Different materials show different types of magnetic properties when exposed to magnetic fields. The property of magnetism arises due to the presence of electrons in an atom or molecule. Each electron within an atom acts like a small magnet. In fact electrons can also be referred to as small loops of current that have the ability to retain the magnetic momentum.

Magnetic properties

The response given by a material when placed in an applied magnetic field is called its magnetic property. The interaction experienced amongst the magnetic dipole moments of constituents atoms and the external magnetic field results in a material with macroscopic magnetic properties. Different materials react differently when exposed to magnetic fields. 

• The property of magnetism

The property of magnet comes mainly from the following two types of electronic motion: 

• Due to the orbital movement of electrons around an atom’s nucleus. 
• Due to the electron spinning around its very own axis.
• Magnetic permeability

Magnetic permeability is the correlation of magnetic induction to the magnetic intensity of a material. Magnetic permeability is a scalar quantity and its symbol is ‘μ’. 

Magnetic permeability aids in the measurement of a material’s resistance to the magnetic field or in other words, it is the measurement of the degree to which the applied magnetic field can potentially penetrate a material.

The magnetic conductivity will be higher if a material has bigger magnetic permeability. 

The magnetic permeability basically helps the magnetic force of lines pass through a substance. 

• What affects magnetic permeability? 

Following are the factors that tend to affect Magnetic Permeability

The permeability of a material tends to depend on several factors like a material’s nature, humidity, temperature, and the frequency of the applied force. 

Note: Magnetic permeability varies with the magnetic field and is always positive. Meanwhile, the substances that behave opposite to the materials having magnetic permeability are called magnetic reluctance.

The formula for Magnetic permeability is given by;

Magnetic permeability (μ) = B/H

Here,  B = magnetic intensity and H = magnetizing field.

SI unit of magnetic permeability = henries per meter (H/m) or newtons per ampere squared meters (N⋅A−2).

• Types of Magnetic Permeability
• Permeability of Free Space
• It is also called the ‘permeability of vacuum or air’ and is represented by: μ0=B0/H
• It is the ratio of magnetic intensity in a vacuum and magnetizing field.
• Permeability of Medium
• It is the ratio of magnetic intensity in the medium to that of the magnetic field.
• It is represented by μ = B/H
• Relative Permeability
• It is a dimensionless quantity. 
• It is the ratio between two quantities having the same units, therefore the relative permeability has technically no unit. However, the Relative permeability of free space is always 1.
• It is represented with; μr= μ/μm
• Magnetic Permeability Materials

Based on a material’s permeability, it is classified into the following subcategories: 

• Diamagnetism

Materials having diamagnetism have a relative permeability value slightly lesser than 1, and this results in the reduction of the magnetic flux density inside materials with diamagnetism. These materials tend to feebly repel in external magnetic fields.

Example: Bismuth, copper, gold, antimony, silver, lead, silicon, mercury

Note: The orbital magnetic moment in an atom happens due to the electron’s orbital motion. Along with this, as mentioned earlier, the electrons tend to spin at their own axis which in turn creates a magnetic moment. The electrons in the atom can spin both clockwise as well as anticlockwise. Similarly, they also tend to spin around the nucleus in clockwise and anticlockwise directions. 

In diamagnetic materials, the orientation of the magnetic moments in atoms and the total magnetic moment is in such a way that the vector sum of this magnetic moment as a whole is zero. 

Characteristics of diamagnetism

• In a diamagnetic substance, the magnetic moment of every atom of a diamagnetic material is zero.
• They can be weakly repelled through an external magnetic moment.
• The diamagnetic substances tend to move from a field of the stronger side to a field of the weaker side if placed in a field of the non-uniform magnetic moment.
• If the diamagnetic substances are placed in the external magnetic field, they get magnetized weakly in the opposite direction of the magnetic field.
• They have negative Magnetic susceptibility

• Paramagnetism

Materials having paramagnetism have a relative permeability value slightly bigger than 1, and this is the reason why paramagnetic materials get feebly magnetic in the magnetic field’s direction when brought in contact with an external magnetic field. 

All paramagnetic atoms have a permanent magnetic dipole moment. This is because when the electrons in an atom with paramagnetism spin tend to orient magnetic moments. However, if there is a thermal motion around the atom, these magnetic orientations due to the electron spinning can also be random. Due to this randomness in orientation in presence of thermal energy, these materials have net magnetic moment zero. 

Example: Platinum, calcium, lithium, tungsten, aluminum

Characteristics of paramagnetism: 

• Every paramagnetic atom has a magnetic moment and is considered a magnetic dipole. 
• If placed near an external magnetic field, these substances tend to be attracted towards the field. 
• If placed in a non-uniform magnetic field they tend to deviate from the weaker side to the stronger one. 
• If the external field is removed they will lose their magnetic properties. 
• Ferromagnetism

Materials with Ferromagnetism don’t have constant relative permeability.

Ferromagnetic materials are considered to have the strongest magnetic properties due to the fact that with the increase in a magnetic field the relative permeability also increases. This is the sole reason why pure iron and many other paramagnetic alloys have values of relative permeability larger than 100000.

Example: Iron, cobalt, and nickel

Characteristics of ferromagnetism:

• Ferromagnetic substances are made up of a large number of small domains.
• They do not lose their magnetic properties even when the external magnetic field is taken out. 
• They become paramagnetic if heated above the curie point. 
• If placed around an external magnetic field, it strongly gets attracted towards the field.
• In a non-uniform magnetic field, they move from the weaker to the stronger side of the magnetic field. 
• If a rod with ferromagnetic material is stationed in a uniform magnetic field, the rod will come to rest while its length will be in parallel with the direction of the magnetic field.

Conclusion

Understanding the concept of magnetic properties is very important to form a strong foundation in chemistry as well as many physics topics. As we discussed earlier, the response given by a material when placed in an applied magnetic field is called its magnetic property. There are chances that different types of materials may behave differently so their properties too. Further, we have studied about magent permeability and its different sub categories too with chatatcteristics. So, it is a complete guide to give you enough knowledge of magnetic materials and their properties.