# How is the field inside a rod magnet in the presence of ferro magnetic material?

 P: 409 How is the field inside a rod magnet in the presence of ferro magnetic material? You're welcome. I found an easier explanation based on equivalent surface and current densities rather than dipoles: In a ferromagnetic material, including magnets , the equivallent volume current density is equal to $\nabla$$\times$M and the surface current density is equal to M$\times$n ( n is the outward normal to the surface). For a cylindrical magnet with its magnetization along z-axix , the volume current density is zero. the surface current have magnitude of M and the direction of a$\phi$. This is like having a solenoid. When the ferromagnetic material is brought close to one of the magnet poles, the induced M inside it has equivalent currents too. Although M inside the body is not as uniform as in the magnet, it has a surface current in the same direction as the magnets current as well as some volume currents too. Altogether, the body acts like another solenoid and its field is superposed with the with magnets own field, increasing it.