The secret of magnetism

As a person whose main research focus is on magnetism, I have been asked this question many times that why some materials exhibit magnetic property while the others do not show it. As you can imagine, like many other properties of materials, the origin of magnetism arises from atomic structure of material. In atomic scale there are two types of electron motion, rotation (spin) of the electron around its axis and rotation of the electron around the atom nuclei in atomic orbitals. These two electron movements independently produce magnetic moments. In simple words, moving of electrons can be considered as tiny electric current which produces a magnetic field in a way that each electron acts like a small magnet. However such magnetic moments exist in all materials, those with full orbitals have a zero magnetic moment because the paired electrons cancel their magnetic moments and only the unpaired electrons or so called free electrons contribute in overall magnetic moment. In order to calculate the strength of these contributions together, the net magnetic moment (J) of atom is defined as follow: J = L+S where L is the total orbital angular momentum quantum number and S is the total spin angular momentum. Considering the above mentioned formula, atoms with unpaired electrons in their d orbital (transition metals like cobalt and nickel) and f orbital (rare-earth elements like neodymium and samarium) have higher net magnetic moment.

spinning-orbiting

Different types of electron motion in an atom.

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