Question

Why does iron filings make a random pattern when kept around the bar magnet

Answer 1

The reason a piece of magnetic material such as iron spontaneously divides into separate domains, rather than exist in a state with magnetization in the same direction throughout the material, is to minimize its internal energy.[3] A large region of ferromagnetic material with a constant magnetization throughout will create a large magnetic field extending into the space outside itself (diagram a, right). This requires a lot of magnetostatic energy stored in the field. To reduce this energy, the sample can split into two domains, with the magnetization in opposite directions in each domain (diagram b right). The magnetic field lines pass in loops in opposite directions through each domain, reducing the field outside the material. To reduce the field energy further, each of these domains can split also, resulting in smaller parallel domains with magnetization in alternating directions, with smaller amounts of field outside the material