Paramagnetism

Paramagnetism is the tendency of the atomic magnetic dipoles, to align with an external magnetic field. This effect occurs due to quantum-mechanical spin as well as electron orbital angular momentum.

Introduction

Paramagnetic materials attract and repel like normal magnets when subject to a magnetic field. This alignment of the atomic dipoles with the magnetic field tends to strengthen it, and is described by a relative magnetic permeability greater than unity (or, equivalently, a small positive magnetic susceptibility).

Related Topics:
Permeability - Unity - Magnetic susceptibility

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Paramagnetism requires that the atoms individually have permanent dipole moments even without an applied field, which typically implies a partially filled electron shell. In pure paramagnetism, these atomic dipoles do not interact with one another and are randomly oriented in the absence of an external field, resulting in zero net moment. If they do interact, they can spontaneously align or anti-align, resulting in ferromagnetism (permanent magnets) or antiferromagnetism, respectively. Paramagnetic behaviour can also be observed in ferromagnetic materials that are above their Curie temperature, and in antiferromagnets above their Neel temperature.

Related Topics:
Electron shell - Ferromagnetism - Antiferromagnetism - Curie temperature - Neel temperature

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In atoms with no permanent dipole moment, e.g. for filled electron shells, a weak dipole moment can be induced in a direction anti-parallel to an applied field, an effect called diamagnetism. Paramagnetic materials also exhibit diamagnetism, but the latter effect is typically orders of magnitude weaker.

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Paramagnetic materials in magnetic fields will act like magnets but when the field is removed, thermal motion will quickly disrupt the magnetic alignment. In general paramagnetic effects are small (magnetic susceptibility of the order of 10-3 to 10-5).

Related Topics:
Thermal motion - Magnetic susceptibility

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