Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session S54: Nanomagnetic Systems: From Spin Textures to Topological StructuresFocus
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Sponsoring Units: GMAG DMP Chair: Anish Rai, University of Delaware Room: Room 306 |
Thursday, March 9, 2023 8:00AM - 8:36AM |
S54.00001: 3D vector nanoimaging of spin textures in nanostructured magnetic materials Invited Speaker: Chen-Ting Liao Understanding topological spin configurations is of paramount importance because of scientific interests and practical applications. Examples of topological spin texture include magnetic Skyrmions and topological magnetic monopoles (TMMs). TMMs are also known as magnetic hedgehogs or Bloch points, which are 3D nonlocal spin textures robust to thermal and quantum fluctuations due to their topology. However, observing the magnetization of TMMs directly and mapping out their interactions at tens of nanometer scales has been challenging – this is due to the lack of high-resolution, non-destructive 3D imaging techniques that can penetrate relatively thick samples. Here, we report the creation of more than 100 stable TMMs in a frustrated ferromagnetic meta-lattice, which is made of silica nanospheres and infiltrated nickel between the spheres. These field-free room temperature TMMs do not possess strong anisotropy or the Dzyaloshinskii-Moriya interaction. The complex 3D curved surfaces of the nanospheres in the meta-lattice create a magnetically frustrated configuration harboring topological spin textures. We further developed a new imaging technique called "3D soft x-ray vector ptychography" to determine the magnetization and emergent magnetic fields of the TMMs with a 3D spatial resolution of 10 nm. This new imaging method utilizes x-ray magnetic circular dichroism, ptychography, scalar and vector tomography, to quantitatively image and reconstruct nanoscale spin textures. The achieved resolution is comparable to the magnetic exchange length of transition metals, enabling us to study monopole-monopole interactions. We observed that TMMs with opposite charges are separated closer than those with the same charges, indicating that the system is near equilibrium. In summary, our work demonstrates that magnetic meta-lattices could be used as a new platform to create and investigate the interactions of TMMs. Furthermore, we expect soft x-ray vector ptychography to be applied broadly to quantitatively image 3D vector fields in magnetic and anisotropic nanomaterials based on facility-scale (synchrotrons) and table-top scale (laser-driven high harmonic generation) x-ray sources. |
Thursday, March 9, 2023 8:36AM - 8:48AM Author not Attending |
S54.00002: Non-local chirality breaking in curvilinear magnetic nanoarchitectures Oleksii M Volkov, Daniel Wolf, Oleksandr V Pylypovskyi, Attila Kákay, Denis D Sheka, Bernd Büchner, Jürgen Fassbender, Axel Lubk, Denys Makarov In magnetism, the magnetization vector remains unaltered upon the space inversion symmetry transformation but changes its sign with time inversion. Breaking of the inversion symmetry within the magnetic lattice unit cell or sample's shape introduces a chiral Dzyaloshinskii-Moriya interaction (DMI) [1,2], which manifests itself in the formation of non-trivial chiral and topological spin textures with a given magnetochirality. The latter can be tailored either at the intrinsic structural level [3] by the adjustment of a material composition or geometrically by the formation of versatile chiral and anisotropic responses in curved magnetic objects even for standard magnetic materials [4,5,6]. Here, we demonstrate the existence of non-local chiral effects in geometrically curved asymmetric permalloy cap with a vortex texture. Using the full-scale simulation we study how the texture is changing with respect to the introduced sample asymmetry. Namely, the equilibrium vortex core obtain both bend and curling deformations, that arise from the asymmetry of the top and bottom surfaces and existence of the non-local chiral effects [7]. The obtained results were confirmed by magnetic imaging using transmission electron microscopy based electron holography for the asymmetric permalloy cap. |
Thursday, March 9, 2023 8:48AM - 9:00AM |
S54.00003: Magnetic textures in topological magnetic nanoparticles Cole Gibson, Jacob Gayles Magnetic materials with the requisite inversion-breaking needed for nonzero Dzyaloshinskii-Moriya interaction (DMI) can host a variety of exotic noncollinear spin textures, including skyrmions. Investigating topological materials in a nanoparticle system holds promise to demonstrate novel spin textures due to the increased number of possible symmetries and length scales compared to bulk and thin-film systems. We use spin dynamics simulations to characterize the magnetic textures of cubic nanoparticles as they undergo a field-cooling, producing phase diagrams of the topological charge with variation of the DMI and external field. These simulations are motivated by ab initio calculations of DMI in nanoparticles that demonstrate strong chiral interaction resulting from structural inversion asymmetry at the nanoparticle surface. Therefore, a symmetry analysis is used to determine DMI direction. Our results show the penetration of the surface texture into the bulk-like interior even for a simple model, and serve as guidance for future inquiries into topological nanoparticles. |
Thursday, March 9, 2023 9:00AM - 9:12AM |
S54.00004: Lifetime enhancement of an atomic spin chain near a diabolic point Robbie Elbertse, Taehong Ahn, Jiyoon Hwang, Jeongmin Oh, Jorn Rietveld, Fernando Delgado, Andreas Heinrich, Sander Otte, Yujeong Bae Body The magnetic lifetime of bistable atomic nanostructures at very low temperatures is governed by quantum tunnelling of magnetization. Here we demonstrate experimentally that this process can be reduced several orders of magnitude by tuning the system close to a so-called diabolic point, resulting in dramatically longer lifetimes. We use a scanning tunnelling microscope with a spin-polarized tip to probe the lifetime of chains of Fe atoms on Cu2N/Cu(100) while applying a strong transverse magnetic field. Unlike other lifetime enhancing factors, such as a longitudinal field, chain length, bias voltage and current strength, the effect of the transverse field is non-monotonic with a pronounced peak around 3-4T. We explain this result through a reduction in the hybridization of the two lowest eigenstates, which exhibit an avoided level crossing in the vicinity of a diabolic point. While the avoided crossing is nearly indistinguishable, the peak in the lifetime is very clear, has a peak width that relates to the energy difference and is robust to variations in the experimental conditions. Using this method, it is shown that there is a significant variation in the g-factors of the individual atoms in the chain that is not symmetric along the chain. The work provides prospects for optimizing spintronic lifetimes through engineering of quantum states. |
Thursday, March 9, 2023 9:12AM - 9:24AM |
S54.00005: Magneto-Optical Effects in Nanostructures of van der Waals Antiferromagnet Vigneshwaran Chandrasekaran, Christopher R DeLaney, Christopher A Lane, Jian-Xin Zhu, Xiangzhi Li, Huan Zhao, Jennifer A Hollingsworth, John D Watt, Andrew Jones, David H Dunlap, Andrei Piryatinski, Sergei A Ivanov, Han Htoon Magneto-optical (MO) effects describe the changes in the polarization state of light upon interaction with magnetic material. Faraday and Kerr effects are examples of such phenomena that could be simply analyzed using conventional optical spectroscopy methods. Since the arrangement of spins contribute to such MO effects in magnetic materials, even a small change in their order could induce change in the polarization state of interacting light. Compared to ferromagnets, antiferromagnets having opposite magnetic sublattices allow manipulation of all polarization orientation. 2D van der Waals antiferromagnets are promising material platform for spintronic and quantum information technology with the control of their dimensions down to an atomic layer thickness. However, nanostructural counterparts of such 2D van der Waals antiferromagnets are rarely explored for their magnetic properties. We argue that the abrupt change in the spin arrangement with the presence of sharp edges allow nano-magnetic structures to exhibit different MO effect compared to bulk by using NiPS3 as a prototype since the photoluminescence here is correlated to spin. |
Thursday, March 9, 2023 9:24AM - 9:36AM |
S54.00006: Magnetism in Two-Dimensional Ilmenenes: Intrinsic Order and Strong Anisotropy Andres Ayuela, Rodrigo H Aguilera-del-Toro, Mikel Arruabarrena, Aritz Leonardo The study of the intrinsic magnetic properties of 2D systems is novel, and most of the materials that have been synthesized are magnetic van der Waals crystals [1,2]. Ilmenene layer is already an exciting two-dimensional material that was recently exfoliated from existing iron titanate ore (TiFeO3) [3] and currently constitutes a representative example of a 2D non-van der Waals compound. In this talk, we report on not only the structural and electronic properties, but also the magnetic properties of the family of ilmenene-like layers with 3d transition metals. The study of the magnetic order reveals that these ilmenenes usually present an intrinsic antiferromagnetic coupling between the 3d magnetic metals that decorate both sides of the Ti-O layer. Our calculations including spin-orbit coupling reveal that magnetic ilmenenes have large magnetocrystalline anisotropy energies when the 3d shell departs from being either ?lled or half-?lled, with their spin orientation being out-of-plane for elements below half ?lling 3d states and in-plane above half ?lling. These interesting magnetic properties of ilmenenes make them useful for future spintronic applications because they could be synthesized as already realized in the iron case. The goal is to establish a broad theoretical groundwork for future research on the magnetism of these ilmenene layers, so that all of them can be synthesized and their interesting properties can be studied in the near future, just as is performed for ilmenites, their 3D stacking counterparts [4]. |
Thursday, March 9, 2023 9:36AM - 9:48AM |
S54.00007: Magneto-dependent photovoltages and switching in permalloy metasurfaces MD Afzalur Rab, David W Keene, Natalia Noginova Permalloy is a soft ferromagnetic material with very high magnetic permeability, commonly used in various magnetic and magnonic studies. Recently, it was found that permalloy structures demonstrate plasmonic behavior and an interesting coupling between optical, magnetic and electric effects, which makes them candidates for spintronic and nanomagnetic applications, and plasmon-induced magnetization switching. Using E-beam evaporation, we deposited permalloy films on flat and profile modulated substrates with submicron periodicity. The photovoltages induced by laser pulse illumination show significant dependence on magnetic field with a characteristic hysteresis. The switching fields depend on the geometry of the structure, being the lowest for flat films, and the highest for grating structures with high amplitude of profile modulation. The photovoltage magnitude increases linearly with an increase in the illumination intensity when the external magnetic field is not in the range of the switching field. More complicated dependence is observed at the range of the switching indicating possible photoinduced magnetization switching due to spin angular momentum transfer from light to matter. |
Thursday, March 9, 2023 9:48AM - 10:00AM |
S54.00008: Magnetic properties of Mn3Sn thin films depending on annealing condition subin Im, Seongbin Seo, Dongchan Jeong, Sanghwa Lee, jiseok Yang, Kab-Jin Kim, Byong-Guk Park, Sanghoon Kim In recent years, antiferromagnets have rapidly attracted attention because it shows several advantages such as no stray field, ultrafast spin dynamics, and current-induced phenomena, compared to ferromagnets. In particular, the non-collinear antiferromagnets (NC-AFM) based on D019 (space group=194, P63/mmc) hexagonal Mn3X (X=Ga, Ge, and Sn) is an important template in antiferromagnetic spintronics owing to nontrivial magnetic properties which are a giant anomalous Hall effect, magnetic spin Hall effect, magnetic Wely fermions, and chiral anomaly. Among the compounds, the magnetic Weyl semimetal Mn3Sn is a prime representative of NC-AFM. In Mn3Sn, the Mn atoms form a triangular sublattice in the c-plane (0001) called Kagome lattice, and their net magnetic moments are disclosed from non-collinear 120° ordered chiral spin structure. This spin texture leads to the existence of Weyl point with opposite chirality in Mn3Sn due to breaking time-reverse symmetry. |
Thursday, March 9, 2023 10:00AM - 10:12AM |
S54.00009: Symmetry in light-driven magnons and chiral phonons Ze-Xun Lin, Swati Chaudhary, Wesley Roberts, Bowen Ma, Martin A Rodriguez-vega, Benjamin J Wieder, Gregory A Fiete We theoretically study the impact of light-driven structural changes on the magnetism of a bilayer honeycomb lattice. High-intensity light can induce large-amplitude phonon displacements and place the system in the non-linear phononics regime. Using symmetry group theory, we analyze the vibrational modes and nonlinear couplings between them. We find that the phonon-induced structural changes generate changes in the magnetic exchange constants of local moments situated on lattice sites. We observe that changes in the lattice symmetry can generate nonzero interlayer Dzyaloshinskii–Moriya interactions, which themselves give rise to new magnetic ground states with canted spins. When the light intensity is increased, we observe a phase transition from a gapped magnon phase to a gapless phase (at finite frequency) characterized by magnon nodal lines. Our work suggests experimental strategies for engineering magnetic ground states and manipulating magnon dispersion in broad classes of layered van der Waals materials. Time permitting, we will also discuss related symmetry analysis in the group theory of chiral phonons. |
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