1,720,980 research outputs found
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
Charge-to-spin conversion phenomena in ion-implanted Pt and quasi-two dimensional electron gas based heterostructures
No full text1. Introduction and theory||2. Experimental methods||3. Enhanced spin Hall effect in S-implanted Pt||4. Dose dependent spin Hall effect in O-implanted Pt and Ox sputtered Pt||5. Disentanglement of intrinsic and extrinsic side-jump scattering induced spin Hall effect in O and N-implanted Pt||6. Giant spin Hall effect in P-implanted Pt layers||7. Beyond Ion-implanted Pt: Room temperature charge-to-spin conversion from q-2DEG-based interfacesSpin Hall effect （SHE）, initially predicted by Dyakonov and Perel in 1971 and later revisited by Hirsch in 1999 [1], is the generation of spin current density js from a charge current density jc. The conversion of jc to js via SHE, can exert a damping-like spin-orbit torque （SOT） tDL on the magnetization of a ferromagnetic （FM） layer attached to the heavy metal （HM）. The charge-to-spin conversion is quantified by the damping-like torque efficiency theta DL, which is given by the relation js = （ℏ/2e）theta DL（jc×sigma）, where ℏ is the reduced Planck constant, e is electronic charge and sigma is polarization of spin current. Typically, 4d and 5d transition metals （such as Pt, Ta and W） are used as the HM, and their corresponding theta DL are found to be ≈0.1. This intrinsic mechanism depends on the Berry curvature of the material, in which an anomalous velocity arises from a momentum-space Berry phase [2]. An increase in theta DL has been found by alloying the HM with Au, Pd and also by incorporating non-metallic elements （with smaller atomic number Z） into the HM. However, in these materials, a complete understanding of the mechanism responsible for the increase in sigma DL remains elusive. Another phenomenon, the Rashba-Edelstein effect （REE）, leads to the generation of nonequilibrium spins at the interface of an inversion asymmetry, in a metal oxide heterostructure [3]. The oxygen vacancies created at the interface lead to mobile conduction electrons forming a quasi-two dimensional electron gas （q-2DEG）. An electron having momentum p, in the presence of an electric field E, experiences an effective magnetic field along （p×E）. This field leads to spin polarization of the electrons and subsequently a spin current flows from the metal oxide heterostructure to the FM and exerts a tDL on the magnetization of the FM [4]. Similar to SHE, we can define a charge-to-spin conversion efficiency theta DL. So far, a relation between the number of oxygen vacancies and theta DL is yet to be found. Overall, a high theta DL as well as an investigation of its mechanism for the origin of SHE and REE is important in switching the magnetization for writing operation in next generation based magnetic random access memory （MRAM）. In this thesis, we perform ion implantation in Pt, using different nonmetallic elements, namely sulfur （S）, oxygen （O）, nitrogen （N）, and phosphorus （P） and study the theta DL via spin-torque ferromagnetic resonance （ST-FMR） measurements [5]. Additionally, we incorporate O in Pt via sputtering, PtOx to compare the sputtering and ion implantation methods. We also compare the q-2DEG created at the interface of SrTiO3/AlN and SrTiO3/Al2O3 in terms of theta DL and a detailed investigation of the angular symmetry of spin-orbit torque （SOT） [6], as well as the calculation of theta DL as a function of temperature and implantation dose （oxygen vacancy） is carried out, revealing the mechanism responsible for enhancement of the SHE （REE）. We use a low energy of 12 keV to implant S in Pt, Pt（S） at a dose of 01016-51016 ions/cm2. Next, we use an energy of 20 keV to implant O and N in Pt, Pt（O） and Pt（N）, respectively at a varying dose of 01016-11017 ions/cm2. Finally, we move to a moderate energy of 30 keV to implant P in Pt in a wide range of 01016-91016 ions/cm2. For Pt（S）, we achieve a high theta DL≈0.50 at 10 K, which is 8-times higher than the theta DL or pure Pt at 10 K. We observe a highly monotonic dose dependence in theta DL of Pt（O） from 0.064 to 0.230 at 293 K, with a smaller trade-off in beta xx from 55.4 to 159.5 mu Ω cm, respectively as we increase the dose from 01016-11017 ions/cm2. For Pt（N）, we attain a high theta DL≈at 293 K for a particular dose of 51016 ions/cm2. Finally, for the Pt（P）, we obtain a giant theta DL≈ at 293 K, which makes it an ideal candidate of spintronics based MRAM. For PtOx, we also report a high theta DL≈ 0.40 attesting that O in Pt enhances the SHE via both ion implantation and sputtering method. Finally, we explore REE of the q-2DEG created at the interface of SrTiO3/amorphous oxides, namely the SrTiO3/AlN and SrTiO3/Al2O3. We observe a very high theta DL ≈ 2.44 for SrTiO3/AlN than theta DL ≈1.01 for SrTiO3/Al2O3 due to a higher oxygen vacancy enabled REE for the former. The high theta DL is an order higher than the theta DL of 5d transition metal such as Pt. For the dominant underlying mechanism for the ion implanted samples, we confirm a linear dependence of spin Hall resistivity from impurities, beta SH imp with the square of resistivity from impurities, beta 2 imp, i.e., beta SH imp ∝ beta imp [7], implying an extrinsic origin of side-jump scattering as the dominant origin of SHE for the Pt（S）, Pt（O）, Pt（N） samples studied as a function of implantation and temperature. On the other hand for the PtOx, we do not get a linear beta SH imp ∝ beta 2 mp especially for the lower concentration （n %） of O in Pt, suggesting an intrinsic mechanism while we obtain an extrinsic side-jump for higher n %. In order to disentangle the dominant extrinsic side-jump from the intrinsic SHE, we express the spin Hall conductivity, sigma xy SH as the sum of intrinsic and extrinsic SHE （skew scattering/side-jump） and study it as a function of square of conductivity, sigma 2 xx [8]. We exclude skew scattering as a possible extrinsic mechanism due to the ion-implanted samples not lying in higher of sigma xx of super clean metals （10 6 < sigma xx < 10 8 Ω-1cm-1） [2]. Then, we show that a sudden decrease in intrinsic spin Hall conductivity, sigma int SH is counterbalanced by the increase in side-jump induced SHE, theta sj SH due to the increase in residual resistivity from impurities, beta xx,0. Hence, for all ion implanted samples, Pt（S）, Pt（O）, Pt（N）, Pt（P）, we find that higher the beta xx,0, higher is the theta sj SH, and lower is the sigma int SH. We obtain a simple model that theta DL via SHE can be enhanced by simply increasing beta xx,0 in a 5d transition metal. Moreover, we find a crossover of intrinsic to extrinsic side-jump SHE as we increase the dose of S, O, N, P ions in Pt from ≈ 01016-11017 in a wide energy range of 12-30 KeV. Overall, the contribution of the extrinsic side jump induced SHE to the increase in theta DL is clearly identified through our studies on the ion implanted samples. To gain insight into the overlooked contribution of oxygen vacancy to the theta DL via REE in q-2DEG, we find that the higher oxygen vacancy created at SrTiO3/AlN in comparison to SrTiO3/Al2O3, not only plays a role in enhancing the electronic transport, but may also lead to a higher theta DL. To confirm the high theta DL in SrTiO3/AlN, we observe a large direct current modulation of resonance linewidth via direct current biased ST-FMR measurements [5] which is 1-2 order higher than Pt. For understanding the angular symmetry of SOT, which is crucial in estimation of theta DL, via ST-FMR lineshape analysis, we study the ST-FMR spectrum as a function of phi （where phi is the angle between microwave current in device and external magnetic field）. In our Pt（S）, Pt（O）, Pt（N）, Pt（P）, and PtOx, we observe no breaking of the two-fold and mirror symmetry of SOT due to the 100 % sin2 phi cos phi dependence of symmetric（S） and antisymmetric （A） component of ST-FMR spectrum leading to simple estimation of theta DL. Whereas for q-2DEG, we observe a broken symmetry of SOT and develop an analysis protocol by filtering out the sin2 phi cos phi from S and A arising from tDL and reliably estimate the thata DL. In conclusion, we report that theta DL can be enhanced in host Pt by incorporating non-metallic impurity such as S, O, N, and P in Pt due to the extrinsic side-jump scattering induced SHE from impurities. We obtain a high theta DL for Pt（S） at 10 K and Pt（P） at 293 K. For the q-2DEG, we observe a high theta DL ≈2.44 for SrTiO3/AlN than theta DL ≈1.01 for SrTiO3/Al2O3, which is an order higher than Pt. We explicitly probe the overlooked contribution of oxygen vacancy to the theta DL enabled by REE. These results suggest that the SHE and REE materials could help us in the development of not only MRAM but also in various spintronic based memory devices utilizing the high charge-to-spin conversion in future.九州工業大学博士学位論文 学位記番号: 情工博甲第374号 学位授与年月日: 令和5年3月24日令和4年
イオン注入したPtおよび擬二次元電子ガスベースのヘテロ構造における電流からスピン流への変換現象
Full text link九州工業大学九州工業大学博士学位論文（要旨）学位記番号：情工博甲第374号 学位授与年月日: 令和5年3月24日thesi
Charge-to-spin conversion phenomena in ion-implanted Pt and quasi-two dimensional electron gas based heterostructures
No full text九州工業大学博士学位論文（要旨）学位記番号：情工博甲第374号 学位授与年月日: 令和5年3月24
イオン注入したPtおよび擬二次元電子ガスベースのヘテロ構造における電流からスピン流への変換現象
Full text link九州工業大学博士（情報工学）1. Introduction and theory||2. Experimental methods||3. Enhanced spin Hall effect in S-implanted Pt||4. Dose dependent spin Hall effect in O-implanted Pt and Ox sputtered Pt||5. Disentanglement of intrinsic and extrinsic side-jump scattering induced spin Hall effect in O and N-implanted Pt||6. Giant spin Hall effect in P-implanted Pt layers||7. Beyond Ion-implanted Pt: Room temperature charge-to-spin conversion from q-2DEG-based interfacesSpin Hall effect （SHE）, initially predicted by Dyakonov and Perel in 1971 and later revisited by Hirsch in 1999 [1], is the generation of spin current density js from a charge current density jc. The conversion of jc to js via SHE, can exert a damping-like spin-orbit torque （SOT） tDL on the magnetization of a ferromagnetic （FM） layer attached to the heavy metal （HM）. The charge-to-spin conversion is quantified by the damping-like torque efficiency theta DL, which is given by the relation js = （ℏ/2e）theta DL（jc×sigma）, where ℏ is the reduced Planck constant, e is electronic charge and sigma is polarization of spin current. Typically, 4d and 5d transition metals （such as Pt, Ta and W） are used as the HM, and their corresponding theta DL are found to be ≈0.1. This intrinsic mechanism depends on the Berry curvature of the material, in which an anomalous velocity arises from a momentum-space Berry phase [2]. An increase in theta DL has been found by alloying the HM with Au, Pd and also by incorporating non-metallic elements （with smaller atomic number Z） into the HM. However, in these materials, a complete understanding of the mechanism responsible for the increase in sigma DL remains elusive. Another phenomenon, the Rashba-Edelstein effect （REE）, leads to the generation of nonequilibrium spins at the interface of an inversion asymmetry, in a metal oxide heterostructure [3]. The oxygen vacancies created at the interface lead to mobile conduction electrons forming a quasi-two dimensional electron gas （q-2DEG）. An electron having momentum p, in the presence of an electric field E, experiences an effective magnetic field along （p×E）. This field leads to spin polarization of the electrons and subsequently a spin current flows from the metal oxide heterostructure to the FM and exerts a tDL on the magnetization of the FM [4]. Similar to SHE, we can define a charge-to-spin conversion efficiency theta DL. So far, a relation between the number of oxygen vacancies and theta DL is yet to be found. Overall, a high theta DL as well as an investigation of its mechanism for the origin of SHE and REE is important in switching the magnetization for writing operation in next generation based magnetic random access memory （MRAM）. In this thesis, we perform ion implantation in Pt, using different nonmetallic elements, namely sulfur （S）, oxygen （O）, nitrogen （N）, and phosphorus （P） and study the theta DL via spin-torque ferromagnetic resonance （ST-FMR） measurements [5]. Additionally, we incorporate O in Pt via sputtering, PtOx to compare the sputtering and ion implantation methods. We also compare the q-2DEG created at the interface of SrTiO3/AlN and SrTiO3/Al2O3 in terms of theta DL and a detailed investigation of the angular symmetry of spin-orbit torque （SOT） [6], as well as the calculation of theta DL as a function of temperature and implantation dose （oxygen vacancy） is carried out, revealing the mechanism responsible for enhancement of the SHE （REE）. We use a low energy of 12 keV to implant S in Pt, Pt（S） at a dose of 01016-51016 ions/cm2. Next, we use an energy of 20 keV to implant O and N in Pt, Pt（O） and Pt（N）, respectively at a varying dose of 01016-11017 ions/cm2. Finally, we move to a moderate energy of 30 keV to implant P in Pt in a wide range of 01016-91016 ions/cm2. For Pt（S）, we achieve a high theta DL≈0.50 at 10 K, which is 8-times higher than the theta DL or pure Pt at 10 K. We observe a highly monotonic dose dependence in theta DL of Pt（O） from 0.064 to 0.230 at 293 K, with a smaller trade-off in beta xx from 55.4 to 159.5 mu Ω cm, respectively as we increase the dose from 01016-11017 ions/cm2. For Pt（N）, we attain a high theta DL≈at 293 K for a particular dose of 51016 ions/cm2. Finally, for the Pt（P）, we obtain a giant theta DL≈ at 293 K, which makes it an ideal candidate of spintronics based MRAM. For PtOx, we also report a high theta DL≈ 0.40 attesting that O in Pt enhances the SHE via both ion implantation and sputtering method. Finally, we explore REE of the q-2DEG created at the interface of SrTiO3/amorphous oxides, namely the SrTiO3/AlN and SrTiO3/Al2O3. We observe a very high theta DL ≈ 2.44 for SrTiO3/AlN than theta DL ≈1.01 for SrTiO3/Al2O3 due to a higher oxygen vacancy enabled REE for the former. The high theta DL is an order higher than the theta DL of 5d transition metal such as Pt. For the dominant underlying mechanism for the ion implanted samples, we confirm a linear dependence of spin Hall resistivity from impurities, beta SH imp with the square of resistivity from impurities, beta 2 imp, i.e., beta SH imp ∝ beta imp [7], implying an extrinsic origin of side-jump scattering as the dominant origin of SHE for the Pt（S）, Pt（O）, Pt（N） samples studied as a function of implantation and temperature. On the other hand for the PtOx, we do not get a linear beta SH imp ∝ beta 2 mp especially for the lower concentration （n %） of O in Pt, suggesting an intrinsic mechanism while we obtain an extrinsic side-jump for higher n %. In order to disentangle the dominant extrinsic side-jump from the intrinsic SHE, we express the spin Hall conductivity, sigma xy SH as the sum of intrinsic and extrinsic SHE （skew scattering/side-jump） and study it as a function of square of conductivity, sigma 2 xx [8]. We exclude skew scattering as a possible extrinsic mechanism due to the ion-implanted samples not lying in higher of sigma xx of super clean metals （10 6 < sigma xx < 10 8 Ω-1cm-1） [2]. Then, we show that a sudden decrease in intrinsic spin Hall conductivity, sigma int SH is counterbalanced by the increase in side-jump induced SHE, theta sj SH due to the increase in residual resistivity from impurities, beta xx,0. Hence, for all ion implanted samples, Pt（S）, Pt（O）, Pt（N）, Pt（P）, we find that higher the beta xx,0, higher is the theta sj SH, and lower is the sigma int SH. We obtain a simple model that theta DL via SHE can be enhanced by simply increasing beta xx,0 in a 5d transition metal. Moreover, we find a crossover of intrinsic to extrinsic side-jump SHE as we increase the dose of S, O, N, P ions in Pt from ≈ 01016-11017 in a wide energy range of 12-30 KeV. Overall, the contribution of the extrinsic side jump induced SHE to the increase in theta DL is clearly identified through our studies on the ion implanted samples. To gain insight into the overlooked contribution of oxygen vacancy to the theta DL via REE in q-2DEG, we find that the higher oxygen vacancy created at SrTiO3/AlN in comparison to SrTiO3/Al2O3, not only plays a role in enhancing the electronic transport, but may also lead to a higher theta DL. To confirm the high theta DL in SrTiO3/AlN, we observe a large direct current modulation of resonance linewidth via direct current biased ST-FMR measurements [5] which is 1-2 order higher than Pt. For understanding the angular symmetry of SOT, which is crucial in estimation of theta DL, via ST-FMR lineshape analysis, we study the ST-FMR spectrum as a function of phi （where phi is the angle between microwave current in device and external magnetic field）. In our Pt（S）, Pt（O）, Pt（N）, Pt（P）, and PtOx, we observe no breaking of the two-fold and mirror symmetry of SOT due to the 100 % sin2 phi cos phi dependence of symmetric（S） and antisymmetric （A） component of ST-FMR spectrum leading to simple estimation of theta DL. Whereas for q-2DEG, we observe a broken symmetry of SOT and develop an analysis protocol by filtering out the sin2 phi cos phi from S and A arising from tDL and reliably estimate the thata DL. In conclusion, we report that theta DL can be enhanced in host Pt by incorporating non-metallic impurity such as S, O, N, and P in Pt due to the extrinsic side-jump scattering induced SHE from impurities. We obtain a high theta DL for Pt（S） at 10 K and Pt（P） at 293 K. For the q-2DEG, we observe a high theta DL ≈2.44 for SrTiO3/AlN than theta DL ≈1.01 for SrTiO3/Al2O3, which is an order higher than Pt. We explicitly probe the overlooked contribution of oxygen vacancy to the theta DL enabled by REE. These results suggest that the SHE and REE materials could help us in the development of not only MRAM but also in various spintronic based memory devices utilizing the high charge-to-spin conversion in future.九州工業大学博士学位論文 学位記番号: 情工博甲第374号 学位授与年月日: 令和5年3月24日令和4年度doctoral thesi
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
- …
