Search

To harness the intriguing properties of two-dimensional van der Waals (vdW) ferromagnets (FMs) for versatile applications, the key challenge lies in the reliable material synthesis for scalable device production. Here, we demonstrate the epitaxial growth of single-crystalline 1T-CrTe2 thin films on 2-inch sapphire substrates. Benefiting from the uniform surface energy of the dangling bond-free Al2O3(0001) surface, the layer-by-layer vdW growth mode is observed right from the initial growth stage, which warrants precise control of the sample thickness and atomically smooth surface morphology across the entire wafer. Moreover, the presence of the Coulomb interaction at the CrTe2/Al2O3 interface serves as an effective tuning parameter to tailor the anomalous Hall response, and the structural optimization of the CrTe2-based spin-orbit torque device leads to a substantial switching power reduction by 54%. Our results may lay out a general framework for the design of energy-efficient spintronics based on configurable vdW FMs., Comment: 20 pages, 4 figures

An elegant approach to overcome the intrinsic limitations of magnetically doped topological insulators is to bring a topological insulator in direct contact with a magnetic material. The aspiration is to realize the quantum anomalous Hall effect at high temperatures where the symmetry-breaking magnetic field is provided by a proximity-induced magnetization at the interface. Hence, a detailed understanding of the interfacial magnetism in such heterostructures is crucial, yet its distinction from structural and magnetic background effects is a rather nontrivial task. Here, we combine several magnetic characterization techniques to investigate the magnetic ordering in MnTe/Bi2Te3 heterostructures. A magnetization profile of the layer stack is obtained using depth-sensitive polarized neutron reflectometry. The magnetic constituents are characterized in more detail using element-sensitive magnetic x-ray spectroscopy. Magnetotransport measurements provide additional information about the magnetic transitions. We find that the supposedly antiferromagnetic MnTe layer does not exhibit an x-ray magnetic linear dichroic signal, raising doubt that it is in its antiferromagnetic state. Instead, Mn seems to penetrate into the surface region of the Bi 2 Te 3 layer. Furthermore, the interface between MnTe and Bi 2 Te 3 is not abrupt, but extending over ∼ 2.2 nm. These conditions are the likely reason that we do not observe proximity-induced magnetization at the interface. Our findings illustrate the importance of not solely relying on one single technique as proof for proximity-induced magnetism at interfaces. We demonstrate that a holistic, multitechnique approach is essential to gain a more complete picture of the magnetic structure in which the interface is embedded.

Understanding the electrical manipulation of the antiferromagnetic order is a crucial aspect to enable the design of antiferromagnetic devices working at THz frequencies. Focusing on collinear insulating antiferromagnetic NiO Pt thin films as a materials platform, we identify the crystallographic orientation of the domains that can be switched by currents and quantify the N el vector direction changes. We demonstrate electrical switching between different T domains by current pulses, finding that the N el vector orientation in these domains is along [ 5 5 19], different compared to the bulk amp; 10216;112 amp; 10217; directions. The final state of the in plane component of the N el vector nIP after switching by current pulses j along the [1 10] directions is nIP amp; 8741;j. By comparing the observed N el vector orientation and the strain in the thin films, assuming that this variation arises solely from magnetoelastic effects, we quantify the order of magnitude of the magnetoelastic coupling coefficient as b0 2b1 3 107J m3. This information is key for the understanding of current induced switching in antiferromagnets and for the design and use of such devices as active elements in spintronic devices

Rupture of an intracranial aneurysm results in aneurysmal subarachnoid hemorrhage (SAH), a subtype of stroke with an incidence of 9 per 100,000 person-years and a case-fatality around 35%. In order to prevent SAH, patients with unruptured intracranial aneurysms can be treated by neurosurgical or endovascular interventions, but both treatment modalities carry a ~5-7% risk of unfavorable outcome due to treatment complications. Therefore, the risk of preventive aneurysm treatment needs to be balanced carefully against the risk of SAH due to aneurysm rupture. Current assessment of the risk of aneurysm rupture, which is mainly based on geographical region, aneurysm size and aneurysm location, is insufficient. This thesis focusses on the improvement of the assessment of aneurysm growth and rupture (Part I), aneurysm wall inflammation as underlying mechanism of aneurysm rupture (Part II), and outcome after preventive aneurysm treatment for a patient perspective (Part III). Chapter 2 is a systematic review and meta-analysis on the literature on patient- and aneurysm-specific risk factors for aneurysm growth. In chapter 3, we studied geometric and morphologic aneurysm-specific risk factors for aneurysm rupture, and found that aspect ratio and irregular shape are robust risk factors for aneurysms rupture, independent of aneurysm size, location, and patient-specific characteristics. In chapter 4 we investigated whether the PHASES score, a risk model for aneurysm rupture, also predicts for aneurysm growth. In chapter 5, we elaborated on the results of chapter 2 through 4, and developed a risk model to predict the risk of aneurysm growth in patients with unruptured intracranial aneurysms. In chapter 6, we investigated whether the seasonal variation in SAH incidence was associated with temperature or increased incidence of influenza-like-illness, a seasonal inflammatory disease. In chapter 7, we investigated the prevalence of gadolinium-enhancement on 3 Tesla MRI and its determinants in a prospectively collected cohort of patients with small unruptured intracranial aneurysms. In chapter 8, we focused on the outcome after preventive aneurysm treatment from a patient perspective. The studies in this thesis help us to provide guidance to patients and their treating clinicians in decisions on treatment and follow-up of unruptured intracranial aneurysms (Part I), it gives supportive evidence for the hypothesis of aneurysm wall inflammation as contributing factor in the pathogenesis of aneurysm rupture and a baseline cohort for future studies on aneurysm wall enhancement as promising biomarker for prediction of aneurysm wall instability (Part II), and a first impression of the losses of functioning, working capacity, and life satisfaction after preventive treatment of unruptured intracranial aneurysms (Part III).

Topological insulators (TIs) are bulk insulators with exotic 'topologically protected' surface conducting modes. It has recently been pointed out that when stacked together, interactions between surface modes can induce diverse phases including the TI, Dirac semimetal, and Weyl semimetal. However, currently a full experimental understanding of the conditions under which topological modes interact is lacking. Here, working with multilayers of the TI Sb₂Te₃ and the band insulator GeTe, we provide experimental evidence of multiple topological modes in a single Sb₂Te₃-GeTe-Sb₂Te₃ structure. Furthermore, we show that reducing the thickness of the GeTe layer induces a phase transition from a Dirac-like phase to a gapped phase. By comparing different multilayer structures we demonstrate that this transition occurs due to the hybridisation of states associated with different TI films. Our results demonstrate that the Sb₂Te₃-GeTe system offers strong potential towards manipulating topological states as well as towards controlledly inducing various topological phases., T.-A.N., D.B., D.A.R. and V.N. acknowledge funding from the Leverhulme Trust, UK, T.-A.N., D.B., A.S., R.M., C.B., D.A.R. and V.N. acknowledge funding from EPSRC (UK). G.M., M.L. and D.G. acknowledge financial support from the DFG-funded priority programme SPP1666.

Klasična poluvodička elektronika na kojoj je bazirana informatička tehnologija, u bliskoj će budućnosti doseći ograničenja u mogućnostima daljnje minjaturizacije. Zbog toga se razvijaju različiti koncepti novih elemenata, koji bi u budućnosti mogli zamijeniti klasične poluvodičke elemente i koji bi mogli biti osnova informatičke tehnologije budućnosti. Jedan od tih novih koncepata je i t.z.v. „racetrack“ memorija, koja počiva na gibanju magnetskih domenskih zidova. Domenske zidove je moguće pomicati pomoću magnetskog polja ili korištenjem spinski polariziranih struja naboja. Oba pristupa imaju ograničenja, pa je u našoj grupi po prvi puta ostvareno korištenje čistih difuzijskih struja spina za pomicanje domenskih zidova. Čista spinska struja (koja ne nosi naboj) nastaje prilikom prolaska električne struje kroz spoj feromagnetskog (FM) i neferomagnetskog (NM) metala, jer dolazi do akumulacije spina u NM, koji potom difundira kroz NM. U specijalno dizajniranim nanostrukturama(nelokalnim spinskim ventilima), koji se sastoje od dva FM-NM spoja povezanih NM elementom, čista spinska struja nastala u jednom FM-NM spoju može se koristiti za manipulaciju magnetizacijom u drugom FM elementu. Osim toga u ovim strukturama se opaža i t.z.v. nelokalni spinski napon (NLSN), koji se manifestira kao razlika u mjerenom električnom naponu na drugom FM-NM spoju u slučaju paralelne i antiparalelne magnetizacije dva FM elementa. U našim istraživanjima koristili smo nelokalne spinske ventile sastavljene od feromagnetske legure Ni80Fe20 i bakra, kod kojih smo proučavali ovisnost NLSN o temperaturi i udaljenosti između feromagnetskih elemenata. To omogućuje određivanje važnih parametara kao što su spinska polarizacija u FM elementu i duljina difuzije spina u NM elementu. Pomoću tih parametara, može se odrediti omjer dobivene čiste spinske struje i korištene električne struje, a time i efikasnosti korištenja čistih spinskih struja za manipuliranje domenskim zidovima.

Magnetic domains and domain walls in epitaxial Fe3O4(100) elements (rings and wires) are imaged using magnetic force microscopy and photoemission electron microscopy. We show that the interplay between the four-fold magnetocrystalline anisotropy and the shape determines the equilibrium domain structure. Domain walls with a characteristic zig-zag structure are observed in Fe3O4(100) elements initially magnetized along one of the magnetocrystalline hard axes. We attribute the formation of zig-zag domain walls to the competition of the four-fold magnetocrystalline anisotropy, the exchange and dipolar coupling. A direct correlation between the wire width and the spin structure of zig-zag domain walls is found. (C) 2011 American Institute of Physics. [doi:10.1063/1.3540678]

The depinning of domain walls due to pure diffusive spin currents in a non-local spin valve was studied on a device consisting of two ferromagnetic permalloy elements, i.e. a wire and a half ring, with copper as the nonmagnetic spin conduit. An injected spin current is absorbed by the Py half ring where it exerts a spin torque on a domain wall placed below the Cu/Py interface. The wall depinning field was determined as a function of the spin current-density and the depinning efficiency is found to be 6 x 10^-14 Tm2/A, which is more than an order of magnitude larger than for conventional current induced domain wall motion. This high efficiency can also be reproduced theoretically, taking into account the strong surface torques exerted by the absorbed spin currents on the domain wall. Current work focuses on a somewhat different geometry consisting of two Py half rings which can be used to rule out possible Oersted field influences. Furthermore, geometries with a non-parallel alignment of the Py elements are being used to investigate the non-collinear spin transfer torque.

We study the depinning of domain walls by pure diffusive spin currents in a nonlocal spin valve structure based on two ferromagnetic Permalloy elements with copper as the nonmagnetic spin conduit. The injected spin current is absorbed by the second Permalloy structure with a domain wall, and from the dependence of the wall depinning field on the spin current density we find an efficiency of 6 x 10^-14 Tm^2/A, which is more than an order of magnitude larger than for conventional current induced domain-wall motion. Theoretically we find that this high efficiency arises from the surface torques exerted by the absorbed spin current that lead to efficient depinning.

A partir de un estudio cualitativo cuyo objetivo ha sido construir un modelo teórico sobre el significado del sistema de cuidados para los profesionales de la salud, la interdisciplinaridad e integralidad en las acciones de salud se destacaron como herramientas importantes para las prácticas del cuidado. El texto tiene como objetivo discutir la integralidad del cuidado y la interdisciplinaridad como herramientas para el cuidado en salud y la responsabilidad como el principio ético para las acciones del cuidado. Trae algunas reflexiones para la revisión del sistema de cuidados en relación a modelos integradores e interdisciplinarios que atiendan a las exigencias de una realidad que se aproxime a la naturaleza y dimensión de lo humano en los escenarios del cuidado a la salud. Em estudo anterior construiu-se modelo teórico sobre o significado do sistema de cuidados para profissionais da saúde. As categorias interdisciplinaridade e integralidade destacaram-se como ferramentas essenciais do cuidado. Nosso objetivo é discutir a integralidade e interdisciplinaridade como ferramentas para o cuidado em saúde e a responsabilidade como o princípio ético para ações de cuidado. Traz reflexões para revisão do sistema de cuidados em direção a modelos integradores e interdisciplinares que se aproximem da natureza e dimensão do humano, nos cenários do cuidado à saúde. Para reduzir a fragmentação do saber e das práticas em saúde e alcançar o homem-sujeito nas suas várias dimensões, a interdisciplinaridade e a integralidade se constituem na prática necessária do Sistema de Cuidados. Para o cuidado em saúde pautado em ações interdisciplinares, integrais/integradoras, torna-se premente a reflexão quanto à responsabilidade ética dos profissionais envolvidos com o cuidar. Mas, como envolvê-los nessa prática? ABSTRACT From a quality study that aimed to build a theoretical model about the understanding of the Health Care System, interdisciplinary and integrality actions were pointed out as important tools of health care actions. The purpose of this text was to discuss the integrality and the interdisciplinary actions of health care as a tool; as well as responsibility as an ethical principle for health care actions. Some thoughts arouse as to the review of the health care system regarding integrated and interdisciplinary models that meet the realistic demands and dimensions of human nature in health care scenarios.

Se trata de una reflexión crítica con base en revisión de literatura y en discusiones desarrolladas en el seminario sobre “El ser humano y la perspectiva de género influenciando el vivir y la salud” de la disciplina “Proceso de Vivir y la Salud Humana” del Doctorado de Enfermería del Programa de Posgrado en Enfermería de la Universidad Federal de Santa Catarina -PEN/UFSC, (Brasil). Además de las discusiones ontológicas, epistemológicas y filosóficas abordadas, las reflexiones sobre género posibilitaron comprender la complejidad del tema y la creciente necesidad de incluirlo en las prácticas de salud/enfermería. Entendiendo el fenómeno “género” no sólo como un objeto de investigación, sino principalmente como una categoría de análisis que traspasa las relaciones entre mujeres y hombres. El estudio posibilitó comprender y ampliar la categoría género más allá de la identidad biológica - reduccionista relacionada solamente al significado sexo. De otro modo, expresa una representación histórico-cultural asociada al poder, al trabajo, la violencia entre otros, influenciando el vivir y la salud. Trata-se de uma reflexão crítica com base em revisão de literatura e em discussões tecidas no seminário sobre “O ser humano e a perspectiva de gênero influenciando o viver e a saúde” da disciplina “Processo de Viver e a Saúde Humana” do Doutorado de Enfermagem do Programa de Pós-Graduação em Enfermagem da Universidade Federal de Santa Catarina PEN/UFSC, (Brasil). Além das discussões ontológicas, epistemológicas e filosóficas abordadas, as reflexões sobre gênero possibilitaram compreender a complexidade do tema e a crescente necessidade de inseri-lo nas práticas de saúde/enfermagem. Entendendo o fenômeno “gênero” não apenas um objeto de investigação, mas principalmente uma categoria de análise que ultrapassa as relações entre mulheres e homens. O estudo possibilitou compreender e ampliar a categoria gênero para além da identidade biológica-reducionista relacionada apenas ao significado sexo. De outro modo, expressa uma representação histórico-cultural associada ao poder, ao trabalho, a violência entre outros, influenciando o viver e a saúde.