Chapter 34: Magnetism of Matter – Diamagnetism & Paramagnetism

Magnetism of Matter – Diamagnetism & Paramagnetism properties originate from the atomic structure, specifically the magnetic moments generated by the orbital motion and spin of electrons. The text explores the fundamental relationship between an orbiting charge's magnetic moment (represented by mu) and its angular momentum (J), showing they are proportional, with the ratio generalized by the g-factor. When atomic magnets are subjected to an external magnetic field, they experience a torque that causes precession, a rotational effect. Larmor's theorem explains this by showing that the system's motion is equivalent to the original movement plus a uniform rotation at the Larmor frequency (often referred to as omega sub P). Diamagnetism itself is shown to be an induced effect where a changing magnetic field creates an electric field that modifies electron orbits, resulting in an induced magnetic moment opposing the applied field, consistent with Lenz's law. Critically, the chapter highlights the failure of classical physics alone to fully explain either diamagnetism or paramagnetism, necessitating the introduction of quantum mechanics. In quantum mechanics, the total angular momentum J and its component in the direction of the magnetic field (J sub Z) are quantized, meaning they can only take on discrete values. This quantization leads to discrete energy levels for an atom in a magnetic field. For the simplest case, like a single electron, only two spin states are possible, referred to as "up" or "down" relative to the field, with the energy differences measured using the fundamental quantity known as the Bohr magneton.