Ferrires, Magnetic Anisotropy, Magnetostriction PDF

Ferrite Ferrite is a ceramic-like material with magnetic properties, which is used in many types of electronic devices. Ferrite is used in: 1 Permanent magnets 2 Ferrite cores for transformers and toroidal inductors 3 Computer memory elements 4 Solid-state devices Ferrites are composed of iron...

Ferrite Ferrite is a ceramic-like material with magnetic properties, which is used in many types of electronic devices. Ferrite is used in: 1 Permanent magnets 2 Ferrite cores for transformers and toroidal inductors 3 Computer memory elements 4 Solid-state devices Ferrites are composed of iron oxide and one or more other metals in chemical combination, and their properties include: Hard Brittle Iron-containing Polycrystalline Generally gray or black Ferrite is also known as ferrate  Properties of ferrites Properties of ferrites include: Significant saturation magnetization High electrical resistivity Low electrical losses Very good chemical stability  Types of Ferrites Ferrites are often classified as "soft" or "hard" in terms of their magnetic properties: 1. Soft ferrites - used in transformer or electromagnetic cores. They have a low coercivity (manganese-zinc ferrite, nickel-zinc ferrite). 2. Hard ferrites- have a high coercivity. They are cheap, and are widely used in household products such as refrigerator magnets (strontium ferrite, barium ferrite). **Soft ferrite does not retain significant magnetization, whereas hard ferrite magnetization is considered permanent.  Magnetic Anisotropy The dependence of magnetic properties on a preferred direction is called magnetic anisotropy. There are different types of anisotropy: Type - depends on 1. magnetocrystalline- crystal structure 2. shape- grain shape 3. stress- applied or residual stresses Magnetic anisotropy strongly affects the shape of hysteresis loops and controls the coercivity and remanence. Anisotropy is also of considerable practical importance because it is exploited in the design of most magnetic materials of commercial importance.  Magnetostriction Magnetostriction is a property of ferromagnetic materials which causes them to expand or contract in response to a magnetic field. This effect allows magnetostrictive materials to convert electromagnetic energy into mechanical energy. As a magnetic field is applied to the material, its molecular dipoles and magnetic field boundaries rotate to align with the field. Figure 11: Molecular dipole rotation during magnetostriction.  As the applied magnetic field increases in intensity, the magnetostrictive strain on the material increases. Ferromagnetic materials that are isotropic and have few impurities are most effective in magnetostriction because these properties allow their molecular dipoles to rotate easily Magnetostriction was first measured by James Prescott Joule (1818-1889) who was able to magnetize an iron sample and measure its the change in length. The opposite effect, in which an applied stress caused the material to create a magnetic field, was discovered by E. Villari (1836-1904). Gustav Wiedemann then discovered that a ferromagnetic rod would oscillate torsionally when exposed to a longitudinal and circular magnetic field.