Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session D30: Focus Session: Magnetic Domains and Domain Walls |
Hide Abstracts |
Sponsoring Units: GMAG DMP Chair: Timothy Phung, IBM Almaden Research Center Room: 206B |
Monday, March 2, 2015 2:30PM - 2:42PM |
D30.00001: Highly efficient in-line magnetic domain wall injector Timothy Phung, Aakash Pushp, Luc Thomas, Charles Rettner, See-Hun Yang, Kwang-Su Ryu, John Baglin, Brian Hughes, Stuart Parkin The creation and manipulation of domain walls (DWs) in magnetic nano-wires is of considerable interest, and forms the basis of several logic and memory devices. Traditionally, the DWs are created in the nano-wires using local magnetic fields from current injection lines fabricated orthogonal to the nano-wires, whereas the synchronous motion of a series of DWs along a nano-wire is achieved using spin transfer torque (STT) from charge currents that transport spin angular momentum. Here we demonstrate a highly efficient and simple DW injection scheme that uses a combination of STT from nanosecond long, uni-polar, current pulses that cross a 90$^{\circ}$ magnetization boundary along with the fringing fields inherently prevalent at the boundary. The 90$^{\circ}$ magnetization boundary is created by local ion-irradiation at the end of a nano-wire exhibiting perpendicular magnetic anisotropy. Remarkably, we find that the currents needed for this ``in-line'' DW injection scheme are at least one hundred times smaller than conventional methods. Additional advantages are its significantly smaller footprint than that of conventional methods, its compatibility to the smallest lithographic dimensions, and, its ability to continuously inject DWs using uni-polar current. This simplified scheme bodes well for the fruition of spintronics based memory and logic devices. [Preview Abstract] |
Monday, March 2, 2015 2:42PM - 2:54PM |
D30.00002: Domain wall motion in sub-100 nm magnetic wire Saima Siddiqui, Sumit Dutta, Jean Anne Currivan, Caroline Ross, Marc Baldo Nonvolatile memory devices such as racetrack memory rely on the manipulation of domain wall (DW) in magnetic nanowires, and scaling of these devices requires an understanding of domain wall behavior as a function of the wire width. Due to the increased importance of edge roughness and magnetostatic interaction, DW pinning increases dramatically as the wire dimensions decrease and stochastic behavior is expected depending on the distribution of pinning sites. We report on the field driven DW statistics in sub-100 nm wide nanowires made from Co films with very small edge roughness. The nanowires were patterned in the form of a set of concentric rings of 10 $\mu $m diameter. Two different width nanowires with two different spacings have been studied. The rings were first saturated in plane to produce onion states and then the DWs were translated in the wires using an orthogonal in-plane field. The position of the DWs in the nanowires was determined with magnetic force microscopy. From the positions of the DWs in the nanowires, the strength of the extrinsic pinning sites was identified and they follow two different distributions in two different types of nanowire rings. For the closely spaced wires, magnetostatic interactions led to correlated movement of DWs in neighboring wires. The implications of DW pinning and interaction in nanoscale DW devices will be discussed. [Preview Abstract] |
Monday, March 2, 2015 2:54PM - 3:06PM |
D30.00003: Reversible electrically-driven magnetic domain wall rotation in multiferroic heterostructures to manipulate suspended on-chip magnetic particles Mark Nowakowski, Hyunmin Sohn, Cheng-yen Liang, Joshua Hockel, Kyle Wetzlar, Scott Keller, Brenda McLellan, Matthew Marcus, Andrew Doran, Anthony Young, Mathias Kl\"aui, Gregory Carman, Jeffrey Bokor, Robert Candler We experimentally demonstrate reversible electrically-driven, strain-mediated domain wall (DW) rotation in Ni rings fabricated on piezoelectric [Pb(Mg$_{1/3}$Nb$_{2/3})$O$_{3}$]$_{0.66}$-[PbTiO$_{3}$]$_{0.34}$ (PMN-PT) substrates. An electric field applied across the PMN-PT substrate induces a strain in the Ni rings producing DW rotation around the ring toward the dominant PMN-PT strain axis by inverse magnetostriction. We observe DWs reversibly cycled between their initial and rotated state as a function of the applied electric field with x-ray magnetic circular dichroism photo-emission electron microscopy. The DW rotation is analytically predicted using a fully coupled micromagnetic/elastodyanmic multi-physics simulation to verify that the experimental behavior is caused by the electrically-generated strain in this multiferroic system. Finally, this DW rotation is used to capture and manipulate magnetic particles in a fluidic environment to demonstrate a proof-of-concept energy-efficient pathway for multiferroic-based lab-on-a-chip applications. [Preview Abstract] |
Monday, March 2, 2015 3:06PM - 3:18PM |
D30.00004: Nucleation of 360 deg DWs in a wire using a local circular field Fikriye Idil Kaya, Anandakumar Sarella, Katherine E. Aidala Understanding domain wall (DW) motion in ferromagnetic nanostructures is important to realize proposed magnetic data storage and logic devices. Interest in $360^{o}$ DWs has increased recently with the recognition that their minimal stray field creates only short range interactions, leading to a potentially higher packing density compared to $180^{o}$ DWs. Our simulations demonstrate the feasibility of nucleating a $360^{o}$ DW at a specific location along a wire by applying a local circular field that is centered in close proximity to the wire. We simulate the field strength as if from a current carrying wire, which can be experimentally realized by passing current through the tip of an AFM [$1,2$]. The successful nucleation of a $360^{o}$ DW depends on the dimensions of the Py wire, on the strength of the circular field, and on the distance of the center of the field from the wire. Once a $360^{o}$ DW is nucleated, its position shifts with time. We use a notch to stabilize the location of the $360^{o}$ DW. We investigate the optimal size and spacing of the notches to allow the greatest packing density with control over the nucleation and annihilation of individual domain walls. [$1$] T Yang et al., Appl. Phys. Lett., $98$, $242505$ ($2011$). [$2$] http://math.nist.gov/oommf [Preview Abstract] |
Monday, March 2, 2015 3:18PM - 3:30PM |
D30.00005: Reversal-mechanism of in-plane current-induced perpendicular switching: the role of controllable domain behaviors C. Bi, J.Q. Xiao, M. Liu We propose a magnetization reversal model to explain the perpendicular switching of a single ferromagnetic layer induced by an in-plane current [1]. Our model includes three ingredients: (1) a steady equilibrium magnetization state with equal up and down domains favored by an applied current; (2) domain Wall (DW) motion under the applied current; (3) the up-down ($\uparrow \downarrow )$ DW and down-up ($\downarrow \uparrow )$ DW motions are separately modulated by an applied field. We experimentally demonstrate ingredient (1) can be satisfied in symmetric Pt/Co/Ni/Co/Pt and asymmetric Pt/Co/AlOx structures arising from the magnon instability induced by conventional spin torques [2] and probable spin-Hall torques (SHT) in asymmetric structures. We show ingredient (2) and (3) can also be satisfied in these structures. This model indicates that SHTs mainly play the role of driving DW motion, and a required external field plays the role of modulating the relative velocity of $\uparrow \downarrow $ and $\downarrow \uparrow $ DWs and thus determines the switching directions. This model also predicts similar switching behaviors in skyrmion structures. [1]L. Liu et al. Science 336, 555 (2012);[2] J. Shibata et al. Phys. Rev. Lett. 94, 076601 (2005). [Preview Abstract] |
Monday, March 2, 2015 3:30PM - 3:42PM |
D30.00006: Domain Wall structures in wide permalloy strips Virginia Estevez, Lasse Laurson We analyze numerically the equilibrium micromagnetic domain wall structures encountered in Permalloy strips of a wide range of thicknesses and widths, with strip widths up to several micrometers. By performing an extensive set of micromagnetic simulations, we show that the equilibrium phase diagram of the domain wall structures exhibits in addition to the previously found structures (symmetric and asymmetric transverse wall and vortex wall) also a double-vortex domain wall for large enough strip widths and thicknesses. In general, shape anisotropy is less important for wider strips, and thus energy minima with more complex spin structures closing the flux more efficiently than those found before for narrow strips may appear. Also several metastable domain wall structures are found, such as structures with three or four vortices or two vortices and an antivortex. We discuss the details of the relaxation process, including the effect of varying the magnitude of the Gilbert damping constant, and the role of using different initial conditions. Finally, we also consider the field-driven dynamics of the double-vortex domain wall. [Preview Abstract] |
Monday, March 2, 2015 3:42PM - 3:54PM |
D30.00007: Lateral Domain Transfer In a Magnetic Nanowire With Perpendicular-to-Plane-Anisotropy For Three-Dimensional Memory Applications Aisha Gokce, Ozhan Ozatay, Bugra Bulut, Coleman Rainey, Jordan A. Katine, Thomas Hauet, Anna Giordano, Giovanni Finocchio Spin torque driven magnetic domain transport has been of great interest with potential applications in three dimensional magnetic race track memory and also for domain wall logic. Here we report on experimental and micromagnetic modelling results of spin torque driven magnetic domain transport in CoNi/Pd multilayers with perpendicular-to-plane anisotropy patterned to form magnetic nanowires with double constrictions where domains can be moved with spin polarized current pulses in between constricted sites. The domain nucleation was triggered by joule heating in the presence of a magnetic tip a few nm above the surface which was otherwise in the remanent state. We show that with low or high amplitude nanosecond current pulses two different types of domain transfer behavior is possible: a replicated or partially displaced domain in the neighboring constriction, or an expansion of the domain into the spacer region and the neighboring pinning site. Micromagnetic modelling of the domain transport in such devices suggests that in addition to the experimentally observed behavior a third regime where the full transfer of a single domain is also attainable. Our study shows that CoNi/Pd nanowires can be of potential practical use in a three dimensional memory structure. [Preview Abstract] |
Monday, March 2, 2015 3:54PM - 4:06PM |
D30.00008: ABSTRACT WITHDRAWN |
Monday, March 2, 2015 4:06PM - 4:18PM |
D30.00009: Dzyaloshinskii-Moriya Domain Walls in Nanotubes Oleg Tretiakov, Arseni Goussev, J.M. Robbins, Valeriy Slastikov We study domain walls in thin ferromagnetic nanotubes with Dzyaloshinskii-Moriya interaction (DMI). Dramatic effects arise from the interplay of space curvature and spin-orbit induced DMI on the domain wall structure in these systems. The domain walls become narrower in systems with DMI and curvature. Moreover, the domain walls created in such nanotubes can propagate without Walker breakdown for arbitrary applied currents, thus allowing for a robust and controlled domain-wall motion. The domain-wall velocity is directly proportional to the non-adiabatic spin transfer torque current term and is insensitive to the adiabatic current term. Application of an external magnetic field along the nanotube axis triggers rich dynamical response of the curved domain wall. In particular, we show that the propagation velocity is a non-linear function of both the applied field and DMI, and strongly depends on the orientation and chirality of the wall. [Preview Abstract] |
Monday, March 2, 2015 4:18PM - 4:54PM |
D30.00010: Thermodynamic theory for thermally driven domain wall motion in magnetic nanostructures Invited Speaker: Xiang Rong Wang It is well-established now that a thermal gradient can be used to manipulate spins in a magnetic texture like skyrmions and domain walls (DWs). A thermal gradient can interact with spins through different channels. For example, a thermal gradient can affect spins through the thermoelectric effects by which spin polarized electric current is generated in a ferromagnetic metal. In turn, the thermally generated electric current can interact with magnetic texture via spin-transfer torque (STT). A thermal gradient can also generate magnons or spin waves that interact with magnetic textures. This effect should be important in a ferromagnetic insulator. Spin waves (or magnons) interact with magnetic domain walls (DWs) in a complicated way that a DW can propagate either along or against magnon flow, similar to its electron counterpart. Probably differ from its electron counterpart where one may attribute the ``wrong'' DW propagation direction to the Dzyaloshinskii-Moriya interaction and various types of torques due to spin-orbit interactions, it will be very difficult to understand why a DW can move along the magnon flow if the angular momentum transfer is the only mechanism behind the magnon driven DW motion. It will also be difficulty to explain why ``wrong'' DW propagation direction has not been observed in thermally driven DW motion in both simulations and experiments. Thus, there must be other interaction(s) between spin waves and magnetic textures. In terms of thermal gradient driven DW propagation along a nanowire, a DW always propagates to the hot region of a magnetic insulator wire. We theoretically illustrate why it is surely so from thermodynamic viewpoint. It is shown that DW entropy is always larger than that of a domain. Equivalently, the free energy difference of a DW and a domain decreases as the temperature increases. The larger DW entropy is related to the increase of magnon density of states at low energy originated from the gapless bound spin waves in DWs. This theory should be applicable to other spin textures like skyrmions as well since bound spin waves generally exist in spin textures. The theory also naturally explains why the magnetic domain widths decrease with the increase of the temperature, a well-known experimental phenomenon. In collaboration with X.S. Wang, Hong Kong University of Science \& Technology. \\[4pt] References: [1] ``Thermodynamic theory for thermal-gradient-driven domain wall motion,'' X. S. Wang and X.R. Wang, Phys. Rev. B 90, 014414 (2014). [Preview Abstract] |
Monday, March 2, 2015 4:54PM - 5:06PM |
D30.00011: Asymmetric domain expansion and dendrite formation in thin films with strong Dzyaloshinskii-Moriya interaction Lucas Caretta, Maxwell Mann, Aik-Jun Tan, Geoffrey Beach The Dzyaloshinskii-Moriya interaction (DMI) at heavy-metal/ferromagnet interfaces can stabilize chiral spin textures [1]. It has recently been shown that field-driven bubble domain expansion in perpendicularly-magnetized thin films is asymmetric under the application of an in-plane field, which can be used to quantify the DMI effective field in the (DW). We have imaged domain expansion in Pt(3nm)/Co(0.9nm)/Pt(x)/GdOx(3nm) films using wide-field Kerr microscopy to characterize this behavior systematically as a function of DMI strength. In the case of null or weak DMI, realized when top and bottom Pt layers are of similar thickness, the in-plane field dependence of the DW velocity is well-described by the simple expansion model derived in Ref. [2]. However, in the case of strong DMI, we find a strongly nonmonotonic behavior due to flattening of the DW, minimizing Zeeman energy and DMI energy. Moreover, we show that when the ratio of the DMI effective field to the perpendicular anisotropy field is large, expanding bubble domains leave behind fine-scale dendritic structures, consisting of coupled 360 degree DWs. We present modeling that qualitatively describes these behaviors. 1. A. Fert et al., Nat. Nano., 8, 152-156 (2013) 2. S.G. Je et al., PRB 88, 214401 (2013) [Preview Abstract] |
Monday, March 2, 2015 5:06PM - 5:18PM |
D30.00012: Static and Dynamic Properties of Magnetic Antivortices in Asteroid-Shaped Permalloy Nanomagnets Ali Taha Habiboglu, Vedat Karakas, Mustafa Mete, Ahmet Coskuner, Yemliha Bilal Kalyoncu, Aisha Gokce, Ozhan Ozatay, Anna Giordano, Mario Carpentieri, Giovanni Finocchio, Federica Celegato, Paola Tiberto Patterned nanomagnets display unconventional spin configurations like vortex, anti-vortex, bubble, which have unique static and dynamic properties. Such micro-magnetic structures are potentially applicable to ultrafast memory, rf oscillators and detectors. Studies on magnetic thin films containing vortex structures exhibit interesting behavior under external field and/or current bias like polarity switching, core displacement and core gyration with high frequencies inside the nanomagnet. In this study, we report on our investigation of stable anti-vortex formation conditions and the subsequent magnetic field/dc current driven excitations in 2x2$\mu$m$^2$ Permalloy based asteroid geometry devices which exhibit an anti-vortex pair nucleation at the center. The Magnetic Force Microscopy images show that the antivortex pair can be rotated around the center by an external magnetic field. We obtain a high frequency (GHz) signal measured via anisotropic magneto-resistance effect (AMR) under constant dc current-bias which triggers antivortex pair gyration around the center of the device through spin transfer torque. We study the dynamic response of the structure as a function of current and field to assess utilization of the device as a practical on-chip microwave oscillator. [Preview Abstract] |
Monday, March 2, 2015 5:18PM - 5:30PM |
D30.00013: Micro-hysteresis in the Faraday Rotation of Bismuth Doped Iron Garnets Mannix Shinn, Dong Ho Wu, Anthony Garzarella, Rongjia Tao There is strong interest in using the Faraday effect (Magneto-Optic effect) for non-invasive detection of weak magnetic fields, since in principle one can construct an ultra-sensitive MO-sensor that could be comparable to a SQUID. Bismuth doped rare earth iron garnets (Bi-RIGs) are a candidate material, however their polarization rotation is often measured at saturating fields. We have found that in some Bi-RIGs there is a coercive field that is less than the noise level of our probe beam, which can lead to mischaracterization of sensitivity. This coercivity appears related to magnetic domain wall motion. In this talk I will discuss our experiments and how domain walls can affect the sensitivity of our MO-sensor. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700