To understand that, we first need to understand what makes such materials into magnets.
At the atomic level, materials that exhibit strong magnetic susceptibility have unpaired electrons in their electronic shells. These unpaired electrons all have a certain spin direction associated with them. Due to this spin, and the revolution of electrons around the nucleus, electrons generate their own magnetism. As all the electrons spin in the same direction for a certain nucleus, their magnetic field directions are also the same. So these magnetic fields add up and give the whole atom a net magnetic field (Mohammad et al., 2003; Rajendran, 2004).
When these atoms are subjected to a magnetic field, they align themselves with the applied magnetic field. When the magnetic field is removed, some of these atoms remain aligned with the magnetic field. These regions where the magnetic field of the atoms is aligned in the same direction are known as domains (Saleemi et al, 2002). For ferromagnetic materials, a net magnetic field is always present. The maximum magnetism that a ferromagnetic material may retain in the absence of an external magnetic field is known as its saturation magnetization. This is an important property which changes when we change the temperature of the magnetic material (Callister, 2007).
There is an important factor which dictates the ease with which atoms align with each other to form domains under the effect of an external magnetic field – the thermal agitation of the atoms. Atoms vibrate and have energy associated with their vibration. This vibration increases as the temperature of the material increases. As the atomic vibration/agitation increases, it becomes harder for these atoms to be forced to be aligned in a certain direction, and vice versa. So, if we apply the same amount of external energy through a