CRESCIMENTO, ESTRUTURA E POLARIZAÇÃO DE TROCA EM BICAMADAS FERROMAGNETO / ANTIFERROMAGNETO PREPARADAS POR DEPOSIÇÃO EM CONDIÇÕES DE EPITAXIA POR FEIXE MOLECULAR: Fe / EuTe(111), Fe / Ni50Mn50(001) e Ni1-xFex / Fe50Mn50

AUTOR(ES)
DATA DE PUBLICAÇÃO

2007

RESUMO

Magnetic interaction at interfaces between different layered magnetic materials is an important current topic in physics and materials science, particularly when combining ferromagnetic metals and semiconductors. The exchange bias effect associated with the exchange coupling between antiferromagnetic (AFM) and ferromagnetic (FM) systems, has been extensively studied both due to its key role in spin valves and tunneling magnetoresistance devices, among others, and due to its interesting basic properties. This work presents three studies of different FM / AFM systems: the exchange bias effect in Fe / EuTe(111) bilayers, the structure and magnetism of Ni50Mn50 and Fe / Ni50Mn50 bilayers epitaxialy grown on a Cu3Au(001) single crystal and, finally, in plane magnetic anisotropies and exchange bias effect in Ni1-xFex / Fe50Mn50 bilayers. Thin films of these systems were prepared under Molecular Beam Epitaxy (MBE) conditions, and characterized by X-ray Photoelectron Spectroscopy (XPS), Auger Electron Spectroscopy (AES), Electron Diffraction (LEED and RHEED), X-ray Diffraction (XRD), Magneto-Optical Kerr Effect (MOKE), Superconducting Quantum Interference Device (SQUID), Ferromagnetic Resonance (FMR) and Conversion Electron Mössbauer Spectroscopy (CEMS). Most of the results presented in this work had not been reported yet, as for example the exchange bias effect in 3d metals / EuTe (AFM) systems and the study of the growth of Ni50Mn50 films on Cu3Au(001). The exchange bias effect in Fe / EuTe(111) bilayers was investigated employing different cooling fields from 2 to 70 kOe. It has been found positive and negative shifts of the magnetic hysteresis loops. These shifts change drastically with the samples aging, pointing to structural modifications of the FM / AFM interface. Ni50Mn50 films with thickness between 9 and 13 monolayers have been grown epitaxialy and layer by layer on Cu3Au(001) crystal. Magnetometry studies in Ni50Mn50 / Cu3Au(001), Fe / Cu3Au(001) and Fe / Ni50Mn50 / Cu3Au(001) suggested an AFM order in the NiMn films with equiatomic concentration. The Ni1-xFex / Fe50Mn50 bilayers presented both exchange anisotropy (EB) and an additional uniaxial anisotropy at the ferromagnetic layer. It has been found that the characteristic directions of these two anisotropy terms are not coincident. Furthermore, it was observed that samples submitted to a short annealing after the magnetic field cooling procedure presented an increase in the exchange bias effect.

ASSUNTO(S)

mechanical structures propriedades magnéticas fisica da materia condensada filmes finos estrutura mecânica surfaces exchange bias análise de superfície thin films

ACESSO AO ARTIGO

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