Ferromagnetism: Magnetic Properties of Materials
by Yuvi K - December 18, 2023
Ferromagnetism: Magnetic Properties of Materials
Ferromagnetism is an effect of certain materials exhibiting a magnetic behavior. It is one of the four primary forms of magnetism, which include ferromagnetism, paramagnetism, diamagnetism, and anisotropy.
The magnetic behavior of ferromagnetic materials is caused by a spontaneous organization of magnetic moments, originating from the unpaired electrons present within the material. This phenomenon is commonly exploited in a wide range of consumer and industrial products including refrigerator magnets, electrical motors, transformers etc.
What is a Magnetic Moment?
The magnetic moment of an object can be described as a measure of the object’s ability to produce a magnetic field. Magnetic moments result from the alignment of the spins and orbital motions of electrons in an atom or molecule. All atoms possess a magnetic moment but, in most cases, the individual moments cancel one another out.
In contrast, when an unpaired electron is present in an atom, the alignment of the electron’s spins and orbital motions results in a net magnetic moment.
What are Electron Spin and Orbital Motion?
Electron spin is an intrinsic form of angular momentum exhibited by the electrons, analogous to the spin of a top. This spin is a quantum mechanical property and is characterized by a two-state system which can be explained in terms of up (spin-up) and down (spin-down) states with a fixed magnetic moment in the opposite directions.
Orbital motion, on the other hand, is the periodic motion in which an electron moves around the nucleus of the atom. This motion also results in a magnetic moment but, unlike electron spin, the direction of this moment is hard to predict.
What is Ferromagnetic Behavior?
Ferromagnetic behavior occurs when certain materials are subjected to a magnetic field and the material exhibits a net magnetization in the direction of the applied field. This behavior arises from the spontaneous alignment of both spin and orbital motions of the unpaired electrons of the material. The alignment of magnetic moments of the unpaired electrons results in a net magnetization of the material, known as spontaneous magnetization (स्वयं आकर्षिता)
Why is Ferromagnetic Behavior Observed?
Ferromagnetic behavior is only found in certain materials; most notably, iron and its alloys. The presence of unpaired electrons in these materials creates a strong local moment, which increases the attractiveness between the electron spins and makes them align to form a net magnetization. This alignment is only possible when the temperature of the material is below a certain critical temperature known as the Curie temperature (क्यूरी तापमान).
Apart from the presence of unpaired electrons, the strength of the magnetization also depends on the crystalline structure of the material. The magnetic particles which represent the magnetic moments in a material form a lattice structure. This lattice structure ensures that the magnetization remains constant even in the presence of an external magnetic field. The strength of the magnetization increases with an increase in the degree of orderliness in the lattice structure.
What are Magnetic Domains?
The individual magnetic moments within the lattice structure, many times form distinct regions known as magnetic domains. Each magnetic domain has its own magnetic moment, which is indicative of the direction of magnetization within that particular domain.
What are Magnetic Materials?
Ferromagnetic materials are those materials that exhibit ferromagnetic behavior. Duc magnetic materials can be classified into three broad categories: hard ferromagnets, soft ferromagnets, and ferrimagnetic materials.
Hard ferromagnets are those materials that retain their magnetic properties even in the absence of an external magnetic field. These materials can be easily magnetized and tend to retain their magnetization even in the presence of a weak external field. Common examples of hard ferromagnets include iron, cobalt, and nickel.
In contrast, soft ferromagnets do not retain their magnetization in the absence of an external field. These materials can still be magnetized with the help of an external field but the magnetization quickly drops back to zero in its absence. Soft ferromagnetic materials include various iron alloys, e.g. iron-silicon and iron-nickel alloys.
Ferrimagnetic materials are those materials with two magnetic sublattices, each with a different magnetic moment but the same orientation. These materials are commonly used in various applications, e.g. in recording media and as magnetic refrigerants. Common examples of ferrimagnetic materials include magnetite, chromium dioxide, and iron oxide.
Conclusion
The magnetic properties of materials depend on the presence of unpaired electrons, their electronic configuration, and the structure of the material. Ferromagnetic behavior is observed in certain materials in response to the presence of an external field and is characterized by the spontaneous alignment of the unpaired electrons in the material. Ferromagnetic materials can be broadly classified into hard ferromagnets, soft ferromagnets, and ferrimagnetic materials, based on their magnetic properties.
