Polynchuk P. Relaxation-free switching of magnetic memory cells based on multilayer nanosystems with antiferromagnetic coupling

The dynamics of magnetization of magnetic memory elements in two cases important for practical implementation is studied in this thesis: 1) under the influence of a magnetic field; 2) with the combined effect of magnetic field pulses and pulses of spin-polarized current. The conditions for magnetization reversal of the synthetic antiferromagnet (SAF) or a memory cell under the influence of these external perturbations are determined. The following control principles are proposed to ensure the magnetization of the free layer of the memory cell under the influence of magnetic field pulses and spin-polarized current. The results obtained are important for technological applications in random access magnetic memory (MRAM) devices. In the introduction to the original part of the dissertation, the relevance of its topic is proved. The purpose is formulated, the object and subject of the study are defined. The novelty of the results is substantiated. Information on the testing of research results at scientific conferences is provided. The first chapter of the thesis analyses the current state of the problem of remagnetization of synthetic antiferromagnets for the purpose of recording information. The physical basis of the methods used to switch the magnetic states of a memory cell in MRAM applications is described. In the second chapter of the thesis, the conditions for the implementation of rapid switching of the magnetization direction of the memory cell under the action of a magnetic field pulse applied perpendicularly to the plane of the free layer of the SAF are defined. The amplitude and duration of laser radiation pulses required to control the magnetization states of the SAF are estimated. It is shown that in the case of implementation of the high-speed mode of SAF magnetization reversal, the laser-induced magnetic field pulsation can be the basis of a modern method of recording information on SAF-type media. In addition, the second chapter of the thesis investigates the change in the magnetic state of a synthetic antiferromagnet under the influence of a spin-polarized current. The influence of the initial angle between the spin-polarized current “polarizer” and the magnetization of the SAF on the amplitude and duration of the current pulse required to remagnetize the memory elements is determined. The third chapter of the thesis theoretically investigates the process of controlling the magnetization of a memory cell under the combined effect of local external magnetic fields, which are created by passing pre-programmed electric currents through control electric in a standart layout. It is shown that by optimizing the shape and duration of current pulses I(t) (t – time), a high-speed relaxation-free mode of switching the magnetic state of the memory cell is achieved. The optimal parameters of field (current) pulses for achieving a fast relaxation-free mode of memory cell magnetization are determined. In the fourth chapter of the thesis, we have theoretically studied a practically important task for spintronics – the problem of controlling the magnetization states of a magnetic memory cell by means of the combined action of local external magnetic fields and spin-polarized currents. The magnetization of a memory cell consisting of three nanolayers separated by two tunnel magnetic junctions under the combined action of a spin-polarized current and magnetic field pulses is investigated. The dynamics of magnetization of the free ferromagnetic layer is studied. The optimum amplitudes and durations of the spin-polarized current pulse and the magnetic field induced by it are analytically calculated to achieve stable, fast, relaxation-free remagnetization of the memory cell.