Every substance has some magnetic properties associated with it. The origin of these properties lies in the electrons. Each electron in an atom behaves like a tiny magnet. Its magnetic moment originates from two types of motions.

(i) Its orbital motion around the nucleus and

(ii) Its spin around its own axis.

Electron being a charged particle and undergoing these motions can be considered as a small loop of current which possesses a magnetic moment. Thus, each electron has a permanent spin and an orbital magnetic moment associated with it. Magnitude of this magnetic moment is very small and is measured in the unit called Bohr magneton, µB. It is equal to 9.27 × 10^–24 Am². On the basis of their magnetic properties, substances can be classified into five categories:

(i) Paramagnetic

(ii) Diamagnetic

(iii) Ferromagnetic

(iv) Antiferromagnetic and

(v) Ferrimagnetic.

Which of the following substances are attracted very strongly by a magnetic field?

Ferromagnetic

Ferromagnetism: A few substances like iron, cobalt, nickel, gadolinium and CrO₂ are attracted very strongly by a magnetic field. Such substances are called ferromagnetic substances. Besides strong attractions, these substances can be permanently magnetised. In solid state, the metal ions of ferromagnetic substances are grouped together into small regions called domains. Thus, each domain acts as a tiny magnet. In an unmagnetised piece of a ferromagnetic substance the domains are randomly oriented, and their magnetic moments get cancelled. When the substance is placed in a magnetic field all the domains get oriented in the direction of the magnetic field and a strong magnetic effect is produced. This ordering of domains persists even when the magnetic field is removed, and the ferromagnetic substance becomes a permanent magnet.