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 Z54: Magnetic Characterization and Imaging |
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Sponsoring Units: GMAG Chair: Alenna Streeter, Boston College Room: Room 306 |
Friday, March 10, 2023 11:30AM - 11:42AM |
Z54.00001: Probabilistic spin-torque switching of perpendicular magnetic tunnel junctions under short current pulses Md Golam Morshed, Ankit Shukla, Laura Rehm, Laura Heller, Yunkun Xie, Samiran Ganguly, Shaloo Rakheja, Andrew D Kent, Avik W Ghosh True random number generators (TRNGs) are fundamental building blocks for various applications ranging from cryptography to stochastic sampling. Magnetic tunnel junctions (MTJs) utilizing low-barrier magnets (LBMs) are typically used to implement magnet-based TRNGs. LBMs have energy barriers of Δ ≤ 10 kT and therefore require low energy to operate. They, however, suffer from slow dynamics, extreme sensitivity to process variations, and are hard to build in practice. Recently, stochastic magnetic actuated random transducer (SMART) devices based on perpendicular MTJs (pMTJs) utilizing medium-barrier magnets (MBMs) have emerged as potential candidates to circumvent these drawbacks [1]. We present a systematic analysis of spin-torque-driven switching of the MBM-based pMTJs (Δ ~ 20 – 40 kT) under short current pulses by numerically solving their dynamics using a 1-D Fokker–Planck equation. We find that our device requires low switching energy (< 100 fJ) and operates at a fast switching speed (< 1 ns). We also analyze the impact of process variations, viz. temperature and material parameters, on the switching probability of our device and show its robustness to them. Our results agree well with the analytical equation, stochastic Landau–Lifshitz–Gilbert equation, and recent experiments and show a path toward creating a fast and energy-efficient TRNG hardware unit for solving optimization problems. |
Friday, March 10, 2023 11:42AM - 11:54AM |
Z54.00002: Development of Dual Split-Ring Resonator for Electron Paramagnetic Resonance and Optically Detected Magnetic Resonance at 115 GHz Michael H Coumans Magnetic resonance (MR) uses microwaves to excite transitions between different spin states and to detect oscillating magnetic fields generated by coherently evolving spin superpositions. Most implementations of MR do this using resonant structures. The efficiency of both processes is enhanced when the Larmor Frequency of the spins coincides with the resonator mode such as the TE011 mode for the rectangular cavity. The local magnetic field at the center of this mode is enhanced roughly as where Q ~ 10,000 at low field. However, at high magnetic field and high frequency, high quality factor resonators and thus high magnetic field enhancement has not been demonstrated as of yet. Here, we report on the development of the planar double split-ring resonator structure for applications at 115 GHz and high magnetic field. |
Friday, March 10, 2023 11:54AM - 12:06PM |
Z54.00003: Radio Frequency Sweeps at uT Fields for Parahydrogen Induced Polarization of Biomolecules Alastair Marshall, Alon Salhov, Christoph Müller, Martin Gierse, Anna J Parker, Jochen Scheuer, Michael Keim, Sebastian Lucas, Christophoros Vassilou, John W Blanchard, Philipp Neumann, Fedor Jelezko, Alex Retzker, Ilai Schwartz, Stephan Knecht Magnetic resonance imaging of the metabolic processes within the human body opens up new methods of studying cancers. It is accomplished through the monitoring of the 13C NMR signal of a metabolite, which has an inherently low signal strength. Hyperpolarization, where parahydrogen is chemically added to an unsaturated precursor molecule, generating an entangled spin state in the product molecule, offers a solution. The spin-order of the hyperpolarized protons is converted into observable 13C magnetization using magnetic field sweeps. However, when using deuterated precursor molecules, the efficiency is severely reduced. We demonstrate that using a radio-frequency sweep, a 50% stronger signal can be measured compared to the protonated molecule. We demonstrate that the technique is robust and works for a large variety of molecules. Furthermore, we show that using optimal control can enhance the speed of polarization transfer, while avoiding transfer to fast relaxing spins. |
Friday, March 10, 2023 12:06PM - 12:18PM |
Z54.00004: Imaging framework for identifying Three-Dimensional Magnetic Structures using Hard X-Rays Srutarshi Banerjee, Junjing Deng, Doga Gursoy, Joerg Strempfer Nanoscale electronic and structural heterogeneities are prevalent in condensed matter physics. Their imaging in 3 dimensions has become an important task for the understanding of material properties. To unravel the connection between nanoscale heterogeneity and macroscopic emergent properties, polarization dependent resonant X-ray spectroscopy and scattering methods have been developed [1]. The experiments require scanning the sample with a coherent beam of focused X-rays with left and right circular polarized X-rays in a nano ptycho-tomographic setup. One key issue is that jitter and misalignment of the rotation axis caused by vibration or drift in the experimental setup lead to misalignment between reconstructed ptychographic images for different tomographic projections or between two circular polarization states. In order to correct this, we develop an image registration and reconstruction framework that can align both left and right circular polarized projection images while reconstructing the magnetic vector tomographically. Experiments were carried out using coherent X-rays at the Velociprobe instrument [2] at the Advanced Photon Source (APS). In the experiment, circularly polarized coherent hard X-rays at photon energies corresponding to the L2 absorption edge of Nd are incident on a cylindrical shaped Nd2Fe14B single crystal. With projection data at 2 different sample tilts, the full 3D magnetization vector field is reconstructed without any prior knowledge or assumptions. |
Friday, March 10, 2023 12:18PM - 12:30PM |
Z54.00005: Single-Shot Randomized Probe Imaging of Structural and Magnetic Samples at a Free Electron Laser Abraham L Levitan, Kahraman Keskinbora, Matteo Pancaldi, Emanuele Pedersoli, Dieter Engel, Flavio Capotondi, Riccardo Comin Single-shot imaging is a natural application for Free Electron Lasers (FELs), which produce sub-picosecond flashes of ultraviolet and x-ray light. Due to their intrinsic coherence, FEL beams are well suited for lensless imaging methods such as Coherent Diffractive Imaging (CDI) and holography. However, these methods only work on isolated samples, so masks need to be deposited on most samples to make them compatible. This limits the field of view to a small, fixed region which must be chosen before the start of the experiment. We recently proposed a diffractive imaging approach called Randomized Probe Imaging (RPI) which removes this requirement. Here, we report reconstructions from the first single-shot RPI data collected at an FEL. In single-shot images from a structural test sample, we achieved a full-pitch resolution of 400 nm and a space-bandwidth product of 30,000. We also imaged magnetic domains images of Co/Pt multilayers at the Co M2,3 resonance with reduced resolution, highlighting the possible role of RPI for time-resolved studies of magnetic systems. We will discuss the advantages and limitations of our data, and the prospects for future imaging studies. |
Friday, March 10, 2023 12:30PM - 12:42PM |
Z54.00006: Imaging Room-Temperature Magnetic Skyrmions in Pt/Co/Cu Multilayers while simultaneously measuring the Hall effect Camelia Selcu, Shuyu Cheng, Nuria Bagues Salguero, Ziling Li, Binbin Wang, Shekhar Das, Denis Pelekhov, P Chris Hammel, David W McComb, Roland K Kawakami Magnetic skyrmions are a leading candidate for next-generation storage technology therefore their motion is of great interest. Here we report the observation of room-temperature skyrmions in epitaxial Pt/Co/Cu multilayers grown on insulating substrates using Magnetic Force Microscopy (MFM) as well as their imaging while simultaneously measuring the Hall effect. To perform imaging in the presence of current flow in the sample, we developed microwave electronics for delivering for fast current pulses with less than 10 ns rise/fall time for MFM experiments. The results of the experiments will be discussed. |
Friday, March 10, 2023 12:42PM - 12:54PM |
Z54.00007: Direct imaging of nanoscale field-driven domain wall oscillations in Landau structures Balram Singh Linear oscillatory motion of domain walls (DWs) in the kHz and MHz regime is crucial when realizing precise magnetic field sensors such as giant magnetoimpedance devices. Numerous magnetically active defects lead to pinning of the DWs during their motion, affecting the overall behavior. Thus, the direct monitoring of the domain wall’s oscillatory behavior is an important step to comprehend the underlying micromagnetic processes and to improve the magnetoresistive performance of these devices. Here,[ref] we report an imaging approach to investigate such DW dynamics with nanoscale spatial resolution employing conventional table-top microscopy techniques. Time-averaged magnetic force microscopy imaging (Figure 1) and Kerr imaging methods4 are applied to quantify the DW oscillations in Ni81Fe19 rectangular structures with Landau domain configuration and are complemented by numeric micromagnetic simulations. We study the oscillation amplitude as a function of external magnetic field strength, frequency, magnetic structure size, thickness and anisotropy and understand the excited DW behavior as a forced damped harmonic oscillator with restoring force being influenced by the geometry, thickness, and anisotropy of the Ni81Fe19 structure. This approach offers new possibilities for the analysis of DW motion at elevated frequencies and at a spatial resolution of well below 100 nm in various branches of nanomagnetism. |
Friday, March 10, 2023 12:54PM - 1:06PM |
Z54.00008: Phase Transitions and Magnetocaloric Effects in Ni50Mn35In12Bi3 and Ni47Mn35In15Bi3 Heusler Alloys Abhiyan Oli The Ni50Mn35In12Bi3 and Ni47Mn35In15Bi3 belongs to Heusler alloys family: X2YZ (where X and Y are typically transition elements or lanthanides while Z atom is from group III or IV) and attracted much interest because of their magnetic and transport properties. The structural, magnetic, magnetocaloric and magnetotransport properties of Ni50Mn35In12Bi3 and Ni47Mn35In15Bi3 has been studied using room-temperature X-ray diffraction (XRD), and magnetization measurements. The results of these measurements will be presented. The Ni47Mn35In15Bi3 shows magnetocaloric effects in the vicinity of its magnetostructural transition (MST) and it’s Curie temperature (Tc=291K) at 100 Oe filed. Magnetic entropy change and magnetoresistance has been calculated for these alloys and will be presented. |
Friday, March 10, 2023 1:06PM - 1:18PM |
Z54.00009: In-Plane and Out-of-Plane Magnetic Behavior in Iron Borate Single Crystal Jacob Franklin, Joshua Bedard, Jacob Pfund, Ilya Sochnikov, Menka Jain
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Friday, March 10, 2023 1:18PM - 1:30PM |
Z54.00010: Manipulating Magnetism in Ce-doped SnO2 Nanocrystals by UV Irradiation and Co Co-doping Yun-Liang Soo, Tai-Sing Wu, Bo-Rui Shih, Horng-Tay Jeng Ultraviolet-light irradiation and Co co-doping have been used to induce magnetic property variations in Ce-doped SnO2 nanocrystals. As demonstrated by Ce L3-edge x-ray absorption near edge structure (XANES) data, UV irradiation generates O vacancies near Ce dopant atoms, reducing the valency of Ce ions, while leaving Co ions intact in the samples. The Ce-L3 and Co-K extended x-ray absorption fine structure (EXAFS) analysis also show that both Ce and Co dopant atoms occupy Sn sites in the SnO2 host. The superconducting quantum interference device (SQUID) measurements reveals room temperature ferromagnetism in (Ce,Co)-codoped SnO2, while the diamagnetic SnO2 host becomes paramagnetic when doped with only one of the two dopant elements. Ultraviolet-light irradiation were found to substantially enhance the ferromagnetism in the (Ce,Co)-codoped samples. Theoretical calculations based on density functional theory (DFT) were carried out to explain the experimentally observed magnetic property variations. |
Friday, March 10, 2023 1:30PM - 1:42PM Author not Attending |
Z54.00011: MBE growth and magnetic behaviors in epitaxial Fe100-xGax on SrTiO3 Tran Thi Toan Recently, Iron-gallium alloy (Fe100-xGax with 0x30) is a promising material for magnetostrictive applications due to its high tetragonal magnetostriction 100 at low magnetic field. Thus, we present understanding about structural and magnetic properties of disordered bcc-Fe crystal structure Fe100-xGax (x = 10, 20, and 30) epitaxial thin films, grown on a piezoelectric SrTiO3 substrate using molecular beam epitaxy. The lattice parameter increases with Ga alloying content, because the Ga atom's atomic radius is larger than the Fe atom's. The films showed metallic behavior with a decrease in electrical resistivity at room temperature with Ga content, due to the increase in carrier density. The room temperature saturation magnetization decreased, from 1575 to 991 emu/cm3 as Ga concentration increased from 10 to 30%. Interestingly, a two-step-hysteresis loop was observed in all samples. Magneto-optical Kerr images confirmed abnormal magnetic domain switching under an applied magnetic field. Specifically, the hysteresis loop of the film with a 10% Ga concentration reveals an obvious kink, whereas the loop of the film with a 30% Ga content is harder to see. As a results, it is possible to modify the magnetic properties of FeGa film by combining it with SrTiO3, a complex ABO3 perovskite oxide with a high piezoelectric constant. Our findings suggested that FeGa is a promising material for controlling magnetic anisotropy using a piezoelectric layer in magnetoelastic coupling devices. |
Friday, March 10, 2023 1:42PM - 1:54PM |
Z54.00012: Scanning tunneling microscopy study of van der Waals metallic magnet Fe3GeTe2 Mengke Liu, Yu Liu, Yaofeng Xie, Yin Min Goh, Pengcheng Dai, Jenny E Hoffman Van der Waals crystals with robust long-range magnetic order down to the monolayer limit are widely sought for the development of electronic and spintronic quantum devices. Fe3GeTe2 is a promising candidate, however the presence of both localized magnetic moments and itinerant electrons in Fe3GeTe2 complicates the theoretical picture of its magnetism. Native defects such as Fe vacancies impact its magnetic ground states and strongly alter its magnetic critical temperature, adding difficulties in interpreting experimental results. Here we use scanning tunneling microscopy (STM) to reveal the electronic structure of Fe3GeTe2 in both real and momentum space, and to correlate local electronic variations with specific atomic defects. Our work provides insight into magnetism in strongly correlated d-electron systems. |
Friday, March 10, 2023 1:54PM - 2:06PM |
Z54.00013: Photocurrent streamline microscopy in micromagnetic heterostructure devices David Mayes, Farima Farahmand, Maxwell Grossnickle, Mark I Lohmann, Mohammed Aldosary, Junxue Li, Vivek M Aji, Justin Song, Nathaniel M Gabor Photoexcited electronic charge carriers in quantum materials are often collected at global contacts far away from the initial excitation, a process that is highly non-local. As described by the Shockley-Ramo theorem, this process involves an intricate spatial pattern of streamlines throughout the given device that depends sensitively on the configuration of current collecting contacts as well as the spatial non-uniformity and tensor structure of conductivity. Here we demonstrate a first-of-its-kind microscopy method to image such streamlines through ultrathin heterostructure devices composed of platinum on yttrium iron garnet (YIG). We do this by combining scanning photovoltage microscopy with a uniform rotating magnetic field to control the direction, as well as spatial position of, local photocurrent, which has enabled us to image these streamlines in a variety of geometries that include conventional Hall bar-type devices as well as unconventional devices with wing-shaped cutouts called electrofoils. In these, we show that the streamlines display geometry-specific contortion, compression, and expansion behavior near the cutouts in much the same way as tracers in a wind tunnel map the flow of air around aerodynamic airfoils. This affords a powerful tool to visualize and characterize charge flow in optoelectronic devices. |
Friday, March 10, 2023 2:06PM - 2:18PM |
Z54.00014: STM Investigation of Surface Reconstruction of FeSn Zengle Huang, Wenqing Chen, Jiaqiang Yan, Brian C Sales, Weida Wu Recently kagome compounds attract lots of research interest due to the flat bands, Dirac fermion and the strong electronic correlation due to the kagome lattice[1-4]. However, there is a lack of study of the surface stability of kagome lattice against high temperature. In this talk, we present the study of the surface reconstruction of kagome Fe3Sn layer of antiferromagnetic metal FeSn with scanning tunneling microscope (STM). We heat FeSn to a series of temperatures below room temperature and investigate the surface morphology evolution. Our results shed light on the stability of kagome surface and thermodynamics of defect formation. |
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