Spinel compounds are of great interest in both fundamental and application-oriented perspectives due to the geometric magnetic frustration inherent to their lattice and the resulting complex magnetic states.Here,we ap...Spinel compounds are of great interest in both fundamental and application-oriented perspectives due to the geometric magnetic frustration inherent to their lattice and the resulting complex magnetic states.Here,we applied x-ray diffraction,magnetization,heat capacity and powder inelastic neutron scattering measurements,along with theoretical calculations,to study the exotic properties of chromite-spinel oxides CoCr_(2)O_(4) and MnCr_(2)O_(4).The temperature dependence of the phonon spectra provides an insight into the correlation between oxygen motion and the magnetic order,as well as the magnetoelectric effect in the ground state of MnCr_(2)O_(4).Moreover,spin-wave excitations in CoCr_(2)O_(4) and MnCr_(2)O_(4) are compared with Heisenberg model calculations.This approach enables the precise determination of exchange energies and offers a comprehensive understanding of the spin dynamics and relevant exchange interactions in complicated spiral spin ordering.展开更多
Cr_2Ge_2Te_6is an intrinsic ferromagnetic semiconductor with van der Waals type layered structure,thus represents a promising material for novel electronic and spintronic devices.Here we combine scanning tunneling mic...Cr_2Ge_2Te_6is an intrinsic ferromagnetic semiconductor with van der Waals type layered structure,thus represents a promising material for novel electronic and spintronic devices.Here we combine scanning tunneling microscopy and first-principles calculations to investigate the electronic structure of Cr_2Ge_2Te_6.Tunneling spectroscopy reveals a surprising large energy level shift and change of energy gap size across the ferromagnetic to paramagnetic phase transition,as well as a peculiar double-peak electronic state on the Cr-site defect.These features can be quantitatively explained by density functional theory calculations,which uncover a close relationship between the electronic structure and magnetic order.These findings shed important new lights on the microscopic electronic structure and origin of magnetic order in Cr_2Ge_2Te_6.展开更多
Spin liquids are exotic materials where the magnetic order is absent due to fluctuations at any finite temperature less than the spin interaction.Their occurrence is attributed to a high degree of ground state degener...Spin liquids are exotic materials where the magnetic order is absent due to fluctuations at any finite temperature less than the spin interaction.Their occurrence is attributed to a high degree of ground state degeneracy.Wannier showed in 1950 that such a large degeneracy of ground state can theoretically take place in a two-dimensional(2D)triangular lattice with Ising spins,a classically geometrical frustrated lattice mode.So far,the geometrically frustrated lattice has a large family of systems:edge-shared triangles as a triangular lattice and corner-shared triangles as a kagomélattice in a 2D system and corner-sharing tetrahedra as a pyrochlore lattice in a three-dimensional system,etc.展开更多
Two-dimensional(2D)Cr_((1+δ))Te_(2)materials exhibit strong magnetic ordering and high Curie temperatures,making them attractive for various applications.It is crucial to achieve controllable synthesis for their succ...Two-dimensional(2D)Cr_((1+δ))Te_(2)materials exhibit strong magnetic ordering and high Curie temperatures,making them attractive for various applications.It is crucial to achieve controllable synthesis for their successful integration into device technologies.In this study,we present the synthesis of phase-controllable 2D Cr_((1+δ))Te_(2)films on the Si(111)substrate via molecular beam epitaxy.The composition and phase transition of the as-grown Cr_((1+δ))Te_(2)films are characterized by using in-situ reflection high-energy electron diffraction,scanning tunneling microscopy,ex-situ X-ray photoelectron spectroscopy,X-ray diffraction,and theoretical calculations.At low growth temperatures,by carefully adjusting the film thickness from 2 to more than 3 layers,we achieve precise control over the phase of Cr_((1+δ))Te_(2),fromCrTe_(2)to Cr intercalated Cr_(2)Te_(3).At a relatively elevated growth temperature,it is demonstrated that the Cr_((1+δ))Te_(2)phase is independent of the film thickness,only Cr_(2)Te_(3)forms and its growth mode is thickness-dependent.These phase transitions at low growth temperatures and growth mode changes at elevated growth temperatures are attributed to interfacial effects and the phase stability of Cr_((1+δ))Te_(2)compounds.Additionally,we utilize scanning tunneling spectroscopy and computations to gain insights into the electronic properties of Cr_(2)Te_(3).The magnetic measurements reveal that the 30-nm Cr_(2)Te_(3)film exhibits ferromagnetic behavior with a Curie temperature of about 180 K.Our work offers a robust method for the controllable growth of high-quality 2D Cr_((1+δ))Te_(2)films on Si substrates,providing an ideal platform for investigating their intrinsic properties and advancing the development of 2D magnet-based spintronics devices.展开更多
基金the financial support from the National Key Research and Development Program of China(Grant No.2022YFA1402702)the National Science Foundation of China(Grant Nos.U2032213 and 12004243)+8 种基金the National Science Foundation of China(Grant No.12274412)the Interdisciplinary Program of Wuhan National High Magnetic Field Center(Grant No.WHMFC 202122)Huazhong University of Science and Technologythe support from the National Natural Science Foundation of China(Grant No.52101236)Guangdong Basic and Applied Basic Research Foundation(Grant No.2021B1515140014)the Guangdong Provincial Key Laboratory of Extreme Conditionsfinancial support from the National Key Research and Development Program of China(Grant Nos.2021YFA1600201 and 2023YFA1607402)the support of NSF-DMR-2003117supported by a beamtime allocation RB1910163 from the Science and Technology Facilities Council。
文摘Spinel compounds are of great interest in both fundamental and application-oriented perspectives due to the geometric magnetic frustration inherent to their lattice and the resulting complex magnetic states.Here,we applied x-ray diffraction,magnetization,heat capacity and powder inelastic neutron scattering measurements,along with theoretical calculations,to study the exotic properties of chromite-spinel oxides CoCr_(2)O_(4) and MnCr_(2)O_(4).The temperature dependence of the phonon spectra provides an insight into the correlation between oxygen motion and the magnetic order,as well as the magnetoelectric effect in the ground state of MnCr_(2)O_(4).Moreover,spin-wave excitations in CoCr_(2)O_(4) and MnCr_(2)O_(4) are compared with Heisenberg model calculations.This approach enables the precise determination of exchange energies and offers a comprehensive understanding of the spin dynamics and relevant exchange interactions in complicated spiral spin ordering.
基金supported by the Basic Science Center Project of NSFC(51788104)the MOST of China(2015CB921000)+6 种基金the support from Tsinghua University Initiative Scientific Research Program and NSFC(11774196)S.H.Z.is supported by the National Postdoctoral Program for Innovative Talents of China(BX201600091)the China Postdoctoral Science Foundation(2017M610858)the support of the National Key Research and Development Program(2016YFA0300404)NSFC Grant(11674326)the Joint Funds of NSFC and the Chinese Academy of Sciences’Large-Scale Scientific Facility(U1432139)supported in part by the Beijing Advanced Innovation Center for Future Chip(ICFC)
文摘Cr_2Ge_2Te_6is an intrinsic ferromagnetic semiconductor with van der Waals type layered structure,thus represents a promising material for novel electronic and spintronic devices.Here we combine scanning tunneling microscopy and first-principles calculations to investigate the electronic structure of Cr_2Ge_2Te_6.Tunneling spectroscopy reveals a surprising large energy level shift and change of energy gap size across the ferromagnetic to paramagnetic phase transition,as well as a peculiar double-peak electronic state on the Cr-site defect.These features can be quantitatively explained by density functional theory calculations,which uncover a close relationship between the electronic structure and magnetic order.These findings shed important new lights on the microscopic electronic structure and origin of magnetic order in Cr_2Ge_2Te_6.
基金G.T.L and J.M.thank the financial support from the National Key Research and Development Program of China(No.2022YFA1402702)National Science Foundation of China(Nos.U2032213,12004243)+1 种基金J.M.thanks the interdisciplinary program Wuhan National High Magnetic Field Center(No.WHMFC 202122)Huazhong University of Science and Technology.G.T.L thanks the project funded by China Postdoctoral Science Foundation(No.2022T150414).
文摘Spin liquids are exotic materials where the magnetic order is absent due to fluctuations at any finite temperature less than the spin interaction.Their occurrence is attributed to a high degree of ground state degeneracy.Wannier showed in 1950 that such a large degeneracy of ground state can theoretically take place in a two-dimensional(2D)triangular lattice with Ising spins,a classically geometrical frustrated lattice mode.So far,the geometrically frustrated lattice has a large family of systems:edge-shared triangles as a triangular lattice and corner-shared triangles as a kagomélattice in a 2D system and corner-sharing tetrahedra as a pyrochlore lattice in a three-dimensional system,etc.
基金funding provided by Shanghai Jiao Tong UniversityNSFC(Grants No.11790313,No.92065201,No.11874256,No.11874258,No.12074247,No.12174252 and No.11861161003)+3 种基金the Ministry of Science and Technology of China(Grants No.2019YFA0308600,2020YFA0309000)the Strategic Priority Research Program of Chinese Academy of Sciences(Grant No.XDB28000000)the Science and Technology Commission of Shanghai Municipality(Grants No.2019SHZDZX01,No.19JC1412701,No.20QA1405100)for financial supportfinancial support from Innovation program for Quantum Science and Technology(Grant No.2021ZD0302500).
文摘Two-dimensional(2D)Cr_((1+δ))Te_(2)materials exhibit strong magnetic ordering and high Curie temperatures,making them attractive for various applications.It is crucial to achieve controllable synthesis for their successful integration into device technologies.In this study,we present the synthesis of phase-controllable 2D Cr_((1+δ))Te_(2)films on the Si(111)substrate via molecular beam epitaxy.The composition and phase transition of the as-grown Cr_((1+δ))Te_(2)films are characterized by using in-situ reflection high-energy electron diffraction,scanning tunneling microscopy,ex-situ X-ray photoelectron spectroscopy,X-ray diffraction,and theoretical calculations.At low growth temperatures,by carefully adjusting the film thickness from 2 to more than 3 layers,we achieve precise control over the phase of Cr_((1+δ))Te_(2),fromCrTe_(2)to Cr intercalated Cr_(2)Te_(3).At a relatively elevated growth temperature,it is demonstrated that the Cr_((1+δ))Te_(2)phase is independent of the film thickness,only Cr_(2)Te_(3)forms and its growth mode is thickness-dependent.These phase transitions at low growth temperatures and growth mode changes at elevated growth temperatures are attributed to interfacial effects and the phase stability of Cr_((1+δ))Te_(2)compounds.Additionally,we utilize scanning tunneling spectroscopy and computations to gain insights into the electronic properties of Cr_(2)Te_(3).The magnetic measurements reveal that the 30-nm Cr_(2)Te_(3)film exhibits ferromagnetic behavior with a Curie temperature of about 180 K.Our work offers a robust method for the controllable growth of high-quality 2D Cr_((1+δ))Te_(2)films on Si substrates,providing an ideal platform for investigating their intrinsic properties and advancing the development of 2D magnet-based spintronics devices.
