What is Residual Magnetism : Types & Its Properties

The antiquity of magnetism was there in the period 600 B.C., itself, but the prominence of this came into the limelight in the 20th century. Later on, scientists started to get knowledge on this concept and made enhancements. Initially, magnetism was observed in the form of a mineral which was lodestone where this comprises oxygen and a chemical combination of iron. In the period between 1540-1603, Gilbert was the first discoverer to explore the spectacle of magnetism through various approaches. For the proper evolution of magnetism theory, there was the involvement of many other scientists. The modern-day understanding of magnetic theory was supporting many domains and industries. And the one topic to be discussed about this theory is “Residual Magnetism”. This article shows a clear concept of residual magnetism, types, and how it can be reduced?

What is Residual Magnetism?

This term is stated as the quantity of magnetization that was left after the removal of the exterior magnetic field. It can also be explained in the way that the amount of flux density which was held by the magnetic substance is termed as residual magnetism and the ability to hold the magnetism is termed as the material’s retentivity.

Residual Magnetism
Residual Magnetism

What is Remanence?

Magnetization takes place by the application of electric current in one path and there will be an increment in the flux density till the time saturation point is attained. In order to demagnetize the magnetic loop, H needs to be modified by changing the path of the current flow.

When there is a change in the value of H in the reverse path, then flux density gets decreased and reaches zero. This property of residual magnetism for the magnetic substance can be eliminated by the application of magnetizing pressure which is called coercive force in the reverse path.

This approach of residual magnetism is extensively seen in the devices like motors, generators, and transformers and it is also defined with the name “Remanence”.

Different Types

Let us now consider the types of remanence and explanation of those

Types of Remanence
Types of Remanence

Residual magnetism is broadly categorized into three types which are:

  • Saturation remanence
  • Isothermal remanence
  • Anhysteretic remanence

Saturation Remanence

This is the whole magnetic moment per every size of the sample. This type of magnetism is represented as MR and in some cases, it is even defined as isothermal residual magnetism (MRS).

Isothermal Remanence

In general, recognition of remanence in the magnetic substances cannot be done just through one approach because every substance has its own sizes, properties, shapes. And so to calculate the remanence of minimal magnetic substances, this approach is used which is represented by Mr(H).

This approach is mainly dependent on the substance’s magnetic field. Here, initially, a magnetic substance is magnetized and then H is applied and deleted. This type is even known as Initial Remanence.

Under this, there are again two classifications

  1. DC Demagnetization Remanence – Here, a magnetic substance is magnetized in one path by the application of an electric current till it gets to the saturation point. Then, an electric current is applied to the substance in the reverse path and disconnecting the magnetic field.
  2. AC Demagnetization Remanence – The name itself denotes that a magnetic substance is magnetized in one path by the application of AC electric current till it gets to the saturation point. This is represented as Ma (H).

Anhysteretic Residual Magnetism

This is another type of remanence where the magnetic substance is positioned in a huge varying magnetic field having a minimal amount of direct current biasing field. In order to get residual magnetism, the amplitude level of the varying field is decreased to the zero levels slowly, and then after the biasing direct current field is disconnected from the circuit.

These are the classifications of remanence.

Reduction of Residual Magnetism

There are multiple approaches where the residual magnetism from the substance can be eliminated. Below are a few methodologies:

  • By using a hot rolled steel substance, remanence can be almost decreased by 45 – 50 percent
  • The saturation range of the magnetic substance might be decreased by the application of a higher range of exciting currents.
  • In order to demagnetize from the residual magnetism, initially, magnetization procedure needs to be initiated having constant pressure and then slowing augmenting till it reaches to saturation level and then after the magnetization is slowly reduced. And this reduces the remanence from the magnetic substance.
  • In the method of magnetizing and demagnetizing the magnetic substance the electrical pressure or the applied electric current need to equally analogous.

So, this is all about the concept of Residual Magnetism. Here, we have gone through what is residual magnetism, its types, and the removal of remanence. In addition, also know what is the significance of remanence?