EFECTO DE LA LONGITUD DEL DIÁMETRO EN LA ESTABILIDAD TÉRMICA DE LA CAPA LIBRE DE LAS MEMORIAS RAM MAGNÉTICAS

ResumenUna de las nuevas aplicaciones del magnetismo en medios de almacenamiento de datos son las memorias RAM magnéticas (MRAM, por sus siglas en inglés). El periodo de tiempo que se puede mantener un bit en una MRAM está íntimamente relacionado con la estabilidad térmica del dispositivo, la cual depende de las propiedades de los materiales utilizados y de la geometría. En el presente trabajo presentamos un estudio de cómo afecta el diámetro del dispositivo a la estabilidad térmica de una MRAM. A partir de los resultados obtenidos es posible explicar que al incrementar del diámetro de una MRAM, en algún punto el proceso de inversión de la magnetización deja de ser una rotación coherente y se convierte un movimiento de pared de dominio, lo cual a su vez ocasiona que la barrera de energía no sea proporcional al volumen, presentándose una disminución en el valor de la barrera de energía.Palabras Claves: Almacenamiento, Estabilidad, MEP, MRAM. EFFECT OF THE LENGTH OF THE DIAMETER ON THE THERMAL STABILITY OF THE FREE LAYER OF MAGNETIC RAM MEMORIESAbstractOne of the novel applications of magnetism in data storage is the use of Magnetic Random Access Memories (MRAM). The period that a bit can be stored in such a device is closely related to the thermal stability, which in turn depends on the materials used, and on the geometry. In the present work, we performed a study on the effect of the junction diameter on the thermal stability of an MRAM. From our results it is possible to explain the reason why when the diameter of an MRAM in increased the reversal process goes from coherent rotation to domain wall movement, leading to a decrease in the energy barrier.Keywords: MEP, MRAM, Storage, Stability

Magnetism in frustrated nanostructures

Artificial Spin Ice (ASI), comprised of ferromagnetic nanobars in a honeycomb geometry, attracts much attention since it is a directly imageable frustrated system which exhibits rich physics including ice-rule behaviour and magnetic monopole excitations. ASI’s nanobars undergo domain wall mediated magnetic reversal in external fields. Understanding and indeed controlling the trajectories of field driven domain walls and hence the order in which ASI’s nanobars are reversed is a crucial step towards mapping out ASI’s full functionality for potential applications. In this thesis, trajectories of domain walls during the early stages of ASI’s magnetic reversal are studied. Data showing domain walls executing non-random walks in the transverse domain wall regime and random walks in the vortex domain wall regime is presented. The former behaviour is linked to the domain wall’s chirality, and as such, attempts to control a domain wall’s initial chirality via triangular injection pads are discussed. In addition, ways in which a vortex domain wall’s chirality may be controlled with ellipsoidal hole obstructions are shown. Artificial Dipolar 2D-XY, a complementary system to ASI, also promises interesting behaviour. In this new frustrated architecture, individual nanobars are replaced with single domain nanodiscs whose magnetisations can point in any in-plane direction. In this thesis, intriguing results from preliminary experiments on this new system are presented. One of the best techniques used to study the magnetisations of nanostructures such as those described above is Lorentz Transmission Electron Microscopy (LTEM). Since the contrast yielded for unusual magnetic states was not well documented, software called Micromagnetic Analysis to Lorentz TEM Simulation (MALTS) was developed in order to aid in analysis of LTEM images. MALTS can simulate the LTEM contrast of any magnetic object of any size, shape or state. A description of its full functionality is also included in this thesis.Open Acces