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Theoretical Study of Magnetic Anisotropy in MgO-based Magnetic Tunnel Junctions
Vojáček, Libor ; Li,, Jing (oponent) ; Chshiev,, Mairbek (vedoucí práce)
A magnetic tunnel junction (MTJ) is a spintronic device commercially used in highly sensitive hard disk drive reading heads. Since 2007 it has helped to sustain the exponential increase in the magnetic storage density. Moreover, it also became the building block of the fast, durable, power-efficient, and non-volatile magnetic random-access memory (MRAM). Just like reading heads, this new type of solid-state memory uses MTJs based on crystalline magnesium oxide (MgO) along with 3d metallic magnetic elements (Fe and Co). Strong magnetic anisotropy in the direction perpendicular to the metal|MgO interface is needed to provide long-term thermal memory stability as the device is downscaled. This work will analyze the magnetocrystalline anisotropy (MCA) of body-centered cubic Fe, Co, and Ni on MgO using ab initio simulations. Numerical code will be developed to calculate the shape anisotropy, crucial to consider in addition to MCA, because together they add up to the effective anisotropy. Finally, a calculation of MCA based on the second-order perturbation theory will be implemented. This will enable us to link the observed anisotropic properties directly to the system’s electronic structure (the band structure and density of states).
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Magneto-optical gradient effect imaging of magnetic textures
Molnár, Tomáš ; Hamrle, Jaroslav (oponent) ; Arregi Uribeetxebarria, Jon Ander (vedoucí práce)
Foundations of magneto-optics (MO), the field studying the influence of magnetic fields and magnetization on the propagation of light within matter, had been laid over a century and a half ago. Since then, MO has become one of the most widely used methods for magnetic imaging at the micro-scale. In addition to the MO Faraday and Kerr effects, which are linear in magnetization, effects quadratic in magnetization (Voigt or Cotton-Mouton effect) or dependent on magnetization-gradients (gradient effect) were later found. In particular, the MO gradient effect was the last to be discovered, but as it only decorated magnetic domain boundaries, it has not attracted so far the same interest as the Kerr effect for magnetic imaging. This work investigates the usefulness of the magneto-optical gradient effect to characterize nanoscale spin configurations, such as domain walls in perpendicularly magnetized materials. We present a novel experimental approach to reveal the properties of the MO gradient effect by exploiting its symmetries with respect to the polarization of light. Further, we analytically express the corresponding signal using an available theoretical model. By comparing simulated MO gradient effect signals obtained from the transfer matrix method and experimentally retrieved signals, we explore the possibility of characterizing the internal spin structure of nanoscale magnetic domain walls.
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Theoretical Study of Magnetic Anisotropy in MgO-based Magnetic Tunnel Junctions
Vojáček, Libor ; Li,, Jing (oponent) ; Chshiev,, Mairbek (vedoucí práce)
A magnetic tunnel junction (MTJ) is a spintronic device commercially used in highly sensitive hard disk drive reading heads. Since 2007 it has helped to sustain the exponential increase in the magnetic storage density. Moreover, it also became the building block of the fast, durable, power-efficient, and non-volatile magnetic random-access memory (MRAM). Just like reading heads, this new type of solid-state memory uses MTJs based on crystalline magnesium oxide (MgO) along with 3d metallic magnetic elements (Fe and Co). Strong magnetic anisotropy in the direction perpendicular to the metal|MgO interface is needed to provide long-term thermal memory stability as the device is downscaled. This work will analyze the magnetocrystalline anisotropy (MCA) of body-centered cubic Fe, Co, and Ni on MgO using ab initio simulations. Numerical code will be developed to calculate the shape anisotropy, crucial to consider in addition to MCA, because together they add up to the effective anisotropy. Finally, a calculation of MCA based on the second-order perturbation theory will be implemented. This will enable us to link the observed anisotropic properties directly to the system’s electronic structure (the band structure and density of states).
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