Chapter 3 Ferrites for non-microwave applications

Publisher Summary This chapter discusses the applications of non-microwave ferrites and their important magnetic properties. The non-microwave applications fall roughly into categories determined by the magnetic properties that can be described with reference to the (B is the change of the induction with respect to the applied field H in the demagnetized state) B/H behavior. The categories are (1) linear B/H, low flux density, (2) non-linear B/H, medium to high flux density, and (3) highly non-linear B/H, square loop or rectangular. The origin of magnetism in ferrites is due to (1) unpaired 3d electrons, (2) superexchange between adjacent metal ions, and (3) nonequivalence in number of corners of a tetrahedron and corners of an octahedron. In the free state, the total magnetic moment of an atom containing 3d electrons is the sum of the electron spin and orbital moments. In an oxide compound—such as ferrite—the orbital magnetic moment is mostly quenched by the electronic fields caused by the surrounding oxygens about the metal ion. The atomic magnetic moment then becomes the moment of the electron spin and is equivalent to the multiplication of Bohr magnetron unit and the number of unpaired electrons. Indirect exchange interaction takes place between adjacent metal ions separated by oxygen ions. The strength of this interaction depends on the degree of orbital overlap of oxygen orbits and the transition metal orbitals.