Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session K53: Emergent Spin Phenomena in 2D LimitFocus Recordings Available
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Sponsoring Units: GMAG DMP Chair: Jaime Fernandez-Baca, Oak Ridge National Laboratory Room: McCormick Place W-475B |
Tuesday, March 15, 2022 3:00PM - 3:36PM |
K53.00001: Longitudinal magnon decay in the quasi-two dimensional antiferromagnet Ba2FeSi2O7 Invited Speaker: Seunghwan Do An ongoing challenge in the study of quantum materials, is to reveal and explain collective quantum effects in spin systems where interactions between different mode types are important. This talk will focus on this problem through a combined experimental and theoretical study of interacting transverse and longitudinal modes in an S=1 easy-planar quantum magnet, Ba2FeSi2O7 [1,2]. Our inelastic neutron scattering measurements show that Ba2FeSi2O7 is a quasi-two-dimensional antiferromagnet with large single-ion anisotropy (D>5J), and the extended spin wave theory analysis demonstrates its close proximity to a quantum critical point. The measured spectrum reveals the emergence, decay, and renormalization of a longitudinal mode throughout the Brillouin zone. The decay of the longitudinal mode is particularly pronounced at the zone center where the decay channels to the transverse modes are most active. A generalization of the standard spin-wave theory is used to account for the many-body effects of the interacting transverse and longitudinal modes in Ba2FeSi2O7. The measured mode decay and renormalization are reproduced by including one-loop corrections, where the kinematic conditions for the interactions are satisfied. |
Tuesday, March 15, 2022 3:36PM - 3:48PM |
K53.00002: Structure–property correlations in magnetic two-dimensional intercalation compounds Samra Husremovic, Daniel K Bediako Recently discovered two-dimensional (2D) magnetic materials are promising candidates for energy-efficient electronics because their atomically thin nature makes them highly responsive to low-energy external stimuli. However, realizing the promise of these materials for ultralow-power electronic devices, requires a new design framework for 2D magnets in which the spin–spin interactions can be precisely tailored by modulating the spatial distribution of spin-bearing atoms/ions. Here, we present structure–property relations in 2D FexTaS2 (x ≤ 0.5), a novel low-dimensional magnetic material, which exhibits hard ferromagnetic behavior down to the thinnest limit (Fe-intercalated bilayer TaS2), with large coercive fields of ~3 T. We systematically alter the distribution and symmetry of spin-bearing ions in 2D FexTaS2 by chemically intercalating Fe2+ centers into few-layer TaS2, a host lattice with no long-range magnetic ordering. We examine the behavior of these 2D magnetic materials using variable-temperature quantum transport, transmission electron microscopy, and optical (Raman, synchrotron X-ray) measurements. These analyses shed new light on the coupled effects of intercalation amount, symmetry, order/disorder, and dimensionality on the magnetic behavior of 2D FexTaS2. More broadly, our intercalation approach to 2D magnets introduces a versatile phase space of low-dimensional magnets, in which magnetic properties can be tuned by the choice of the host material and intercalant identity/amount, in addition to the manifold degrees of freedom available to other atomically thin materials. |
Tuesday, March 15, 2022 3:48PM - 4:00PM |
K53.00003: Quantum Mechanical Tunneling in A Molecular Magnet Vertical Heterojunction Xuanyuan Jiang, Andrew V Brooks, Duy Le, Yundi Quan, John J Koptur-Palenchar, Richard G Hennig, Talat S Rahman, Xiaoguang Zhang, Arthur F Hebard We have fabricated EGaIn/CoPc/ITO heterojunctions where sublimated cobalt phthalocyanine (CoPc) films as thin as 5 nm are sandwiched between transparent bottom-layer ITO and top-layer soft-landing eutectic GaIn (EGaIn) electrodes. The roughness of the CoPc films was determined by AFM to be 1.6 nm, and a crystalline ordering with molecules lying parallel to the ITO surface was confirmed by XRD. The differential conductance measurements of the 5 nm thick sample reveal the onset of a superconducting gap below Tc at 6 K (the transition temperature of metastable β-Ga in the EGaIn contact) thereby providing incontrovertible evidence for direct quantum mechanical tunneling processes through the magnetic molecules in our heterojunctions. In addition, Simmons' model fits of our current-voltage characteristics show a weak temperature dependence of tunneling barrier width and height. External magnetic field dependence of the differential conductance suggests coupling of the tunnel currents to both electronic and magnetic states of the CoPc molecules. |
Tuesday, March 15, 2022 4:00PM - 4:12PM |
K53.00004: First-principles study on p-orbital Half-Metallicity in Two-Dimensional Gallium Nitride Seungjun Lee, Hussain Alsalman, Wei Jiang, Tony Low, Young-Kyun Kwon Based on the first-principles calculation, we revealed that a two-dimensional gallium nitride (2D-GaN), which was recently synthesized in-between graphene and SiC or wurtzite GaN substrate, exhibits itinerant ferromagnetism. We found that graphene stabilizes a local octahedral structure of 2D-GaN, whose unusual half-filled quasi-flat bands lead to a spontaneous phase transition to its ferromagnetic phase from normal metal. More intriguingly, its magnetic property is closely related to in-plane lattice constant, and thus under tensile strain, 2D-GaN eventually exhibits p-orbital half-metallicity. To investigate its magnetic property, we simplified its magnetic structure with a 2D Heisenberg model and performed a Monte Carlo simulation. Our simulation revealed that its half-metallicity could be stabilized with a small amount of external magnetic field, and its Curie transition temperature is estimated to be TC ~ 160K. |
Tuesday, March 15, 2022 4:12PM - 4:24PM |
K53.00005: Electron spin resonance of individual molecules for magnetic sensing in an STM Chris Lutz, Gregory Czap, Mark Sherwood Scanning tunneling microscopy (STM) gives atomic resolution for physical properties such as the electronic density of states, spin polarization, and spin and vibrational excitations. We aim to extend these capabilities to include magnetic field sensing by using electron spin resonance (ESR) of a tip-attached molecular spin. ESR in an STM has been used previously to sense spin resonance in individual transition metal atoms and small molecules deposited on the surface, making each spin center a sensitive local magnetic field detector of its atomic-scale neighborhood. Sufficient spin coherence times are obtained by using a thin epitaxial insulating film to controllably isolate the resonant spin centers from the conducting substrate. We explore the use of molecular spins transferred intact to the STM tip. The molecule's structure provides the required isolation from the metallic tip's conduction electrons. Scanning ESR should serve as versatile tool for investigating atomic-scale magnetism by detecting the local magnetic fields of molecules, self-assembled layers, and custom-assembled nanostructures. |
Tuesday, March 15, 2022 4:24PM - 4:36PM |
K53.00006: Gapless Dirac magnons in CrCl3 John A Schneeloch, Yongqiang Cheng, Yu Tao, Luke Daemen, Guangyong Xu, Qiang Zhang, Despina A Louca The compounds CrX3 (X=Cl, Br, I) are layered materials that have received much attention for their few-layer magnetism and potential to host topological magnons. Two types of magnetic order are observed: out-of-plane ferromagnetism (FM) for CrBr3 and CrI3, and in-plane FM order with the spin direction alternating antiferromagnetically in the perpendicular direction for CrCl3. Nearest-neighbor FM coupling on the honeycomb lattice layers would result in a graphene-like magnon dispersion with Dirac nodes at the K point, though in CrBr3 and CrI3 gaps due to the Dzyaloshinskii-Moriya interaction have been reported. For CrCl3, however, we report neutron scattering measurements showing that gapless Dirac magnons are present at low temperature. For higher temperatures, the magnon features gradually soften and broaden on the scale of 10s of K, with only subtle changes at TN~14 K. On cooling below ~50 K, an in-plane negative thermal expansion and a phonon anomaly are seen, in contrast to CrBr3 where such behaviors occur abruptly at the ordering temperature. DFT calculations show that these behaviors arise from increasing in-plane spin correlations. We suggest that differing anisotropy (easy-plane for CrCl3 vs. easy-axis for CrBr3) are responsible for the different temperature dependence. |
Tuesday, March 15, 2022 4:36PM - 4:48PM |
K53.00007: Intercalation-induced New Magnetic Phase in Quasi Two-Dimensional Fe2.7GeTe2 SRINIVASA RAO SINGAMANENI, Hector Iturriaga, Thuc T Mai, Angela R Hight Walker, Cedomir Petrovic Layered quasi-two-dimensional (2D)van der Waals (vdW) magnetic materials gained a great deal of research interest for their exceptional physical properties (layer-dependent magnetism, gate-tunable magnetism, etc.) and promising potential next-generation spintronics applications. Of particular importance, the magnetic behavior of Fe2.7GeTe2 (FGT), a vdW itinerant ferromagnet, has been shown to exhibit variable magnetic properties as a function of layer thickness, gate voltage, doping, pressure, etc. However, it is completely unknown how the magnetic properties of FGT are altered upon intercalation with organic molecules. In this work, we show our ability in tuning the magnetic properties of FGT using tetrabutyl ammonium (TBA+) via electrochemical intercalation. We find that a new (hard) (ferro) magnetic phase is introduced as well as the magnetic anisotropy is reduced upon the intercalation of FGT with TBA. Our experimental findings suggest that the electron doping upon the intercalation could cause changes in the magnetic properties of FGT. We will present and discuss our in-depth experimental findings resulting from X-ray diffraction, magnetometry, and Raman spectroscopic measurements. |
Tuesday, March 15, 2022 4:48PM - 5:00PM |
K53.00008: Evolution of the carrier concentration and its effects on the Currie Temperature in ultra-thin Fe3GeTe2 films. Ryan L Roemer, Hyungki Shin, Ke Zou, Chong Liu Recently, Fe3GeTe2 (FGT) has generated much interest due to its |
Tuesday, March 15, 2022 5:00PM - 5:12PM |
K53.00009: Two-dimensional magnetic order in Cr-based chalcogenides Jan Phillips, Victor Pardo, Adolfo O Fumega Long-range ferromagnetic order in the single-layer limit has been reported in different chromium-based chalcogenides with layered structure. Ab initio calculations based on the density functional theory of different Cr-based chalcogenides are analyzed approaching the two-dimensional limit. A wide range of stoichiometries and different structures have been considered. Their dynamic stability, -in particular in the 2D limit-, and electronic structure will be discussed, but the main focus of the study will be on which cases our calculations predict an out-of-plane magnetic anisotropy that could lead to a long-range ferromagnetic order in the two-dimesional limit. The analysis will be complemented with additional tuning parameters, such as strain, pressure, the stability of charge density waves (CDW), stoichiometry and other different structural details. We will discuss what parameters work in favour or against the appearance of a two-dimensional ferromagnetic order and provide some general remarks applicable to the whole transition metal chalcogenide family of materials. |
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