Bulletin of the American Physical Society
2018 Annual Meeting of the APS Four Corners Section
Volume 63, Number 16
Friday–Saturday, October 12–13, 2018; University of Utah, Salt Lake City, Utah
Session J02: CMP + Materials 3: Magnetism 1 |
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Chair: Dagmar Weickert, Florida State University Room: JFB 102 |
Saturday, October 13, 2018 8:00AM - 8:12AM |
J02.00001: Probing Magnetic Ordering in Magnetite Nanoparticles using x-rays Karine Chesnel, Johnathon Rackham, Brittni Newbold, Roger Harrison, Mark Transtrum Understanding the nanoscale magnetic properties of magnetic nanoparticles is crucial for their applications in nanotechnologies and in medicine. While macroscopic properties of magnetic nanoparticles have been extensively studied via magnetometry, information about the nanoscale magnetic order is often lacking. We will see how the nanoscale magnetic order can be revealed by x-rays using the technique of x-ray resonant magnetic scattering. Scattering profiles collected under different conditions of magnetic field and at different temperatures will be presented. We will see how the magnetic orders at low magnetic field values, near to remanence, strongly depend on particle size. Smaller 5 nm particles exhibit a random superparamagnetic behavior, whereas bigger 11 nm particles show antiferromagnetic correlations. |
Saturday, October 13, 2018 8:12AM - 8:24AM |
J02.00002: Ferroelectric polarization switching induced charge versus strain mediated interfacial magnetic phases in oxide heterostructures Binod Paudel, Igor Vasiliev, Mahmoud Hammouri, Edwin Fohtung We studied ME coupling at La0.67Sr0.33MnO3/PbZr0.2Ti0.8O3 interface on STO (001) substrate as a function of polarization direction on PZT layer with combined results from polarized neutron reflectometry (PNR) experiments and DFT calculations. PNR results show antiferromagnetic (AFM) phases on few unit cells of ferromagnetic (FM) LSMO at the interface for polarization directions away from the sample interface due to self- and negatively polarized PZT. However, interface remains ferromagnetic for positive polarization. Furthermore, there is increase in bulk LSMO magnetization while going from positive, self to negative polarization directions. To find the origin of such ME coupling is either charge or strain mediated, magnetic phase evolution as a function of strains is studied from DFT calculations for both polarization. For negative polarization, both A-AFM and FM phases exist for zero strain and A-AFM and FM phases start to dominate with increasing negative and positive strain respectively. The magnetic moments are significantly dropped within few unit cells of LSMO interface for negative and intact for positive polarization, which purports the results from PNR . |
Saturday, October 13, 2018 8:24AM - 8:36AM |
J02.00003: Magnetic Domain Memory in Thin Films Mason Lane Parkes, Karine Chesnel, Colby S Walker Exchange coupling between the ferromagnetic and anti-ferromagnetic layers in [Co/Pd]/IrMn film causes a phenomenon known as magnetic domain memory (MDM), where the material returns to the same magnetic domain configuration after a magnetic field has been applied, even all the way to saturation. Information about MDM is obtained through coherent x-ray resonance magnetic scattering (XRMS) images taken using synchrotron radiation. Previous results showed that the degree of MDM depends on the magnitude of the field being applied when cooling the material below a certain blocking temperature. More recent experiments appear to indicate a disappearance of the MDM and we are investigating the cause of this loss. My particular research has focused on varying certain parameters in the cross-correlation process we use to determine the MDM. I will also show new magneto-transport data collected at synchrotron facility at different temperatures and in different conditions to investigate a possible effect of x-ray illumination causing a loss of MDM. |
Saturday, October 13, 2018 8:36AM - 8:48AM |
J02.00004: Zero Temperature Quantities Controlling the Ferroelectric Curie Temperature. Sharad Mahatara, Andrew Supka, Boris Kiefer, Troy Lyons, Laalitha Liyanage, Pino D'Amico, Rabih Al Rahal Al Orabi, Priya Gopal, Cromac Toher, Arrigo Calzolari, Stefano Curtarola, Marco Buongiorno Nardelli, Marco Fornari Ferroelectric materials show spontaneous, reversible ionic displacement and induced spontaneous electrical polarization below the Curie temperature, TC. The displaced charge density can directly couple to an external electrical field with applications in SONAR, electromechanical energy harvesting, and transduction. The elastic properties of a materials may contain information associated with local distortion and provide qualitative descriptors for temperature effects. Using AFLOWπ, we have implemented and tested the accuracy of the Lagrangian methodology of elastic constants for selected alkali halides with NaCl and CsCl structure and for selected rocksalt carbides and nitrides. We expanded this approach to a few ferroelectric materials in the perovskite family. Data available through the AFLOWLIB and other repositories were used to establish correlations between zero temperature quantities and the experimentally observed TC. We will discuss the results of our statistical analysis and how low zero temperature descriptors such as ionic displacement and elastic constants can be used to accelerate materials discovery and design in the technologically important class of ferroelectrics. |
Saturday, October 13, 2018 8:48AM - 9:00AM |
J02.00005: The effect of x-ray photons on the magnetic domain memory in a [Co/Pd] / IrMn multilayers Colby Singint Walker, Karine Chesnel, Mason Parks I am studying the effect that coherent x-rays potentially have on the magnetic domain memory in a [Co / Pd] / IrMn multilayers. To investigate this potential effect we have used both XRMS (xray resonant magnetic scattering) together with magneto-transport to track the exchange bias while the sample is illuminated with x-rays. A loss of exchange bias would indicate that the x-rays illuminating the sample have an effect on the exchange coupling between the ferromagnetic [Co/Pt] layer and the antiferromagnetic [IrMn] layer, causing the exchange bias. Studying a possible loss of exchange bias necessitates collecting reference magneto-transport data to compare with data from x-ray scattering experiments at the APS (Advance Photon Source). |
Saturday, October 13, 2018 9:00AM - 9:12AM |
J02.00006: Magnetic Irreversibility in VO2/Ni Bilayers Joshua P Lauzier, Logan Sutton, Jose De La Venta The temperature dependence of the magnetic properties of VO2/Ni bilayers was studied. VO2/Ni bilayers were grown via magnetron sputtering and their magnetic properties were measured using a Vibrating Sample Magnetometer. VO2 exhibits a well-known Structural Phase Transition (SPT) at 330-340 K, from a low temperature monoclinic (M) to a high temperature rutile (R) structure. The SPT of VO2 induces an inverse magnetoelastic effect that strongly modifies the coercivity and magnetization of the Ni films (1). Growth conditions allow tuning of the magnetic properties. Above the transition temperature, Ni deposited on (M) VO2 shows a coercivity enhancement whereas Ni deposited on (R) VO2 shows suppression of the coercivity. Samples were cycled several times to check if the changes in coercivity and magnetization were reversible (2). Bilayers with Ni deposited on (R) VO2 show reversibility, samples with Ni deposited on (M) VO2 shown an irreversibility after the first SPT. This irreversibility can be associated with cracking of the VO2 layer as it relieves stress due to the transition and has implications for the resistance versus temperature behavior of the VO2. 1 J. Lauzier et al., J. Appl. Phys. 122, (2017). 2 J. Lauzier et al., J. Phys. Condens. Matter 30, (2018). |
Saturday, October 13, 2018 9:12AM - 9:24AM |
J02.00007: Emergent Flat band lattices in spatially periodic magnetic fields Muhammad Tahir, Hua Chen Motivated by the recent discovery of Mott insulating phase and unconventional superconductivity due to the flat bands in twisted bilayer graphene, we propose more generic ways of getting two-dimensional (2D) emergent flat band lattices using either 2D Dirac materials or ordinary electron gas subject to moderate periodic magnetic fields with zero spatial average. We provide simple formulas for the "magic ratios" between the field strength and its wavenumber for getting flat bands, and give an intuitive explanation for their origin by constructing coarse-grained lattice models. Our work provides new, flexible platforms for exploring interaction-driven phases in 2D systems with arbitrary superlattice symmetries. |
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