Current-induced switching of in-plane magnets by Spin-Orbit Torques

One of the possible tools that can be exploited for data storage nowadays are the Random Access Memories. The main advantage of this technology is that it allows to achieve almost identical writing and reading times, regardless of the position of the information inside the memory. One of the possible implementations of RAM is represented by the Magnetic RAM (MRAM), which relies on the magnetic properties of the materials in order to store data. MRAMs represent non-volatile types of Random Access Memories. The MRAM is based upon the possibility to manipulate the resistance value of a multi-layer structure according to the relative orientation of the magnetization between the ferromagnetic layers. This resistance manipulation allows obtaining a two state system (high resistance vs low resistance) that can be read as a 0/1 state in the digital framework. Nowadays, almost the totality of the commercialized devices relies on systems where the magnetization pointing is out-of-plane of the multi-layer structures. However, it is possible in principle also to exploit systems displaying an in-plane magnetization. Indeed, the interest toward such systems has been recently growing given the possibility to exploit new physical phenomena for the information writing and reading that could lead to an increased efficiency and endurance of the devices. It is such a system that has been taken into account and analysed in this thesis. Indeed, the main purpose was to verify the possibility to induce magnetization switching via Spin Orbit Torque (SOT) in in-plane ferromagnets. To obtain an in-plane system Pt/Co bi-layers have been fabricated. On top of that, heavy metal (HM)/ferromagnetic (FM) bi-layers represent the perfect systems in order to be able to achieve the reversal of the magnetization based upon SOTs. We use the conversion of electric current into spin current in the HM, with a subsequent torque exertion over the FM magnetization. The chosen shapes for the devices under test were the Hall bars and Hall crosses. Such shapes are particularly suitable in order to perform harmonic Hall voltage measurements. However, not only electrical static characterization was carried out, but also time-resolved transport and optical characterization played an important role in the development of this thesis. In fact, the specific geometry of the in-plane magnetization makes these systems particularly interesting for time-resolved measurements. Moreover, the magneto-optical observation allows inspecting the magnetization switching of the sample eliminating the uncertainties due to spurious electrical signals. The results obtained with the magnetooptical technique revealed to be the most successful. It was possible to retrieve the specific condition parameters needed for the switching. On the other side, the time-resolved measurements did not lead to the desired results. Indeed, we are not sure about the magnetic nature of the observed signals with such a technique. The absence of clear magnetization switching signal during these measurements could be due to the inadequacy of both the samples and the setup itself. Overall, the presented thesis tries to provide an analysis of the current-induced magnetization switching in in-plane magnets, presenting not only the results obtained using different measurement setups but also their possible interpretations, with a final outlook on the in-plane technology and the possible steps that can be taken in order to improve its implementation.