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Ferromagnetism basics

This page covers Ferromagnetism basics and Antiferromagnetism basics.It mentions characteristics of types of magnetic materials.

Ferromagnetism is characterized by the presence of parallel alignment of magnetic dipole moment. It occurs in Fe, Co, Ni, Gd and Dy.

The common characteristics of ferromagnetic materials is partly filled inner electron shells. They follow Curie Weiss Law. Below Curie temperature they exhibit ferromagnetism but above curie temperature they behave as paramagnetic materials.

The total internal field which exists in these materials is ,
Hi = H + γ*M
γ = Molecular Field Constant
M = Magnetization
H = Applied Field

Magnetic Anisotropy: In materials such as iron, magnetic properties depends upon direction in which they are measured. This phenomenon is referred as magnetic anisotropy.

Magnetostriction: When the material such as ferromagnetic is magnetized, its physical dimension changes. This phenomenon is referred as magnetostriction.

Villari Effect: This is converse of the magnetostriction. When strain is applied, there will be change in the magnetic property of the material.

Antiferromagnetism basics

These type of materials will have small susceptibility at all temperatures. As the temperature decreases, Xm increases but at a critical temperature TN known as neel temperature goes maximum. If temperature is further lowered it further decreases.

The variation of susceptibility with temperature of an antiferromagnetic material above critical temperature TN is given by following equation.
Xm = C/(T-θ) ,
C = Curie temperature
θ = paramagnetic curie temperature

Magnetic Material types

Types of magnetic material include diamagnetic, paramagnetic, ferromagnetic, antiferromagnetic and ferrimagnetic. Following table mentions characteristics of these magnetic materials.

magnetic material type Susceptibility (Xm) Xm*Vs*T relation Examples
Diamagnetic Approx. -10-n Independent Atoms of solids having closed shells and some metals Au, Ge etc.
Paramagnetic Approx. 10-5 Xm = C/T (Curie Law)
Xm = C/T - θ (Curie Weiss Law)
Atoms possessing odd number of electrons, ionic crystals etc.
Ferromagnetic Very large and positive Xm tends to ∞ Iron, Cobalt, Nickel, Godolinium
Antiferromagnetic Small and positive Xm decreases with temperature Salts and oxides of transition metals e.g. NiO, MnF2
Ferrimagnetic Large and positive Xm tends to ∞ Ferrites e.g. Fe3O4


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