Magnetic field lines are closed curves as they propagate from the North pole outside the magnet’s body to the magnet’s body and from the south pole to the north pole inside the magnet’s body. Hence, the magnetic field lines are closed.
Correspondingly, do magnetic fields always form loops?
A magnetic field of force is set up between the two poles. … The magnetic lines (flux lines) are continuous and always form loops. These invisible lines can be seen if you sprinkle iron filings on a piece of paper placed over a bar magnet (Figure 3.1. 1).