Carlos de Francisco

Magnetic Disaccommodation in Ferrites with Nonmagnetic Divalent Substitutions

The after-effect processes in magnetite with nonmagnetic divalent substitutions are studied by means of disaccommodation techniques. We have recorded at room and high temperatures the time evolution of the initial magnetic susceptibility after sample demagnetization for polycrystalline specimens with nominal composition MxFe3-xO4+?, M being a divalent cation such as Zn2+, Mg2+, or Ca2+. These ions replace Fe2+ inside the spinel structure and, consequently, affect the original process III in magnetite. We have found that the presence of these ions involves the splitting of process III into similar processes, according to the position of the substituting ions. In addition, high-temperature processes are discussed on the basis of vacancy-mediated diffusion of nonmagnetic metallic ions.

Direct Determination of Relaxation Parameters in Deep-Level Transient Spectroscopy Experiments

A robust technique for deep-level transient spectroscopy is presented. The method is based on a single temperature scan of capacitance transients. The relaxation parameters, energy trap level, amplitude and pre-exponential factor, can be directly computed from experimental data by means of a set of closed-form expressions. The usefulness of this method is tested by analyzing the deep-level signal on a palladium-doped silicon diode