Magnetic materials: Understanding their classification

Magnetic materials are materials that can produce a magnetic field or be influenced by a magnetic field. They can be naturally occurring materials, such as lodestone, or synthetic materials, such as neodymium magnets. These materials have the ability to interact with magnetic fields due to their atomic structure and/or  molecular spins . Magnetic materials are widely used in various applications such as electric motors, generators, MRI machines, and magnetic storage devices. These materials are classified into two categories based on their behaviour in a magnetic field and their applications.

According to their behaviour in a magnetic field

a) Diamagnetic materials are not magnetized in a magnetic field and do not retain any magnetic properties once the field is removed. Examples include copper, silver, gold, and bismuth.

b) Paramagnetic materials are weakly attracted by a magnetic field and exhibit temporary magnetism while in the field. Examples include aluminum, platinum, and titanium.

c) Ferromagnetic materials exhibit strong magnetism even in the absence of an external magnetic field. These materials can be magnetized and retain their magnetism after the external field is removed. Examples include iron, nickel, and cobalt.

d) Antiferromagnetic materials exhibit a magnetic ordering in which the magnetic moments of adjacent atoms align in opposite directions, resulting in zero net magnetization. Examples include chromium and manganese.

e) Ferrimagnetic materials exhibit a magnetic ordering in which the magnetic moments of adjacent atoms align in opposite directions but are not equal in magnitude, resulting in a net magnetization. Examples include magnetite and ferrites.

The first two types (dia and para) are commonly referred to as non-magnetic. They exhibit weak response to an external field. The other three are those that are commonly referred to as magnetic materials. They respond very strongly to external magnetic field and applied in wide variety of application.

Based on application

a) Hard magnetic materials are materials that retain their magnetism even in the absence of an external field, and require a large amount of energy to be demagnetized. They are used in applications where a permanent magnet is required, such as in electric motors, loudspeakers, and MRI machines. Examples include alnico, samarium cobalt, and neodymium magnets.

b) Soft magnetic materials are materials that can be easily magnetized and demagnetized, and are used in applications where the magnetic field needs to be rapidly and repeatedly switched on and off, such as in transformers, inductors, and magnetic shielding. Examples include iron-silicon alloys, nickel-iron alloys, and iron-cobalt alloys.

In summary, the classification of magnetic materials is important in understanding their behaviour in magnetic fields and their applications. Diamagnetic and paramagnetic materials are commonly referred to as non-magnetic, while ferromagnetic, antiferromagnetic, and ferrimagnetic materials are commonly referred to as magnetic materials. Hard magnetic materials retain their magnetism, while soft magnetic materials can be easily magnetized and demagnetized.