Material selection of permanent magnets, considering thermal properties correctly

Abstract

Permanent magnets are used in a wide variety of applications: sensors, motors, actuators, alternators, hard drives, and speakers. While ceramic magnets (hard ferrite) were the material of choice for the last three decades, neodymium iron boron magnets, bonded and sintered, have surpassed ceramic magnets as the benchmark material for new designs. Three factors are key to the preference for rare earth magnets: superior room temperature magnetic properties, declining material cost, and improved corrosion resistance. With a bewildering array of data available, designers occasionally associate the wrong magnetic property with an important design parameter, leading to disappointing performance. This is particularly true for thermal characteristics. We review the thermal properties of the common permanent magnet materials, with emphasis on neodymium iron boron, and relate the characteristics to material selection.