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 GG03: V: Cooperative Phenomena, Magnetic Domains, and Domain Walls |
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Sponsoring Units: GMAG Chair: Jie Ma, Shanghai Jiao Tong Univ Room: Virtual Room 3 |
Monday, March 20, 2023 12:30PM - 12:42PM |
GG03.00001: Spin and electronic excitations in 4f atomic chains on Au(111) substrates David W Facemyer, Vijay Singh, Naveen Dandu, Anh T Ngo, Sergio E Ulloa High spin systems, like those that incorporate rare earth 4f elements (REEs), are increasingly relevant in many fields. Although research in such systems is sparse, the large Hilbert spaces they occupy are promising for many applications. In this work, we examine a one-dimensional linear array of europium (Eu) atoms on a Au(111) surface, and study their electronic and magnetic excitations. Ab initio calculations using VASP with GGA+U, spin-orbit coupling, and the HSE hybrid functional are employed to study the structure. We find Eu atoms to exhibit minimal charge transfer, indicating physisorption of neutral atoms with a net spin-7/2 when on gold. Examining various spin-projection configurations, we can evaluate first and second neighbor exchange energies to obtain J1 ≈ -0.947 K and J2 ≈ 4.29 K for the relaxed-chain atomic separation of a ≈ 5 Å. These parameters are used in an isotropic Heisenberg model to obtain the full spin excitation spectrum of a physically realizable four-atom chain. The large J2|J1| ratio results in a singlet ground state with dimer-like antiferromagnetic correlations between second neighbors. The seemingly small J1 values significantly affect the spectra, underscoring the important role that nearest-neighbor coupling plays in this system, including possible Dzyaloshinskii-Moriya interactions. Spin-flip excitations are calculated to extract differential conductance profiles as those obtained by scanning tunneling microscopy techniques. We uncover interesting behavior for local higher spin excitations, especially as we track their dispersion with applied magnetic fields. |
Monday, March 20, 2023 12:42PM - 12:54PM |
GG03.00002: Hubbard interactions in magnetic monolayers: FePS$_3$ and CrI$_3$ Fatemeh Haddadi, Edward Linscott, Marco Gibertini, Iurii Timrov, Nicola Marzari Hubbard-corrected density-functional theory has proven to be successful in addressing self-interaction errors in 3D magnetic materials. However, the effectiveness of this approach for 2D magnetic materials has been much less explored. Here, we use PBEsol+$U$ and its extensions PBEsol+$U$+$V$ to investigate the electronic, structural, and vibrational properties of 2D antiferromagnetic FePS$_3$ and ferromagnetic CrI$_3$. The Hubbard parameters (onsite $U$ and intersite $V$) are computed self-consistently using density-functional perturbation theory (DFPT) [PRB 98, 085127 (2018)], thus fully from first-principles. We show that for FePS$_3$ Hubbard corrections are crucial for obtaining the experimentally observed insulating state with the correct crystal symmetry, with Hubbard-corrected vibrational frequencies in good agreement with Raman experiments. Finally, we discuss CrI$_3$, and the requirements it elicits in correcting the relative positions of the majority and minority conduction bands via a spin-resolved $U$ [PRB 98, 235157 (2018)]. |
Monday, March 20, 2023 12:54PM - 1:06PM |
GG03.00003: Electronic Structure and Magnetism of [(FePc)nH2Pc] Superlattices: A First-principles Study Shuanglong Liu, Jie-Xiang Yu, Silas Hoffman, Xiaoguang Zhang, Hai-Ping Cheng Recent experimental work on quasi-1D [(FePc)nH2Pc] superlattices by Vargas et al. revealed interesting magnetic properties. In this study we applied density functional theory (DFT) with the Hubbard U correction to examine two model systems, [(FePc)nH2Pc] with n = 3 and 4. Since FePc systems are prone to local energy minima due to different d-orbital occupations, we used d-orbital occupation matrix control and identified a lower energy state compared to previous studies. Our calculations included spin-orbit interactions that are done self-consistently. Based on DFT total energies, we estimate the exchange coupling constants and zero-field-splitting parameters for an effective spin Hamiltonian of each superlattice. We found that an FePc molecule adjacent to an H2Pc molecule has smaller on-site magnetic anisotropy. The exchange interaction between two FePc molecules that are separated by an H2Pc molecule is over 600 times smaller than that between two adjacent molecules. The antisymmetric exchange or the Dzyaloshinskii–Moriya interaction is two orders smaller than the isotropic exchange interaction. Finally, we present calculated magnetization and magnetic susceptibility for both [(FePc)3H2Pc] and [(FePc)4H2Pc] superlattices. We hope to shed some light on the application of MPc systems to quantum information science. Further studies of spin dynamics are underway. |
Monday, March 20, 2023 1:06PM - 1:18PM |
GG03.00004: Magnon band in twisted bilayer CRI3 yunzhe liu We use Holstein–PrimakoffTransformation and symmetry analysis to get the Hamiltonian for magnon dispersion in twisted bilayer CrI3. We reveal how to use DFT calculation to get all indepedent parameters in the Hamiltonian. We find flat Γ magnon bands and DIrac cons in the band dispersion. With the intralayer Dzyaloshinskii- Moriya interactions, the Dirac cons can be opened. |
Monday, March 20, 2023 1:18PM - 1:30PM |
GG03.00005: Self-consistent magnetic dynamic susceptibility in the itinerant magnets Vladimir P Antropov, mark Auslender We propose a linear response approach for studying magnetic excitations in itinerant magnets using spin dynamic susceptibility. The method is self-consistent and based on the Mori correlation function theory. The self-consistency is obtained directly using corresponding spin-spin current and spin current-spin current correlators. With such approach no introduction of any enhancement factor aka Stoner parameter is needed. We discuss the advantages of such an approach relative to traditional standard linear response schemes. The density functional studies of magnetic excitations in 3d metals will be presented and compared with earlier results. |
Monday, March 20, 2023 1:30PM - 1:42PM |
GG03.00006: Twisted Magnon Frequency Comb and Penrose Superradiance Peng Yan, Zhenyu Wang, Huaiyang Yuan, Yunshan Cao Quantization effects of the nonlinear magnon-vortex interaction in ferromagnetic nanodisks are studied. |
Monday, March 20, 2023 1:42PM - 1:54PM |
GG03.00007: Surface Acoustic Waves and Magnetic Domain Wall Motion Christopher L Keck, Anil Adhikari, Shireen Adenwalla The interest in domain wall based memories in materials with perpendicular magnetic anisotropy has motivated our study into how strain affects domain wall pinning. Specifically, we have investigated the effects of high frequency strain on domain wall motion in ferromagnetic stripes. A pair of interdigital transducers were lithographically patterned on 128° Y cut LiNbO3, resulting in surface acoustic waves (SAW) at a resonance frequency of 244.75 MHz. Stripes with widths ranging from 2 to 5 μm of Co/Pt multilayers were patterned between the two IDTs, with notches at 8 um intervals serving as geometrically defined pinning sites. We characterized the pinning behavior of the notches using a scanning MOKE stage, for a range of magnetic fields and pulse widths, both with and without strain. The latter data allowed for us to extract the pinning potential and depinning field for each notch. Measurements of the depinning probabilities over a range of SAW amplitudes indicate that as the SAW amplitude increases, the characteristic depinning time decreases monotonically showing that strain assists in domain wall depinning by lowering the energy required. |
Monday, March 20, 2023 1:54PM - 2:06PM Author not Attending |
GG03.00008: Energy Efficient In-memory Computing with Quantized Magnetic Domain Wall Racetrack Devices Walid Al Misba, Dhritiman Bhattacharya, Christopher Jensen, Gong Chen, Daniel B Gopman, Damien Querlioz, Kai Liu, Jayasimha Atulasimha Traditional von-Neumann computing for data intensive classification tasks with deep neural networks (DNNs) consumes a significant amount of power and incurs huge latency [1]. In-memory computing reduces physical separation between memory and computational units by arranging the computational memory units in the crossbar and obviates the need for shuttling data. Magnetic racetrack memory with a single domain wall (DW) can be actuated with spin orbit torque current and allows for efficient vector-matrix multiplication computation in DNN architectures. However, the racetrack memory devices’ response is stochastic and of low-resolution nature in practical scenarios which can hurt DNN accuracy. We have shown previously that these issues can be mitigated with quantized neural network (QNN) learning [2]. In this study, we will experimentally demonstrate the DW motion control in a ferromagnetic racetrack where different DW positions correspond to different memory states and report a QNN implementation with such racetrack memory-based synapses. |
Monday, March 20, 2023 2:06PM - 2:18PM |
GG03.00009: Interface and Surface Effects on Domain Wall Depinning Fields Babu R Sankhi, Ujjal Lamichhane, Soumya Mandal, Ritesh Sachan, Emrah Turgut, Derek Meyers We study the impacts of interfaces and thin film surfaces on magnetic domain wall depinning field, velocity as well as other magnetic properties by controlling the aluminum oxide thickness on the perpendicularly magnetized Pt/Co/AlOx heterostructures. It is observed that the maximum values of coercivity and depinning field and minimum domain wall velocity for the 5 nm ALOx thickness at room temperature. We adopted the low-temperature magneto-resistive transport measurement to investigate CoOx content at the Co/AlOx interface and atomic force microscopy images are used for the quantification surface roughness of all samples. The wide range of variation of the coercive field at the lowest possible temperature of 25 k is observed and the 5 nm aluminum oxide thickness sample’s coercivity lies very close to the mean value of all samples revealing the significant variation of CoOx content at the interface. In addition, We found a very small dependence of RMS values of surface roughness with the AlOx thickness which is also consistent with the depinning field variation trend at room temperature. Our work is helpful to design magnetic heterostructures by controlling the depinning field and other magnetic characteristics applicable in the field of low-power next-generation data storage devices. |
Monday, March 20, 2023 2:18PM - 2:30PM |
GG03.00010: Electron paramagnetic resonance of n-type silicon for application in 3D thermometry Darshan Chalise, David G Cahill While there are several 2D thermometry techniques that provide excellent spatial, temporal and temperature resolution, there is a lack of 3D thermometry techniques that work for a wide range of materials and offer good resolution in time, space and temperature. X-ray diffraction (XRD) and nuclear magnetic resonance (NMR) imaging can provide 3D temperature information. However, XRD is typically limited to crystalline materials while NMR is largely limited to liquids where the resonance lines are sufficiently narrow. We investigate electron paramagnetic resonance (EPR) of n-type silicon as a possible means of 3D thermometry. The temperature dependence of the spin-lattice relaxation rate (1/T1) of conduction electrons in n-type Si have been extensively studied for low dopant concentrations and follows a T3 law due to phonon broadening. For heavily-doped Si, which is desirable for good signal to noise ratio (SNR) for application in thermometry, impurity scattering is expected to decrease the temperature dependence of 1/T1. However, the effect of impurity scattering on the spin-lattice relaxation rate, or equivalently the EPR linewidth, at temperatures approaching room temperature and high carrier concentrations has not been experimentally studied. Our results show that, in heavily doped n-type Si, spin-lattice relaxation induced by impurity scattering does not drastically decrease the temperature dependence of EPR linewidths. In P-doped Si with donor concentration of 7 × 1018 /cm3, the EPR linewidth has a T5/2 temperature dependence; the temperature dependence decreases to T3/2 when the donor concentration is 7 × 1019 /cm3. While the temperature dependence of linewidth decreases for heavier doping, EPR linewidth is still a sensitive thermometer. Our results show that EPR linewidth can be a sensitive thermometer for application in 3D thermometry with systems embedding microparticles of heavily doped n-type Si. |
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