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.

What is 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 substances 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, 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 characterize 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 polarized in the same direction as this precession, for example, interacts intensely with the magnetic dipole moments when polarized 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 magnetized 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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2. 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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3. 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).

Magnetism is a property of magnets by virtue of which they attract different objects. Magnetism is a mechanical effect and it is related to electron spin.  Magnetism is due to movement of charges. Magnetism is the combined effect of electric and magnetic effects of a magnet. There are different types of magnetism. 

Ferromagnetism is a type of magnetism. It is a physical phenomenon in which some materials such as iron strongly attract each other. It is a common phenomenon that can be observed during daily lives. 

The most important requirement for a ferromagnetic material is that ions and atoms should have permanent magnetic moments. Some ions and atoms have a permanent magnetic moment that may be taken as a dipole and it consists of a North Pole and South Pole that are separated from each other. 

Examples of Ferromagnetic Material

Heusler alloy is made up of ferromagnetic materials but it is not a ferromagnetic alloy. On the other hand, stainless steel is made of non-magnetic materials but it is a ferromagnetic material. Non-crystalline ferromagnetic materials are made by expedite cooling of the liquid. They have very low hysteresis loss, low coercivity, high electrical resistivity, and high permeability.

Antiferromagnetism

Antiferromagnetism is a process in which the forces acting between two adjacent atomic dipoles have signs opposite to that of ferromagnets. Ferrous oxide, manganese, nickel oxide, posse’s antiferromagnetism.

Ferromagnetism is produced in ferromagnets and the ferromagnets should have net angular momentum which is obtained through the orbital component of the spin component.