Diamagnetism

Introduction

Diamagnetism is a quantum mechanical phenomenon where certain materials create an induced magnetic field in a direction opposite to an externally applied magnetic field, and are consequently repelled by the applied magnetic field. All materials display diamagnetism to some extent, but the effect is generally very small and can only be detected with sensitive equipment.

Historical Overview

The discovery of diamagnetism is credited to Michael Faraday in 1845. Faraday discovered that all materials, when placed in an external magnetic field, respond to that field with a magnetic moment that is generally very small but always opposes the direction of the applied field. This is in contrast to paramagnetism, where materials are attracted to an external magnetic field.

Photograph of a recreation of Michael Faraday's experiment demonstrating diamagnetism.

Fundamental Principles

Diamagnetism is a result of changes in the orbital motion of electrons due to an external magnetic field. The magnetic moment of a diamagnetic material will always be in the opposite direction to an externally applied magnetic field. This is due to the Larmor precession of the electron orbits.

Diamagnetic Materials

Diamagnetic materials are those that are repelled by a magnetic field. Examples of diamagnetic substances include water, wood, most organic compounds, and some metals, such as copper and gold. Diamagnetic materials have a negative magnetic susceptibility, meaning they repel magnetic fields.

Applications of Diamagnetism

Diamagnetism has a number of practical applications. For example, it is used in magnetic levitation, allowing objects to float in air without any support, other than the magnetic fields. Another application is in the medical field, where diamagnetic substances are used in magnetic resonance imaging (MRI) for contrast enhancement.

Diamagnetism vs. Other Types of Magnetism

Diamagnetism is one of the three types of magnetism, the other two being paramagnetism and ferromagnetism. While all materials display some form of diamagnetism, the effect is usually too small to be noticeable unless the material is purely diamagnetic.