Behaviour and Classification of Magnetic Materials
Not all magnets are the same. They differ in properties and behaviour. One way of classifying magnetic behaviour and ascertaining properties corresponding to that behaviour is through magnetic susceptibility. According to this concept, magnetic materials are classified into diamagnetic, paramagnetic, and ferromagnetic materials. This classification is made based on the magnetic susceptibility of various materials. It provides information about the material structure, location of atoms, and their bonding. This article will help you revise the properties and basis of the classification of these three major types.
Magnetic Susceptibility and Its Characteristics
It is a measure of how susceptible material is to getting magnetised when placed in a magnetic field. Magnetic Susceptibility is expressed as $\chi $.
The following are some important characteristics of magnetic susceptibility:
It is dimensionless.
It is a proportionality constant.
It occurs due to the interaction between the electrons and nuclei of any material and the externally applied magnetic field.
It helps in categorising materials into dia, para, and ferromagnets.
The formula for calculating magnetic susceptibility $\chi $ is $\frac{M}{H}$, where M is the magnetisation of the material and H is applied magnetic field intensity.
Diamagnetic Materials
Diamagnetic materials get freely magnetised when placed in a magnetic field but in the opposite direction. In other words, diamagnetic materials are repelled by magnetic forces and tend to move from a stronger to weaker part of the applied magnetic field. Diamagnetism is a common property exhibited by most materials irrespective of the temperature. The effect is very negligible when compared to the other types.
A Diamagnetic Specimen Placed in an External Magnetic Field
In the above figure, the diamagnetic specimen placed in a uniform magnetic field does not allow, i.e., repels the magnetic field lines to pass through it. In case a diamagnetic material is placed in a non-uniform magnetic field, it will try to move from the point of high to low magnetic field strength. Examples of diamagnetic materials include Copper, Silver, Zinc, Antimony, Gold, Water, Glass, NaCl, Marble, Glass, etc. The magnetic susceptibility of diamagnetic materials will be small and negative, i.e., $-1\le \chi \le 0$
Paramagnetic Materials
The paramagnetic materials get weakly magnetised if placed in an external magnetic field. In other words, they will try to move from points exhibiting weak magnetic strength to points exhibiting a relatively stronger magnetic field strength. The atoms of a paramagnetic material will experience a dipole moment, interact with one another, and get aligned spontaneously when placed in an external magnetic field.
According to Curie’s law, the magnetism of a paramagnetic material is inversely proportional to the absolute temperature up to a point where the material reaches a point of saturation, i.e., $M=\dfrac {C}{T} ~H$, where C is curie’s constant.
Examples of paramagnetic materials include Manganese, Platinum, Chromium, Aluminium, etc. The magnetic susceptibility of paramagnetic materials is small and positive, i.e., $\chi >0$.
Ferromagnetic Materials
Ferromagnetic materials get strongly magnetised in an external magnetic field. Hence, they get attracted to permanent magnets, unlike paramagnetic materials. In addition, ferromagnetic materials will try to move from a region of a weaker magnetic field to a region of a stronger magnetic field. Similar to paramagnetic materials, the atoms of ferromagnets will experience a dipole moment, interact with one another, and get aligned spontaneously when placed in an external magnetic field. However, the direction of alignment on a macroscopic scale is common leading to a net magnetization which results in strong magnetization behaviour.
A Ferromagnetic Specimen in an External Magnetic Field
Examples of ferromagnetic materials include Cobalt, Iron, Nickel, Gadolinium, and certain alloys like Alnico etc. The magnetic susceptibility of such materials is large and positive, i.e., $\chi >1000$.
Properties of Dia, Para, and Ferromagnetic Materials
Conclusion
Based on the magnetic susceptibility, materials are classified into dia, para, and ferromagnetic materials. It is important to understand their individual behaviour and properties when placed in an externally applied magnetic field as it helps in building useful applications. Also, the importance of temperature in maintaining the properties is to be borne in mind.
FAQs on Properties of Diamagnetic, Paramagnetic and Ferromagnetic Materials for JEE
1. What are super paramagnets?
Superparamagnetic materials in addition to exhibiting net paramagnetism, exhibit powerful ferromagnetic ordering. This happens at the microscopic level most of the time. Curie’s law says that at high temperatures, the magnetisation of most of the paramagnetic materials will directly depend on the strength of the applied magnetic field. They follow Curie’s law of temperature and have very high Curie constants. An example of a super paramagnet is Ferro liquid.
2. What are a few applications of ferromagnetic materials?
Ferromagnetic materials can be permanently magnetised and a few applications of such materials are in transformers, credit cards, loudspeakers, generators, and recording devices. They are also used for the storage of non-volatile information.
