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6.6 Ferromagnetism
6.6.1 Basic Characteristics
In addition to permanent magnetic moments as contained in paramagnetic materials, ferromagnetic materials consist of ordered regions or domains of single orientation of magnetic moment giving rise to large finite magnetization in the absence of a magnetic field, much like polarization in ferroelectric materials (see Module 5). This phenomenon is observed below a critical temperature called as Curie Temperature, above which the material behave like a paramagnetic material.
| Figure 6.10 Schematic representation of spins in a ferromagnetic material |
When a varying magnetic field is applied to a ferromagnetic material, the material exhibits a ferroelectric-like hysteresis loop between magnetization and the magnetic field as shown below. In this figure, notice how the domain structure changes with field in the initial stages of magnetization.
| Figure 6.11 Ferromagnetic hysteresis loops |
Most of the ferromagnetic materials are elemental metals such as iron, nickel, cobalt etc. However some oxides such as chrmoimum oxide, CrO2, are ferromagnetic oxides. These oxides also tend to be conducting and behave like metals. |
