It would be very wrong that we talk about the magnetic field and not talk about hysteresis. It is common for all ferromagnetic materials to have the property of hysteresis. But, what is hysteresis? Nothing, It is just a lagging of magnetization behind the magnetic field in any ferromagnetic materials.
In this present article, we will discuss Hysteresis loop class 12, definition, types, applications, and its energy losses, So let’s get started…
What is hysteresis?
The term “hysteresis” is derived from ὑστέρησις, an Ancient Greek word meaning “deficiency” or “lagging behind”. This term was coined by Sir James Alfred Ewing in 1881 to describe the behavior of magnetic materials.
Generally, hysteresis refers to a delay between the entry and exit of a system when there is a change in direction. Hysteresis is something that happens with ferromagnetic materials so that if a varying magnetization signal is applied, the resulting magnetism that is created follows that applied signal, but with a delay. This delay is termed hysteresis.
Definition: Hysteresis is the lagging of magnetic flux density (B) behind the magnetic field strength (H).
Systems that show hysteresis are non-linear and can be mathematically difficult to some hysteretic models, such as the Preisach model (originally applied to ferromagnetism) and the Bouc-Wen model (that attempt to capture the general characteristics of hysteresis), and there are also phenomenological models for particular phenomena such as the Jiles-Atherton model for ferromagnetism.
All ferromagnetic materials describe the phenomena of hysteresis. To give you a better grasp of the concept, we will take a ferromagnetic material that is placed inside a current-carrying coil. Due to the magnetic field that is passing through the material gets magnetized. But, If we reverse the direction of current then the material gets demagnetized, this process is known as hysteresis.
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Types of Hysteresis
There are two types of hysteresis.
- Rate-dependent hysteresis: In rate-dependent hysteresis, there is a lag between input and output. An example is a sinusoidal input X(t) that results in a sinusoidal output Y(t), but with a phase lag φ
- Rate-independent hysteresis: Systems with rate-independent hysteresis have a persistent memory of the past that remains after the transients have disappeared.
What is hysteresis loop?
The hysteresis loop (also known as the hysteresis curve) is a four-quadrant graph that shows the relationship between the induced magnetic flux density (B) and the magnetizing field strength (H). Sometimes, this loop is referred to as the B-H loop. This loop is formed by measuring the magnetic flux that emits from the ferromagnetic material when the external magnetizing field changes.
The curve that you are seeing in the above figure is a hysteresis loop or curve. This curve is called a loop because this is a closed figure which is extended to all four quadrants, and has no end. If we look at the graph then we will find that it is just the plotting of field density (B) for various values of magnetizing force (H). Let’s analyze this hysteresis loop in brief.
- If the magnetic field strength(H) increases from 0, then the magnetic flux density (B) also increases.
- As the magnetic field increases then the value of magnetism also increases and finally reaches point A which is called saturation point where B becomes constant.
- With a decrease in the value of the magnetic field intensity (H), there is a decrease in the value of magnetism (B). But at B, H is equal to zero. At this point, material retains some amount of magnetism is called retentivity or residual magnetism.
- When there is a decrease in the magnetic field intensity (H) towards the negative side, magnetism also decreases. At point C the material becomes completely demagnetized.
- The force that is required to remove the retentivity of the material is known as Coercive force (C).
- The cycle is continued in the opposite direction, where it attends its saturation at point is D, retentivity point is E, and coercive force is F.
- Due to the forward and opposite direction of the process, the cycle becomes complete and this cycle is called the hysteresis loop.
Retentivity and Coercivity
All ferromagnets have the property that it retains some magnetization when the external magnetizing field is removed completely. This property of ferromagnetic materials is called retentivity or remanence.
But, if we want to demagnetize the remaining magnetization in a ferromagnetic material, we applied magnetizing field (H) in the opposite direction. The magnetizing field (H) needed to demagnetize the magnetic material completely is known as its coercivity.
Retentivity
The property of the ferromagnetic material to retain some magnetization even in the absence of the external magnetizing field is known as retentivity or remanence.
- It is the ability of material to retain a certain amount of magnetic property when the external magnetizing field is removed.
- The value of B at point b in the hysteresis loop show the retentivity of the material.
Coercivity
It is the magnetizing force applied in the negative direction to demagnetize the remaining magnetization in a ferromagnetic material completely is called coercivity. The value of H at point c in the hysteresis loop shows the coercivity.
Advantages of Hysteresis Loop
The shape and size of the hysteresis loop depend on the nature of the magnetic material. The choice of magnetic material needed for a particular application often depends on the shape and size of the hysteresis loop. The advantages of the hysteresis loop are given below:
- The smaller the hysteresis loop area of a magnetic material, the smaller the hysteresis loss. For example, the area of the hysteresis loop for silicon steel is very small, which is why silicon steel is widely used for making cores of transformers and rotating machines that are subject to rapid reversals of magnetism.
- The relevance of retentivity and coercivity is provided by the hysteresis loop of material
- The B-H graph can be used to determine residual magnetism, which aids in material selection for electromagnets.
Application of hysteresis
Hysteresis can be found in fields of chemistry, physics, engineering, economics, and biology. Common examples also include magnetic hysteresis, ferroelectric hysteresis, superconducting hysteresis, mechanical hysteresis, optical hysteresis, electron beam hysteresis, adsorption hysteresis, economic hysteresis, etc. Either way, we’ll look at some of the important uses of hysteresis.
- Most of the applications of hysteresis are found in ferromagnets. It is mainly used to store memory, such as hard drives, magnetic tapes, and credit cards.
- Hysteresis is applied in many artificial systems such as thermostats and Schmitt triggers designed to prevent unwanted, frequent, or undesired rapid switching.
- Sometimes hysteresis is intentionally built into computer algorithms.
- Hysteresis can be observed when decreasing the angle of attack of a wing after stall, with respect to the lift and drag coefficients.
- The existence of bubble shape hysteresis has important consequences in interfacial rheology experiments involving bubbles.
- In biology, it is found in cell biology and genetics, in immunology, in neurosciences, in respiratory physiology, in the physiology of speech and language, in ecology, and in epidemiology.
Energy Losses due to Hysteresis
- A transformer is the best example of anaysizing the energy loss due to hysteresis because we know that energy is needed during the process of magnetization and demagnetization.
- During the cycle of magnetization and demagnetization of magnetic substances, energy is expended and this energy appears as heat. This heat loss is known as hysteresis loss.
- The loss of energy per unit of volume of the substance is equal to the area encosed by the hysteresis curve. In transformers due to the continuous process of magnetization and demagnetization, energy is lost in the form of heat continuously, due to this loss of energy, the efficiency of the transformer is reduced.
- To stop this loss of energy, the soft iron core is used in transformers because the energy loss or hysteresis loss in the case of soft iron is much lower than in other materials.
Difference between the soft magnet, and hard magnet
The difference between soft and hard magnets is given below table:
| Soft magnet | Hard magnet |
| Easy Magnetization and demagnetization | Magnetization and demagnetization is difficult |
| The Retentivity of soft magnets is higher | The Retentivity of hard magnets is lower |
| Lower coercivity | Higher coercivity |
| Soft magnets lose less energy | Hard magnets lose large energy |
| The hysteresis loop area is small | The hysteresis loop area is large |
| Higher magnetic permeability | Lower magnetic permeability |
| I and χ are both high | I and χ are both low |
| Temporary magnets | Permanent magnets |
| Examples: Ferrous-nickel alloy, Ferrites, etc | carbon steel, steel, tungsten, chromium steel, etc. are examples of hard magnets |
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Magnetization and Demagnetization
The method of developing magnetic properties in a magnetic substance is known as magnetization. With the help of an electric current or a powerful magnet, any magnetic material can be magnetized.
- If a magnetic substance is placed in an external magnetizing field, the material becomes magnetized and if the external magnetizing field is reversed, the material demagnetizes.
- When ferromagnetic materials are inserted into a current-carrying coil, the magnetizing field H produced by the current pushes some or all of the material’s atomic magnetic dipoles to align with the external magnetizing field, and hence it gets magnetize.