What is the source of magnetism in materials?

The source of magnetism in materials primarily arises from the behavior of electrons, specifically their motion and spin. In atoms, electrons move in orbits around the nucleus, and this movement generates a magnetic field. Additionally, electrons have a property called spin, which is a form of intrinsic angular momentum that also contributes to the overall magnetic moment of the atom.

When considering magnetic materials, those that exhibit ferromagnetic properties, like iron, have unpaired electrons. The alignment of these unpaired electrons' spins in the same direction leads to a net magnetic moment, which manifests as the material being magnetized. This intrinsic property of electrons is what establishes their significant role as the source of magnetism.

In contrast, protons and neutrons, found in the nucleus of an atom, do possess some magnetic properties due to their spin, but they do not play a significant role in the macroscopic magnetic behavior of materials. Molecules can exhibit magnetism when their constituent atoms have unpaired electrons that produce a net magnetic moment, but the foundational source of magnetism still remains with the electrons. Thus, understanding the role of electrons is crucial for grasping the fundamentals of magnetism in materials.