1,720,966 research outputs found
TUNING OF MAGNETOELECTRIC COUPLING IN MULTIFERROIC HETEROSTRUCTURES
Full text linkThe work presented in this thesis deals with the optical and thermal control of magnetism in multiferroic heterostructures. The main goal was to investigate the interfacial magnetic modifications of magnetic properties of ferromagnetic (FM) thin films deposited on photo-ferroelectric (FE) substrates, as a function of two external stimuli, specifically visible light excitation and thermal treatments. The photo-induced effects of low-power 405 nm visible light illumination on the ferroelectric and magnetic properties of PMN-0.4PT/Ni heterostructures were investigated by combining electrical, structural, magnetic, and spectroscopic characterizations, in both pristine and polarized states of the PMN-PT substrate. The results show that under light illumination, the photostriction of PMN-PT induces an interfacial strain on the magnetostrictive Ni layer. This leads to an optical modification of the Ni orbital moment, leading up to a 45% reduction in coercive field under illumination, as observed by Magneto-Optic Kerr effect (MOKE). The light-induced variation in the Ni orbital moment was experimentally observed for the first time in multiferroic heterostructures, via sum-rule analysis of x-ray magnetic circular dichroic measurements (XMCD). The observed effect is strongly reduced after polarizing the PMN-PT substrate out-of-plane. This was justified by the larger photostrictive contribution coming from the in-plane FE domains. These results shed light on the delicate energy balance that leads to sizeable light-induced effects in multiferroic heterostructure. The scope is also to highlight the novelty and importance of the presented work, which emphasizes on the photostrictive effect induced by laser illumination in the PMN-PT/FM heterostructure and its effect on the Ni thin film via inverse magnetostriction mechanism. Concerning the thermal treatment effects on multiferroic heterostructures, this aspect was characterized on PMN-0.4PT/Fe heterostructures. The study was done by combining structural, magnetometric, and spectroscopic characterizations. X-ray diffraction (XRD) and micro-Raman spectroscopy were used to characterize the structural properties of PMN-PT substrate, whereas MOKE magnetometry was performed to analyze the in-plane magnetic response of Fe thin films deposited on top. The pristine unannealed substrate exhibited a larger presence of out-of-plane FE domains, with broad and inhomogeneous features in the 2D reciprocal space maps of XRD, signifying the presence of a low crystalline quality of the ferroelectric structure. Once annealed for 15 minutes above the first-order phase transition, the majority of the domain population shifted towards the in-plane direction, showing in addition an overall improved crystalline quality. Further annealing led to a return to a mostly out-of-plane domain population. These structural modifications of PMN-PT upon annealing tailored the magnetic anisotropy of Fe film in different manners, exploiting the magnetoelastic interfacial coupling. Specifically, the angular dependence of the magnetic response of Fe passed from an isotropic one in the pristine case to an anisotropic one after short annealing, due to the larger presence of in-plane tetragonal domains. These results place thermal treatments as an additional parameter to be exploited for tuning the magnetic properties of multiferroic heterostructures. The results obtained with the two presented external stimuli, i.e., light illumination and thermal treatments, exploit the rich set of properties of ferroelectric materials and pave the way for further investigations, either by combining them or by further optimizing the choice of materials.The work presented in this thesis deals with the optical and thermal control of magnetism in multiferroic heterostructures. The main goal was to investigate the interfacial magnetic modifications of magnetic properties of ferromagnetic (FM) thin films deposited on photo-ferroelectric (FE) substrates, as a function of two external stimuli, specifically visible light excitation and thermal treatments. The photo-induced effects of low-power 405 nm visible light illumination on the ferroelectric and magnetic properties of PMN-0.4PT/Ni heterostructures were investigated by combining electrical, structural, magnetic, and spectroscopic characterizations, in both pristine and polarized states of the PMN-PT substrate. The results show that under light illumination, the photostriction of PMN-PT induces an interfacial strain on the magnetostrictive Ni layer. This leads to an optical modification of the Ni orbital moment, leading up to a 45% reduction in coercive field under illumination, as observed by Magneto-Optic Kerr effect (MOKE). The light-induced variation in the Ni orbital moment was experimentally observed for the first time in multiferroic heterostructures, via sum-rule analysis of x-ray magnetic circular dichroic measurements (XMCD). The observed effect is strongly reduced after polarizing the PMN-PT substrate out-of-plane. This was justified by the larger photostrictive contribution coming from the in-plane FE domains. These results shed light on the delicate energy balance that leads to sizeable light-induced effects in multiferroic heterostructure. The scope is also to highlight the novelty and importance of the presented work, which emphasizes on the photostrictive effect induced by laser illumination in the PMN-PT/FM heterostructure and its effect on the Ni thin film via inverse magnetostriction mechanism. Concerning the thermal treatment effects on multiferroic heterostructures, this aspect was characterized on PMN-0.4PT/Fe heterostructures. The study was done by combining structural, magnetometric, and spectroscopic characterizations. X-ray diffraction (XRD) and micro-Raman spectroscopy were used to characterize the structural properties of PMN-PT substrate, whereas MOKE magnetometry was performed to analyze the in-plane magnetic response of Fe thin films deposited on top. The pristine unannealed substrate exhibited a larger presence of out-of-plane FE domains, with broad and inhomogeneous features in the 2D reciprocal space maps of XRD, signifying the presence of a low crystalline quality of the ferroelectric structure. Once annealed for 15 minutes above the first-order phase transition, the majority of the domain population shifted towards the in-plane direction, showing in addition an overall improved crystalline quality. Further annealing led to a return to a mostly out-of-plane domain population. These structural modifications of PMN-PT upon annealing tailored the magnetic anisotropy of Fe film in different manners, exploiting the magnetoelastic interfacial coupling. Specifically, the angular dependence of the magnetic response of Fe passed from an isotropic one in the pristine case to an anisotropic one after short annealing, due to the larger presence of in-plane tetragonal domains. These results place thermal treatments as an additional parameter to be exploited for tuning the magnetic properties of multiferroic heterostructures. The results obtained with the two presented external stimuli, i.e., light illumination and thermal treatments, exploit the rich set of properties of ferroelectric materials and pave the way for further investigations, either by combining them or by further optimizing the choice of materials
Electronically ordered ultrathin Cr2O3 on Pt(1 1 1) in presence of a multidomain graphene intralayer
Full text linkIn the last decade, reducing the dimensionality of materials to few atomic layers thickness has allowed exploring new physical properties and functionalities otherwise absent out of the two dimensional limit. In this regime, interfaces and interlayers play a crucial role. Here, we investigate their influence on the electronic properties and structural quality of ultrathin Cr2O3 on Pt(1 1 1), in presence of a multidomain graphene intralayer. Specifically, by combining Low-Energy Electron Diffraction, X-ray Photoelectron Spectroscopy and X-ray Absorption Spec-troscopy, we confirm the growth of high-quality ultrathin Cr2O3 on bare Pt, with sharp surface reconstructions, proper stoichiometry and good electronic quality. Once a multidomain graphene intralayer is included at the metal/oxide interface, the Cr2O3 maintained its correct stoichiometry and a comparable electronic quality, even at the very first monolayers, despite the partially lost of the morphological long-range order. These results show how ultrathin Cr2O3 films are slightly affected by the interfacial epitaxial quality from the electronic point of view, making them potential candidates for graphene-integrated heterostructures
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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