Ferrites are essential magnetic materials in the field of telecommunications devices, high frequency electronics, power electronics for various applications: inductors, transformers, circulators, energy conversion and amplification. In all these applications, it is essential to control the effect of mechanical stresses on the magnetic properties in order to improve device performance and achieve energy savings. Indeed, the effects of magneto-elastic couplings (or magnetostriction), which occur at second order with respect to all the magnetic properties, can contribute to intrinsic losses that are difficult to reduce without disturbing the established optimum. An original solution has however been identified in the literature (“Magnetic and dielectric properties of the spinel ferrite system Ni0.65Zn0.35Fe2-xMnxO4”, Journal of Applied Physics 61, 3868, 1987). This pathway based on the Jahn-Teller effect remains poorly studied and poorly understood, in particular because this effect is set up from a threshold concentration and not in a linear manner.
The objective of this thesis is to improve the performance of NiZn(Cu) ferrites by reducing the sensitivity of the magnetic properties to mechanical stresses by performing doping to induce a Jahn-Teller effect. The demonstration of this effect, and the finer understanding of the role of the composition on the magnetic properties is also an objective. The work will be promoted through publications and participation in international congresses. The most effective compositions could be used for industrial applications.