s based on work done by Dr. Karl Strnat and Dr. Alden Rey at Wright-Patterson Air Force Base and the University of Dayton, respectively. In particular, Dr. Strnat and Dr. Rey developed the first formulation of SmCo₅. They are generally ranked similarly in strength to neodymium magnets, but have higher temperature ratings and higher coercivity. They are brittle, and prone to cracking and chipping. Samarium–cobalt magnets have maximum energy products (BH_max) that range from 16 megagauss-oersteds (MG·Oe) to 33 MG·Oe, that is approx. 128 kJ/m³ to 264 kJ/m³; their theoretical limit is 34 MG·Oe, about 272 kJ/m³. They are available in two "series", namely Series 1:5 and Series 2:17.

Sintered Samarium Cobalt magnets exhibit magnetic anisotropy, meaning they can only be magnetized in the axis of their magnetic orientation. This is done by aligning the crystal structure of the material during the manufacturing process.

These samarium–cobalt magnet alloys (generally written as SmCo₅, or SmCo Series 1:5) have one atom of rare earth samarium per five atoms of cobalt. By weight this magnet alloy will typically contain 36% samarium with the balance cobalt. The energy products of these samarium–cobalt alloys range from 16 MG·Oe to 25 MG·Oe, that is, approx. 128–200 kJ/m³. These samarium–cobalt magnets generally have a reversible temperature coefficient of -0.05%/°C. Saturation magnetization can be achieved with a moderate magnetizing field. This series of magnet is easier to calibrate to a specific magnetic field than the SmCo 2:17 series magnets.

In the presence of a moderately strong magnetic field, unmagnetized magnets of this series will try to align their orientation axis to the magnetic field, thus becoming slightly magnetized. This can be an issue if postprocessing requires that the magnet be plated or coated. The slight field that the magnet picks up can attract debris during the plating or coating process, causing coating failure or a mechanically out-of-tolerance condition.

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