The Relationship Between Temperature and Neodymium Magnets

　Too hot?

　　What is the maximum allowable temperature of neodymium magnets? What if the magnet exceeds this temperature? How to read the demagnetization curve? Temperature issues and neodymium magnets can be a complicated issue. In this article, we will try to simplify some concepts and answer some common questions.

　　Basic knowledge

　　On the "Specifications" page, two key temperatures are listed: the maximum operating temperature and the Curie temperature.

　　The Curie temperature is the temperature at which all magnetization of the magnet is lost.

　　The maximum operating temperature (hereinafter referred to as MaxOpTemp) is a general number given for each different grade of magnet material. Although not entirely correct, this is a good guide for many situations. Between MaxOpTemp and Curie temperature, a certain proportion of magnetization is irreversibly lost.

　　Magnetic strength: In this article, magnetic strength is the key indicator. The product of B times H is usually used to describe the strength of neodymium magnets. For example, the maximum BH (called BHmax) of a grade N42 magnet is 42MGOe. This number is directly related to the pull box 1, which is the attraction of a single magnet stuck to a large steel plate. You can also express it as a magnetic field measured in Gauss at certain locations. We specify the Gaussian surface field measured on the surface of the magnet. Magnetic intensity is neither power nor work, and cannot be expressed in power.

　　Reversible loss: Until MaxOpTemp, you will see some loss of magnetic strength at these high temperatures. After returning the magnet to room temperature, it will return to its original strength. These losses are small, usually within 5% to 10%.

　　Irreversible loss: Above MaxOpTemp, some magnetization will be lost. When you return the magnet to room temperature, it will be weaker than before the heating process. Magnets with irreversible losses can theoretically be re-magnetized to the original strength, or very close to the original strength.

　　Permanent loss: above the temperature of the initial sintered magnet material, structural changes will occur, causing the magnet to be permanently demagnetized. The externally applied magnetic field will not restore the strength of the magnet. For Strong Neodymium Magnets, this temperature is very high, usually above 900°C to 1000°C.

　　How much power will I lose at a given temperature?

　　We must research more deeply to answer this geek question. Let's start with a better estimate of MaxOpTemp. The MaxOpTemp of a given magnet largely depends on how it is "used online". For a magnet in free space, this means that it depends on the shape of the magnet.

　　Yes, that's right, MaxOpTemp depends on the shape of the magnet. This is a difficult concept to understand, especially when we are accustomed to seeing operating temperature as a material property. Whether in a tall glass or in a wide bowl, water will boil at 100°C. However, magnets are not that simple.

　　This measure of shape is called permeability coefficient. Sometimes called BH, working slope or load line. You can use our magnet calculator to find the permeability coefficient of neodymium magnets of any size/shape in free space. Generally, the number of tall and narrow magnets is larger, and the number of thin and wide magnets is smaller.