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1.
Phys Rev Lett ; 124(21): 217202, 2020 May 29.
Artigo em Inglês | MEDLINE | ID: mdl-32530667

RESUMO

We report on the study of both perpendicular magnetic anisotropy (PMA) and Dzyaloshinskii-Moriya interaction (DMI) at an oxide/ferromagnetic metal (FM) interface, i.e., BaTiO_{3} (BTO)/CoFeB. Thanks to the functional properties of the BTO film and the capability to precisely control its growth, we are able to distinguish the dominant role of the oxide termination (TiO_{2} vs BaO) from the moderate effect of ferroelectric polarization in the BTO film, on the PMA and DMI at an oxide/FM interface. We find that the interfacial magnetic anisotropy energy of the BaO-BTO/CoFeB structure is 2 times larger than that of the TiO_{2}-BTO/CoFeB, while the DMI of the TiO_{2}-BTO/CoFeB interface is larger. We explain the observed phenomena by first principles calculations, which ascribe them to the different electronic states around the Fermi level at oxide/ferromagnetic metal interfaces and the different spin-flip process. This study paves the way for further investigation of the PMA and DMI at various oxide/FM structures and thus their applications in the promising field of energy-efficient devices.

2.
Nano Lett ; 19(5): 3019-3026, 2019 05 08.
Artigo em Inglês | MEDLINE | ID: mdl-30933564

RESUMO

Study of resonant tunneling through multimetallic quantum well (QW) structure is not only important for the fundamental understanding of quantum transport but also for the great potential to generate advanced functionalities of spintronic devices. However, it remains challenging to engineer such a structure due to the short electron phase coherence length in metallic QW system. Here, we demonstrate the successful fabrication of double-QW structure in a single fully epitaxial magnetic tunnel junction (MTJ) heterostructure, where two Fe QW layers are sandwiched between three MgAlO x tunnel barriers. We show clear evidence of the coherent resonant tunneling through the discrete QW states in the two QWs. The coherent resonant tunneling condition is fulfilled only when the middle barrier between the two QWs is thin enough and available QW states are present simultaneously in both QWs under a certain bias. Compared to the single QW structure, the resonant tunneling in double-QW MTJ produces strong conductivity oscillations with much narrower peak width (about half) owing to the enhanced energy filtering effect. This study presents a comprehensive understanding of the resonant tunneling mechanism in MTJ with multiple QWs, which is essential for future development of new spintronic devices operating in the quantum tunneling regime.

3.
J Phys Condens Matter ; 31(29): 295501, 2019 Jul 24.
Artigo em Inglês | MEDLINE | ID: mdl-30965305

RESUMO

ThTaN3 is known as a rare cubic perovskite nitride topological crystalline insulator (TCI). Here, we propose, using first-principles calculations, that compressive uniaxial (0 0 1) strained ThTaN3 can host a three dimensional nodal-chain semimetal state when spin-orbit coupling (SOC) is ignored. When SOC is turned on, the nodal-chain is gapped out, resulting in a pair of type-II Dirac points as protected by C 4 crystal symmetry. Intriguingly, under an increasing compressive uniaxial (0 0 1) strain, a new pair of type-I Dirac points emerges, realizing a novel Dirac semimetal that hosts both type-I and type-II Dirac points in momentum space. The electronic structures of the projected surfaces are also discussed, and the unique Fermi arcs are observed. Our results make ThTaN3 a promising platform for experimental realization of multiple types of Dirac fermions in a single material system.

4.
Adv Mater ; 31(21): e1900776, 2019 May.
Artigo em Inglês | MEDLINE | ID: mdl-30957913

RESUMO

2D transition metal dichalcogenides have attracted much attention in the field of spintronics due to their rich spin-dependent properties. The promise of highly compact and low-energy-consumption spin-orbit torque (SOT) devices motivates the search for structures and materials that can satisfy the requirements of giant perpendicular magnetic anisotropy (PMA) and large SOT simultaneously in SOT-based magnetic memory. Here, it is demonstrated that PMA and SOT in a heavy metal/transition metal ferromagnet structure, Pt/[Co/Ni]2 , can be greatly enhanced by introducing a molybdenum disulfide (MoS2 ) underlayer. According to first-principles calculation and X-ray absorption spectroscopy (XAS), the enhancement of the PMA is ascribed to the modification of the orbital hybridization at the interface of Pt/Co due to MoS2 . The enhancement of SOT by the role played by MoS2 is explained, which is strongly supported by the identical behavior of SOT and PMA as a function of Pt thickness. This work provides new possibilities to integrate 2D materials into promising spintronics devices.

5.
Med Sci Monit ; 24: 8804-8811, 2018 Dec 05.
Artigo em Inglês | MEDLINE | ID: mdl-30517088

RESUMO

BACKGROUND Fractalkine is widely expressed throughout the brain and spinal cord, where it can exert effects on pain enhancement and hyperalgesia by activating microglia through CX3C chemokine receptor 1 (CX3CR1), which triggers the release of several pro-inflammatory cytokines in the spinal cord. Fractalkine has also been shown to increase cytosolic calcium ([Ca2+]i) in microglia. MATERIAL AND METHODS Based on the characteristics of CX3CR1, a G protein-coupled receptor, we explored the role of inositol 1,4,5-trisphosphate (IP3) signaling in fractalkine-induced inflammatory response in BV-2 cells in vitro. The effect and the underlying mechanism induced by fractalkine in the brain were observed using a mouse model with intracerebroventricular (i.c.v.) injection of exogenous fractalkine. RESULTS [Ca2+]i was significantly increased and IL-1ß and TNF-α levels were higher in the fractalkine-treated cell groups than in the farctalkine+ 2-APB groups. We found that i.c.v. injection of fractalkine significantly increased p-p38MAPK, IL-1ß, and TNF-α expression in the brain, while i.c.v. injection of a fractalkine-neutralizing antibody (anti-CX3CR1), trisphosphate receptor (IP3R) antagonist (2-APB), or p38MAPK inhibitor (SB203580) prior to fractalkine addition yielded an effective and reliable anti-allodynia effect, following the reduction of p-p38MAPK, IL-1ß, and TNF-α expression. CONCLUSIONS Our results suggest that fractalkine leads to hyperalgesia, and the underlying mechanism may be associated with IP3/p38MAPK-mediated calcium signaling and its phlogogenic properties.


Assuntos
Receptor 1 de Quimiocina CX3C/efeitos dos fármacos , Quimiocina CX3CL1/fisiologia , Hiperalgesia/metabolismo , Animais , Cálcio/metabolismo , Sinalização do Cálcio , Linhagem Celular , Quimiocina CX3CL1/metabolismo , China , Injeções Espinhais , Inositol 1,4,5-Trifosfato/metabolismo , Interleucina-1beta/metabolismo , Ativação de Macrófagos , Camundongos , Microglia/metabolismo , Proteína Quinase 14 Ativada por Mitógeno/metabolismo , Dor/tratamento farmacológico , Receptores de Quimiocinas , Transdução de Sinais/efeitos dos fármacos , Medula Espinal/metabolismo , Fator de Necrose Tumoral alfa/metabolismo
6.
Sci Rep ; 8(1): 12356, 2018 Aug 17.
Artigo em Inglês | MEDLINE | ID: mdl-30120368

RESUMO

Using first-principles calculations, we demonstrate several approaches to control Dzyaloshinskii-Moriya Interaction (DMI) in ultrathin films with perpendicular magnetic anisotropy. First, we find that DMI is significantly enhanced when the ferromagnetic (FM) layer is sandwiched between nonmagnetic (NM) layers inducing additive DMI in NM1/FM/NM2 structures. For instance, when two NM layers are chosen to induce DMI of opposite chirality in Co, e.g. NM1 representing Au, Ir, Al or Pb, and NM2 being Pt, the resulting DMI in NM1/Co/Pt trilayers is enhanced compared to Co/Pt bilayers. Moreover, DMI can be significantly enhanced further in case of using FM layer comprising Fe and Co layers. Namely, it is found that the DMI in Ir/Fe/Co/Pt structure can be enhanced by 80% compared to that of Co/Pt bilayers reaching a very large DMI amplitude of 5.59 meV/atom. Our second approach for enhancing DMI is to use oxide capping layer. We show that DMI is enhanced by 60% in Oxide/Co/Pt structures compared to Co/Pt bilayers. Moreover, we unveiled the DMI mechanism at Oxide/Co interface due to Rashba effect, which is different to Fert-Levy DMI at FM/NM interfaces. Finally, we demonstrate that DMI amplitude can be modulated using an electric field with an efficiency factor comparable to that of the electric field control of perpendicular magnetic anisotropy in transition metal/oxide interfaces. These approaches of DMI controlling pave the way for skyrmion and domain wall motion-based spintronic applications.

7.
ACS Appl Mater Interfaces ; 10(36): 30614-30622, 2018 Sep 12.
Artigo em Inglês | MEDLINE | ID: mdl-30125490

RESUMO

The ferroelectric control of spin-polarization at ferromagnet (FM)/ferroelectric organic (FE-Org) interface by electrically switching the ferroelectric polarization of the FE-Org has been recently realized in the organic multiferroic tunnel junctions (OMFTJs) and gained intensive interests for future multifunctional organic spintronic applications. Here, we report the evidence of ferroelectric "ailing-channel" in the organic barrier, which can effectively pin the ferroelectric domain, resulting in nonswitchable spin polarization at the FM/FE-Org interface. In particular, OMFTJs based on La0.6Sr0.4MnO3/P(VDF-TrFE) ( t)/Co/Au structures with different P(VDF-TrFE) thickness ( t) were fabricated. The combined advanced electron microscopy and spectroscopy studies clearly reveal that very limited Co diffusion exists in the P(VDF-TrFE) organic barrier when the Au/Co electrode is deposited around 80K. Pot-hole structures at the boundary between the P(VDF-TrFE) needle-like grains are evidenced to induce "ailing-channels" that hinder efficient ferroelectric polarization of the organic barrier and result in the quenching of the spin polarization switching at Co/P(VDF-TrFE) interface. Furthermore, the spin diffusion length in the negatively polarized P(VDF-TrFE) is measured to be about 7.2 nm at 20K. The evidence of the mechanism of ferroelectric "ailing-channels" is of essential importance to improve the performance of OMFTJ and master the key condition for an efficient ferroelectric control of the spin polarization of "spinterface".

8.
Nanoscale ; 10(25): 12062-12067, 2018 Jul 05.
Artigo em Inglês | MEDLINE | ID: mdl-29911217

RESUMO

The interfacial Dzyaloshinskii-Moriya interaction (DMI) in ferromagnetic/heavy metal ultra-thin film structures has attracted a lot of attention thanks to its capability to stabilize Néel-type domain walls (DWs) and magnetic skyrmions for the realization of non-volatile memory and logic devices. In this study, we demonstrate that magnetic properties in perpendicularly magnetized Ta/Pt/Co/MgO/Pt heterostructures, such as magnetization and DMI, can be significantly influenced by the MgO thickness. To avoid the excessive oxidation of Co, an ultrathin Mg layer is inserted to improve the quality of the Co-MgO interface. By using field-driven domain wall expansion in the creep regime, we find that non-monotonic tendencies of the DMI field appear when changing the thickness of MgO. With the insertion of a monatomic Mg layer, the strength of the DMI could reach a high level and saturate. We conjecture that the efficient control of the DMI is a result of subtle changes of both Pt/Co and Co/MgO interfaces, which provides a method to optimize the design of ultra-thin structures achieving skyrmion electronics.

9.
Nat Mater ; 17(7): 605-609, 2018 07.
Artigo em Inglês | MEDLINE | ID: mdl-29807987

RESUMO

The possibility of utilizing the rich spin-dependent properties of graphene has attracted much attention in the pursuit of spintronics advances. The promise of high-speed and low-energy-consumption devices motivates the search for layered structures that stabilize chiral spin textures such as topologically protected skyrmions. Here we demonstrate that chiral spin textures are induced at graphene/ferromagnetic metal interfaces. Graphene is a weak spin-orbit coupling material and is generally not expected to induce a sufficient Dzyaloshinskii-Moriya interaction to affect magnetic chirality. We demonstrate that indeed graphene does induce a type of Dzyaloshinskii-Moriya interaction due to the Rashba effect. First-principles calculations and experiments using spin-polarized electron microscopy show that this graphene-induced Dzyaloshinskii-Moriya interaction can have a similar magnitude to that at interfaces with heavy metals. This work paves a path towards two-dimensional-material-based spin-orbitronics.

10.
Medicine (Baltimore) ; 97(18): e0629, 2018 May.
Artigo em Inglês | MEDLINE | ID: mdl-29718874

RESUMO

RATIONALE: Acute phlegmonous gastritis (PG) is a rare and often fatal condition mainly characterized by severe bacterial infection of the gastric wall. Case reports of PG over the past century average about 1 per year. Early diagnosis and immediate treatment are crucial to achieve positive outcomes. PATIENT CONCERNS: A 47-year-old man was referred to our hospital because of abdominal pain, high fever, and vomiting for 4 days, with aggravation for 24 hours. Physical examination revealed epigastric abdominal pain, rebound pain, and abdominal wall tightness. Abdominal CT showed thickening of the stomach wall with edema and gas. DIAGNOSES: On the basis of symptoms and CT imaging findings, the patient was diagnosed with acute PG. INTERVENTIONS: Antibiotic therapy and operation. OUTCOMES: The patient immediately underwent an operation after conservative treatment using antibiotics proved ineffective. The whole stomach was obviously swollen, and the anterior side and posterior wall of the stomach were nigrescent necrotic. Hence, total gastrectomy was performed followed by reconstruction (roux-en-y), and pus that accumulated in the stomach wall was cultured. At postoperative broad-spectrum antibiotic coverage, the patient finally recovered. LESSONS: Acute PG is a rare infection of the gastric wall especially after antibiotic treatment. Given the fast progression of this disease, early recognition and immediate action are crucial to achieve positive outcomes.


Assuntos
Gastrectomia/métodos , Gastrite , Estômago , Anastomose em-Y de Roux/métodos , Antibacterianos/administração & dosagem , Diagnóstico Precoce , Intervenção Médica Precoce/métodos , Gastrite/diagnóstico , Gastrite/fisiopatologia , Gastrite/terapia , Humanos , Masculino , Pessoa de Meia-Idade , Necrose , Estômago/diagnóstico por imagem , Estômago/patologia , Tomografia Computadorizada por Raios X/métodos , Resultado do Tratamento
11.
Zhongguo Zhen Jiu ; 37(4): 386-390, 2017 Apr 12.
Artigo em Chinês | MEDLINE | ID: mdl-29231590

RESUMO

OBJECTIVE: To observe the difference in the clinical therapeutic effects on bronchial asthma in children of different body constitutions treated with sanfu pingchuan plaster and sanjiu zhichuan plaster. METHODS: One hundred and twenty-two children of bronchial asthma were divided into three groups according to TCM body constitutions, 42 cases in the qi deficiency constitution group, 40 cases in the yang deficiency constitution group and 40 cases in the phlegm damp constitution group. From 2011 to 2013, the acupoint plaster was applied to all of the children in the three groups during the dog days and the third nine-day period after the winter solstice each year. The average attack frequency and onset days of bronchial asthma and relevant immune function indicators were observed during treatment and 1 year after treatment in the children and the therapeutic effects were evaluated. RESULTS: ①In 2014, the acute attacks of bronchial asthma were (1.2±0.9) times and (1.4±0.4) times in the qi deficiency constitution group and the yang deficiency constitution group, all lower than (3.0±0.5) times in the phlegm damp constitution group (both P<0.05) separately. ②After treatment, in the qi deficiency constitution group and yang deficiency constitution group, the values of IgG, IgA and IgM were all increased as compared with those before treatment (all P<0.05). ③The total effective rate was over 95% in the children of the three groups. The clinical control rates in the qi deficiency constitution group and the yang deficiency constitution group were higher apparently than that in the phlegm damp constitution group, indicating the significant difference statistically (both P<0.05). CONCLUSIONS: The combined treatment of sanfu pingchuan plaster and sanjiu zhichuan plaster are effective on bronchial asthma in the children of different body constitutions. The therapeutic effects for the qi deficiency constitution and the yang deficiency constitution are more apparent than that for the phlegm damp constitution.


Assuntos
Pontos de Acupuntura , Asma/terapia , Constituição Corporal , Deficiência da Energia Yang/terapia , Criança , Humanos , Imunoglobulina A/sangue , Imunoglobulina G/sangue , Imunoglobulina M/sangue , Muco , Qi
13.
Phys Rev Lett ; 118(21): 219901, 2017 May 26.
Artigo em Inglês | MEDLINE | ID: mdl-28598656

RESUMO

This corrects the article DOI: 10.1103/PhysRevLett.115.267210.

14.
Adv Mater ; 28(46): 10204-10210, 2016 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-27709711

RESUMO

Organic multiferroic tunnel junctions based on La0.6 Sr0.4 MnO3 /poly(vinylidene fluoride) (PVDF)/Co structures are fabricated. The tunneling magneto-resistance sign can be changed by electrically switching the ferroelectric polarization of PVDF barrier. It is demonstrated that the spin-polarization of the PVDF/Co spinterface can be actively controlled by tuning the ferroelectric polarization of PVDF. This study opens new functionality in controlling the injection of spin polarization into organic materials via the ferroelectric polarization of the barrier.

15.
Appl Opt ; 55(10): 2692-700, 2016 04 01.
Artigo em Inglês | MEDLINE | ID: mdl-27139674

RESUMO

If a used "vertical beam" is not perfectly vertical in a measurement, a cosine error will be introduced into it. To decrease and compensate for this cosine error, a measurement system is proposed to measure the deviation of the laser beam from the vertical direction. The structure of our measurement system is illustrated, and a model for solving for the deviation angle is established. As the distance of the beam spots on the charge-coupled device is the essential parameter for the measurement results, the acquisition process for this distance is explained. Moreover, the accuracy of the algorithm used in the acquisition process is also tested by experiments. Further, a self-correction module is designed and applied to reduce the error caused by the corner cube reflector in the system. The characteristics of the measurement system such as the resolution, stability, temperature drift, and direction accuracy are analyzed through experiments. The combined uncertainty of the measurement system is calculated to be 11×10-6 rad.

16.
Nat Nanotechnol ; 11(5): 449-54, 2016 05.
Artigo em Inglês | MEDLINE | ID: mdl-26809057

RESUMO

Magnetic skyrmions are chiral spin structures with a whirling configuration. Their topological properties, nanometre size and the fact that they can be moved by small current densities have opened a new paradigm for the manipulation of magnetization at the nanoscale. Chiral skyrmion structures have so far been experimentally demonstrated only in bulk materials and in epitaxial ultrathin films, and under an external magnetic field or at low temperature. Here, we report on the observation of stable skyrmions in sputtered ultrathin Pt/Co/MgO nanostructures at room temperature and zero external magnetic field. We use high lateral resolution X-ray magnetic circular dichroism microscopy to image their chiral Néel internal structure, which we explain as due to the large strength of the Dzyaloshinskii-Moriya interaction as revealed by spin wave spectroscopy measurements. Our results are substantiated by micromagnetic simulations and numerical models, which allow the identification of the physical mechanisms governing the size and stability of the skyrmions.

17.
Nano Lett ; 16(1): 145-51, 2016 Jan 13.
Artigo em Inglês | MEDLINE | ID: mdl-26641927

RESUMO

We report strongly enhanced perpendicular magnetic anisotropy (PMA) of Co films by graphene coating from both first-principles and experiments. Our calculations show that graphene can dramatically boost the surface anisotropy of Co films up to twice the value of its pristine counterpart and can extend the out-of-plane effective anisotropy up to unprecedented thickness of 25 Å. These findings are supported by our experiments on graphene coating on Co films grown on Ir substrate. Furthermore, we report layer-resolved and orbital-hybridization-resolved anisotropy analysis, which help understanding of the physical mechanisms of PMA and more practically can help design structures with giant PMA. As an example, we propose superexchange stabilized Co-graphene heterostructures with a robust constant effective PMA and linearly increasing interfacial anisotropy as a function of film thickness. These findings point toward possibilities to engineer graphene/ferromagnetic metal heterostructures with giant magnetic anisotropy more than 20-times larger compared to conventional multilayers, which constitutes a hallmark for future graphene and traditional spintronic technologies.

18.
Sci Rep ; 5: 18173, 2015 Dec 11.
Artigo em Inglês | MEDLINE | ID: mdl-26656721

RESUMO

Spin-transfer-torque magnetic random access memory (STT-MRAM) attracts extensive attentions due to its non-volatility, high density and low power consumption. The core device in STT-MRAM is CoFeB/MgO-based magnetic tunnel junction (MTJ), which possesses a high tunnel magnetoresistance ratio as well as a large value of perpendicular magnetic anisotropy (PMA). It has been experimentally proven that a capping layer coating on CoFeB layer is essential to obtain a strong PMA. However, the physical mechanism of such effect remains unclear. In this paper, we investigate the origin of the PMA in MgO/CoFe/metallic capping layer structures by using a first-principles computation scheme. The trend of PMA variation with different capping materials agrees well with experimental results. We find that interfacial PMA in the three-layer structures comes from both the MgO/CoFe and CoFe/capping layer interfaces, which can be analyzed separately. Furthermore, the PMAs in the CoFe/capping layer interfaces are analyzed through resolving the magnetic anisotropy energy by layer and orbital. The variation of PMA with different capping materials is attributed to the different hybridizations of both d and p orbitals via spin-orbit coupling. This work can significantly benefit the research and development of nanoscale STT-MRAM.

19.
Phys Rev Lett ; 115(26): 267210, 2015 Dec 31.
Artigo em Inglês | MEDLINE | ID: mdl-26765026

RESUMO

The Dzyaloshinskii-Moriya interaction (DMI) has been recently recognized to play a crucial role in allowing fast domain wall dynamics driven by spin-orbit torques and the generation of magnetic Skyrmions. Here, we unveil the main features and microscopic mechanisms of DMI in Co/Pt bilayers via first principles calculations. We find that the large DMI of the bilayers has a dominant contribution from the spins of the interfacial Co layer. This DMI between the interfacical Co spins extends very weakly away from the interface and is associated with a spin-orbit coupling in the adjacent atomic layer of Pt. Furthermore, no direct correlation is found between DMI and proximity induced magnetism in Pt. These results clarify the underlying mechanisms of DMI at interfaces between ferromagnetic and heavy metals and should help optimizing material combinations for domain wall and Skyrmion-based devices.

20.
Sichuan Da Xue Xue Bao Yi Xue Ban ; 45(4): 717-9, 723, 2014 Jul.
Artigo em Chinês | MEDLINE | ID: mdl-25286704

RESUMO

OBJECTIVE: To compare postoperative quality of life (QOL) of patients receiving proximal gastrectomy (PG) for adenocarcinoma of gastroesophagealjunction (AEG) throughgastric tube anastomosis and traditional esophagogastrostomy. METHODS: Between January 2010 and February 2011, 112 patients were diagnosed as AEG in our hospital. All patients underwent curative operations. Two post-PG alimentary tract reconstruction methods were adopted: gastric tube anastomosis (n = 60) and traditional direct anastomosis (n = 52). The European Organization for Research and Treatment of Cancer (EORTC) Quality of life Questionnaire Core-30 (EORTC QLQ-C30) and QLQ-STO22 were used to assess QOL of those patients before and two years after operations. RESULTS: There were no statistically significant differences between the two groups of patients in clinical and pathologic characteristics, clinical pathological characteristics and preoperative QOL (P > 0.05). Two years after operations, the patients receiving traditional direct anastomosis showed higher scores in reflux, body image, and nausea and vomiting compared with those receiving gastric tube anastomosis. No statistical differences were found between the two groups of patients in general health, physical function, role function, fatigue and pain (P > 0.05). CONCLUSION: Gastric tube reconstruction could improve the postoperative QOL of AEG patients.


Assuntos
Adenocarcinoma/cirurgia , Junção Esofagogástrica/patologia , Gastrectomia , Qualidade de Vida , Neoplasias Gástricas/cirurgia , Anastomose Cirúrgica , Procedimentos Cirúrgicos do Sistema Digestório , Refluxo Gastroesofágico , Humanos , Período Pós-Operatório , Procedimentos Cirúrgicos Reconstrutivos
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