Perna, Salvatore (2017) Nonlinear Magnetization Dynamics in Multilayered Spintronic Nanodevices. [Tesi di dottorato]

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Item Type: Tesi di dottorato
Lingua: English
Title: Nonlinear Magnetization Dynamics in Multilayered Spintronic Nanodevices
Creators:
CreatorsEmail
Perna, Salvatoresalvatore.perna@unina.it
Date: 4 October 2017
Number of Pages: 126
Institution: Università degli Studi di Napoli Federico II
Department: Ingegneria Elettrica e delle Tecnologie dell'Informazione
Dottorato: Information technology and electrical engineering
Ciclo di dottorato: 29
Coordinatore del Corso di dottorato:
nomeemail
Riccio, Danieledaniele.riccio@unina.it
Tutor:
nomeemail
d'Aquino, MassimilianoUNSPECIFIED
Date: 4 October 2017
Number of Pages: 126
Uncontrolled Keywords: Nanomagnetism, Spintronics, Nonlinear Dynamics
Settori scientifico-disciplinari del MIUR: Area 09 - Ingegneria industriale e dell'informazione > ING-IND/31 - Elettrotecnica
Date Deposited: 22 Nov 2017 11:44
Last Modified: 08 Mar 2018 13:32
URI: http://www.fedoa.unina.it/id/eprint/11877
DOI: 10.6093/UNINA/FEDOA/11877

Abstract

A theoretical and numerical investigation of spintronic nano-devices working either as a memory device or as an oscillator device is addressed. The typical structure of such a device consists in two ferromagnetic layers separated by a non-magnetic layer. One ferromagnetic layer is fixed magnetized, while in the other one the magnetization is free to change subject to external excitations, e.g magnetic field . The magnetization dynamics can be also excited via the spin-transfer-torque (STT) mechanism by making pass an electric current through the device. In the first part of the thesis it is considered a device where the free layer is uniformly magnetized and the magnetic anisotropy is partially compensated by the magnetostatic effect, which depends by the geometry of the layer. The main results are the determination of the parameters range where the compensation reduces the switching current threshold and the relation between the self-oscillations current and frequency. In the second part of the thesis a larger device is considered. For this reason the magnetic state of the free layer is not uniform but it is in a vortex state. By injecting an electric current through a small nanocontact, the STT excites the vortex precessions around the nanocontact. For this system, it is derived a collective variables model consistent with the numerically observed vortex deformation and describing the relation between the vortex oscillations frequency and the electric current value. Furthermore the model has been used to study and predict the synchronization of the vortex oscillations with a microwave magnetic field circularly polarized. The diagram describing the possible vortex oscillations regimes (synchronized, unsynchronized) and transition mechanisms is derived. It is predicted and numerically confirmed a large hysteretic effect in the synchronization, which increases with the amplitude of the microwave field. Finally it is shown the impact of the hysteresis on the synchronization of multiple vortex nano-oscillators.

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