Injection, transport and manipulation of pure spin currents in metallic lateral spin valves

114 p.El trabajo realizado en esta tesis se basa en el uso de válvulas de espín laterales (LSV de las siglas en inglés), las cuales consisten de dos electrodos ferromagnéticos (FM) conectados por un canal no magnético (NM), para la creación de corrientes de espín puras. Estas corrientes están totalmente desacopladas de la corriente de carga, lo que permite obtener las propiedades de inyección de espín de un sistema FM/NM, así como las propiedades de transporte de espín de un material NM, sin efectos espurios.En la primera parte de la tesis, se realiza un estudio de propiedades básicas de inyección y transporte de espín en LSVs de Co/Cu y de Py/Cu. Para ello, la polarización de espín del Co y del Py se obtiene y compara en función de la temperatura, y la longitud de difusión de espín del Cu se obtiene en función de la temperatura y las dimensiones del canal.La segunda parte de la tesis se basa en la manipulación de corrientes de espín. Para ello, en primer lugar el ya conocido efecto Hanle es analizado en LSVs con diferentes interfaces FM/NM. En segundo lugar, se propone una nueva manera de manipulación de espín, basada en la interacción entre el espín y la magnetización de un substrato FM aislante, la cual se controla aplicando compos magnéticos pequeños. La teoría que explica dicha manipulación es desarrollada y posteriormente verificada mediante nuestros experimentos.ABSTRACT OF THE PHD THESISThe work realized throughout this thesis is based on the use of lateral spin valves (LSV), which consist of two ferromagnetic (FM) electrodes, bridged by a non-magnetic (NM) cannel. Thanks to their non-local geometry, they provide a way of creating pure spin currents. The fact that such currents are completely decoupled from the charge, avoiding any spurious effect, makes LSVs an effective for the obtention of spin-injection properties of a FM/NM system, as well as spin-transport properties of a NM metal. In the first part of the thesis, Co/Cu and Py/Cu LSVs are used in order to carry out a basic study about spin-injection and spin-transport properties. With that purpose the spin polarization of Py and Co are obtained and compared as a function of temperature. In addition, the spin-diffusion length of Cu is obtained as a function of temperature and of the different dimensions of the Cu cannel.The second part of the thesis is based on the manipulation of the pure spin currents. First of all, the already known Hanle effect is analized in LSVs with different FM/NM interface resistances. Furthermore, a novel manner of spin manipulation is proposed, based on the interaction between the spins and the magnetization of a FM insulator (FMI) substrate, which is controlled by applying small magnetic field. We develop a theory for explaining such manipulation, which is proven by our experiments.CIC nanoGune : nanoscience cooperative research cente

Injection, transport and manipulation of pure spin currents in metallic lateral spin valves

114 p.El trabajo realizado en esta tesis se basa en el uso de válvulas de espín laterales (LSV de las siglas en inglés), las cuales consisten de dos electrodos ferromagnéticos (FM) conectados por un canal no magnético (NM), para la creación de corrientes de espín puras. Estas corrientes están totalmente desacopladas de la corriente de carga, lo que permite obtener las propiedades de inyección de espín de un sistema FM/NM, así como las propiedades de transporte de espín de un material NM, sin efectos espurios.En la primera parte de la tesis, se realiza un estudio de propiedades básicas de inyección y transporte de espín en LSVs de Co/Cu y de Py/Cu. Para ello, la polarización de espín del Co y del Py se obtiene y compara en función de la temperatura, y la longitud de difusión de espín del Cu se obtiene en función de la temperatura y las dimensiones del canal.La segunda parte de la tesis se basa en la manipulación de corrientes de espín. Para ello, en primer lugar el ya conocido efecto Hanle es analizado en LSVs con diferentes interfaces FM/NM. En segundo lugar, se propone una nueva manera de manipulación de espín, basada en la interacción entre el espín y la magnetización de un substrato FM aislante, la cual se controla aplicando compos magnéticos pequeños. La teoría que explica dicha manipulación es desarrollada y posteriormente verificada mediante nuestros experimentos.ABSTRACT OF THE PHD THESISThe work realized throughout this thesis is based on the use of lateral spin valves (LSV), which consist of two ferromagnetic (FM) electrodes, bridged by a non-magnetic (NM) cannel. Thanks to their non-local geometry, they provide a way of creating pure spin currents. The fact that such currents are completely decoupled from the charge, avoiding any spurious effect, makes LSVs an effective for the obtention of spin-injection properties of a FM/NM system, as well as spin-transport properties of a NM metal. In the first part of the thesis, Co/Cu and Py/Cu LSVs are used in order to carry out a basic study about spin-injection and spin-transport properties. With that purpose the spin polarization of Py and Co are obtained and compared as a function of temperature. In addition, the spin-diffusion length of Cu is obtained as a function of temperature and of the different dimensions of the Cu cannel.The second part of the thesis is based on the manipulation of the pure spin currents. First of all, the already known Hanle effect is analized in LSVs with different FM/NM interface resistances. Furthermore, a novel manner of spin manipulation is proposed, based on the interaction between the spins and the magnetization of a FM insulator (FMI) substrate, which is controlled by applying small magnetic field. We develop a theory for explaining such manipulation, which is proven by our experiments.CIC nanoGune : nanoscience cooperative research cente

Temperature dependence of spin diffusion length and spin Hall angle in Au and Pt

We have studied the spin transport and the spin Hall effect as a function of temperature for platinum (Pt) and gold (Au) in lateral spin valve structures. First, by using the spin absorption technique, we extract the spin diffusion length of Pt and Au. Secondly, using the same devices, we have measured the spin Hall conductivity and analyzed its evolution with temperature to identify the dominant scattering mechanisms behind the spin Hall effect. This analysis confirms that the intrinsic mechanism dominates in Pt whereas extrinsic effects are more relevant in Au. Moreover, we identify and quantify the phonon-induced skew scattering. We show that this contribution to skew scattering becomes relevant in metals such as Au, with a low residual resistivity.Comment: 13 pages, 5 figure

Global Multi-Regional Input-Output methodology reveals lower energy footprint in an alternative community project

Identifying the energy needs of citizens and taking into account different lifestyles and patterns of consumption is a first step for a global transformation towards renewable, fair and democratic energy systems. Currently, Total Primary Energy Supply (TPES) is the most widely used metric of energy consumption, which only includes the energy consumed within a country. This research addresses an alternative indicator, Total Primary Energy Footprint (TPEF), which also includes the energy embedded in imported goods and services. The research is innovative in its pioneering combination of a Global Multi-Regional Input-Output (GMRIO) methodology with household budget surveys (HBS) and consumption to production sectorial bridge matrices to calculate TPEF at a small community level. Errekaleor, the largest off-grid alternative intentional community located in Basque Country, Spain, was taken as a case study. The results show, firstly, that alternative communal living can reduce energy consumption. In terms of the specific case study, even if direct residential energy consumption (4.46 MWh center dot cap-1 center dot yr-1) was shown to be 32 % and 15% higher in Errekaleor as compared with Basque and Spanish averages, a TPEF of 31.10 MWh center dot cap-1 center dot yr-1 per capita was determined for the community, 24 % and 14 % below the regional and national averages. Secondly, the relevance of indirect energy embedded in acquired goods and services in determining consumption-based energy use was shown. This accounts for 80.7 % of total consumption in Spain, 74.9 % in the Basque Country, and 66.3 % in Errekaleor. Within Errekaleor, individual arrangements impacted significantly, as people living in families have 33.5 % smaller energy footprints (28.45 MWh center dot cap-1 center dot yr-1) than individuals living alone (42.79 MWh center dot cap-1 center dot yr-1), who have a TPEF above the Basque average. Thus, the combination of GMRIO and HBS in the analyzed bottom-up case study made an important contribution in terms of clarifying the existing debate about the relative energy efficiency of alternative communities.The research was funded by the team “EKOPOL: TRANSITION PATHWAYS” recognised by the Basque Government (IT-1567-22) and the University of the Basque Country (GIC-18/22)

Modulation of pure spin currents with a ferromagnetic insulator

We propose and demonstrate spin manipulation by magnetically controlled modulation of pure spin currents in cobalt/copper lateral spin valves, fabricated on top of the magnetic insulator Y$_3$Fe$_5$O$_{12}$ (YIG). The direction of the YIG magnetization can be controlled by a small magnetic field. We observe a clear modulation of the non-local resistance as a function of the orientation of the YIG magnetization with respect to the polarization of the spin current. Such a modulation can only be explained by assuming a finite spin-mixing conductance at the Cu/YIG interface, as it follows from the solution of the spin-diffusion equation. These results open a new path towards the development of spin logics.Comment: 5 pages and 4 figures + supplemental material (10 pages, 7 figures