Banca de DEFESA: NÚBIA RIBEIRO MACHADO

Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.
STUDENT : NÚBIA RIBEIRO MACHADO
DATE: 03/12/2020
TIME: 08:30
LOCAL: Plataforma Google Meet
TITLE:

Dynamics of magnetization and Barkhausen noise in ferromagnetic

KEY WORDS:

Barkhausen noise, statistical properties, multilayer films, domain wall dynamics

PAGES: 113
BIG AREA: Ciências Exatas e da Terra
AREA: Física
SUMMARY:

Since its discovery in 1919, Barkhasen noise (BN) has been widely used as an important tool to characterize soft magnetic materials, to understand the complex magnetization process and, in particular, to investigate the dynamics of domain walls. In recent years, BN has attracted great interest as an example of the manifestation of crackling noise in magnetic systems. In the particular case of the dynamics of domain walls and BN, most studies concentrate on explaining statistical properties such as the distributions of area and duration of jumps, average area and power spectrum, which can be described by power laws with exponents, τ, α, 1/σνz e ϑ  respectively. These power laws, which present a cutoff, are considered as a characteristic of the critical behavior of the magnetization process. In this work, we focus on the study of  Barkhausen noise in ferromagnetic multilayer films using the traditional inductive method and the statistical properties of  Barkhausen jumps. Specifically, were obtained Barkhausen noise time series for multilayer films with Co77Fe23B10(10 nm)/Ag(2 nm), Co77Fe23B10(10 nm)/Ta(2 nm) ,  Ni81Fe19(10nm)/Ag(2 nm) e Ni81Fe19(10nm)/Ta(2 nm) and structures consisting of 10, 15, 25 and 50 stacked bilayers. Motivated by the results obtained in polycrystalline and amorphous films with diferent thicknesses, through the method, we investigate the dynamics of magnetization through critical exponents of the distributions of area, duration, average area and power spectrum, obtained experimentally, to understand the efects the dimensionality of the system and the range of interactions on exponents due to the movement of domain walls. From theoretical predictions of models that describe the dynamics of a ferromagnetic domain wall driven by an external magnetic field through a disordered environment, it was observed that the exponents obtained experimentally, when compared to theoretical models, present three-dimensional magnetic behavior with long-range dipolar interaction, regardless of the number of stacked bilayers, the spacer and the field frequency suggesting a single universality class for the set of exponents. In particular, dependence on exponents τ and α for polycrystalline multilayers was not observed, a fingerprint of field theory-medium that describes three-dimensional polycrystalline magnetic materials. Our resuls reveal an artificially structured three-dimensional DWs dynamics due to the act of stacking bilayers with two-dimensional magnetic behavior. Finally, we raise possibilities of the coupling between the layers as an indicator of the stability of the exponents

BANKING MEMBERS:
Presidente - 1508681 - FELIPE BOHN
Externo ao Programa - 1753234 - GUSTAVO ZAMPIER DOS SANTOS LIMA
Interno - 1294916 - MADRAS VISWANATHAN GANDHI MOHAN
Externo à Instituição - RUBEM LUÍS SOMMER - CBPF
Externo à Instituição - SERGIO LUIZ ALVES DE QUEIROZ - UFRJ