What is Remanence – The Ultimate Guide
We can describe remanence as a magnetic material‘s ability to still have magnetic properties even after the magnetic inducer has been withdrawn. The material will have residual magnetism even without an external magnetic field.
This remanence varies based on the type of magnet. You will find that magnets such as neodymium have a very high remanence compared to ferrite magnets.
The level of remanence of a magnet can tell you how strong that magnet is. We can analyze such using a hysteresis curve that entails the induced magnetic flux against the magnetization strength.
Types of Remanence
· Isothermal Remanence
When measuring remanence, you have to take several readings to get a precise value. An example is in magnetic tapes that have very many magnetic particles.
For you to measure such, you have to incrementally add remanence or subtract it in bits. You will have to demagnetize your magnet and then introduce a magnetic field.
This magnetic field you introduce is what causes remanence in your magnet. This is the type of remanence we call isothermal and we denote it using the symbol Mr(H).
· Saturation Remanence
When measuring the hysteresis loop of a magnet, we use a tool called a vibrating sample magnetometer. We can take the zero field intercept and use the value to denote the magnets’ remanence.
We can describe saturation remanence as the ratio of magnetic moment to the volume sample. We can denote it using the symbol M(rs).
· Anhysteretic Remanence
We can achieve this remanence by subjecting a magnet to a large AC field. You have to include some form of DC bias field for full remanence.
You need to gradually tone down the amplitude of your AC to zero. This will give your magnet what we call anhysteretic magnetization.
After this, you can withdraw the DC bias magnetic field. The result is your magnet acquiring an anhysteretic remanence.
We usually measure remanence using the formula
M(r) = M(s) x δ
Where: M(r) = remanence
M(s) = saturation magnetization
δ = Remanent coefficient
Let us take a practical example of how we can calculate remanence. We can consider a magnetic material having a saturation magnetism of 2.4.
Let’s say it has a remanent coefficient of 1.2, we can calculate its remanence using the formula:
M(r) = M(s) x δ
M(r) =2.4 Tesla x 1.2
M(r) = 2.88 Tesla
This tells us that our material has a magnetization of 2.88Tesla after you remove any induced magnetic field. This is the remanence of your magnet.
It is possible for your magnet to completely lose its remanence. When you expose your magnet to either very strong vibrations or conditions having extreme heat, it will lose remanence.
There are chances that such remanence loss may be permanent and irreversible. This will depend on the intensity of vibrations or how much heat you have subjected your magnet to.
Let us look at how significant remanence is in our everyday applications:
· Data Storage
Remanence properties are the basis of operation for computer hard disks and the microchips found in credit cards. Remanence ensures that your data is secured in them.
For additional data, you just have to play around with magnetic orientation. This action updates and preserves any data that you want stored.
· Permanent Magnets
All permanent magnets require remanence. You will find an extremely high resonance factor in such magnets.
It is because of this remanence that they are strong magnets. This is even after you withdraw any induced magnetism on such magnets.
· Scientific Research
Remanence is the best way we can use to explain paleo-magnetism. This is based on the fact that some materials have traces of magnetic field when they formed.
When we discuss the remanence of neodymium magnets, we are talking about all hard magnetic materials. In as much as the values for individual magnets are different, the concept is the same.
For clarity, we will have to compare the hysteresis curves of both soft and hard magnets. The remanence of neodymium magnets ranges between 1 to 1.3 Tesla.
This is around thrice the remanence value of ferrite magnets. You will notice a high remanence in the graph of hard magnetic materials even after you withdraw the induced magnetism.
This is major because you will have to use an excess magnetic field when magnetizing hard magnets. On the other hand, soft magnetic materials will rapidly lose their magnetism when you withdraw their induced magnetism.
As we have seen, remanence is a very important factor when we are dealing with matters of magnetism. Having a grasp of its formula and how you can calculate it can broaden your understanding of how magnets work.