Paramagnetism

Paramagnetism is a form of <a href="/facts/Magnetism/eo75vApl">magnetism</a> whereby some materials are weakly attracted by an externally applied <a href="/facts/Magnetic_field/Ta8Ev588">magnetic field</a>, and form internal, <a href="/facts/Magnetization/zxrtXzTN">induced magnetic fields</a> in the direction of the applied magnetic field. In contrast with this behavior, <a href="/facts/Diamagnetism/dgFavn9K">diamagnetic</a> materials are repelled by magnetic fields and form induced magnetic fields in the direction opposite to that of the applied magnetic field. Paramagnetic materials include most <a href="/facts/Chemical_element/0jducgWD">chemical elements</a> and some <a href="/facts/Chemical_compound/37FXqqtv">compounds</a>; they have a relative <a href="/facts/Magnetic_permeability/GA7CcRLU">magnetic permeability</a> slightly greater than 1 (i.e., a small positive <a href="/facts/Magnetic_susceptibility/hWMbGTjP">magnetic susceptibility</a>) and hence are attracted to magnetic fields. The <a href="/facts/Magnetic_moment/VpAQKJtr">magnetic moment</a> induced by the applied field is linear in the field strength and rather weak. It typically requires a sensitive analytical balance to detect the effect and modern measurements on paramagnetic materials are often conducted with a <a href="/facts/SQUID/2FEvJ5wG">SQUID</a> <a href="/facts/Magnetometer/dqX9g1og">magnetometer</a>.
Paramagnetism is due to the presence of <a href="/facts/Unpaired_electron/yJTW1urJ">unpaired electrons</a> in the material, so most atoms with incompletely filled <a href="/facts/Atomic_orbital/tKhgl6mL">atomic orbitals</a> are paramagnetic, although exceptions such as <a href="/facts/Copper/I8PEE8oX">copper</a> exist. Due to their <a href="/facts/Spin_(physics)/4Jvp7e8P">spin</a>, unpaired electrons have a <a href="/facts/Magnetic_dipole_moment/VpAQKJtr">magnetic dipole moment</a> and act like tiny magnets. An external magnetic field causes the electrons' spins to align parallel to the field, causing a net attraction. Paramagnetic materials include <a href="/facts/Aluminium/7wmR8jYE">aluminium</a>, <a href="/facts/Oxygen/acyn6o8r">oxygen</a>, <a href="/facts/Titanium/53ArnDoy">titanium</a>, and <a href="/facts/Iron_oxide/KDo8hLWn">iron oxide</a> (FeO). Therefore, a simple <a href="/facts/Rule_of_thumb/RopfGsJ0">rule of thumb</a> is used in chemistry to determine whether a particle (atom, ion, or molecule) is paramagnetic or diamagnetic: if all electrons in the particle are paired, then the substance made of this particle is diamagnetic; if it has unpaired electrons, then the substance is paramagnetic.
Unlike <a href="/facts/Ferromagnetism/fH3HFnSl">ferromagnets</a>, paramagnets do not retain any magnetization in the absence of an externally applied magnetic field because <a href="/facts/Thermal_motion/WUaJuMHU">thermal motion</a> randomizes the spin orientations. (Some paramagnetic materials retain spin disorder even at <a href="/facts/Absolute_zero/U3UyPl2K">absolute zero</a>, meaning they are paramagnetic in the <a href="/facts/Ground_state/ML7cfCug">ground state</a>, i.e. in the absence of thermal motion.) Thus the total magnetization drops to zero when the applied field is removed. Even in the presence of the field there is only a small induced magnetization because only a small fraction of the spins will be oriented by the field. This fraction is proportional to the field strength and this explains the linear dependency. The attraction experienced by ferromagnetic materials is non-linear and much stronger, so that it is easily observed, for instance, in the attraction between a <a href="/facts/Refrigerator_magnet/4WL3E5UY">refrigerator magnet</a> and the iron of the refrigerator itself.

Paramagnetism open-in-new

Paramagnetism