According to Wikipedia:
A magnetic domain is a region within a magnetic material where individual magnetic moments of the atoms are aligned with one another and point in the same direction thus resulting in uniform magnetisation in that region.
Below Curie temperature, a piece of magnetic material such as iron spontaneously divides into separate magnetic domains rather than stay in a state with magnetisation in the same direction in order to minimise its internal energy.
A large region of ferromagnetic material with a constant magnetisation throughout will create a large external magnetic field which requires a lot of magnetostatic energy.
To reduce this energy, the magnetic material can split itself into smaller domains which acts to contain the magnetic field within itself in closed loops, with small amounts of field outside the material. However, the domain structure of actual magnetic materials does not usually form by the process of large domains splitting into smaller ones. The equilibrium domain configuration simply appears when the material is cooled below Curie temperature.
Curie temperature is the temperature above which certain materials lose their permanent magnetic properties to be replaced by induced magnetism, what does "permanent magnetic properties" mean exactly? Would spontaneous magnetism in ferromagnetic materials be one of these properties(1)? Or is it referring to the state where magnetic domains aligned with an external magnetic field are pinned in place by defects in the crystal lattice(2)?
If it refers to the second point(2), what's the difference between ferromagnetism and induced magnetism (or permanent magnets and temporary ones)? How can iron, for example, be a ferromagnet and an induced magnet? Is induced magnetism similar to paramagnetism?
I'm not too sure what exactly is meant by the second paragraph; does it mean that when all the magnetic domains are aligned in the same direction by an external magnetic field and when that external field is removed and the material is cooled below the Curie temperature, it will "lose" its external magnetic field? But then what happens when you heat it above the temperature, does it just cause the magnetic domains to return back to its initial lowest energy state or does it destroy these domains? I'm confused because this is what was mentioned on the site:
Aren't paramagnetic materials materials that don't have magnetic domains?