Which particle in an atom is responsible for a material's magnetic property?

The particle in an atom primarily responsible for a material's magnetic properties is the electron. Specifically, the alignment of the spins of unpaired electrons in an atom determines its magnetic behavior. In ferromagnetic materials, for example, the spins of these unpaired electrons tend to align parallel to each other, resulting in a net magnetic moment. In contrast, materials with paired electrons typically exhibit no net magnetic moment, making them non-magnetic.