Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session A52: van der Waals Magnets IFocus Recordings Available
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Sponsoring Units: GMAG DMP FIAP Chair: Xiaoxiao Zhang, University of Florida Room: McCormick Place W-475A |
Monday, March 14, 2022 8:00AM - 8:36AM |
A52.00001: Light –controlled magnetism in 2D vanadium dichalchogenides and related semiconductors Invited Speaker: Valery Ortiz Jimenez Atomically thin transition metal dichalcogenide (TMD) semiconductors hold enormous potential for modern optoelectronic devices, magnetic sensing, and quantum computing applications. By inducing long-range ferromagnetism (FM) in these semiconductors by stacking them with other magnetic TMDs or through the introduction of small amounts of a magnetic dopant, it is possible to extend their potential in emerging spintronic applications. Here, we demonstrate light-mediated, room temperature (RT) FM in V-doped WS2 (V-WS2) and V-WSe2 monolayers and in VSe2/TS2 (T=Mo, W) heterostructures. In our work, we developed a novel, ultrasensitive magnetometer using the principle of magneto-LC resonance, which employs a soft ferromagnetic microwire coil driven near resonance. This allows us to probe real-time change in the magnetic permeability of a sample placed in the core of the coil, upon application of an external stimulus. Using this technique, we measured light intensity dependent magnetic permeability of V-WS2 (V-WSe2) monolayers subject to light illumination. The magnetic permeability of the monolayer is found to depend on laser intensity, confirming light control of RT magnetism in this 2D material. Guided by density functional theory calculations, we attribute this phenomenon to excess holes in the conduction and valence bands, and carriers trapped in magnetic doping states, which mediates the magnetization of the V-WS2 (V-WSe2) monolayer. We also used demonstrated light-mediated RT magnetism in VSe2/MoS2 or VSe2/WS2 heterostructures. This is attributed to photon absorption at the MoS2 (WS2) layer that generates electron-hole pairs, thus mediating their magnetization, an effect which is enhanced by confinement effects. These findings provide unique routes to exploit light-controlled FM at RT in 2D-TMD dilute magnetic semiconductors and their heterostructures and potentially establish a new subfield named “photo-spintronics”. |
Monday, March 14, 2022 8:36AM - 8:48AM |
A52.00002: All optical control of magnetization in 2D atomically thin CrI3 Peiyao Zhang, Ting-Fung Chung, Warren L Huey, Sui Yang, Joshua E Goldberger, Xiang Zhang Switching magnetization via circularly polarized photons addresses fundamental questions of magneto-optical interactions between circularly polarized photons and magnetic materials, which enables the development of magneto-optical memory devices, such as all-optical magnetic recorder. Recently discovered 2D magnetic materials have offered a great platform to study the control of magnetic properties. Many experimental efforts have been focused on the control of magnetic properties using methods including application of an electric field, electrostatic doping, strain, pressure, etc. Controlling the magnetization without an application of external magnetic field has attracted much interests in the field of spintronics. Here, we present an all-optical helicity dependent control of magnetization in 2D atomically thin CrI3. Our results allow for a better understanding of the all-optical magnetization switching mechanisms and open up possibilities on all optical control of 2D magnet based ferromagnetic bits. |
Monday, March 14, 2022 8:48AM - 9:00AM |
A52.00003: Photoexcited carrier dynamics and magnetic order-induced band splittings in CrSiTe3 Leigh M Smith, Giriraj Jnawali, Seyyedesadaf Pournia, Eli A Zoghlin, Iraj Abbasian Shojaei, Stephen D Wilson, Jacob Gayles Magnetic van der Waals 2D ferromagnetic semiconductors hold great promise for future spin-optoelectronic. Understanding how materials properties are impacted by magnetic ordering and the spin-orbit interactions is critically needed information for the development of applications. We use ultrafast transient reflectance (TR) and photocurrent (PC) spectroscopies to investigate the band structure and photoexcited carrier dynamics of a CrSiTe3 (CST) nanosheet in the paramagnetic (PM, 300K) and ferromagnetic (FM, 10 K) phases. We observe both a decrease of the direct bandgap and emergence of a 120 meV splitting of the direct optical transition when the FM phase is present. DFT band structure calculations which include spin-orbit coupling suggest that the band modifications are driven by a FM ordering-induced band splitting between the Te ?? and the Cr ?? states at the valence and conduction band edges. We find that the majority of carriers photoexcited at the direct gap recombine within picoseconds through defect-mediated recombination, but that 2-3 % of the electrons scatter into indirect conduction band valleys resulting in very long-lived electrons and holes. Those long-lived carriers contribute to the broadband PC response of CST devices that also features indirect absorption. These results provide critical insights into the dynamics and energy landscape of photoexcited electrons and holes, and how they are impacted by spin-ordering effects in layered ferromagnets. |
Monday, March 14, 2022 9:00AM - 9:12AM |
A52.00004: Magnetic proximity effect in van der Waals heterostructures Yusen Ye, Di Xiao, Yafei Ren, Chong Wang, Ting Cao, Jimin Qian Monolayer transition metal dichalcogenide (TMD) are two-dimensional (2D) semiconductors that possess valley degrees of freedom. The two inequivalent valleys at K and K' form a Kramer's pair, where they are degenerate states in the presence of time-reversal symmetry. To lift this degeneracy, time-reversal symmetry must be broken, and one way of doing so is to stack TMD onto a 2D magnet. In this talk, using physically motivated models and first-principles calculations, we will address how stacking of a monolayer TMD with a 2D magnet could tune the lattice and electronic structures of TMD, with a particular focus on the control of the valley degrees of freedom. We will also address the physical consequences of interlayer coupling and proximity effects from various magnetic phases. |
Monday, March 14, 2022 9:12AM - 9:24AM |
A52.00005: Magnetic Properties of Epitaxial Fe3GeTe2 and Their Heterostructures with Topological Insulators Wenyi Zhou, Alexander Bishop, Igor Lyalin, Shuyu Cheng, Menglin Zhu, Jinwoo Hwang, Roland K Kawakami As a 2D van der Waals material, Fe3GeTe2 (FGT) stands out because of its strong perpendicular magnetic anisotropy and high Curie temperature (TC). A lot of interesting phenomena have been studied in FGT thin films and heterostructures, such as skyrmions and room temperature ferromagnetism. However, most studies are based on exfoliated FGT. Here, we ultilize molecular beam epitaxy for high-quality epitaxial monolayer and multilayer FGT. Cross-sectional transmission electron microscopy (TEM) shows an atomically-sharp interface between the FGT film and Ge(111) substrate. We also developed heterostructures with topological insulators such as FGT/Bi2Te3 and FGT/SnTe which are very interesting for spin-orbit torque and magnetic topological states. Magneto-optic Kerr Effect (MOKE) and Anomalous Hall Effect (AHE) were used to confirm square hysteresis loops and MOKE microscopy made it possible for us to catch a glimpse of its domain structure during magnetization switching. By doing MOKE measurements on both FGT/Ge and FGT/Bi2Te3, we observed an enhancement of TC in the FGT/Bi2Te3 system. Finally, we utilized MOKE to probe the few-layer limit to determine the layer dependence of FGT films on Bi2Te3. |
Monday, March 14, 2022 9:24AM - 9:36AM |
A52.00006: Coupling between magnetic order and charge transport in the two-dimensional magnetic semiconductor CrSBr Evan J Telford, Avalon H Dismukes, Raymond L Dudley, Ren A Wiscons, Kihong Lee, Jessica Yu, Sara Shabani, Allen O Scheie, Kenji Watanabe, Takashi Taniguchi, Di Xiao, Abhay N Pasupathy, Colin Nuckolls, Xiaoyang Zhu, Cory R Dean, Xavier Roy Semiconductors, featuring tunable electrical transport, and magnets, featuring tunable spin configurations, form the basis of nearly all information technologies. A long-standing challenge has been to realize materials that integrate these two distinct properties. Two-dimensional (2D) materials offer a new platform to realize this concept, but the recently discovered 2D magnetic semiconductors are found to be electrically insulating in their magnetic phase. Here we demonstrate tunable electron transport within the magnetic phase of the 2D semiconductor CrSBr and reveal strong coupling between its magnetic order and charge transport. This provides a previously unrealized opportunity to characterize the layer-dependent magnetic order of CrSBr down to the monolayer via magnetotransport. Exploiting the sensitivity of magnetoresistance to magnetic order, we uncover a second magnetic transition ascribed to the ferromagnetic ordering of magnetic defects. The magnetoresistance of this hidden magnetic phase can be dynamically and reversibly tuned by varying the carrier concentration using an electrostatic gate, providing a new mechanism for controlling charge transport in 2D magnets. |
Monday, March 14, 2022 9:36AM - 9:48AM |
A52.00007: Reversible strain-induced magnetic phase transition in a van der Waals magnet John Cenker, Shivesh Sivakumar, Kaichen Xie, Aaron Miller, Pearl S Thijssen, Zhaoyu Liu, Avalon H Dismukes, Jordan M Fonseca, Eric Anderson, Xiaoyang Zhu, Xavier Roy, Di Xiao, Jiun-Haw Chu, Ting Cao, Xiaodong Xu Mechanical deformation of a crystal can have a profound effect on its physical properties. For instance, even small modifications of bond geometry can completely change the size and sign of magnetic-exchange interactions, and thus the magnetic ground state. Here, we report drastic strain tuning of the magnetic properties of the A-type layered antiferromagnetic semiconductor CrSBr. This is achieved by designing a strain device which can apply continuous, in-situ uniaxial tensile strain approaching several percent to 2D materials at cryogenic temperatures. Using this apparatus, we realize a reversible strain-induced antiferromagnetic to ferromagnetic phase transition at zero magnetic field and strain control of the out-of-plane spin canting process. First-principles calculations reveal that the tuning of the in-plane lattice constant strongly modifies the interlayer magnetic exchange interaction, which changes sign at the critical strain. Our work creates new opportunities for harnessing the strain control of magnetism and other electronic states in low dimensional materials and heterostructures. |
Monday, March 14, 2022 9:48AM - 10:00AM |
A52.00008: Thermally generated magnon transport in quasi-two-dimensional antiferromagnetic materials Frank Feringa, Bart Van Wees Magnon spintronics studies the transport of spin currents through an insulating and magnetically ordered material using magnons [1]. Electrically and thermally induced magnons can be transported in insulating ferromagnetic [2] and antiferromagnetic materials [3]. In particular, antiferromagnetic materials have interesting properties for future spintronic applications: they possess no net magnetic moment and are therefore robust against magnetic perturbations and have ultrafast dynamics. We investigate the transport of magnons in the insulating antiferromagnetic van der Waals materials: MnPS3, NiPS3, FePS3, and CoPS3. The spin structure depends on the transition metal: MnPS3 and FePS3 are uniaxial antiferromagnets whereas NiPS3 and CoPS3 are easy plane antiferromagnets. The spin currents are injected electrically, via the spin Hall effect, and thermally, via joule heating, and detected via the inverse spin Hall effect using the nonlocal geometry as described in Ref.[2]. We observe thermally injected magnon transport in MnPS3, NiPS3, and FePS3 as a function of an in-plane orientation of an external magnetic field [4]. Next to that, the Spin Hall magnetoresistance measurements in Pt on top of FePS3 show a strong correlation to the magnetic susceptibility of FePS3 [5]. |
Monday, March 14, 2022 10:00AM - 10:12AM |
A52.00009: Topological semimetal and insulator features in ferromagnetic MPX3 (M = Mn, Fe, Co, Ni; X= S, Se) monolayers Natalya Sheremetyeva, Anay Saraf, Sinead M Griffin, Geoffroy Hautier Two-dimensional layered materials (2DMs) continue to attract interest as building blocks for novel devices as their properties can be tuned by controlling such parameters as e.g. layer-stacking order or external pressure. Moreover, the 2DM family has recently grown to include robust magnetic materials allowing for an additional degree of freedom via control of the magnetic-ordering states. Here, the electronic and topological properties of MPX3 (M = Mn, Fe, Co, Ni, and X= S, Se) monolayers in their ferromagnetic state were studied using density functional theory. Monolayer MnPSe3 exhibits topological semimetal features that transform into topological insulator features when spin-orbit-coupling is introduced. While monolayer MnPS3 is a trivial insulator, topological features are found under a small pressure of 2%. These findings are further investigated using symmetry indicator approaches where we identify the origins of the non-trivial topology in these materials and suggest routes for achieving it experimentally. A thorough discussion on the choice of the Hubbard-U parameter is also presented. Our findings provide a potential avenue for uncovering new topological phases in ferromagnetic non-groundstates after the application of an external magnetic field. |
Monday, March 14, 2022 10:12AM - 10:24AM |
A52.00010: Linear polarized photoluminescence from crystalline nanoflakes of NiPS3 antiferromagnet prepared by wet-chemical synthesis Vignesh Chandrasekaran, David G Parobek, Andres E Llacsahuanga Allcca, Xiangzhi Li, Huan Zhao, Andrew Jones, Sergei A Ivanov, Han Htoon Using photoluminescence (PL) spectroscopy, we observe crystalline nanoflakes of NiPS3 prepared by wet-chemical synthesis with a lateral size of about tens of nm and a thickness ranging from few to tens of nm having sharp emission peaks (< 0.1nm linewidth) with the emission wavelengths distributed from 560nm to 680nm (~2.2eV to 1.8eV) and exhibiting blinking, spectral diffusion and photobleaching characteristics. Interestingly, they show strong linear polarized emission (95% to 100%) which are dependent on the excitation linear polarization. In comparison, the exfoliated layers of 2D vdW NiPS3 have a sharp emission peak at 842nm (1.472eV) which also shows a linear polarized emission (70% to 80%) with no dependence to the excitation polarization. We also observe multiple equidistant phonon replicas in our nanoflakes similar to the reported phonon bound states in 2D vdW NiPS3. Considering the antiferromagnetic nature of NiPS3 and the linear polarized emission, we attribute the sharp emission peaks to the spin-induced process analogous to the 2D vdW NiPS3. |
Monday, March 14, 2022 10:24AM - 10:36AM |
A52.00011: Nonlinear Piezomagnetism in Antiferromagnetic Dirac System Zhenqiao Huang Piezomagnetism (PZM) is characterized by a linear coupling between magnetization and mechanical strain in crystals. Recent work proposes that PZM can be realized in the C-paired spin valley locking (SVL) system with finite doping. Here we systematically investigate PZM in strained C-paired SVL systems and conclude two scenarios where one needs finite doping and the other does not. Particularly, in antiferromagnetic (AFM) Dirac systems with C-paired SVL, PZM in the second scenario can present a nonlinear coupling between net magnetization and strain. We refer to this nonlinear coupling in the Dirac system as nonlinear PZM, which is beyond the PZM with linear coupling in the previous works. Via first-principles calculation, this nonlinear PZM is predicted to exist in monolayer AFM Fe2S which is a C-paired SVL system with Dirac cones. In sum, we discover nonlinear PZM in the Dirac system, which not only offers a more comprehensive understanding of PZM but also provides more opportunities for the device application of AFM materials. |
Monday, March 14, 2022 10:36AM - 10:48AM |
A52.00012: Optical and magnetic properties of heterostructures of magnetic 2D materials Alejandro Molina-Sanchez, Fayssal Mahrouche, Karim Rezouali, Joaquin Fernández-Rossier The combination of magnetic 2D materials with distinct magnetic order in heterostructures can lead to layered materials with new magnetic properties. In this work, we study heterobilayers composed of VOCl and FeOCl monolayers, two insulating oxides with distinct magnetic order. VOCl monolayers are ferromagnetic and FeOCl monolayers are antiferromagnetic. We compute the magnetic anisotropy of the heterobilayers using density functional theory calculations including the Hubbard correction. In addition we propose a spin model to describe the first principles calculations. We have found that interlayer coupling is weak and hence the magnetic order of each monolayers is preserved in the heterobilayer. Thus, the heterobilayer combines antiferromagnetic and ferromagnetic orders. Interlayer exchange should lead both to exchange bias and to the emergence of hybrid collective modes that combine FM and AF magnons. The energy band of the heterobilayer show a type II band alignment, and feature spin-splitting of the states of the AF layer due to the breaking of the inversion symmetry. |
Monday, March 14, 2022 10:48AM - 11:00AM |
A52.00013: Current-induced quasiparticle magnetic multipole moments Hua Chen, Muhammad Tahir Magnetic ordering that goes beyond the standard dipolar order has attracted significant attention in recent years, but it remains an open question how to effectively manipulate such nontrivial order using external perturbations. In this context, we present a theory for Cartesian magnetic multipole moments carried by electric currents in either magnetic or non-magnetic conductors. We consider the magnetic multipole moments of quasiparticle wave packets, which can circumvent the conceptual difficulties in defining higher-order multipole moments in periodic crystals. As a prototypical example, we pointed out that the low-energy quasiparticles in multi-layer black phosphorous host magnetic octupole moments, which can result in a nonequilibrium magnetic octupole polarization in the presence of electric currents. |
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