## What is Maximum Working Temperature of a Permanent Magnet?

Permanent magnets are widely applied in various motors, sensors/instruments and electronics, their temperatures almost vary more or less during work. These temperature variations are resulted from eddy current effect and/or ambient temperature variation. Due to thermal fluctuation and magnetic domain evolution, a permanent magnet loses some or all magnetic flux when its temperature elevates. Here comes a question, how high temperature can a permanent magnet withstand to work? For a commercial permanent magnet, the upper temperature limit is called maximum… Read More

## What are Temperature Coefficients α and β of Permanent Magnets?

A permanent magnet’s magnetic properties change as a variation of temperature. For a permanent magnet, remanence (Br) and intrinsic coercivity (Hcj or Hci) are two major parameters, it is important to consider their changes with corresponding temperature variation at work. In order to describe the relative changes, they are calculated according to the following two formulas: α = [Br(T1)-Br(T2)]/Br(T1)/[ T1-T2]×100                              (1) β = [Hcj(T1)-Hcj(T2)]/Hcj(T1)/[T1-T2]×100     … Read More

## What is the Strongest Commercial Permanent Magnet in the World?

Researchers and engineers have never stopped their steps to discover and develop novel permanent magnets since 1910s, and several types of permanent magnets had been commercialized and they have been widely used in motion, energy, electronics, medical and other high technologies in our daily life. However, little breakthrough has been taken in the past 18 years of the 21st century. In the current market, almost all types of commercial permanent magnets (ferrite, NdFeB, SmCo and AlNiCo, etc.) were discovered and… Read More

## How to Magnetize and Demagnetize a Permanent Magnet, respectively?

Due to random orientation for micro magnetic domains, a permanent magnet usually does not provide any magnetic flux when it is produced. It needs to be magnetized to saturation for use. So how to magnetize a permanent magnet? The basic principle is using a coil, i.e. an electromagnet, to generate a magnetic field. The generated magnetic field increases as the charging current increases, it drives micro magnetic domains of a permanent magnet rotate to the magnetization direction. When all the… Read More

## Do Magnets ever Lose Their Magnetism or Get Weaker?

Actually permanent magnets are not permanent. A Permanent Magnet is a material which has ability to resist demagnetization, including filed demagnetization and thermal demagnetization. The ability is characterized by a physical parameter called coercivity. In regard to field demagnetization, if a demagnetizing field or reverse field is smaller than a permanent magnet’s coercivity, the permanent magnet will keep the same magnetic flux (the demagnetizing process is linear and reversible when the demagnetizing field is lower than a threshold value) or… Read More

## Corrosion Resistance of Rare Earth Permanent Magnets

In the Rare Earth Permanent Magnets family, the 1st generation 1:5 type SmCo magnets and 2nd generation 2:17 type SmCo magnets have high corrosion resistance due to the high cobalt content. Just like ferrite/ceramic magnets and AlNiCo magnets, SmCo magnets usually do not need any treatment for applications. The 3rd generation NdFeB magnets, however, are not the same. Although they have superior magnetic properties, they are more vulnerable to corrosion in humid environments, resulting in the deterioration of magnetic properties… Read More

Samarium cobalt (SmCo) magnets include 1:5 type (SmCo5) and 2:17 type (Sm2Co17) magnets. Both types of SmCo magnet grades basically include three parts, i.e. “letter 1” + “number” + “letter 2”. The three parts in sintered SmCo magnet grades present material type, (BH)max value (in CGS unit) and Hcj level, respectively. The part “letter 1” are “XG” and “XGS” for sintered SmCo5 and Sm2Co17 magnets, respectively. Besides, the Hcj levels of sintered SmCo5 magnets include “default” (Hcj ≥ 15 kOe)… Read More