Search query: CrI3 xiaodong xu

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abstract: Controlling magnetism via electric fields addresses fundamental questions of magnetic phenomena and phase transitions1 3, and enables the development of electrically coupled spintronic devices, such as voltage controlled magnetic memories with low operation energy4 6. Previous studies on dilute magnetic semiconductors such as (Ga,Mn)As and (In,Mn)Sb have demonstrated large modulations of the Curie temperatures and coercive fields by altering the magnetic anisotropy and exchange interaction2,4,7 9. Owing to their unique magnetic properties10 14, the recently reported two dimensional magnets provide a new system for studying these features15 19. For instance, a bilayer of chromium triiodide (CrI3) behaves as a layered antiferromagnet with a magnetic field driven metamagnetic transition15,16. Here, we demonstrate electrostatic gate control of magnetism in CrI3 bilayers, probed by magneto optical Kerr effect (MOKE) microscopy. At fixed magnetic fields near the metamagnetic transition, we realize voltage controlled switching between antiferromagnetic and ferromagnetic states. At zero magnetic field, we demonstrate a time reversal pair of layered antiferromagnetic states that exhibit spin layer locking, leading to a linear dependence of their MOKE signals on gate voltage with opposite slopes. Our results allow for the exploration of new magnetoelectric phenomena and van der Waals spintronics based on 2D materials.Electrical control of magnetism in a bilayer of CrI3 enables the realization of an electrically driven magnetic phase transition and the observation of the magneto optical Kerr effect in 2D magnets.
author_names: Bevin Huang

Genevieve Clark

D R Klein

David MacNeill

Efren Navarro-Moratalla

Kyle L Seyler

N P Wilson

Michael A McGuire

David H Cobden

Di Xiao

Wang Yao

Pablo Jarillo-Herrero

Xiaodong Xu
title: Electrical control of 2D magnetism in bilayer CrI3
venue: Nature Nanotechnology
year: 2018

abstract: Monolayer valley semiconductors, such as tungsten diselenide (WSe2) possess valley pseudospin degrees of freedom that are optically addressable but degenerate in energy. Lifting the energy degeneracy by breaking time reversal symmetry is vital for valley manipulation. This has been realized by directly applying magnetic fields or via pseudomagnetic fields generated by intense circularly polarized optical pulses. However, sweeping large magnetic fields is impractical for devices, and the pseudomagnetic fields are only effective in the presence of ultrafast laser pulses. The recent rise of two dimensional (2D) magnets unlocks new approaches to controlling valley physics via van der Waals heterostructure engineering. Here, we demonstrate the wide continuous tuning of the valley polarization and valley Zeeman splitting with small changes in the laser excitation power in heterostructures formed by monolayer WSe2 and 2D magnetic chromium triiodide (CrI3) The valley manipulation is realized via the optical control of the CrI3 magnetization, which tunes the magnetic exchange field over a range of 20 T. Our results reveal a convenient new path toward the optical control of valley pseudospins and van der Waals magnetic heterostructures.
author_names: Kyle L Seyler

Ding Zhong

Bevin Huang

Xiayu Linpeng

N P Wilson

Takashi Taniguchi

Kenji Watanabe

Wang Yao

Di Xiao

Michael A McGuire

Kai-Mei C Fu

Xiaodong Xu
title: Valley Manipulation by Optically Tuning the Magnetic Proximity Effect in WSe2/CrI3 Heterostructures.
venue: Nano letters
year: 2018

abstract: An intrinsic magnetic tunnel junction An electrical current running through two stacked magnetic layers is larger if their magnetizations point in the same direction than if they point in opposite directions. These so called magnetic tunnel junctions, used in electronics, must be carefully engineered. Two groups now show that high magnetoresistance intrinsically occurs in samples of the layered material CrI3 sandwiched between graphite contacts. By varying the number of layers in the samples, Klein et al. and Song et al. found that the electrical current running perpendicular to the layers was largest in high magnetic fields and smallest near zero field. This observation is consistent with adjacent layers naturally having opposite magnetizations, which align parallel to each other in high magnetic fields. Science, this issue p. 1218, p. 1214 The atomic layers of the material CrI3 act as spin filters in graphite/CrI3/graphite junctions. Magnetic multilayer devices that exploit magnetoresistance are the backbone of magnetic sensing and data storage technologies. Here, we report multiple spin filter magnetic tunnel junctions (sf MTJs) based on van der Waals (vdW) heterostructures in which atomically thin chromium triiodide (CrI3) acts as a spin filter tunnel barrier sandwiched between graphene contacts. We demonstrate tunneling magnetoresistance that is drastically enhanced with increasing CrI3 layer thickness, reaching a record 19,000% for magnetic multilayer structures using four layer sf MTJs at low temperatures. Using magnetic circular dichroism measurements, we attribute these effects to the intrinsic layer by layer antiferromagnetic ordering of the atomically thin CrI3. Our work reveals the possibility to push magnetic information storage to the atomically thin limit and highlights CrI3 as a superlative magnetic tunnel barrier for vdW heterostructure spintronic devices.
author_names: Tiancheng Song

Xinghan Cai

Matisse Wei-Yuan Tu

Xiaoou Zhang

Bevin Huang

N P Wilson

Kyle L Seyler

Lin Zhu

Takashi Taniguchi

Kenji Watanabe

Michael A McGuire

David H Cobden

Di Xiao

Wang Yao

Xiaodong Xu
title: Giant tunneling magnetoresistance in spin filter van der Waals heterostructures
venue: Science
year: 2018

abstract: A van der Waals heterostructure of monolayer WSe2 and ferromagnetic CrI3 enables exceptional control of valley pseudospin. The integration of magnetic material with semiconductors has been fertile ground for fundamental science as well as of great practical interest toward the seamless integration of information processing and storage. We create van der Waals heterostructures formed by an ultrathin ferromagnetic semiconductor CrI3 and a monolayer of WSe2. We observe unprecedented control of the spin and valley pseudospin in WSe2, where we detect a large magnetic exchange field of nearly 13 T and rapid switching of the WSe2 valley splitting and polarization via flipping of the CrI3 magnetization. The WSe2 photoluminescence intensity strongly depends on the relative alignment between photoexcited spins in WSe2 and the CrI3 magnetization, because of ultrafast spin dependent charge hopping across the heterostructure interface. The photoluminescence detection of valley pseudospin provides a simple and sensitive method to probe the intriguing domain dynamics in the ultrathin magnet, as well as the rich spin interactions within the heterostructure.
author_names: Ding Zhong

Kyle L Seyler

Xiayu Linpeng

Ran Cheng

Nikhil Sivadas

Bevin Huang

Emma Schmidgall

Takashi Taniguchi

Kenji Watanabe

Michael A McGuire

Wang Yao

Di Xiao

Kai-Mei C Fu

Xiaodong Xu
title: Van der Waals engineering of ferromagnetic semiconductor heterostructures for spin and valleytronics
venue: Science Advances
year: 2017

abstract: Description
author_names: Tiancheng Song

Eric Anderson

Matisse Wei-Yuan Tu

Kyle L Seyler

Takashi Taniguchi

Kenji Watanabe

Michael A McGuire

Xiaosong Li

Ting Cao

Di Xiao

Wang Yao

Xiaodong Xu
title: Spin photovoltaic effect in magnetic van der Waals heterostructures
venue: Science advances
year: 2021

abstract: We have synthesized unique colloidal nanoplatelets of the two dimensional (2D) van der Waals ferromagnet CrI3 and have characterized these nanoplatelets structurally, magnetically, and by magnetic circular dichroism spectroscopy. The CrI3 nanoplatelets have lateral dimensions of ~25 nm and thicknesses of only ~4 nm, corresponding to just a few CrI3 monolayers. Magnetic and magneto optical measurements demonstrate robust 2D ferromagnetic ordering with Curie temperatures similar to bulk CrI3, despite their small size. These data also show magnetization steps akin to those observed in micron sized few layer 2D sheets associated with concerted spin reversal of individual CrI!3 layers within few layer van der Waals stacks. Similar data have also been obtained for CrBr3 and anion alloyed Cr(I1 xBrx)3 nanoplatelets. These results represent the first example of lateral nanostructures of 2D van der Waals ferromagnets of any composition. The demonstration of robust ferromagnetism at nanometer lateral dimensions opens new doors for miniaturization in spintronics devices based on van der Waals ferromagnets.
author_names: Michael C De Siena

Sidney E Creutz

Annie Regan

Paul Malinowski

Qianni Jiang

Kyle T Kluherz

Guomin Zhu

Zhong Lin

James J De Yoreo

Xiaodong Xu

Jiun Haw Chu

Daniel R Gamelin
title: 2D van der Waals Nanoplatelets with Robust Ferromagnetism.
venue: Nano letters
year: 2020

abstract: The coupling between spin and charge degrees of freedom in a crystal gives rise to magneto optical effects with applications in the sensitive detection of local magnetic order, optical modulation and data storage. In two dimensional magnets these effects manifest themselves in the large magneto optical Kerr effect1,2, spontaneous helical light emission3,4 from ferromagnetic (FM) monolayers and electric field induced Kerr rotation5 7 and giant second order non reciprocal optical effects8 in antiferromagnetic (AFM) bilayers. Here we demonstrate the tuning of inelastically scattered light through symmetry control in atomically thin chromium triiodide (CrI3) In monolayers, we found an extraordinarily large magneto optical Raman effect from an A1g phonon mode due to the emergence of FM order. The linearly polarized, inelastically scattered light rotates by ~40deg, more than two orders of magnitude larger than the rotation from the magneto optical Kerr effect under the same experimental conditions. In CrI3 bilayers, the same phonon mode becomes Davydov split into two modes of opposite parity, which exhibit divergent selection rules that depend on inversion symmetry and the underlying magnetic order. We demonstrate the magneto electrical control over these selection rules by activating or suppressing Raman activity for the odd parity phonon mode and the magneto optical rotation of scattered light from the even parity phonon mode. Our work underlines the unique opportunities provided by two dimensional magnets to control the combined time reversal and inversion symmetries to manipulate Raman optical selection rules and for exploring emergent magneto optical effects and spin phonon coupled physics.Symmetry control in atomically thin chromium triiodide enables the observation of tunable magneto optical Raman effects in the 2D limit.
author_names: Bevin Huang

John Cenker

Xiaoou Zhang

Essance L Ray

Tiancheng Song

Takashi Taniguchi

Kenji Watanabe

Michael A McGuire

Di Xiao

Xiaodong Xu
title: Tuning inelastic light scattering via symmetry control in the two dimensional magnet CrI3
venue: Nature Nanotechnology
year: 2020

abstract: Layered antiferromagnetism is the spatial arrangement of ferromagnetic layers with antiferromagnetic interlayer coupling. The van der Waals magnet chromium triiodide (CrI3) has been shown to be a layered antiferromagnetic insulator in its few layer form1, opening up opportunities for various functionalities2 7 in electronic and optical devices. Here we report an emergent nonreciprocal second order nonlinear optical effect in bilayer CrI3. The observed second harmonic generation (SHG; a nonlinear optical process that converts two photons of the same frequency into one photon of twice the fundamental frequency) is several orders of magnitude larger than known magnetization induced SHG8 11 and comparable to the SHG of the best (in terms of nonlinear susceptibility) two dimensional nonlinear optical materials studied so far12,13 (for example, molybdenum disulfide) We show that although the parent lattice of bilayer CrI3 is centrosymmetric, and thus does not contribute to the SHG signal, the observed giant nonreciprocal SHG originates only from the layered antiferromagnetic order, which breaks both the spatial inversion symmetry and the time reversal symmetry. Furthermore, polarization resolved measurements reveal underlying C2h crystallographic symmetry and thus monoclinic stacking order in bilayer CrI3, providing key structural information for the microscopic origin of layered antiferromagnetism14 18. Our results indicate that SHG is a highly sensitive probe of subtle magnetic orders and open up possibilities for the use of two dimensional magnets in nonlinear and nonreciprocal optical devices.Large second harmonic generation is observed in antiferromagnetic bilayers of CrI3, providing information about the microscopic origin of layered antiferromagnetism and motivating the use of two dimensional magnets in nonlinear optical devices.
author_names: Zeyuan Sun

Yangfan Yi

Tiancheng Song

Genevieve Clark

Bevin Huang

Yuwei Shan

Shuang Wu

Di Huang

Chunlei Gao

Zhanghai Chen

Michael A McGuire

Ting Cao

Di Xiao

Wei-Tao Liu

Wang Yao

Xiaodong Xu

Shiwei Wu
title: Giant nonreciprocal second harmonic generation from antiferromagnetic bilayer CrI3
venue: Nature
year: 2019

abstract: Magnetic anisotropy is crucially important for the stabilization of two dimensional (2D) magnetism, which is rare in nature but highly desirable in spintronics and for advancing fundamental knowledge. Recent works on CrI3 and CrGeTe3 monolayers not only led to observations of the long time sought 2D ferromagnetism, but also revealed distinct magnetic anisotropy in the two systems, namely Ising behavior for CrI3 versus Heisenberg behavior for CrGeTe3. Such magnetic difference strongly contrasts with structural and electronic similarities of these two materials, and understanding it at a microscopic scale should be of large benefits. Here, first principles calculations are performed and analyzed to develop a simple Hamiltonian, to investigate magnetic anisotropy of CrI3 and CrGeTe3 monolayers. The anisotropic exchange coupling in both systems is surprisingly determined to be of Kitaev type. Moreover, the interplay between this Kitaev interaction and single ion anisotropy (SIA) is found to naturally explain the different magnetic behaviors of CrI3 and CrGeTe3. Finally, both the Kitaev interaction and SIA are further found to be induced by spin orbit coupling of the heavy ligands (I of CrI3 or Te of CrGeTe3) rather than the commonly believed 3d magnetic Cr ions.Monolayer magnetism: Kitaev interaction comes into playInterplay between two anisotropic interactions Kitaev and single ion is responsible for magnetism in ferromagnetic thin films. Teams led by Hongjun Xiang at Fudan University in China and Laurent Bellaiche at the University of Arkansas in the US led to the use of first principles calculations to elucidate magnetic anisotropy in two different two dimensional ferromagnetic materials with different magnetic behaviors. By developing a predictive Hamiltonian and a tight binding model, the origin of two dimensional magnetism in chromium iodine and chromium germanium tellurium monolayers was revealed to be Kitaev interactions and their interplay with single ion anisotropy. Both the Kitaev and single ion anisotropies were induced by the spin orbit coupling of the heavy ligand elements iodine and tellurium. Research into Kitaev interactions in unconventional systems may contribute towards better understanding of interesting physics.
author_names: Changsong Xu

Junsheng Feng

Hongjun Xiang

Laurent Bellaiche
title: Interplay between Kitaev interaction and single ion anisotropy in ferromagnetic CrI3 and CrGeTe3 monolayers
venue: npj Computational Materials
year: 2018

abstract: Stacking order can influence the physical properties of two dimensional van der Waals materials1,2. Here we applied hydrostatic pressure up to 2 GPa to modify the stacking order in the van der Waals magnetic insulator CrI3. We observed an irreversible interlayer antiferromagnetic to ferromagnetic transition in atomically thin CrI3 by magnetic circular dichroism and electron tunnelling measurements. The effect was accompanied by a monoclinic to rhombohedral stacking order change characterized by polarized Raman spectroscopy. Before the structural change, the interlayer antiferromagnetic coupling energy can be tuned up by nearly 100% with pressure. Our experiment reveals the interlayer ferromagnetic ground state, which is established in bulk CrI3 but not observed in native exfoliated thin films. The observed correlation between the magnetic ground state and the stacking order is in good agreement with first principles calculations3 8 and suggests a route towards nanoscale magnetic textures by moire engineering3,9. Pressure induced changes in the magnetic order of atomically thin van der Waals crystals are revealed and attributed to changes in the stacking arrangement.
author_names: Tingxin Li

Shengwei Jiang

Nikhil Sivadas

Zefang Wang

Yang Xu

Daniel Weber

Joshua E Goldberger

Kenji Watanabe

Takashi Taniguchi

Craig J Fennie

Kin Fai Mak

Jie Shan
title: Pressure controlled interlayer magnetism in atomically thin CrI3
venue: Nature Materials
year: 2019