Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session B47: Interfaces, Coupling, and Ultra-Thin MaterialsFocus
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Sponsoring Units: GMAG Chair: Nathan Satchell, Univ of Leeds Room: 710/712 |
Monday, March 2, 2020 11:15AM - 11:27AM |
B47.00001: X-ray Orbital Angular Momentum from Artificial Antiferromagnets containing Edge Dislocations Xiaoqian Chen, Justin Woods, Roland Koch, Barry W Farmer, Claudio Mazzoli, Wen Hu, Rajesh V Chopdekar, Wai-Kwong Kwok, Lance Eric De Long, Sujoy Roy, Jeffrey Hastings Artificial spin lattices (ASLs), including artificial spin ices, consist of patterned magnetic nanostructures that mimic Ising spins. Here we show that a permalloy, square ASL with a double edge dislocation exhibits an ordered antiferromagnetic ground state, unlike square ASLs with a single dislocation.1 We demonstrate that soft x-rays resonantly scattered from this magnetic texture carry orbital angular momentum. Moreover, x-ray OAM from these samples can be modulated using and temperature and applied magnetic fields. X-ray beams carrying orbital angular momentum (OAM) have potential applications in nanoscale imaging, spectroscopy, and manipulation, but current means of generating x-ray OAM are difficult to modulate or reconfigure.2 Scattering from ASLs may offer a potential path to flexible control of x-ray OAM. |
Monday, March 2, 2020 11:27AM - 11:39AM |
B47.00002: Enhancement of magnetoelectric coupling by insertion of Co atomic layer into Fe3Si/BaTiO3(001) interfaces identified by first-principles calculations Yasunari Hamazaki, Yoshihiro Gohda Magnetoelectric (ME) coupling of Ferromagnetic(FM)/ferroelectric(FE) interfaces is stronger than those of single phase multiferroic materials. Especially, interface ME effect caused by bonding effect between interfacial atoms has been reported in many FM/FE interfaces and observed at room temperature. In this study, we examine interface ME coupling at Fe3Si/Co/BaTiO3 heterostructures by using first-principles calculations based on density functional theory to clarify the influence of atomic-layer insertion on the ME effect. D03-type Fe3Si has only 0.1 % lattice mismatch with tetragonal BaTiO3 (001), and it is considered as promising to emerge the interfacial ME effect. We construct several interface structures and compare the energy of each structure. Comparing the Fe3Si/BaTiO3 interface with the Fe3Si/Co/BaTiO3 interface, it is found that the interface ME effect is greatly increased when Co is inserted. We also clarify the differences in ferroelectric displacement and magnetic properties between Fe3Si/BaTiO3 and Fe3Si/Co/BaTiO3. |
Monday, March 2, 2020 11:39AM - 11:51AM |
B47.00003: Long-range exchange coupling in Co/Nb/Co trilayers Victor González, Nicolas M Vargas, S Mercone, Edgar J Patino, Ivan K. Schuller, Juan Ramirez Long-range interlayer exchange coupling (IEC) in multilayers has been a topic of extensive research, both experimental and theoretical. IEC can be induced by two ferromagnetic (FM) layers spaced by a thin non-magnetic (NM) material. In this work, we performed vector model Vibrating Sample Magnetometer (V-VSM), Magneto-optic Kerr effect and magnetoresistance (MR) measurements as a function of temperature from 1K up to room temperature. Interestingly, we observed an oscillatory behavior of the magnetic coercive field usually associated with IEC without fully antiferromagnetic compensation of the ferromagnetic layers at all temperatures. This may suggest an additional Long-range exchange coupling mechanism beyond the direct exchange. |
Monday, March 2, 2020 11:51AM - 12:27PM |
B47.00004: Reduced exchange interactions in thin perpendicularly magnetized magnetic tunnel junction free layers and spin-transfer reversal mechanisms Invited Speaker: Jamileh Beik Mohammadi Perpendicularly magnetized magnetic tunnel junctions (pMTJs) are being widely developed for spin-transfer torque magnetic random-access memories for data storage and embedded memories. The magnetic properties of the pMTJ free layer affect the dynamic properties of the free layer, such as the spin-torque switching efficiency and the switching speed, and therefore the device performance. |
Monday, March 2, 2020 12:27PM - 12:39PM |
B47.00005: Strain-driven spin-Hall antiferromagnetic memory for 180° switching Arun Parthasarathy, Nikhil Rangarajan, Shaloo Rakheja Antiferromagnets exhibit ultrafast spin dynamics with response times in the picosecond range, produce negligible stray fields, and are promising to design high-density nonvolatile memories. NiO is an antiferromagnetic insulator whose Néel order can be switched by 90° using electric current in the spin-Hall system NiO/Pt [1], or piezoelectric strain in Ni/NiO/PMN-PT [2]. Although these switching schemes allow storage of information, the 90° state is thermally metastable. |
Monday, March 2, 2020 12:39PM - 12:51PM |
B47.00006: Inter-particle magnetic correlations and fluctuations in assemblies of Fe3O4 nanoparticles Karine Chesnel, Johnathon Rackham, Colby Walker, Brittni Pratt, Dalton Griner, Roger Harrison, Mark Transtrum Magnetite (Fe3O4) nanoparticles (NPs) are increasingly used in biomedical applications such as drug & gene delivery, hyperthermia, or MRI. While the structural and magnetic properties of bulk Fe3O4 is well known [1], knowledge is still lacking about the spatio-temporal magnetic behavior of collections of Fe3O4 NPs. We here investigate the inter-particle magnetic correlations within the NP assembly throughout the superparamagnetic transition using x-ray resonant magnetic scattering (XRMS) [2]. By exploiting the light polarization, we extract the local inter-particle magnetic order. We show a dependence on particle size, suggesting an enhancement of magnetic couplings for bigger particles. [3] Additionally, we show a model based on NP chains, which we use to fit the XRMS data, suggesting ferromagnetic ordering at high external magnetic field, and the emergence of antiferromagnetic ordering near remanence. [4] Finally we investigate the slow dynamics of magnetic fluctuations between NPs by using photon correlation spectroscopy and show a drastic change through the superparamagnetic transition. |
Monday, March 2, 2020 12:51PM - 1:03PM |
B47.00007: Modeling Magnetic Correlations in magnetite Nanoparticle Assemblies Using X-ray Magnetic Scattering Data Johnathon Rackham, Karine Chesnel, Mark Transtrum, Roger Harrison, Steve Kotter, Brittni Pratt Magnetic nanoparticles are increasingly used in nanotechnologies and biomedical applications, such as drug targeting, MRI, and bio-separation. Magnetite (Fe3O4) nanoparticles stand to be effective in these roles due to the non-toxic nature of magnetite and its ease of manufacture. To be more effective in these applications, a greater understanding of the magnetic behavior of the individual magnetite nanoparticles is needed when a collection of them is used. This research seeks to discover the local magnetic ordering of ensembles of magnetite nanoparticles occurring at various stages of the magnetization process. To complete this study, we use resonant x-ray magnetic scattering, which provides information about the magnetic orders in the material. Here we discuss the modeling of the magnetic scattering data using a one-dimensional chain of nanoparticles with a mix of ferromagnetic, anti-ferromagnetic, and random order and the model's validation against empirical gaussian fits. The model utilizes twelve variable parameters and we used a Levenberg-Marquardt algorithm to find the best fit parameters. By fitting the model to the experimental data, we extracted information about the magnetic correlations in the nanoparticle assembly. |
Monday, March 2, 2020 1:03PM - 1:39PM |
B47.00008: Strain Control of Magnetism in LaCoO3 Invited Speaker: Er-Jia Guo
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Monday, March 2, 2020 1:39PM - 1:51PM |
B47.00009: "Boundary Conditions in Granular Magnetic Nanostructures with Dzyaloshinski- Moriya Interactions" Ahsan Ullah, Balamurugan Balasubramanian, Wenyong Zhang, David Sellmyer, Ralph Skomski Magnetic nanostructures such as compacted ensembles of metallic nanoparticles and melt-spun ribbons often but not always yield a topological Hall-effect contribution caused by the Berry phase of the conduction electrons. Among the experimental systems recently investigated in our group are MnSi, NiMnGa, NiMnIn, and Co-Si, The Berry-phase effect depends on the spin structure, which is strongly affected by real-structure feature such as easy-axis orientation and grain boundaries. Chemical inhomogeneities at grain boundaries yield ▽A terms in the materials equations (partial differential equations), where A is the exchange stiffness. For sharp interfaces, this term corresponds to Erdmann-Weierstrass (EW) boundary conditions. In the presence of Dzyaloshinski-Moriya interactions (D), there are ▽D terms and modifications to the EW condition. The effect of the boundary conditions on spin structure and Berry phase is far-reaching and epitomized by the contrast between Bessel and modified Bessel functions in grains with cylindrical symmetry. |
Monday, March 2, 2020 1:51PM - 2:03PM |
B47.00010: The effect of x-ray illumination on magnetic domain memory in
[Co/Pd] / IrMn multilayers Colby Walker, Mason L Parkes, David J Keavney, Eric Fullerton, Karine Chesnel
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Monday, March 2, 2020 2:03PM - 2:15PM |
B47.00011: Quantification of mixed Bloch/Néel character in a Co/Pd DMI multilayer thin film with Lorentz transmission electron microscopy. Joseph Garlow, Shawn D. Pollard, Marco Beleggia, Hyunsoo Yang, Yimei Zhu Chiral magnetic order stabilized by the Dzyaloshinskii-Moriya interaction holds promise for a range of spintronic device applications such as for magnetic-based memory and logic. Yet, direct methods for the quantification of their exact structure remains a challenge and is crucial towards understanding the fundamental physics associated with their ordering and manipulation. Here, we present an approach to quantify the mixed Bloch-Néel character of domain walls stabilized by the Dzyaloshinskii-Moriya interaction in Co/Pd multilayers. Analysis of the observed intensities under varied imaging conditions yield vital parameters that dictate their stability and properties, namely, the degree of mixed Bloch-Néel character (η = 56° ± 5°), the domain wall width (w = 10 ± 2 nm), the strength of the Dzyaloshinskii-Moriya interaction (D = 1.0 – 1.1 mJ/m2), and the exchange stiffness (A = 23 – 30 pJ/m). This approach provides the necessary framework to quantify the magnetic structure for a broad array of topological spin systems using Lorentz phase microscopy. |
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