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Ferromagnetism and Antiferromagnetism: Basics and Material Types

ferromagnetism antiferromagnetism magnetic material curie temperature magnetic susceptibility

This page covers the basics of Ferromagnetism and Antiferromagnetism. It also touches upon the characteristics of different types of magnetic materials.

Ferromagnetism is defined by the parallel alignment of magnetic dipole moments within a material. This phenomenon occurs in elements like Iron (Fe), Cobalt (Co), Nickel (Ni), Gadolinium (Gd), and Dysprosium (Dy). A key characteristic of ferromagnetic materials is that they have partially filled inner electron shells.

These materials follow the Curie-Weiss Law. Below the Curie temperature, they exhibit ferromagnetism, while above it, they behave as paramagnetic materials.

The total internal field within these materials is given by:

Hi = H + γ*M

Where:

  • γ = Molecular Field Constant
  • M = Magnetization
  • H = Applied Field

Magnetic Anisotropy:

In materials like iron, the magnetic properties are dependent on the direction in which they are measured. This phenomenon is called magnetic anisotropy.

Magnetostriction:

When a ferromagnetic material is magnetized, its physical dimensions change. This effect is known as magnetostriction.

Villari Effect:

This is the converse of magnetostriction. When strain is applied to the material, there will be a change in its magnetic properties.

Antiferromagnetism Basics

These materials exhibit small susceptibility at all temperatures. As the temperature decreases, the magnetic susceptibility (Xm) increases, but at a critical temperature (TN), known as the Neel temperature, it reaches a maximum. If the temperature is lowered further, the susceptibility decreases again.

The variation of susceptibility with temperature of an antiferromagnetic material above the critical temperature TN is given by the following equation:

Xm = C/(T-θ)

Where:

  • C = Curie temperature
  • θ = Paramagnetic Curie temperature

Magnetic Material Types

Types of magnetic materials include diamagnetic, paramagnetic, ferromagnetic, antiferromagnetic, and ferrimagnetic.

The following table summarizes the characteristics of these magnetic materials:

Magnetic Material TypeSusceptibility (Xm)Xm*Vs*T relationExamples
DiamagneticApprox. -10-6IndependentAtoms of solids having closed shells and some metals (Au, Ge, etc.)
ParamagneticApprox. 10-5Xm = C/T (Curie Law)Atoms possessing an odd number of electrons, ionic crystals, etc.
Xm = C/T - θ (Curie Weiss Law)
FerromagneticVery large and positiveXm tends to ∞Iron, Cobalt, Nickel, Gadolinium
AntiferromagneticSmall and positiveXm decreases with temperatureSalts and oxides of transition metals (e.g., NiO, MnF2)
FerrimagneticLarge and positiveXm tends to ∞Ferrites (e.g., Fe3O4)