Manipulação da orientação de spins em filmes finos antiferromagnéticos de CoO por deformações estruturais

Author(s)

Marina Raboni Ferreira

• Document type: Master's Dissertation
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Instituto de Física Gleb Wataghin
• Defense date: 2020-05-12

Examining board members

Márcio Medeiros Soares; Felipe Bohn; Eduardo Granado Monteiro da Silva

• Advisor: Márcio Medeiros Soares; Marcos César de Oliveira

Abstract

Spintronics is the research branch that uses the electron spin as the degree of freedom for transporting, processing, and storing information. In recent years, many studies have been focusing on applying antiferromagnetic (AFM) thin films as active layers for spintronic devices. Although AFM materials present many interesting properties, such as robustness against magnetic fields perturbations and ultrafast spin dynamics, the magnetic moment manipulation in such materials is very challenging. One approach to overcome that is through the application of controlled structural deformations to the film crystalline structure, which promote alterations to its magnetocrystalline anisotropy energy. Therefore, the goal of this Master's work is to study the possibility of manipulating the spin orientation in AFM Cobalt Oxide (CoO) thin films through the application of a controlled macroscopic strain. For this purpose, polycrystalline CoO thin films were deposited onto flexible cruciform Kapton substrates using reactive Magnetron Sputtering. To controllably perform in-plane extensive and compressive bi-axial deformations to such films, we developed a Bi-axial Multi Analysis Strain Instrument (2D-MASI). A device compatible with multiple synchrotron radiation techniques (e.g. X-ray Diffraction and X-ray Absorption Spectroscopy) and sample environments (e.g. low temperatures and high vacuum). The sample crystalline structure deformation was characterized by in-situ X-ray Stress Analysis (XSA) measurements. As a result, while performing an in-plane bi-axial extension, we observed an increase of the in-plane Bragg distances (dhkl) along with a decrease of the out-of-plane dhkl values. Moreover, by performing in-plane contraction experiments along a single direction, we observed an opposite behavior than the described above (interplanar distances' in-plane contraction and out-of-plane extension). Finally, to connect the results obtained by XSA with the sample magnetic behavior, we performed X-ray Magnetic Linear Dichroism (XMLD) experiments. During these measurements, we acquired multiple absorption spectra for different strain states. By analyzing the intensity changes within the spectrum peaks, we deduced that the sample mechanical deformation was indeed causing the film's spin axis to tilt. More specifically, the analysis of the XMLD data acquired at low temperatures suggests a tendency of spin axis orientation parallel to the film direction which is contracted the most (AU)

• FAPESP's process: 18/12926-9 - Strain control of spin orientation in antiferromagnetic thin films
• Grantee: Marina Raboni Ferreira
• Support Opportunities: Scholarships in Brazil - Master