Ferrimagnetic Materials

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Crystal Ferrimagnetic Materials

Superconductor trains, scanning electron microscopy, electron beam physical vapour deposition, and internal and external disc hard drives are examples of advanced scientific devices that use the magnetic properties of materials.

Magnetism is divided into five categories:

  1. Diamagnetism,

  2. Paramagnetism,

  3. Ferromagnetism,

  4. Antiferromagnetism,

  5. Ferrimagnetism.

Each form of magnetism is distinct from the others, because of variations in the composition and crystal structures of the materials, as well as how electrons inside these materials react to a magnetic field. 

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 In this article, we will discuss Ferrimagnetic materials.


Ferrimagnet

Ferrimagnetic materials definition is, in which the magnetic dipoles of the atoms on various subset are opposed, as in antiferromagnetism, but the opposing moments are unequal in ferrimagnetic materials, leaving a random net magnetization. Crystal ferrimagnetic materials, including antiferromagnetic materials, have populations of atoms with contrasting magnetic moments. Since the magnitudes of these moments are unequal in ferrimagnet compounds, a random magnetization exists. A mixture of dipole-dipole interactions and exchange interactions arising from the Pauli exclusion theory induce magnetization of ferrimagnetic materials. The key distinction is that in a ferrimagnetic substance, the unit cell contains various groups of atoms.


The magnetic dipole moments in ferrimagnetic substance are differentiated into subsets and are categorised as a subset of antiferromagnetic materials. This occurs because the subset of ferrites is made up of various materials or ions, such as M2+ and M3+.  Each subset can be treated as a ferromagnetic material, with the net magnetization for ferrimagnetic materials determined by the difference between the magnetic dipole moments of the subset. 

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Ferrimagnetic and ferromagnetic materials both are unlike, which are usually metals, are ceramics, specifically ceramic oxides.


Ferrites are the most common ferrimagnetic materials used in technical devices. Ferrites are electrically insulating transitional metal oxides with the general chemical formula MOFe2O3, where M is a divalent ion such as Mn2+, Fe2+, Co2+, or Ni2+.


The best examples of ferrimagnetic materials are magnetite (Fe3O4). One iron ion is divalent, while the other two are trivalent. The net moment results from the divalent iron ion when the two trivalent ions coincide with opposite moments and cancel each other. A type of magnetite was found in the historic lodestone and was the first magnetic material detected. 


Properties of Ferrimagnetic Materials

High resistivity and anisotropic properties characterise ferrimagnetic materials. An externally applied field is responsible for anisotropy. When this applied field aligns with the magnetic dipoles, it produces a net magnetic dipole moment which allows the magnetic dipoles to rotate counterclockwise at a frequency controlled by the applied field, which is known as Larmor or precession frequency. A microwave pulse circularly polarised in the same direction as this precession, for example, interacts intensely with the magnetic dipole moments when polarised in the opposite direction, the effect is negligible. The microwave signal will travel through the material when the contact is solid. Microwave devices such as isolators, circulators, and gyrators make use of this directional property. Optical isolators and circulators are also made from ferrimagnetic materials. Ancient magnetic properties of Earth and other planets are studied using ferrimagnetic minerals found in different rock forms.


Applications of Ferrimagnetism

Ferrites have the following applications:

  1. Ferrites are important in engineering study and technology study because, like iron, cobalt, and nickel, they have a spontaneous magnetic moment below the Curie temperature.

  2. Ferrites are used as a core of coils in microwave frequency systems and computer memory core components because of their low eddy current losses.

  3. Ferrites are not suitable for high field and high power applications, such as pumps, turbines, and power transformers, due to their poor permeability and flux density when compared to iron, but they are suitable for low field and low power applications.

  4. Ferrites are used in electrical circuits as ferromagnetic insulators.

  5. Ferrites, such as ZnO, are used in low-frequency timers. Refrigerators, air conditioners, and other appliances use them as controls.

  6. In the recording, ferrites are used as a magnetic head transducer.


Difference Between Ferromagnetic and Ferrimagnetic Materials

Ferro and ferrimagnetism are two types of magnetism, magnetism is the familiar force that draws or repels some metals and magnetised particles.

Ferrimagnetic and ferromagnetic are both relatively solid compared to other types of magnets and have played important roles in human history. 

  1. Ferrimagnetism comes in an oxide of iron called magnetite, with the chemical formula Fe3O4. The mineral is historically important because humans found millennia ago that when natural magnetite lodestone was floating in the water, it still pointed north, resulting in the first navigational compass. On another side, Ferromagnetism comes in some elements such as iron, nickel and cobalt. The magnetic domains in these components converge in the same direction and parallel to each other, resulting in solid permanent magnets.

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  1. When magnetic moments are paired in the same direction, it is called ferromagnetism. On other hand, magnetism is termed ferrimagnetism because magnetic moments are aligned in unequal numbers in parallel and antiparallel directions, resulting in a net moment.

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  1. Domains of different sizes are common in ferromagnetic materials. Every domain's spin magnetic moments are normally aligned parallel to one another. Ferrimagnetic materials are similar to anti-ferromagnetic materials, but one set of spins is not equal to the magnitude of the other set of spins (say opposite spins).

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FAQs (Frequently Asked Questions)

Q1. What is Superparamagnetic Material?

Answer: Superparamagnetism is a property found in microscopic, single-domain magnetic particles that has no magnetic memory. Superparamagnetic materials, unlike ferromagnetic materials, do not maintain any net magnetization after the external field is eliminated. To put it another way, they don't have a magnetic memory. It has much in common with ferromagnetism than with paramagnetism. As exposed to an external magnetic field, this particle produces a high internal magnetization due to electron exchange coupling within the domain, making it superparamagnetic. 

Q2. Is Net Magnetization Zero in Ferrimagnetic Materials?

Answer: No. Since most of these compounds include cations of two or more kinds, the subset contains two different types of ions, each with a separate magnetic moment with two different types of atoms, and therefore net magnetization is not zero.