Ferromagnetism
Introduction
Ferromagnetism is a fundamental property of certain materials that exhibit strong magnetic properties. The phenomenon is named after iron (ferrum in Latin), a common ferromagnetic material. Ferromagnetic materials are able to maintain a permanent magnetic moment in the absence of an external magnetic field, a property that distinguishes them from other substances that are merely paramagnetic or diamagnetic.
Fundamental Principles
The underlying principle of ferromagnetism is the alignment of electron spins. In ferromagnetic materials, a large number of electron spins align parallel to each other within a region called a magnetic domain. This alignment is due to a quantum mechanical property known as exchange interaction.
Magnetic Domains
Magnetic domains are regions within a ferromagnetic material where the electron spins are aligned. The direction of the magnetic moment in each domain is random, but the moments of individual domains can be aligned with an external magnetic field, causing the material to become magnetized. This process is known as domain wall movement.
Curie Temperature
The Curie temperature is the temperature above which a ferromagnetic material loses its ferromagnetic properties and becomes paramagnetic. This occurs because the thermal energy becomes sufficient to disrupt the alignment of the electron spins.
Exchange Interaction
Exchange interaction is the quantum mechanical effect responsible for the alignment of electron spins in a ferromagnetic material. The interaction is a result of the Pauli exclusion principle, which states that no two electrons can occupy the same quantum state simultaneously.
Ferromagnetic Materials
Common ferromagnetic materials include iron, nickel, cobalt, and their alloys. Certain rare earth elements such as gadolinium and dysprosium also exhibit ferromagnetic properties. In addition, some compounds and alloys that do not contain any of these elements can also be ferromagnetic, such as certain types of ferrites.
Applications
Ferromagnetic materials have a wide range of applications due to their magnetic properties. They are used in the manufacture of permanent magnets, magnetic storage media, transformers, inductors, and various types of sensors. In addition, they are also used in the medical field for magnetic resonance imaging (MRI) and in the construction industry for magnetic levitation trains.