Research

I work on magnetization dynamics of ferromagnetic materials. In particular:

    1. Barkhausen noise, in bulk and thin films;
    2. Magnetoimpedance in thin films;
    3. Production and structural and magnetic characterization of ferromagnetic thin films;
    4. Production and structural, morphological, magnetic, and thermal characterization of magnetic nanoparticles for application in hyperthermia.

Follow some words about each line:

Barkhausen noise

(In collaboration with R. L. Sommer, M. A. Corrêa, and G. Durin)

Barkhausen noise corresponds to the time series of voltage pulses detected by a sensing coil wound around a ferromagnetic material submitted to a variable magnetic field. The noise is produced by sudden and irreversible changes of magnetization, mainly due to the irregular motion of the domain walls (DWs) in a disordered magnetic material, a result of the interactions between the DWs and pinning centers, such as defects, impurities, dislocations, and grain boundaries.

Since the discovery of the effect in 1919, BN has been widely used as a tool to characterize soft magnetic materials. However, in the past years, BN has attracted much interest as the manifestation in magnetic systems of the so-called crackling noise. From this point of view, its study becomes very important since a wide variety of systems, such BN, earthquakes, micro-fractures and superconductors, present similar dynamical critical behavior, where the dynamics takes place in avalanches. In all these systems, the dynamics and the statistical properties seem to be independent of the microscopic and macroscopic details of the samples, being, however, controlled just by a few general properties, such as the system dimensionality and the range of the relevant interactions.

In the particular case of BN, due to its stochastic character, most of the recent studies aim to obtain and explain noise statistical functions, such as the distribution of jump sizes, distribution of durations, average size vs. duration, and power spectrum. All of them are, in general, well described by cutoff-limited power-laws, understood as a fingerprint of the the critical dynamics, and are associated to the exponents tau, alpha, 1/snz and v, respectively.

However, recently, also the avalanche average shape has been considered and it became a powerful tool to investigate such complex system.

Here, we aim to investigate experimentaly and theoretically the Barkhausen noise in thin ferromagnetic films. The main idea is to measure the experimental critical exponents, as well as the new avalanche average shape, and compare them with the theoretical results, in order to obtain further information on the domain wall dynamics in thin films and systems with reduced dimensions.

Magnetoimpedance

(In collaboration with M. A. Corrêa, and R. L. Sommer)

The magnetoimpedance effect (MI) corresponds to the change in complex impedance Z=R+iX of a ferromagnetic sample submitted to an external magnetic field H.

Since it was first observed, MI has attracted considerable interest not only for its contribution to understanding fundamental physics associated to magnetization dynamics, but also due to potential technological applications in magnetic sensors and integrated devices based on the magnetoimpedance effect, even in more complex integrated circuits architectures, such as microprocessors. For this reason, experimental studies on MI has been widely performed in magnetic ribbons, microwires, and in recent decades, in magnetic films with several structures.

Here, we aim to investigate experimentaly the magnetoimpedance effect in magnetic films with several structures, such as single layered, multilayered, and structured multilayered samples. The main idea is to study the effect of the sample structure on the Z curves, as well as to understand the magnetization dynamics and the different mechanisms that govern the MI changes at distinct frequency ranges.

Production and structural and magnetic characterization of ferromagnetic thin films

(In collaboration with M. A. Corrêa, and R. L. Sommer)

Ferromagnetic thin films have attracted an increasing interest not only due to their importance in the fundamental physics viewpoint, but also due to their technological relevance since they can be employed in a wide range of technological devices. Here, we aim to investigate the structural and magnetic properties of ferromagnetic films in order to understand and control the production of samples with specific features.

Production and structural, morphological, magnetic, and thermal characterization of magnetic nanoparticles for application in hyperthermia

(In collaboration with S. N. de Medeiros, and M. Morales)

Magnetic nanoparticles are of great technological interest since they are used in several applications, in particular, biological applications. Here, we aim to produce magnetic particles and investigate the structural, morphological, magnetic, and thermal properties of magnetic nanoparticles with potential for application in magnetic hyperthermia.