Magnetic Properties of Solids

The SI unit of magnetic field strength is Tesla (T), named after the Serbian-American electrical engineer Nikola Tesla.

Ferromagnetic materials are strongly attracted to magnets and can be magnetized. Iron (Fe) is a ferromagnetic material, while copper (Cu), aluminum (Al), and gold (Au) are not.

The magnetic permeability of a vacuum is a constant, denoted by the symbol μ0, and its value is approximately 4π x 10^-7 T m/A.

In a material, the magnetic flux density (B) is related to the magnetic field strength (H) by the equation B = μ0H, where μ0 is the magnetic permeability of the vacuum.

The Curie temperature is the temperature at which a ferromagnetic material becomes paramagnetic. Above the Curie temperature, the material loses its ferromagnetic properties and becomes paramagnetic.

Paramagnetic materials are weakly attracted to magnets and can be magnetized. Copper (Cu) is a paramagnetic material, while iron (Fe), aluminum (Al), and gold (Au) are not.

The magnetic susceptibility of a material is the ratio of the magnetization of the material to the magnetic field strength applied to it.

Ferromagnetic materials are strongly attracted to magnets, can be magnetized, and have a high magnetic susceptibility. Paramagnetic materials are weakly attracted to magnets, cannot be magnetized, and have a low magnetic susceptibility.

Diamagnetic materials are repelled by magnets, have a negative magnetic susceptibility, and have a high magnetic permeability. Paramagnetic materials are attracted to magnets, have a positive magnetic susceptibility, and have a low magnetic permeability.

The Meissner effect is the expulsion of magnetic fields from a superconductor. When a superconductor is cooled below its critical temperature, it expels all magnetic fields from its interior.

The Josephson effect is the flow of electric current between two superconductors separated by a thin insulating layer. The current flows without any resistance, even if the voltage across the junction is zero.

The phenomenon of magnetic hysteresis is the dependence of the magnetization of a material on its magnetic history. When a material is magnetized, its magnetization does not immediately return to zero when the magnetic field is removed. Instead, it follows a hysteresis loop, which is a plot of magnetization versus magnetic field strength.

Hard magnetic materials have a high coercivity, are difficult to magnetize, and retain their magnetization for a long time. Soft magnetic materials have a low coercivity, are easy to magnetize, and lose their magnetization quickly.

Magnetic materials are used in a wide variety of applications, including electric motors and generators, transformers, magnetic resonance imaging (MRI), and magnetic recording media.