Spin waves are collective excitations of an ensemble of spins. In very recent years, they have emerged as new means to encode, transmit and process information, alternatively to the traditional silicon-based technology, which relies on the motion of charged particles. The use of spin waves promises outstanding advantages such as Joule-heat-free transport of information, operability up to the THz regime and wave-based computing. In order to exploit the potential benefits provided by spin waves, the current effort is devoted to the design and engineering of materials adequate for their excitation, propagation and manipulation. A newly developed technique, Thermally Assisted Magnetic – Scanning Probe Lithography (tam-SPL), appears particularly suitable for the fabrication in Ferromagnet-Antiferromagnet (FM, AF) exchange-biased systems of arbitrary, reversible but enduring magnetic patterns useful for implementing the functionalities of spin waves into practical devices. In the first part of this thesis work, tam-SPL was employed to pattern magnetic domains and create Néel domain walls in an in-plane magnetized system. For the first time, the motion of spin waves along domain walls, operated as waveguides, was imaged with spatial and temporal resolution via scanning transmission x-ray microscopy. Propagation, steering and interaction of spin waves was observed, demonstrating the feasibility of the domain walls as nano-conduits. In the second part, with the aim of developing a material more adapted to operations with spin waves, optimization was performed of a FM-AF heterostructure exhibiting perpendicular magnetic anisotropy and out-of-plane exchange bias. The fine tuning of the perpendicular anisotropy of the FM, of the exchange bias field and of the reversal temperature of the AF was achieved. tam-SPL was tested on the developed system and successfully employed to pattern magnetic domains, as proved by magnetic force microscopy and magneto-optical-Kerr-effect microscopy. Initial investigation of the possibility of exciting spin waves by means of spin-orbit-torque effects was carried out. The findings of the experimental investigation constitute the proof of concept for the conduction of innovative experiments on the generation and transmission of spin waves in the devised and improved system.
Le onde di spin sono eccitazioni collettive di sistemi di spin. Negli ultimi anni la comunità scientifica ha iniziato a considerarle come nuovi mezzi per la codifica, la trasmissione e l'elaborazione di informazione, in alternativa alla tradizionale tecnologia del silicio basata sul trasporto di particelle cariche. L'impiego delle onde di spin promette significativi vantaggi quali il trasporto di informazione senza dissipazione di energia per effetto Joule, l'operabilità a elevate frequenze (fino al THz) e il calcolo analogico basato sull'uso di onde. Al fine di sfruttare i potenziali benefici derivanti dall'impiego delle onde di spin, attualmente lo sforzo è rivolto alla progettazione e ingegnerizzazione di materiali adeguati alla loro eccitazione, propagazione e manipolazione. In sistemi Ferromagnete-Antiferromagnete (FM, AF) con interazione di scambio all'interfaccia (``exchange bias''), una tecnica appena sviluppata, Thermally Assisted Magnetic – Scanning Probe Lithography (tam-SPL), si presta alla fabbricazione di strutture magnetiche arbitrarie che combinano reversibilità e robustezza; tali strutture appaiono di grande utilità in vista dell'implementazione e dell'uso delle onde di spin in dispositivi pratici. Nella prima parte di questo progetto di tesi, la tecnica tam-SPL è stata impiegata per creare domini magnetici e pareti di dominio di Néel in un film magnetizzato in piano. Per la prima volta, il moto di onde spin lungo pareti di domino impiegate come nano-condotti è stato studiato con risoluzione sia spaziale sia temporale attraverso la microscopia a scansione per trasmissione di raggi x. Sono state osservate la propagazione, la curvatura e l'interazione di onde di spin, dimostrando in tal modo l'adeguatezza delle pareti di dominio come nano-condotti. Nella seconda parte, al fine di sviluppare un sistema migliore per operazioni che coinvolgano tali onde, è stato ottimizzata una struttura FM-AF in modo che possa disporre contemporaneamente di anisotropia magnetica ed exchange bias FM-AF entrambi perpendicolari al film sottile. A questo scopo, l'anisotropia magnetica del FM, l'exchange bias e le proprietà termiche dell'AF sono state attentamente calibrate. Come dimostrato per mezzo della microscopia a forza magnetica e della microscopia ottica ad effetto Kerr, l'applicazione di tam-SPL ha consentito con successo la creazione di domini magnetici nella nuova struttura sviluppata. Infine, lo studio iniziale degli effetti dovuti all'interazione di spin-orbita ha confermato la potenzialità di eccitare onde di spin per mezzo di correnti nel sistema ottimizzato. I risultati della ricerca costituiscono insieme la base per lo svolgimento di esperimenti innovativi di generazione e trasmissione di onde di spin.
Magnetic patterning of exchange-biased systems for nanomagnonics
SALA, GIACOMO
2016/2017
Abstract
Spin waves are collective excitations of an ensemble of spins. In very recent years, they have emerged as new means to encode, transmit and process information, alternatively to the traditional silicon-based technology, which relies on the motion of charged particles. The use of spin waves promises outstanding advantages such as Joule-heat-free transport of information, operability up to the THz regime and wave-based computing. In order to exploit the potential benefits provided by spin waves, the current effort is devoted to the design and engineering of materials adequate for their excitation, propagation and manipulation. A newly developed technique, Thermally Assisted Magnetic – Scanning Probe Lithography (tam-SPL), appears particularly suitable for the fabrication in Ferromagnet-Antiferromagnet (FM, AF) exchange-biased systems of arbitrary, reversible but enduring magnetic patterns useful for implementing the functionalities of spin waves into practical devices. In the first part of this thesis work, tam-SPL was employed to pattern magnetic domains and create Néel domain walls in an in-plane magnetized system. For the first time, the motion of spin waves along domain walls, operated as waveguides, was imaged with spatial and temporal resolution via scanning transmission x-ray microscopy. Propagation, steering and interaction of spin waves was observed, demonstrating the feasibility of the domain walls as nano-conduits. In the second part, with the aim of developing a material more adapted to operations with spin waves, optimization was performed of a FM-AF heterostructure exhibiting perpendicular magnetic anisotropy and out-of-plane exchange bias. The fine tuning of the perpendicular anisotropy of the FM, of the exchange bias field and of the reversal temperature of the AF was achieved. tam-SPL was tested on the developed system and successfully employed to pattern magnetic domains, as proved by magnetic force microscopy and magneto-optical-Kerr-effect microscopy. Initial investigation of the possibility of exciting spin waves by means of spin-orbit-torque effects was carried out. The findings of the experimental investigation constitute the proof of concept for the conduction of innovative experiments on the generation and transmission of spin waves in the devised and improved system.| File | Dimensione | Formato | |
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2017_12_Sala.pdf
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https://hdl.handle.net/10589/137022