What is Magnetic Hysteresis : B-H Curve & Its Applications

The word hysteresis was introduced from an Ancient Greek word where the meaning refers to “lagging behind” or “inadequacy”. The term magnetic hysteresis was founded in the year 1890 by scientist James Alfred Ewing to know the performance and conductivity of the magnetic substances. Before 1890, the work on this concept of hysteresis in mechanical networks was performed by James Maxwell. Consequently, the models that were developed from hysteresis gained more signification in the works related to absorption and magnetism. Then, mathematical analysis of magnetic hysteresis was known in the period of 1970s by Mark Krasnosel and his team. And now our article explains magnetic hysteresis, the B-H curve, its behavior, and applications.

What is Magnetic Hysteresis?

This is the phenomenon of magnetization density ‘B’ which is lags following the magnetic force ‘H’ which occurs in a magnetic substance is termed as “Magnetic Hysteresis”. To be clear, it can be explained as when a magnetic substance is under magnetization for the first time and then in another way, which completes one full cycle of magnetization, then there develops flux density that lags behind the magnetization force.


Magnetic Material
Magnetic Material

For magnetic substances such as iron, even when they are not under the magnetic field, some portion of the alignment will be maintained. To make them non-magnetized, it needs either application of heat or magnetic field in the reverse direction. There exist various types of magnetic substances like para, dia, Ferro, and anti-ferromagnetic materials. With the ferromagnetic substances, the hysteresis loop can be easily developed.

Magnetic Hysteresis Loop

The hysteresis loop defines the relationship that exists between the magnetizing field and the amount of magnetization effect. At the time of modifying the external magnetic field in a ferromagnet material, the hysteresis loop will be developed. The below graph describes the positions and detailed analysis.

Hysteresis Loop
Hysteresis Loop

The loop is formed while measuring B for multiple H values and if these values are outlined as a graphical form, then it forms a loop. Here,

  • The value of ‘B’ gets increased when ‘H’ value is simultaneously increased.
  • Increasing the magnetic field impact enhances the magnetism value and at the end, it gets to the point ‘A’, which is termed as a saturation point where ‘B’ stays at constant.
  • By decreasing the magnetic field amount, the magnetism impact also gets decreased. But ‘B’ and ‘H’ values are similar which is ‘0’, the magnetic substance holds few magnetism properties and this is defined as either residual magnetism or as retentivity.
  • And when there is a decline in the effect of a magnetic field, magnetism property will also get decrease. And at ‘C’, the material gets entirely demagnetized and has zero magnetic properties.
  • Both these forward and reverse direction procedures complete one entire cycle and form a loop that is termed as a hysteresis loop.

Magnetization or B-H Curve

With the above basic theory, we are clear that magnetic hysteresis curves are different for different types of materials. From the below picture, it was observed that flux density is increasing correspondingly to the field strength till it comes to a specific value and after this point flux density stays as constant even field strength remains to increase.

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This happens due to the reason that there exists a restriction on the flux density amount which might be developed by the core as the entire domains present in the iron substance are exactly aligned. After this, it shows no impact on ‘M’, and in the graph, the point where the flux density is at maximum value is termed as Magnetic Saturation.

Saturation develops because of random alignment of the molecule arrangement inside the core substance and this modifies the small particles inside the substance to get in exact alignment. When the value of ‘H’, increases, there will be a more perfect arrangement of the molecular particles till they reach to develop increased flux density. And also increment in the magnetic field strength because of enhancement in electric current vale across the coil will show no effect

Magnetic Hysteresis Loops for Soft and Hard Materials

The result of magnetic hysteresis is the unused energy dissipation in the heat form where the dissipated energy is in linear proportion to the extent of the hysteresis loop. The losses developed because of magnetic hysteresis also shows the effect on the alternating type of transformers where there is frequent variation in the current direction. Because of this, magnetic poles in the core material creates losses as they are continually reverse their direction. The below pictures depict the hysteresis loop in both the soft and hard materials.

In soft magnet

Loop in Soft Magnet
Loop in Soft Magnet

In hard magnet

Hysteresis Curve in Hard Magnet
Hysteresis Curve in Hard Magnet

Revolving coils that are present in DC systems will also develop hysteresis losses as they have continual passage through the south and north magnetic pole. As it is already stated that, the hysteresis loop graph is based on the behavior of the magnetic material that is used.

Residual Magnetism

From the magnetic hysteresis loop, the amount of flux density that is maintained by the magnetic substance is termed as residual magnetism. And the amount of maintenance it is called as the substance retentivity.

Coercive Force

The amount of the magnetizing force which is necessary to remove the remaining magnetic property from the material is termed as Coercive force. To finish up the hysteresis loop, the magnetic force ‘H’ is more enhanced in the opposite direction until it comes to a saturation point. And the value of ‘H’, will reach zero and the loop comes to the path ‘de’, where the path ‘oe’ is the residual magnetic property when the path is in the opposite direction.

Magnetic hysteresis outcomes in the intemperance of wasted energy as in the heat form. The energy that is dissipated is relative to the extent of the hysteresis loop. Especially there exist two kinds of magnetic material where those are soft magnetic material and hard magnetic material.

Applications

A few of the applications of magnetic hysteresis are:

As magnetic substances have an extended range of hysteresis loop, these are implemented in the devices such as

  • Hard disk
  • Audio recording devices
  • Magnetic tapes
  • Credit cards

Also, there exists constricted magnetic hysteresis loop substances and these are used in

Employed in damping the angular motion of satellites in the minimal earth orbit as because of the advent of the space age.

And finally, this is all about the concept of magnetic hysteresis. In this article, we got to know about the hysteresis loop, B-H curve, residual magnetism, coercive force, and how the loop differs for soft and hard magnetic substance and its applications. It is further important to know about what is the importance of a hysteresis loop?

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