Define Ferrimagnetism
Based on the presence of permanent dipoles and their orientations magnetic materials are classified into five categories. Magnetism arises due to several aspects. Mainly we have permanent magnetic materials and non-permanent permanent magnetic materials. Ferrimagnetism is one of the permanent magnetism i.e., the materials will possess the permanent dipole orientations.
Ferrimagnetism is a type of permanent magnetism that happens in solids during which the magnetic fields related to individual atoms spontaneously align themselves, some parallel, or within the same direction (identical to ferromagnetism), et al. generally antiparallel, or paired off in opposite directions ( similar to antiferromagnetism).
Ferrimagnetic Material:
Ferrimagnetism is an idea that was originally proposed to the world by Néel to describe the magnetic ordering phenomena in ferrites, in which Fe ions appear in two different ionic states and hence experience different magnetic moments with mutual antiferromagnetic coupling. The ferromagnet can be considered in a loose analogy as a two-sublattice antiferromagnet with 丨M\[_{A}\]丨≠丨M\[_{B}\]丨. In this context of magnetic properties of the materials, ferrimagnets appear sometimes in the literature under the name uncompensated antiferromagnet.
As a consequence, a net spontaneous magnetization is observed at temperatures below the ordering temperature T\[_{C}\]. different forms of M\[_{S}\](T) curves are found for ferrimagnets depending on the temperature variation of sublattice magnetizations.
The ferrimagnetic effect is observed when the magnetic moments of the domains in the substance are aligned in parallel and antiparallel directions such that they are not equal in numbers. Ferrimagnetic substances or particles are weakly attracted by a magnetic flux as compared to ferromagnetic substances.
The ferrimagnets are also corresponded to antiferromagnets, in that the exchange coupling between adjacent magnetic ions leads to antiparallel alignment of the localized moments. So, entire magnetization occurs because the magnetization of one sublattice is greater than that of the oppositely oriented sublattice.
The observed ferrimagnetic susceptibility and the magnetization of ferrimagnets can be reproduced using the Weiss molecular theory or Weiss molecular field theory. The localized-moment model applies very well to ferrimagnetic materials since most are ionic solids with largely localized electrons.
Ferrimagnetic Materials:
Ferrimagnetism occurs chiefly in magnetic oxides referred to as ferrites. Natural magnetism is generally observed by lodestones, recorded as early because the 6th century BC is that of ferrite, the mineral magnetite, a compound containing negative oxygen ions O\[^{2-}\] and positive iron ions in two states, iron(II) ions, Fe\[^{2+}\], Fe\[^{3+}\]. The oxygen ions aren't magnetic, but both iron ions are.
Did You know:
Ferrites are considered to be of high importance in engineering and technology because they possess a spontaneous moment of a magnet below the Curie temperature just an iron, cobalt, Nickel. Because of the very low eddy current losses, ferrites are used as a core of coils in microwave frequency devices and memory core elements. Due to relatively low permeability and flux density compared to iron, ferrites are not suitable for use in the high field and high power applications, such as motors, generators and power transformers, but they can be used in low field and low power applications.
FAQs on Ferrimagnetism
1. What is ferrimagnetism and how does it arise in materials?
Ferrimagnetism is a type of magnetism observed in solids where atomic magnetic moments align in an antiparallel fashion, but the opposing moments are unequal in magnitude. This imbalance results in a net spontaneous magnetisation. It typically arises in crystalline materials like ferrites, where different ions (e.g., Fe²⁺ and Fe³⁺) with different magnetic strengths occupy various sites in the crystal lattice, leading to an incomplete cancellation of magnetic moments.
2. What is the main difference between ferromagnetic and ferrimagnetic materials?
The key difference lies in the alignment of atomic magnetic moments. In ferromagnetic materials, all atomic moments align in the same direction (parallel), resulting in a very strong net magnetic moment. In ferrimagnetic materials, atomic moments align in opposite directions (antiparallel), but because these opposing moments are unequal, a weaker net magnetic moment still exists.
3. How does ferrimagnetism differ from antiferromagnetism?
Both ferrimagnetism and antiferromagnetism involve the antiparallel alignment of atomic magnetic moments. However, in an antiferromagnetic material, the opposing magnetic moments are equal in magnitude, causing them to completely cancel each other out and resulting in zero net magnetisation. In contrast, ferrimagnetic materials have unequal opposing moments, which leads to an incomplete cancellation and a non-zero net magnetic moment.
4. Why do ferrimagnetic materials show a net magnetic moment despite having antiparallel atomic moments?
Ferrimagnetic materials exhibit a net magnetic moment because the alignment of their atomic moments is a form of uncompensated antiferromagnetism. This means the magnetic moments pointing in one direction are either stronger or more numerous than the moments pointing in the opposite direction. The vector sum of these unequal, opposing moments is non-zero, resulting in the material having a spontaneous magnetisation below its Curie temperature.
5. What are some common examples of ferrimagnetic materials?
The most important class of ferrimagnetic materials are ferrites. These are ceramic compounds of iron oxides combined with other metallic elements. Common examples include:
- Magnetite (Fe₃O₄), a natural magnet also known as lodestone.
- Cubic ferrites, such as Manganese ferrite (MnFe₂O₄) and Nickel ferrite (NiFe₂O₄).
- Hexagonal ferrites, like Barium ferrite (BaFe₁₂O₁₉), used in permanent magnets.
- Yttrium Iron Garnet (YIG), used in microwave applications.
6. Why are ferrites, which are ferrimagnetic, preferred for high-frequency applications over ferromagnetic materials?
Ferrites are preferred for high-frequency devices like transformer cores and inductors because they are electrical insulators with very high resistivity. This property significantly reduces energy loss caused by eddy currents at high frequencies. While ferromagnetic materials like iron are stronger magnets, their high electrical conductivity leads to large, wasteful eddy currents, making them inefficient for such applications.
7. What happens to a ferrimagnetic material when it is heated above its Curie temperature?
When a ferrimagnetic material is heated above its specific Curie temperature (TC), the thermal energy becomes powerful enough to disrupt the ordered alignment of the atomic magnetic moments. As a result, the spontaneous magnetisation vanishes, and the material loses its ferrimagnetic properties. Above this temperature, it behaves like a paramagnetic material, with its magnetic moments oriented randomly.
