Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session V36: Magnetic ImagingFocus Live
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Sponsoring Units: GMAG DMP Chair: Andreas Berger, CIC nanoGUNE |
Thursday, March 18, 2021 3:00PM - 3:36PM Live |
V36.00001: Coherent Diffraction Imaging of magnetic nanostructures using table-top and facility scale EUV/X-ray sources Invited Speaker: Emma Cating-Subramanian The advent of materials with complex nanoscale magnetic textures stemming from geometric frustration, careful tuning of the Dzyaloshinskii–Moriya interaction, or direct light-induced manipulation of spins, etc., has opened up exciting avenues of research both into the fundamental physics of these systems and into their potential applications. Understanding the dynamics and structure of nanoscale spin textures requires techniques with femtosecond temporal resolution, nanometer spatial resolution, and magnetic contrast. Because of their small size and low contrast, intricate nanoscale magnetic textures have proven difficult to image directly in 3D without prior knowledge of the sample. Correlative multi-modal spectro-microscopy using complementary nanoscale imaging and spectroscopic techniques at both the tabletop and facility scale provides access to a more complete range of elemental, chemical, electronic, magnetic, structural, and dynamic properties of complex samples. For example, by combining the element-specific magnetic contrast of resonant x-ray magnetic circular dichroism with the exquisite spatial and temporal resolution and phase-contrast of x-ray ptychography, and incorporating vector-tomographic reconstruction algorithms we comprehensively characterize complex magnetic, nanostructured, layered, and heterogeneous samples. |
Thursday, March 18, 2021 3:36PM - 3:48PM Live |
V36.00002: Formation of Field-Free Skyrmion Arrays in Pt/Co/Ni/Ir-based Multilayer Thin Films Maxwell Li, Anish Rai, Ashok Pokhrel, Arjun Sapkota, Tim Mewes, Claudia K.A. Mewes, Marc De Graef, Vincent Sokalski Magnetic skyrmions are topologically protected spin textures which have garnered a great deal of attention in recent years for their favorable properties for nonvolatile memory and neuromorphic computing applications. The deterministic chirality of these objects are stabilized by the Dzyaloshinskii-Moriya interaction (DMI) and typically require a perpendicular magnetic field to be stabilized but often appear with fairly low densities. Here we demonstrate a simple method to form high-density skyrmion arrays at remanence following the brief application of a large in-plane magnetic field. We characterize these arrays using Lorentz transmission electron microscopy and observe that the size of the observed skyrmions are strongly influenced by the strength of interfacial DMI. We also find the angle of the applied field with respect to the film normal strongly influences the formation of arrays as opposed to labyrinthine domains. This is particularly apparent around bend contours of the TEM membrane which can have large variations in apparent tilt. |
Thursday, March 18, 2021 3:48PM - 4:00PM Live |
V36.00003: Spin polarized STM imaging of nanoscale Néel Skyrmions in an SrIrO3/SrRuO3 Perovskite Bilayer Joseph Corbett, Keng-Yuan Meng, Jacob Repicky, Reyes Garcia-Diaz, James R Rowland, Adam S Ahmed, Noboru Takeuchi, Jonathan Guerrero Sanchez, Fengyuan Yang, Jay A. Gupta Interfaces in perovskite heterostructures exhibit a range of emergent properties that have attracted considerable interest. We use spin-polarized scanning tunneling microscopy to directly image isolated nanoscale Néel Skyrmions in a SrIrO3 /SrRuO3 bilayer system that are among the smallest reported to date in any system. Atomically resolved imaging and tunneling spectroscopy identified island-like SrIrO3 (SIO) grains and valleys of exposed SrRuO3 (SRO). Statistically we found that Skyrmions must be fully contained within, but may be smaller than, any given SrIrO3 region with an average diameter of 3 nm. Additionally, skyrmions were observed on SrIrO3 islands of varying thickness without loss of SPSTM contrast, suggesting the magnetic texture lies within the SrIrO3 island in addition to the underlying SRO. Density functional theory calculations suggest this is due to a small induced magnetic moment associated with IrO layers in the SIO film. Furthermore, we observed some skyrmions readily switch between the ferromagnetic and skyrmionic states, while other skyrmions are firmly pinned. No discernible surface defects seem to drive the pinning, suggesting an interfacial mechansim. |
Thursday, March 18, 2021 4:00PM - 4:12PM Live |
V36.00004: Evidence for a Kondo Spin Resonance in Magnetic Iron Nanoislands on Antiferromagnetic Chromium Nitride (001) Arthur Smith, Khan Alam, Rodrigo Ponce, Yingqiao Ma, Andrew Foley, Ashok Shrestha, Gregorio Cocoletzi, Noboru Takeuchi We have explored the electronic properties of iron nanoislands on antiferromagnetic chromium nitride substrates [1] using low-temperature (4.2K) scanning tunneling spectroscopy, and we find sharp peaks or V-dips at the Fermi level for the nanoislands which are not seen in plain iron, chromium, or chromium nitride surfaces. Spectra are acquired using both a normal W tip and an Fe-coated W tip, and the spectra show some similarities as well as important differences. The Fermi level peak/dip features can also be mapped spatially using dI/dV conductance mode imaging. Comparisons to theoretical results based on first principles calculations allow us to determine magnetic structural models and compare the observed spectra with the calculated density of states which supports a possible Kondo spin resonance interpretation in terms of a ferromagnetic nanoisland which is magnetically de-coupled from an antiferromagnetic CrN substrate.[2] |
Thursday, March 18, 2021 4:12PM - 4:24PM Live |
V36.00005: Dynamic widefield imaging of strain using quantum defects in diamond Shishir Dasika, Kasturi Saha The Nitrogen vacancy (NV) center based wide field imaging provides the ability to parallelly readout the state of an array of micromagnets. |
Thursday, March 18, 2021 4:24PM - 4:36PM Live |
V36.00006: NV- center magnetometry using Bayesian inference and sequential experiment design Sergey Dushenko, Sean M Blakley, Kapildeb Ambal, Robert McMichael In magnetometry using NV- centers, we demonstrate more than order-of-magnitude speed up with sequential Bayesian experiment design as compared with the conventional frequency-swept measurements. |
Thursday, March 18, 2021 4:36PM - 4:48PM Live |
V36.00007: A Magnon Scattering Platform Tony Zhou, Joris Carmiggelt, Lisa Gachter, Ilya Esterlis, Dries Sels, Rainer Stohr, Chunhui Du, Daniel Fernandez, Joaquin Rodriguez-Nieva, Felix Buettner, Eugene Demler, Amir Yacoby Scattering experiments have revolutionized our understanding of nature. Examples include the discovery of the nucleus, crystallography, and electron microscopy. Scattering techniques differ by the type of the particles used, the interaction these particles have with target materials and the range of wavelengths used. Here, we demonstrate a new 2-dimensional table-top scattering platform for exploring magnetic properties of materials on mesoscopic length scales. Coherent magnons are launched and scattered off a magnetic target. The scattered waves are then recorded using a scanning NV center magnetometer (1, 2) that allows sub-wavelength imaging and operation under conditions ranging from cryogenic to ambient environment. While most scattering platforms measure only the intensity of the scattered waves, our imaging method allows for spatial determination of both amplitude and phase of the scattered waves thereby allowing for a reconstruction of the target scattering potential. Our results (3) establish magnon scattering experiments as a new platform for studying correlated many-body systems. |
Thursday, March 18, 2021 4:48PM - 5:00PM Live |
V36.00008: Nanoscale magnetization and microwave current imaging using scanning-probe magneto-thermal microscopy* Chi Zhang, Jason M Bartell, Jonathan Karsch, Isaiah Gray, Gregory Fuchs High resolution, time-resolved magnetic microscopy is crucial for understanding novel magnetic phenomenon such as skyrmions, spinwaves, and domain walls. Currently, achieving 10-100 nanometer spatial resolution with 10-100 picosecond temporal resolution is beyond the reach of most table-top techniques. We have developed a near-field magnetic microscope based on the time-resolved anomalous Nernst effect. Our technique involves scanning a sharp gold tip within a near-field optical excitation. The resulting tip-sample interaction creates a nanoscale thermal gradient for magneto-thermal microscopy and its extension to imaging an applied current density. We study the characteristics of near-field thermal excitation with a picosecond laser and demonstrate magnetic imaging of a multi-domain state. We present below 100 nm spatial resolution from imaging current density around a nano-constriction, and picosecond temporal resolution enabling phase-sensitive dynamics studies. Our results suggest a new approach to nanoscale spatiotemporal magnetic microscopy in an accessible, table-top form to aid in the development of high-speed magnetic devices. |
Thursday, March 18, 2021 5:00PM - 5:12PM Live |
V36.00009: Current flux imaging of a micromagnetic electrofoil David Mayes, Maxwell Grossnickle, Mark I Lohmann, Junxue Li, Vivek M Aji, Jing Shi, Justin Song, Nathaniel Monroe Gabor Spin current—the flow of angular momentum mediated by electrons—is a unique probe of non-trivial phases in ultrathin magnetic heterostructures. Electron spin, however, is highly sensitive to nearby electromagnetic fields; thus, it is important to characterize nonlocal effects in spintronic devices. The high spin orbit coupling of platinum in conjunction with the ferrimagnetic insulator Yttrium Iron Garnet (YIG) provides an optimal platform for evaluating spin current as a robust probe. Combining scanning photovoltage microscopy with a highly uniform rotating magnetic field, we probe the photoresponse of atomically pristine Pt/YIG heterostructures. Similar to how tracers in a wind tunnel map the flow of air around an aerodynamic airfoil, we use a scanning laser beam as a source of directional spin and charge current to map the flow around precisely engineered wing shaped devices, or electrofoils. Spin current scatters electrons in plane and away from the external magnetic field, producing moving charges that interact with the local electric flux to generate a global voltage. By manipulating the spin current we produce unique images, which exhibit surprising geometric effects, that are fully described by a straightforward application of the Shockley-Ramo theorem. |
Thursday, March 18, 2021 5:12PM - 5:24PM Live |
V36.00010: Nitrogen-induced reconstructions on the Cr(001) surface Emiliano Ventura-Macias, Jonathan Guerrero Sanchez, Joseph Corbett, Arthur Smith, Noboru Takeuchi Cr is an essential material for various spintronic devices due to its magnetic properties. Nevertheless, it is necessary to selectively introduce a contaminant –like Nitrogen– during its synthesis to stabilize its highly-reactive surface. The main drawback is that N changes the electronic and magnetic properties; so, describing the adsorption and properties of adsorbed N is necessary. We described different reconstructions models of N on Cr(001) using DFT calculations andSTM data. With a theoretical thermodynamic analysis we identified the stable models for different growth conditions. From the four stable models, two were already described experimentally, while we confirmed the other two with a comparison of theoretical STM images and STM experiments. Both are in a c(2x2) configuration and the first one has N adsorbed on the hollow sites, while the second has N substituting surface Cr. The electronic and magnetic properties of both models confirmed that they preserve the main characteristics of the clean Cr surface. |
Thursday, March 18, 2021 5:24PM - 5:36PM Live |
V36.00011: Optically Probing Quantum Materials at milliKelvin Temperatures Yun-Yi Pai, Claire Marvinney, Matthew Feldman, Chengyun Hua, Jong-ryul Jeong, Benjamin Lawrie Scanning confocal microscopy offers plentiful mesoscale material information that bridges atomic-scale scanning probes and bulk characterization techniques. MilliKelvin (mK) microscopes have become indispensable tools for the description of phases and quantum critical points with critical temperatures that are inaccessible in helium cryostats. Here, we demonstrate Raman microscopy at mK on quantum paraelectric strontium titanate. Resolved TO phonon modes are consistent with the recent claim that strontium titanate is intrinsically microscopically polar. Additionally, with magneto-optical Kerr imaging, we spectrally resolve the magnetic response from yttrium iron garnet (YIG) as a step toward magneto-optical imaging at mK temperatures with YIG indicator crystals. |
Thursday, March 18, 2021 5:36PM - 5:48PM Live |
V36.00012: Magnetic imaging of thin film α-Fe2O3 using a single-spin magnetometer Qiaochu Guo, Yang Cheng, Pengxiang Zhang, Isaiah Gray, Fengyuan Yang, Luqiao Liu, Katja Nowack, Gregory Fuchs Antiferromagnetic (AF) materials have great potential in spintronic applications thanks to their sub-picosecond timescale dynamics, thermally stable spin order, and insensitivity to external magnetic fields. α-Fe2O3 is an AF insulator with canted spins that display weak ferromagnetism at room temperature. It has recently been used to demonstrate spin orbit torque manipulation of Néel order using spin Hall magnetoresistance as the readout mechanism [1,2]. To better understand the magnetism of α-Fe2O3 and how it is manipulated, here we report magnetic imaging of α-Fe2O3 thin films with a nitrogen-vacancy center based scanning magnetometer. Our results show sub-micron scale magnetic features detected 50 nm above the sample. We will discuss our progress in directly observing current switching of the Néel order in an insulating AF thin film. |
Thursday, March 18, 2021 5:48PM - 6:00PM Live |
V36.00013: Topological Control of Magnetic Textures Hanu Arava, Frank Barrows, Mark D Stiles, Amanda K Petford-Long We report a topological mechanism to stabilize magnetic textures, such as a vortex structure, in a permalloy disk. The topology in the disk is set by four permalloy ellipsoids surrounding the disk. We introduce a discretized formulation of the winding number to identify the nature of the topology, associated with different magnetic configurations, in the surrounding ellipsoids. |
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