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 B56: Magnetic Domain and Artifically Structured Magnetic Materials |
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Sponsoring Units: GMAG Chair: Kyle Fruhling, Boston College Room: Room 304 |
Monday, March 6, 2023 11:30AM - 11:42AM |
B56.00001: Spin-relaxation of Defect Center Qubit by Off-Resonant Pinned Domain Wall Oscillations Jyotirmay Dwivedi, Jeffrey G Rable, Nitin Samarth The nitrogen-vacancy (NV) center, a fluorescent defect in diamond, has emerged as a powerful room temperature quantum sensor for probing the local properties of ferromagnetic textures; for example, it has been used for static imaging of domain walls (DW) [Nat. Commun.6, 6733 (2015] and skyrmions [Nat Commun.9, 2712 (2018)], as well as dynamic measurements of magnetic vortex gyrations [J. Appl. Phys., 130, 083903 (2021)]. Here, we demonstrate off-resonant spin relaxation of NV centers in deterministically placed nanodiamonds via the GHz-scale oscillations of a pinned DW. By placing the nanodiamonds over a pinning site determined by a notch in the wire and shape anisotropy, we reliably measure the spin dynamics of both a nucleated and denucleated control case. Then, we compare these results to micromagnetic simulations to further confirm our results. This work expands the menagerie of magnetization dynamics that can be detected with NV centers and builds the foundation for future DW qubit coupling experiments, presenting a powerful new avenue for local microwave driving and qubit addressability. |
Monday, March 6, 2023 11:42AM - 11:54AM Author not Attending |
B56.00002: Several magnetic orders in CrBr3 crystals Sergey Grebenchuk, Magdalena Grzeszczyk, Zhaolong Chen, Maciej Koperski, Kostya S Novoselov The variety of two-dimensional (2D) materials increases day by day, vastly expanding the range of phenomena that can be investigated in two dimensions, as well as the types of van der Waals (vdW) heterostructures that can be created. Recently obtained 2D magnets are more sensitive to external perturbations, which opens vast possibilities and ways of controlling magnetism in them. The magnetic properties of two-dimensional and even bulk van der Waals materials can depend significantly on the structure. For example, CrI3 crystals have ferromagnetic interlayer coupling, whereas just a few layers of CrI3 have an antiferromagnetic interlayer interaction. Moreover, bilayers of CrI3 and CrBr3 have different magnetic coupling between layers for different stacking orders. In this work, by using cryogenic magnetic force microscopy we study one of the layered vdW magnet, CrBr3, in the thickness range from 10 nm up to 800 nm, and discover that several types of magnetic orders can coexist within the same crystal, resulting in a peculiar overlay of different domain patterns in the magnetic force microscopy signal. In such a system, one can observe stripe domains in a few top layers, and less ordered non-periodic domains of inner layers simultaneously, which suggests local antiferromagnetic interlayer coupling on the boundaries of two subsystems. Then, we developed a model which assumes that by applying an external magnetic field, layers of one ordering join another subsystem, which is very different from the response of usual ferromagnetic materials with out-of-plane uniaxial anisotropy. |
Monday, March 6, 2023 11:54AM - 12:06PM |
B56.00003: Extraction of Exchange-Bias Field from Domain Wall Creep Dynamics in Ferromagnet/Antiferromagnet Thin Film Heterostructures M. Usama Hasan, Geoffrey S Beach Domain wall creep in ultrathin ferromagnets is generally a well understood phenomena that has been observed in a wide range of systems. Although many technologically important magnetic systems utilize or host different types of interlayer coupling such as exchange bias (antiferromagnet/ferromagnet) or RKKY (ferromagnet/ferromagnet) - where an “effective” field which has its origin in the interlayer coupling is very important in dictating the overall behavior of the system - domain wall creep in such systems has not been studied as much. In this work, we use a simple modification to the typically used creep equation in order to take into account the presence of the "effective" field due to the antiferromagnet in an antiferromagnet/ferromagnet heterostructure. The utility of this method is demonstrated in Pt/Co/Pt/Co1-xNixO heterostructures, by accurately extracting the exchange-bias field using MOKE microscopy at a local (10-100 microns) level. In systems where magnetization reversal occurs via domain nucleation and growth, we show that focused laser MOKE can sometimes provide erroneous exchange-bias values because of the stochastic nature of the domain nucleation process, and that a reliable measurement can be performed using the method discussed. Furthermore, we show that by combining focused laser MOKE and domain wall creep based experiments, the exchange-bias experienced by domain nucleation sites and the exchange-bias experienced by the propagating domain wall away from the nucleation sites can be separately measured and be significantly different from each other. |
Monday, March 6, 2023 12:06PM - 12:18PM |
B56.00004: Non-linear evolution of magnetic domain structure following ultrafast laser excitation Rahul Jangid, Nanna Zhou Hagström, Kyle Rockwell, FNU Meera, Justin shaw, Jeffrey A Brock, Matteo Pancaldi, Flavio Capotondi, Emanuele Pedersoli, Dario D Angelis, Hans T Nembach, Stefano Bonetti, Eric E Fullerton, Mark W Keller, Roopali Kukreja, Ezio Iacocca, Thomas J Silva We utilized time-resolved small-angle X-ray magnetic scattering at FERMI free electron laser to measure the ultrafast response of mixed domain state in CoFe/Ni multilayers. The mixed domain state consists of coexisting perpendicularly magnetized labyrinth and stripe domains. 2D fitting routine was employed to disentangle the individual ultrafast change in period (1/q) and inhomogeneity (1/ Γ) of labyrinth and stripe domains from magnetic scattering [1]. We observed a linear dependence of scattered intensity as a function of pump fluence. A nonlinear ultrafast contraction and broadening in the scattering was observed for labyrinth domains where below a certain fluence threshold (≈ 7 mJ/cm2), small changes were observed. Above this threshold, q and Γ increased drastically as a function of fluence and at the highest measured fluence of 13.4 mJ/cm2, a change of 5.5 % and 27 % for q and Γ respectively was observed for labyrinth domains as reported previously [2, 3]. In contrast, stripe domains show significantly weaker change when pumped [1, 4]. We report clear evidence of difference in quench and recovery timescales for magnetization and domain structure evolution. Our studies hint to domain wall velocities of up to 104 m/s and a clear dependence of the magnetization dynamics on the domain pattern highlighting the role of nanoscale morphology on the ultrafast magnetization behavior. |
Monday, March 6, 2023 12:18PM - 12:30PM |
B56.00005: Thermal fluctuations in magnetic domain in the van der Waals antiferromagnet NiPS3 Youjin Lee, Suhan Son, Giung Park, Jingyuan Cui, Je-Geun Park NiPS3 is an XXZ-type van der Waals material with an antiferromagnetic transition at 150 K. It is easily exfoliated in monolayer due to relatively weak van der Waals interlayer bonding, which realizes the two-dimensional magnet in real space. To probe the magnetic order and local electronic state in NiPS3, we investigate the exfoliated NiPS3 with a photoemission microscope with linearly polarized x-rays. In this work, we observe the magnetic domain in the van der Waal antiferromagnet NiPS3. We confirm the domains originate from the magnetic order by temperature dependency. The domain contrasts decrease as the temperature increases. Above Neel temperature, the domain contrasts get very weak or vanish. In addition, the thermal fluctuation of magnetic domain is captured. When cooled down, multi-domains merge into one domain. |
Monday, March 6, 2023 12:30PM - 12:42PM |
B56.00006: Anisotropic magnetic domain in magnetic Weyl semimetal candidate Co3Sn2S2 Yi Luo, Jonathan Gaudet, Mekhola Sinha, Chris J Lygouras, Lisa M DeBeer-Schmitt, Tyrel M McQueen, Collin L Broholm We use small-angle neutron scattering (SANS) to study the formation and field evolution of the magnetic domains in the magnetic Weyl semimetal candidate Co3Sn2S2. For zero-field-cooling (ZFC) measurement at 145 K (below Tc ≈177 K), we observe highly anisotropic magnetic scattering signals best described by a 2d x 1d product form. We determine the out-of-plane (1d) correlation length ξc=8.2(2.5) μm and observe the large-q tails of the in-plane (2d) magnetic scattering indicating a lower cut-off of the in-plane correlation length ξa ≥0.25 μm. The magnetic domains are aligned upon applying a field of 0.1 T and form an isotropic structure when the field is reduced back to zero. Our work compliments the previously reported magneto-optic Kerr microscopy [1] and give the first characterization of the domain structure along the out-of-plane direction in Co3Sn2S2. We also conduct detailed bulk magnetization measurements and observe a nucleation temperature Tn=135(5) K and the influence of inhomogeneity on the magnetization curves. |
Monday, March 6, 2023 12:42PM - 12:54PM |
B56.00007: Coupling of magnetism and plastic deformation in Heusler intermetallic alloys Bailey Rhodes, Justin Mayer, Yolita Eggeler, Shuozhi Xu, Tresa Pollock, Ram Seshadri, Irene J Beyerlein, Daniel Gianola Intermetallic alloys designed for their magnetic functionality often experience mechanical duress due to in-service stresses, which may impact their performance. Here, we investigate the impact of mechanical stresses leading to plastic deformation on the magnetic properties of the Heusler intermetallic alloy. Experimental magnetization measurements collected before and after grinding powders of the alloy demonstrate that the ferromagnetic saturation magnetization is dramatically impacted by crystalline defects imposed by mechanical stress. Density Functional Theory (DFT) γ-surfaces paired with Phase Field Dislocation Dynamics (PFDD) simulations predict that mechanical stresses lead to the formation of nano-scale planar defects that introduce a new environment hosting antiferromagnetic character. In situ micro-mechanical compression experiments were used to interrogate the orientation-dependent mechanical behavior of single crystals. Differential Phase Contrast Scanning Transmission Electron Microscopy (DPC STEM) performed for the deformed material reveals the local interplay between ferromagnetic domains and nano-scale planar defects resulting of plastic deformation. |
Monday, March 6, 2023 12:54PM - 1:06PM |
B56.00008: Skyrmion Dynamics and a Resulting Spin Wave Fractal Network Probed with SANS Nan Tang, Namila C Liyanage, Sergio A Montoya, Sheena K Patel, Lizabeth J Quigley, Alexander Grutter, Michael Fitzsimmons, Sunil K Sinha, Julie A Borchers, Eric E Fullerton, Lisa M DeBeer-Schmitt, Dustin A Gilbert Magnetic skyrmions present interesting and unique pseudo-particle behaviors which arise from their topological protection. Key among these behaviors is their microwave dynamic modes, which have potential as coupled spin torque oscillators with applications in on-chip wireless communications. Due to the small size and magnetic-only contrast of skyrmions, coupled with the high frequency of the dynamics – typically in the GHz regime – it is extremely challenging to perform in-situ measurements of these excitations. This work reports the use of small angle neutron scattering (SANS) to capture the dynamics in hybrid skyrmions. Using a static out-of-plane magnetic field and an in-plane microwave dynamic excitation, driven gyration modes are generated in hybrid skyrmions. Coincident with the resonance conditions for the dynamics, the SANS pattern shows a large increase in the low-q scattering intensity in the form of a decay function which is absent in the off-resonant measurements. This scattering pattern is reasonably well fit with a Lorentzian model, representing spin wave excitation, however, a better fit is achieved using a mass fractal model, which suggests the spin waves form a long-range network-like structure. These results offer new insights into the nanoscale dynamics of magnetic skyrmions, but also present a unique use of SANS to probe high-speed dynamics. |
Monday, March 6, 2023 1:06PM - 1:18PM |
B56.00009: The unusual ferromagnetism of LaCrGe3 through the lens of magnetic domain depinning Rahim R Ullah, Valentin Taufour, Xiangdong Zhu, Peter Klavins The ferromagnetic compound LaCrGe3 (TC = 85 K) has proven to be a playground for studying the suppression of ferromagnetism under pressure. While LaCrGe3 is known as an example in which a ferromagnetic quantum critical point is avoided by the appearance of an alternative magnetic phase, certain probes also revealed features similar to the ones in UGe2 and ZrZn2 which indicate two ferromagnetic phases FM1 and FM2. In LaCrGe3, however, the existence of FM1 and FM2 has not been recognized in magnetization measurements so far. I will present our results from coercivity measurements and from a simple domain de-pinning model which support the presence of two FM phases. This revelation allows us to explain the unusual magnetization curve seen in previous studies, and may help to explain a range of anomalous behaviors observed in LaCrGe3 at ambient pressure. |
Monday, March 6, 2023 1:18PM - 1:30PM |
B56.00010: Curvature-induced effects in domain wall dynamics in stripes with spatially varying cross section Kostiantyn Yershov, Denis D Sheka Here we study both analytically and numerically the influence of curvature and cross section deformation effects on the motion of a domain wall in curved stripes which corresponds to geometry of recent experiments [1]. We base our study on a phenomenological Landau-Lifshitz-Gilbert equations using collective variable approach based on a q-Φ model. We show that (i) curvature and nonzero gradient of cross-section deformation result in a modification of a ground state and can be interpreted as an effective magnetic field. (ii) The presence of a nonzero gradient of cross section deformation also results in a pinning potential for domain walls in addition to the curvature-induced potential [2]. In effective equations of motions the spatially varying cross section and curvature appear as a driving forces which can suppress or reinforce the action of each other. The eigenfrequency oscillations of domain wall in vicinity of the pinning potential is obtained as a function of curvature and cross section deformation and their gradients. All analytical predictions are well confirmed by full scale micromagnetic simulations. |
Monday, March 6, 2023 1:30PM - 1:42PM |
B56.00011: Giant thermal stability and efficient current-driven motion of chiral magnetic domain walls in ferromagnet-synthetic antiferromagnet lateral junctions Jiho Yoon, See-Hun Yang, Jae-Chun Jeon, Andrea Migliorini, Ilya Kostanovskiy, Tianping Ma, Stuart Parkin Electrical current driven manipulation of chiral spin textures, such as chiral magnetic domain walls (DWs), is of great interest in both fundamental research and technological applications for spintronic memories, and logic devices1,2. Of particular interest are synthetic antiferromagnetic racetracks (SAFs) in which antiferromagnetically coupled chiral DWs can be efficiently moved by current3. However, overcoming the trade-off between energy efficiency, namely a low threshold current density to move the DW, and thermal stability still remains a major challenge. Here we show that chiral DWs in a synthetic antiferromagnet-ferromagnet (FM) lateral junction are highly thermally stable whilst the DWs can be efficiently moved across the junction by current4. We experimentally demonstrate that thermal fluctuations are equivalent to an effective magnetic field, thereby, surprisingly, increasing the energy barrier and further stabilizing the DW in the junction to even higher temperatures, which is in sharp contrast with conventional FMs or SAFs. Furthermore, we show that chiral DWs can be strongly confined within a FM region sandwiched in between adjacent SAFs and yet can be readily moved into the SAF regions by current. Our novel approaches overcome the aforementioned trade-off thereby allowing for reliable and versatile DW-based memory, and logic, and beyond. |
Monday, March 6, 2023 1:42PM - 1:54PM |
B56.00012: Zener carriers, Jahn-Teller distortion, and colossal magnetoresistance effect in manganites Hongze Li, Yaohua Liu, Jiaming He, Jianshi Zhou La1-xSrxMnO3 (LSMO) is a well-known system with colossal magnetoresistance (CMR) effect. The competition of ferromagnetic (FM) correlation and antiferromagnetic (AFM) correlation associated with the Zener carriers is the key to understand CMR effect. In La0.875Sr0.125MnO3, CMR effect mainly occurs in the paramagnetic state between Curie temperature and Jahn-Teller distortion temperature. Neutron diffuse scattering (NDS) on La0.875Sr0.125MnO3 single crystals has been used to investigate the short-range magnetic ordering in the paramagnetic phase. Magnetic related rod-like shaped and sphere-like shaped NDS features are obsereved in the JT ordered state. Reconstruction of magnetic correlations by 3D delta magnetic pair distribution function (3D-ΔmPDF) indicates that rod-like shaped NDS features are related to type-A AFM correlation and sphere-like shaped NDS features are related to 3D FM correlation, confirming the coexistence of AFM and FM correlations in the JT ordered state. The 3D FM correlation is resulted from orbital mixing due to the local structure, while the type-A AFM correlation occurs from superexchange interaction as a result of JT distortion. The Zener carriers released in the vicinity of TC under external magnetic field are responsible for the CMR effect. |
Monday, March 6, 2023 1:54PM - 2:06PM |
B56.00013: Modification of Nanosphere Templates for Nanocap and Antidot Magnetic Thin Film Fabrication Alejandro Zafra, Jiyeong Gu Previous work with curved magnetic thin films, such as nanocap thin films, has suggested the formation of magnetic vortex states that arise from their geometry. Furthermore, controlling the size and shape of the particles used for templates during fabrication may help tune the magnetic behavior. This study aims to better understand the parameters that give rise to these magnetic states - such as nanosphere diameter, nanocap shape, and gap between the nanocaps - by modifying polystyrene nanosphere templates. Templates were modified via reactive ion etching (RIE), or by removing the nanosphere monolayer to create antidot thin films. Investigation into the etching of nanosphere templates by changing gas pressure and etching time, as well as comparing different particle sizes, achieved a recipe for a controlled etching. Focused ion beam (FIB) used for cross-sectional imaging show the etched nanospheres change to spheroid shapes and sheds light on the coverage during thin film deposition. Magnetic hysteresis loop measurements were carried out to observe switching property, and magnetic force microscopy to visualize the magnetic configuration of these modified nanocap thin films. |
Monday, March 6, 2023 2:06PM - 2:18PM |
B56.00014: Domain wall dynamics and magnetization switching in the presence of spin-orbit torques in low-symmetry materials Edward Schwartz, Alexey A Kovalev, Kirill D Belashchenko, Wuzhang Fang Conventional field-like and damping-like spin orbit torques (SOT) which appear at heavy-metal / ferromagnet interfaces are possible due to the breaking of inversion symmetry. Further symmetry breaking due to the structure of the materials allows for the possibility of additional types of SOT. In this work, we build a collective coordinate model to describe the motion of a ferromagnetic domain wall in response to low symmetry SOT. Our results show that these low symmetry SOT can be used to control the motion of domain walls in ways not possible using ordinary field-like or damping-like SOT. We then use ab initio methods to verify the presence of these torques in a CuPt/CoPt bilayer with threefold rotational symmetry, and apply this model to show how SOT compatible with this symmetry can allow the deterministic reversal of perpendicular magnetization, even in the absence of external magnetic fields, and compare our results to micromagnetic simulations. |
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