News and posts

Poster Session

 

Poster 1 Himanshu Bangar Indian Institute of Technology Delhi Spin pumping from Ni80Fe20 into monolayer TMD
Poster 2 Fernando Bartolome ICMA, Universidad de Zaragoza - CSIC Magnetism of FePc/Ag(110) + O2 Monolayer Phases
Poster 3 Magdalena Birowska University of Warsaw, Faculty of Physics, Poland 2D magnetic crystal: An ab initio study of MnPS3
Poster 4 Adam Budniak Technion - Israel Institute of Technology Exfoliated CrPS4 with promising photoconductivity
Poster 5 Xin Chen Department of Physics and Astronomy, Uppsala University 3d Transition Metal Clusters on Defected Graphene
Poster 6 Victor Manuel Garcia-Suarez University of Oviedo Electronics without bridging components
Poster 7 Md Anamul Hoque Chalmers University of Technology Charge - spin conversion in layered semimetal
Poster 8 Bogdan Karpiak Chalmers University of Technology Magnetic proximity in graphene/CGT heterostructure
Poster 9 Daljit Kaur DAV University, Jalandhar Magnetic investigations in VSe2 and CrSe2 nanorods
Poster 10 Roland Kawakami The Ohio State University Epitaxial growth of van der Waals magnets
Poster 11 Liqin Ke Ames Laboratory, U.S. Department of Energy Electron correlations and spin excitations in CrI3
Poster 12 Safe Khan UCL Intercalating sodium atoms in a vdWs magnet

 

2D Magnets, Heterostructures, and Spintronic Devices

Cheng Gong

Magnetism, one of the most fundamental physical properties, has revolutionized significant technologies such as data storage and biomedical imaging, and continues to bring forth new phenomena in emerging materials and reduced dimensions. The recently discovered magnetic 2D van der Waals materials (hereafter abbreviated as “2D magnets”) provide ideal platforms to enable the atomic-thin, flexible, lightweight magneto-optic and magnetoelectric devices. The seamless integration of 2D magnets with dissimilar electronic and photonic materials further opens up exciting possibilities for unprecedented properties and functionalities. In this tutorial, I will start with the fundamentals on 2D magnetism, and continue to speak on our experimental observation of 2D ferromagnet, analyze the current progress and the existing challenges in this emerging field, and show how we push the boundary by exploring the potential of 2D antiferromagnets for spintronics.

Quantum Phase Transition and Ising Superconductivity in transition metal dichalcogenides

Jianting Ye

Many recent discoveries on novel electronic states were made on 2D materials. Especially, by making artificial bilayer systems, new electronic states such as superconductivity and ferromagnetism have been reported. This talk will discuss quantum phase transitions and Ising superconductivity induced in 2D transition metal dichalcogenides. Using ionic gating, quantum phases such as superconductivity can be induced by field-effect on many 2D materials. In transition metal dichalcogenides, Ising-like paring states can form at K and K’ point of the hexagonal Brillouin zone. Also, we will discuss how to couple two Ising superconducting states through Josephson coupling by inducing superconductivity symmetrically in a suspended bilayer. This method can access electronic states with broken local inversion symmetry while maintaining the global inversion symmetry [3]. Controlling the Josephson coupling and spin-orbit coupling is an essential step for realizing many exotic electronics states predicted for the coupled bilayer superconducting system with strong spin-orbit interactions.

[1] Lu, J. M. Zheliuk O, et al., Science 350 1353 (2015).
[2] Lu, J. M. Zheliuk O, et al., Proceedings of the National Academy of Sciences 115 3551 (2018).
[3] Zheliuk O, Lu, J. M., et al., Nature Nanotechnology 14 1123 (2019).

Interface induced magnetism and skyrmions in layered heterostructure materials

Kang L Wang

 

Layered materials have recently been investigated for exploring magnetic properties.  This talk will discuss the magnetism of layered materials including those of magnetic doped materials as well the interface proximity-induced ferromagnetism by proximity with antiferromagnetic materials.  We will begin by describing layered magnetic doped topological insulators (TI), SbBiTe, for achieving quantum anomalous Hall.  Then we will discuss the proximity-induced magnetism in doped and undoped TIs when interfaced with different kinds of antiferromagnets, such as CrSb and MnTe, with a perpendicular and an in-plane Nel orders, respectively.  Antiferromagnets interfaced with a magnet is shown being to yield skyrmions, whose topological charge can be controlled by cooling under applied magnetic fields.   Atomically thin 2-D van der Waals magnetic materials (FeGeTe and alike) also have drawn significant interests. We observed interface Nel-type skyrmions in FeGeTe/WeTe2 heterostructures from the topological Hall effect below the temperature of 150 K, with the varying sizes for different temperatures, and the skyrmions were also confirmed by Lorentz transmission electron microscopy. A Dzyalosinskii-Moriya interaction with an energy of 1.0 mJ/m2, obtained from the aligned and stripe-like domain structure, is shown to be sufficiently large to support and stabilize the skyrmions.

 

 

 

Spin transport in magnetic 2D materials and heterostructures

Wei Han

 

The two-dimensional (2D) van der Waals magnets have provided new platforms for exploring quantum magnetism in the flatland and for designing 2D ferromagnet-based spintronics devices.

 

In this talk, I will discuss the spin transport in magnetic 2D materials and their heterostructures. Firstly, I will discuss magnon-mediated spin transport in an insulating 2D van der Waals antiferromagnetic MnPS3. Long distance magnon transport over several micrometers is observed in quasi-2D MnPS3. The transport of magnons could be described using magnon-dependent chemical potential, and long magnon relaxation length of several micrometers are obtained. Then, I will discuss the spin transport in a metallic 2D van der Waals ferromagnetic Fe0.29TaS2 and its heterostructures. Via systematically measuring Fe0.29TaS2 devices with different thickness, it is found that the dominant AHE mechanism is skew scattering in bulk single crystal, and the contribution from intrinsic mechanism emerges and become more relevant as the Fe0.29TaS2 thickness decrease. The spin-dependent scattering at the Fe0.29TaS2/superconductor interface will be also discussed, which reveals a large magnetoresistance that can be explained by the anisotropic Andreev reflection.

Exotic Spin transport in two-dimensional topological materials

José H. Garciá A. 

The manifestations of spin-orbit coupling in two-dimensional materials with reduced symmetries, such as MoTe2 or WTe2 in their 1T' or 1Td phases, can lead to hitherto unexplored ways to control the electronic spins. In this talk, I will present numerical simulations that demonstrate that due to a combination of a persistent canted spin texture and hotspot of the berry curvature, transition metal dichalcogenides show a tunable canted spin Hall effect. The canting angle depends on the microscopic spin-orbit coupling parameters and can be tuned through the electronic environment. Moreover, the persistent spin texture spam over a broad energy range allowing for long spin relaxations even in the metallic regime.  These findings vividly emphasize how crystal symmetry governs the intrinsic spin phenomenology and how it can be exploited to broaden the range and efficiency of spintronic functionalities. We also propose specific experimental guidelines for the confirmation of the effect.

Spin current effects in 2D magnets/heavy metal bilayers

Jing Shi

2D van der Waals (vdW) magnetic materials offer exciting new opportunities to study interfacial phenomena arising from or enhanced by the atomically flat interfaces. I will present our recent studies on three types of bilayer systems composed of vdW magnet and Pt: Cr2Ge2Te6/Pt, Fe3GeTe2/Pt, and Pt/CI3.  In each bilayer, the exfoliated vdW magnet consists of 10’s atomic layer units and the sputtered 5 nm Pt layer is either below or above the vdW magnet. In Cr2Ge2Te6/Pt and Pt/CI3, both Cr2Ge2Te6 and CI3 are insulating, we use induced magneto-transport properties in Pt to probe the spin states and magnetic domains in the insulating magnets [1-3]. Unlike these two insulating magnets, Fe3GeTe2 is a metallic ferromagnet which has the highest Curie temperature among all 2D vdW magnets, strong perpendicular magnetic anisotropy, and more resistive than Pt; therefore, it is an excellent 2D magnet for investigating the spin-orbit torque effects. We demonstrate that Fe3GeTe2/Pt has a spin-orbit torque efficiency comparable with that in the best bilayers made with 3D magnets and the Fe3GeTe2 magnetization can be switched with a relatively low critical current density [4]. These excellent properties show great potential of 2D materials for spintronic applications.

  1. B. Niu, T. Su, et al., Nano Lett. 20, 553 (2020). DOI: 10.1021/acs.nanolett.9b04282.
  2. M. Lohmann, et al., Nano Lett. 19, 2397 (2019). DOI: 10.1021/acs.nanolett.8b05121.
  3. T. Su, et al., 2D Materials 7, 045006 (2020). DOI:10.1088/2053-1583/ab9dd5.
  4. M. Alghamdi, M. Lohmann, et al., Nano Lett. 19, 4400 (2019). DOI: 10.1021/acs.nanolett.9b01043.

Orbital Hall Effect in 2D Materials

Tatiana G. Rappoport

The field of spintronics blossomed in the last decade, driven by the use of spin-orbit coupling to generate and manipulate spin currents in non-magnetic materials. In these systems, the efficient conversion between charge and spin currents is mediated by spin-orbit. Great progress in the manipulation of the orbital angular momentum of light has also been achieved in the last decades, leading to a large number of relevant applications. Still, electron orbitals in solids were less exploited, even though they are known to be essential in several underlying physical processes in material science. The orbital-Hall effect (OHE), similarly to the spin-Hall effect (SHE), refers to the creation of a transverse flow of orbital angular momentum that is induced by a longitudinally applied electric field. The OHE has been explored mostly in three dimensional metallic systems, where it can be quite strong. However, several of its features remain unexplored in two-dimensional (2D) materials.

We then investigate the OHE in multi-orbital 2D insulators, such as transition metal dichalcogenides. We show that the OHE in these systems is associated with exotic momentum-space orbital textures. This intrinsic property emerges from the interplay between orbital attributes and crystalline symmetries and does not rely on the spin-orbit coupling. Our results indicate that multi-orbital 2D materials can display robust OHE that may be used to generate orbital angular momentum accumulation, and produce strong orbital torques that are of great interest for developing novel spin-orbitronic devices.

Spin currents in collinear and non-collinear antiferromagnets

Jakub Zelezny

Spin currents are one of the key concepts of spintronics. In the past, two types of spin currents have been predominantly discussed and utilized: the spin-polarized current in ferromagnetic materials and the spin Hall effect. The spin-polarized current only exist in magnetic materials, has a non-relativistic origin and flows in the same direction as the charge current. In contrast, the spin Hall effect exists also in non-magnetic materials, has typically a relativistic origin and is transverse to the charge current. In recent years it has been discovered, however, that the phenomenology of spin currents is much richer. We have shown that the spin-polarized current can also exist in some antiferromagnetic materials and that a new type of spin Hall effect exists, which has origin in the magnetic order, and occurs in ferromagnetic and some antiferromagnetic materials [1]. This effect is now referred to as the magnetic spin Hall effect and has been recently experimentally demonstrated in non-collinear antiferromagnet Mn3Sn [2]. We have also shown that the conventional spin Hall effect can exist in some non-collinear magnetic systems even in absence of the relativistic spin-orbit interaction [3].
Furthermore, we have found that a non-relativistic magnetic spin Hall effect can exist in a collinear antiferromagnet [4]. Such system is distinct from systems where the transverse spin currents have been previously discussed because in the non-relativistic limit it conserves spin and thus it allows for spin-charge conversion in a spin-conserving system. Here we review the various types of spin currents that can occur in magnetic systems and give general conditions for their existence as well as a symmetry classification. In addition, we present calculations of these novel spin currents in various collinear and non-collinear antiferromagnets.

[1] J. Železný et al., Phys. Rev. Lett. 119, 187204 (2017)
[2] M. Kimata et al., Nature 565, 627–630 (2019)
[3] Y. Zhang et al: New J. Phys. 20 ( 2018 )
[4] R. G. Hernández el., arXiv:2002.07073 (2020)

Observation of a Magnetopiezoelectric Effect in Antiferromagnetic Metals

Yuki Shiomi

Magnetopiezoelectric effect [1,2], which refers to a linear strain response to electric currents and its inverse response in low-symmetric magnetic metals, is a generalization of magnetoelectric effects in insulators to metals. In metallic materials with high conduction-electron densities, static (dc) piezoelectric responses are not allowed, even if the metals have a symmetry group low enough to support a static polarization. This is because the static surface charge density is screened out by bulk conduction electrons. However, it was recently proposed [1] that dynamic distortion can arise in response to electric currents without screening effects in antiferromagnetic metals that simultaneously break time-reversal and spatial-inversion symmetries. Note that another magnetopiezoelectric effect of a topological origin has also been proposed recently [2].
Here, we have experimentally studied the magnetopiezoelectric effect [3-5] in antiferromagnetic conductors with low crystal symmetries: EuMnBi2 [3,5] (TN = 315 K) and CaMn2Bi2 [4] (TN = 150 K). Using laser Doppler vibrometry at low temperatures, we found that dynamic displacements emerge along the [110] direction upon application of ac electric currents in the c direction in EuMnBi2 below TN [3,5]. The displacement signals showing up in response to the electric current increase in proportion to the applied electric currents. We confirmed that such displacements are not observed along the c direction of EuMnBi2 or EuZnBi2 with nonmagnetic Zn ions, consistent with the symmetry requirement of the magnetopiezoelectric effect [1]. As temperature increases from the lowest temperature, the displacement signals decrease monotonically, showing that magnetopiezoelectric signals are larger for higher conductivity states as opposed to the conventional piezoelectric effect.

[1] H. Watanabe and Y. Yanase, Phys. Rev. B 96, 064432 (2017).
[2] D. Varjas, A. G. Grushin, R. Ilan, and J. E. Moore, Phys. Rev. Lett. 117, 257601 (2016).
[3] Y. Shiomi, H. Watanabe, H. Masuda, H. Takahashi, Y. Yanase, and S. Ishiwata, Phys. Rev. Lett. 122, 127207 (2019).
[4] Y. Shiomi, Y. Koike, N. Abe, H. Watanabe, and T. Arima, Phys. Rev. B 100, 054424 (2019).
[5] Y. Shiomi, H. Masuda, H. Takahashi, and S. Ishiwata, Sci. Rep. 10, 7574 (2020).