Ferromagnetism

Magnetism has been a major topic of research for centuries. We define a Magnet as an object that can create an invisible magnetic field that to cause attraction of opposite poles and repelling of similar poles. Further, the magnetic field comprises an orbital section around which the electrons spins. The force produced as a result causes two objects to attract or repulse without converting into a magnet. However, when a piece of metal like Iron converts into a permanent magnet despite the absence of a magnetic force field, we term it as Ferromagnetism.

Introduction to Ferromagnetism

Substances like Iron, cobalt, Nickel, etc. exhibit a phenomenon which we refer to as “long-range ordering”. The unpaired electrons present in the outer orbit line up in a position parallel to the magnetic field and creates a magnetic domain.

The force within this magnetic domain creates a permanent magnetism of the substance that remains even after the magnetic force has been removed

The amount of magnetization obtainable by a Ferromagnetic material based on the intensity of the applied magnetic field is termed as Relative Permeability

Ferromagnets have a differential Relative permeability that fluctuates based on the magnetization field.

Various types of Magnetic Phenomenon

Based on the electron’s orbital behaviour, and interactions of various materials, the types of magnetism can be widely classified.

1. Diamagnetic Substance

When a substance shows very weak magnetic interactions despite the presence of an external magnetic field it is termed Diamagnetism.

It is generally seen in substances that have a fully complete outer orbital ring. Also, these substances are not susceptible to temperature change.

Eg – NaCl, H2O, SiO2, CaCO3

2. Paramagnetic substance

When a substance is weakly affected by the magnetic field due to the presence of an unpaired electron on the outer orbital ring, the phenomenon is termed Paramagnetism

However, in the case of Paramagnetism, the magnetism though present is nullified if the external field is removed. Only during the presence of a force field partial alignment occurs directed towards the field. This results in a positive susceptibility.

Eg – Biotite, Pyrite, Nontronite

3. Ferromagnetic substance

When we see magnetic interactions regardless of the presence or absence of a magnetic field, we term it as Ferromagnetic Substance. They show strong attraction towards the magnetic field.

What is Curie Temperature and Hysteresis?

• Curie Temperature –

Electromagnetic fluctuation within the magnetic domain can cause randomized temperature changes which a change in the electron exchange. The temperature at which this phenomenon occurs is termed Curie Temperature.

The magnetization saturation at Curie Temperature is generally at a neutral or zero. Curie Temperature plays a very distinctive role as a diagnostic test for distinguishing various minerals from each other.

• Hysteresis –

Ferromagnetic substances generally have a very good retentive memory. Despite the removal of the applied force field, the majority of these ferromagnetic minerals tend to show magnetic properties.

This property is termed Hysteresis. However, the hysteresis properties of a material are not fixed and it can vary based on extrinsic factors like Domain, temperature magnetic grain size, etc.

Causes of Ferromagnetism

When neighbouring dipoles of an atom align in a symmetrical manner. It causes an unpaired electron to be displaced into the outer orbital ring, a distinct change in the magnetic moment occurs.

The atomic dipole moment gives rise to a magnetic domain which creates a force filled with polarity in the object.

What is Ferrimagnetism?

We must never confuse Ferromagnetism with Ferrimagnetism.

The crystalline structures of ionic compounds have a very distinctive magnetic ordering. Consisting primarily of two sub-lattices held together by oxygen molecule, the anions produced during magnetization causes a phenomenon where the anti-parallel alignment of the latices spin occurs.

The net magnetic moment occurs in this state despite the magnetic moment is not being equal. This phenomenon is termed Ferrimagnetism.

Though similar to a Ferromagnetic substance, it is this distinctive unequal magnetic moment and a different magnetic ordering value that differentiates a Ferrimagnet.

Similar to a Ferromagnetic substance, Ferrimagnet also has a spontaneous magnetization value that is below Curie temperature. They are also paramagnetic when the temperature goes beyond Curie Point.

What are the properties of a Ferromagnet?

1. The magnetic field changes always influence Ferromagnets.
2. Ferromagnets are in a constant dipole moment in their atomic state
3. The atomic dipole moment is always parallel to the direction of the magnetic field
4. Magnetic saturation of a Ferromagnet varies based on the intensity of magnetization.
5. Even in absence of a magnetic field, Ferromagnets shows a relatively high magnetism
6. Magnetic intensity(M) is effected in a linear direction based on the magnetizing field (H)
7. Magnetic Susceptibility (X) is calculated based on the intensity of the magnetization divided by the strength of the magnetized field. X= M/H

8. The magnetic field greatly influences relative permeability as the internal field of a material is generally stronger
9. The pole showing the strongest magnetic field is the general direction of attachment of a ferromagnet
10. Liquification of the ferromagnetic substance results in abrupt temperature changes thus causing it to lose its magnetic properties entirely.

What are the types of Ferromagnetic materials?

There are two types of Ferromagnetic Materials:

• Unmagnetized Ferromagnetic Substances

The atoms inside these materials have a wide range of magnetic domains that have a very haphazard and individual magnetic moment. This results in a constant Unmagnetised state.

• Magnetized Ferromagnetic Substances

In some Unmagnetised ferromagnetic when the external magnetic field is applied, the magnetic domain automatically rotates to face the exact direction of the magnetic force field. This causes magnetization of the Ferromagnets.

What are the advantages and disadvantages of using Ferromagnets?

Advantages

1. Large Electrical resistance margin
2. Cheaper alternative
3. The high rate of permeability
4. Operable in temperature changes as high as 300 degree Celsius
5. Ferromagnets are generally very stable

Disadvantages

1. Magnetic field influences the strength of magnetism, so a weaker magnetic field can create a less stable magnetization.

Application of Ferromagnetism in day to day life activities –

Ferromagnets have a very wide range of usability since their conceptualization. Thus, some of the primary sections where we use it:

• Transformer Cores
• Magnetic tapes
• Hard drives
• Generators
• Telephonic devices
• Electrical motors

FAQ on Ferromagnetism

Question 1: What is the difference between Ferromagnetism and Paramagnetism?

Answer 1: In Ferromagnetism a distinctive repulsion or attraction is seen. Further, the uniform movement of the electron in the direction of the force field causes this.

Moreover, in the case of Paramagnetism, the electrons have no specific spin direction which results in a very weak repulsion and attraction which is barely negligible.

Question 2:How do you identify a Ferromagnetic object from a Magnet?

Answer 2: The ferromagnetic object shows a similar feature like a magnet. However, on removing the magnetic force field, a Ferromagnet object still remains in the oriented direction of the force field.