paramagnetism

paramagnetism: see magnetism.

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paramagnetism

Kind of magnetism that occurs in materials weakly attracted by a strong magnet. Compounds containing iron, palladium, platinum, and the rare-earth elements exhibit strong paramagnetism because they have atoms with some incomplete inner electron shells. Their unpaired electrons make the atoms behave like tiny permanent magnets that align with and strengthen an applied magnetic field. As the temperature rises, strong paramagnetism decreases because of the greater random motion of the atoms. Weak paramagnetism, found in many solid metallic elements, is independent of temperature.

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paramagnetism [¦par·ə′mag·nə‚tiz·əm]

(electromagnetism)

A property exhibited by substances which, when placed in a magnetic field, are magnetized parallel to the field to an extent proportional to the field (except at very low temperatures or in extremely large magnetic fields).

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Paramagnetism

A property exhibited by substances which, when placed in a magnetic field, are magnetized parallel to the field to an extent proportional to the field (except at very low temperatures or in extremely large magnetic fields). Paramagnetic materials always have permeabilities greater than 1, but the values are in general not nearly so great as those of ferromagnetic materials. Paramagnetism is of two types, electronic and nuclear.

The following types of substances are paramagnetic:

1. All atoms and molecules which have an odd number of electrons. According to quantum mechanics, such a system cannot have a total spin equal to zero; therefore, each atom or molecule has a net magnetic moment which arises from the electron spin angular momentum. Examples are organic free radicals and gaseous nitric oxide.

2. All free atoms and ions with unfilled inner electron shells and many of these ions when in solids or in solution. Examples are transition, rare-earth, and actinide elements and many of their salts. This includes ferromagnetic and antiferromagnetic materials above their transition temperatures. For a discussion of these materials See Antiferromagnetism, Ferrimagnetism, Ferromagnetism

3. Several miscellaneous compounds including molecular oxygen and organic biradicals.

4. Metals. In this case, the paramagnetism arises from the magnetic moments associated with the spins of the conduction electrons and is called Pauli paramagnetism.

Relatively few substances are paramagnetic. Aside from the Pauli paramagnetism found in metals, the most important paramagnetic effects are found in the compounds of the transition and rare-earth elements which have partially filled 3d and 4f electron shells respectively.

Electronic paramagnetism arises in a substance if its atoms or molecules possess a net electronic magnetic moment. The magnetization arises because of the tendency of a magnetic field to orient the electronic magnetic moments parallel to itself.

Nuclear paramagnetism arises when there is a net magnetic moment due to the magnetic moments of the nuclei in a substance. Nuclear magnetic moments are about 10³ times smaller than electron magnetic moments. As a result, nuclear paramagnetism produces effects 10⁶ times smaller than electron paramagnetic or diamagnetic effects. See Diamagnetism, Magnetic resonance, Nuclear moments