Permanent magnets are able to maintain their magnetic properties over a long period of time, which is why they are referred to as "permanent." The key factor that contributes to their permanence is the alignment of the magnetic domains within the material.
In a permanent magnet, such as one made of ferromagnetic materials like iron, cobalt, or nickel, the magnetic domains are regions within the material where the atomic magnetic moments are aligned in the same direction. These domains act like tiny magnets within the material. In an unmagnetized state, these domains have random orientations, canceling each other's magnetic fields and resulting in a net magnetization of zero.
To make a permanent magnet, the material is subjected to a strong external magnetic field. This external field aligns the magnetic domains in a preferred direction, causing them to point in the same direction. Once the external field is removed, the aligned domains tend to remain in their new orientation due to the exchange interactions and the magnetic anisotropy of the material.
The exchange interactions, which arise from the quantum mechanical exchange of electrons between neighboring atoms, help stabilize the alignment of the magnetic moments. Additionally, the magnetic anisotropy of the material, which is the tendency of the material to have preferred directions of magnetization, reinforces the alignment of the domains.
These two factors, exchange interactions and magnetic anisotropy, make it energetically favorable for the magnetic domains to remain aligned even in the absence of an external field. As a result, the permanent magnet retains its magnetization and exhibits a stable magnetic field.
It's important to note that while permanent magnets are highly durable, they can be demagnetized under certain conditions, such as exposure to high temperatures, strong opposing magnetic fields, or physical impacts that disrupt the alignment of the domains. However, under normal operating conditions, they can effectively convert between mechanical and electrical energy without wearing out.