why monopoles doesn't exist in nature in case of a magnet
Hi ,
A magnetic monopole does not exist . Just as the two faces of a current loop cannot be physically separated, magnetic North pole and the South pole can never be separated even on breaking a magnet to its atomic size. A magnetic field is produced by an electric field and not by a monopole.
Magnetism in bar magnets and electromagnets is not caused by magnetic monopoles , and indeed, there is no known experimental or observational evidence that magnetic monopoles exist.
Hope this helps.