What is Maximum Working Temperature of a Permanent Magnet?

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 working temperature. In both fields of theory and application, the temperature elevation dependent flux loss is commonly divided into two parts,… Read More

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What are Temperature Coefficients α and β of Permanent Magnets?

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

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What is the Strongest Commercial Permanent Magnet in the World?

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 developed in the 20th century. In the following figure, it depicts the development of some permanent magnets’ maximum energy product… Read More

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How to Magnetize and Demagnetize a Permanent Magnetic Material, respectively?

How to Magnetize and Demagnetize a Permanent Magnetic Material, respectively? Due to random orientation for micro magnetic domains, a permanent magnetic material or 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 magnetic material? 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 magnetic material rotate to the magnetization direction. When all the micro magnetic domains aligned along the same direction, the permanent magnetic material is magnetized to… Read More

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Do Permanent Magnets ever Lose Their Magnetism or Become Weaker Over Time?

Do Permanent Magnets ever Lose Their Magnetism or Become Weaker Over Time? 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 will lose some flux (the demagnetizing process is nonlinear and irreversible when the demagnetizing field is higher than… Read More

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Corrosion Resistance of Rare Earth Permanent Magnets

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 and eventual disintegration and failure. So what is the corrosion mechanism of NdFeB magnets? Generally it is an inter-granular corrosion evolution process. When… Read More

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How to Understand the Rare Earth Permanent Magnets’ Grades? Part 3 – Sintered Samarium Cobalt Magnets

How to Understand the Rare Earth Permanent Magnets’ Grades? Part 3 – Sintered Samarium Cobalt Magnets Samarium cobalt (SmCo) magnets include 1:5 type (SmCo5) and 2:17 type (Sm2Co17) magnets. For both of sintered SmCo5 and Sm2Co17 magnets, their grades basically include three parts, i.e. “letter 1” + “number” + “letter 2”. Similar to sintered NdFeB magnets, the three parts in sintered SmCo magnets’ grades also present material type, (BH)max value (in CGS unit) and Hcj level, respectively. The difference is that the left 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… Read More

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What are Rare Earth Permanent Magnets (REPMs)?

What are Rare Earth Permanent Magnets (REPMs)? Rare earth permanent magnets (REPMs) are permanent magnets which are based on some rare earth elements (Sm, Nd, Pr, Dy, Ce, etc.) to form critical magnetic structures. In regard to crystal structures, REPMs include a. 1:5 type SmCo magnets (hexagonal CaCu5 type structure) also called 1st generation REPMs, b. 2:17 type SmCo magnets (rhombohedral Th2Zn17 type structure) also called 2nd generation REPMs and c. Nd2Fe14B magnets (tetragonal crystal structure) also called 3rd generation REPMs. Compared with other types of permanent magnets such as ceramic/ferrite magnets and AlNiCo magnets, REPMs have much higher maximum energy product and coercivity which allow them to be applied… Read More

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What is a Permanent Magnet?

What is a Permanent Magnet? A permanent magnet is a material that is able to provide magnetic flux when magnetized with an applied magnetic field. The ability is characterized by two key parameters: remanence and coercivity. Generally, a permanent magnet’s intrinsic coercivity (Hcj) is higher than 300kOe (in CGS unit) or 24kA/m (in SI unit). With higher coervivity, a permanent magnet has higher ability to resist demagnetization, including field demagnetization from the electric or magnetic circuit and thermal demagnetization from the working temperature in various motors and/or electric machines applications. A commercial permanent magnet requires relatively high remanence and coercivity at an affordable cost. In regards to material types, commercial… Read More

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