Browsing by Department "Nanjing Tech University"

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  • Enhanced Ferromagnetism and Tunable Magnetism in Fe3GeTe2Monolayer by Strain Engineering
    (2020-06-10) Hu, Xiaohui; Zhao, Yinghe; Shen, Xiaodong; Krasheninnikov, Arkady V.; Chen, Zhongfang; Sun, Litao
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Recent discovery of intrinsic ferromagnetism in Fe3GeTe2 (FGT) monolayer [ Deng, Y.; et al. Nature 2018, 563, 94-99; Fei, Z.; et al. Nat. Mater. 2018, 17, 778-782 ] not only extended the family of two-dimensional (2D) magnetic materials but also stimulated further interest in the possibility to tune their magnetic properties without changing the chemical composition or introducing defects. By means of density functional theory computations, we explore strain effects on the magnetic properties of the FGT monolayer. We demonstrate that the ferromagnetism can be largely enhanced by the tensile strain in the FGT monolayer due to the competitive effects of direct exchange and superexchange interaction. The average magnetic moments of Fe atoms increase monotonically with an increase in biaxial strain from -5 to 5% in FGT monolayer. The intriguing variation of magnetic moments with strain in the FGT monolayer is related to the charge transfer induced by the changes in the bond lengths. Given the successful fabrication of the FGT monolayer, the strain-tunable ferromagnetism in the FGT monolayer can stimulate the experimental effort in this field. This work also suggests an effective route to control the magnetic properties of the FGT monolayer. The pronounced magnetic response toward the biaxial strain can be used to design the magnetomechanical coupling spintronics devices based on FGT.
  • Enhancing Ferromagnetism and Tuning Electronic Properties of CrI3 Monolayers by Adsorption of Transition-Metal Atoms
    (2021-05-12) Yang, Qiang; Hu, Xiaohui; Shen, Xiaodong; Krasheninnikov, Arkady V.; Chen, Zhongfang; Sun, Litao
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Among first experimentally discovered two-dimensional (2D) ferromagnetic materials, chromium triiodide (CrI3) monolayers have attracted particular attention due to their potential applications in electronics and spintronics. However, the Curie temperature Tc of the CrI3 monolayer is below room temperature, which greatly limits practical development of the devices. Herein, using density functional theory calculation, we explore how the electronic and magnetic properties of CrI3 monolayers change upon adsorption of 3d transition-metal (TM) atoms (from Sc to Zn). Our results indicate that the electronic properties of the TM-CrI3 system can be tuned from semiconductor to metal/half-metal/spin gapless semiconductor depending on the choice of the adsorbed TM atoms. Moreover, the adsorption can improve the ferromagnetic stability of CrI3 monolayers by increasing both magnetic moments and Tc. Notably, Tc of CrI3 with Sc and V adatoms can be increased by nearly a factor of 3. We suggest postsynthesis doping of 2D CrI3by deposition of TM atoms as a new route toward potential applications of TM-CrI3 systems in nanoelectronic and spintronic devices.
  • Investigation on spray cooling heat transfer performance with different nanoparticles and surfactants
    (2021-11-02) Bao, Jun; Wang, Yu; Kosonen, Risto; Xu, Xinjie; Liu, Jinxiang
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    The spray cooling enhancement method has consistently been the focus area for research as a highly effective cooling method that can alter the properties of spray media by allowing the addition of different types of additives. In this study, an open spray cooling system was established for experimental purposes. Firstly, the effects of nozzles on the spray cooling characteristics were investigated through four kinds of nozzle experiments. Al2O3-H2O, TiO2-H2O, ZrO2-H2O, and SiO2-H2O nanofluids were chosen as cooling substances based on the optimal nozzles, and the effects of the type and concentration of nanoparticles on cooling performance were studied. Based on the performance of the nanoparticles, sodium dodecyl benzenesulfonate(SDBS) was selected as the surfactant for Al2O3 and TiO2 nanoparticles, while cetyltrimethyl ammonium bromide(CTAB) was selected as the surfactant for ZrO2 and SiO2 nanoparticles. The effects of surfactants with different concentrations on the heat transfer performance of nanofluids were studied. The results showed that when the mass fraction of SiO2 nanoparticles was 0.2% and CTAB was 0.005%, an optimal cooling effect was achieved; which was 5.9% higher than that of water and 1.7% higher than that obtained without CTAB.
  • Strain robust spin gapless semiconductors/half-metals in transition metal embedded MoSe2monolayer
    (2020-08-26) Yang, Qiang; Kou, Liangzhi; Hu, Xiaohui; Wang, Yifeng; Lu, Chunhua; Krasheninnikov, Arkady V.; Sun, Litao
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    The realization of spin gapless semiconductor (SGS) and half-metal (HM) behavior in two-dimensional (2D) transition metal (TM) dichalcogenides is highly desirable for their applications in spintronic devices. Here, using density functional theory calculations, we demonstrate that Fe, Co, Ni substitutional impurities can not only induce magnetism in MoSe2 monolayer, but also convert the semiconducting MoSe2 to SGS/HM system. We also study the effects of mechanical strain on the electronic and magnetic properties of the doped monolayer. We show that for all TM impurities we considered, the system exhibits the robust SGS/HM behavior regardless of biaxial strain values. Moreover, it is found that the magnetic properties of TM-MoSe2 can effectively be tuned under biaxial strain by controlling the spin polarization of the 3d orbitals of Fe, Co, Ni atoms. Our findings offer a new route to designing the SGS/HM properties and modulating magnetic characteristics of the TM-MoSe2 system and may also facilitate the implementation of SGS/HM behavior and realization of spintronic devices based on other 2D materials.
  • Tunable electronic properties and enhanced ferromagnetism in Cr2Ge2Te6monolayer by strain engineering
    (2021-11-26) Liu, Lifei; Hu, Xiaohui; Wang, Yifeng; Krasheninnikov, Arkady V.; Chen, Zhongfang; Sun, Litao
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Recently, as a new representative of Heisenberg's two-dimensional (2D) ferromagnetic materials, 2D Cr2Ge2Te6 (CGT), has attracted much attention due to its intrinsic ferromagnetism. Unfortunately, the Curie temperature (T C ) of CGT monolayer is only 22 K, which greatly hampers the development of the applications based on the CGT materials. Herein, by means of density functional theory computations, we explored the electronic and magnetic properties of CGT monolayer under the applied strain. It is demonstrated that the band gap of CGT monolayer can be remarkably modulated by applying the tensile strain, which first increases and then decreases with the increase of tensile strain. In addition, the strain can increase the Curie temperature and magnetic moment, and thus largely enhance the ferromagnetism of CGT monolayer. Notably, the obvious enhancement of T C by 191% can be achieved at 10% strain. These results demonstrate that strain engineering can not only tune the electronic properties, but also provide a promising avenue to improve the ferromagnetism of CGT monolayer. The remarkable electronic and magnetic response to biaxial strain can also facilitate the development of CGT-based spin devices.