Question: a decrease in magnetic field strength is link to what

title: Magnetic domain
text: 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 . 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 .