Anisotropic Magnetoresistance State Space of Permalloy Nanowires with Domain Wall Pinning Geometry
Corte-León, Héctor; Nabaei, Vahid; Manzin, Alessandra; Fletcher, Jonathan; Krzysteczko, Patryk; Schumacher, Hans W.; Kazakova, Olga
2014-01-01
The domain wall-related change in the anisotropic magnetoresistance in L-shaped permalloy nanowires is measured as a function of the magnitude and orientation of the applied magnetic field. The magnetoresistance curves, compiled into so-called domain wall magnetoresistance state space maps, are used to identify highly reproducible transitions between domain states. Magnetic force microscopy and micromagnetic modelling are correlated with the transport measurements of the devices in order to identify different magnetization states. Analysis allows to determine the optimal working parameters for specific devices, such as the minimal field required to switch magnetization or the most appropriate angle for maximal separation of the pinning/depinning fields. Moreover, the complete state space maps can be used to predict evolution of nanodevices in magnetic field without a need of additional electrical measurements and for repayable initialization of magnetic sensors into a well-specified state. PMID:25116470
Helium ion beam milling to create a nano-structured domain wall magnetoresistance spin valve.
Wang, Yudong; Boden, S A; Bagnall, D M; Rutt, H N; de Groot, C H
2012-10-01
We have fabricated and measured single domain wall magnetoresistance devices with sub-20 nm gap widths using a novel combination of electron beam lithography and helium ion beam milling. The measurement wires and external profile of the spin valve are fabricated by electron beam lithography and lift-off. The critical bridge structure is created using helium ion beam milling, enabling the formation of a thinner gap (and so a narrower domain wall) than that which is possible with electron beam techniques alone. Four-point probe resistance measurements and scanning electron microscopy are used to characterize the milled structures and optimize the He ion dose. Successful operation of the device as a spin valve is demonstrated, with a 0.2% resistance change as the external magnetic field is cycled. The helium ion beam milling efficiency as extracted from electrical resistance measurements is 0.044 atoms/ion, about half the theoretical value. The gap in the device is limited to a maximum of 20 nm with this technique due to sub-surface swelling caused by injected ions which can induce catastrophic failure in the device. The fine patterning capabilities of the helium ion microscope milling technique indicate that sub-5 nm constriction widths could be possible. PMID:22972003
NASA Astrophysics Data System (ADS)
Münchenberger, Jana; Reiss, Günter; Thomas, Andy
2012-04-01
The possibility of controlling the resistance of a memristive giant magnetoresistance (GMR) system via current-induced domain-wall motion was investigated. For a narrow spin-valve structure, current-induced domain-wall motion in the free layer can be detected once the current density exceeds a critical threshold. Then, the resistance of the device depends on the position of the domain wall. The GMR system shows a MR ratio of 10% in the as-prepared state. Narrow stripes were fabricated by e-beam lithography and ion-beam etching with a width of 200 nm. The stripes exhibit GMR ratios up to 8% at room temperature. Micromagnetic simulations of the domain-wall motion in the free layer allow an estimation of the time scale of the domain-wall migration in the stripe. Furthermore, the simulations were compared with measured critical current densities in the free layer with and without an applied external field.
NASA Astrophysics Data System (ADS)
Gushi, Toshiki; Ito, Keita; Higashikozono, Soma; Takata, Fumiya; Oosato, Hirotaka; Sugimoto, Yoshimasa; Toko, Kaoru; Honda, Syuta; Suemasu, Takashi
2016-09-01
The magnetic structure of the domain wall (DW) of a 30-nm-thick Fe4N epitaxial film with a negative spin polarization of the electrical conductivity is observed by magnetic force microscopy and is well explained by micromagnetic simulation. The Fe4N film is grown by molecular beam epitaxy on a SrTiO3(001) substrate and processed into arc-shaped ferromagnetic nanostrips 0.3 μm wide by electron beam lithography and reactive ion etching with Cl2 and BCl3 plasma. Two electrodes mounted approximately 12 μm apart on the nanostrip register an electrical resistance at 8 K. By changing the direction of an external magnetic field (0.2 T), the presence or absence of a DW positioned in the nanostrip between the two electrodes can be controlled. The resistance is increased by approximately 0.5 Ω when the DW is located between the electrodes, which signifies the negative anisotropic magnetoresistance effect of Fe4N. The electrical detection of the resistance change is an important step toward the electrical detection of current-induced DW motion in Fe4N.
NASA Astrophysics Data System (ADS)
Okuda, Mitsunobu; Miyamoto, Yasuyoshi; Miyashita, Eiichi; Saito, Nobuo; Hayashi, Naoto; Nakagawa, Shigeki
2015-05-01
Current-driven magnetic domain walls in magnetic nanowires have attracted a great deal of interest in terms of both physical studies and engineering applications. The anomalous Hall effect measurement is widely used for detecting the magnetization direction of current-driven magnetic domains in a magnetic nanowire. However, the problem with this measurement is that the detection point for current-driven domain wall motion is fixed at only the installed sensing wire across the specimen nanowire. A potential solution is the magnetic domain scope method, whereby the distribution of the magnetic flux leaking from the specimen can be analyzed directly by contact-scanning a tunneling magnetoresistive field sensor on a sample. In this study, we fabricated specimen nanowires consisting of [Co (0.3)/Pd (1.2)]21/Ta(3) films (units in nm) with perpendicular magnetic anisotropy on Si substrates. A tunneling magnetoresistive sensor was placed on the nanowire surface and a predetermined current pulse was applied. Real-time detection of the current-driven magnetic domain motion was successful in that the resistance of the tunneling magnetoresistive sensor was changed with the magnetization direction beneath the sensor. This demonstrates that magnetic domain detection using a tunneling magnetoresistive sensor is effective for the direct analysis of micro magnetic domain motion.
Baer, Oliver; Narayanan, Rajamani; Neuberger, Herbert; Witzel, Oliver
2007-03-15
We propose using the extra dimension separating the domain walls carrying lattice quarks of opposite handedness to gradually filter out the ultraviolet fluctuations of the gauge fields that are felt by the fermionic excitations living in the bulk. This generalization of the homogeneous domain wall construction has some theoretical features that seem nontrivial.
Yoon, Seungha; Jang, Youngman; Lee, Seungkyo; Cho, B K
2011-07-01
We investigated a technique for proving the pinning behaviors of a domain wall (DW) in spin-valve stripes with artificial configurations, which consist of a nano-wire, a large pad and sharp tip at the ends of the wire, and a circular ring at the center. It was found from the GMR measurement at various positions that a DW was pinned at a ring during DW's propagation from the side of pad to the side of tip. Micromagnetic simulation revealed that the initial onion magnetic states of the ring changes continuously to final reverse onion state via counterclockwise vortex state when a counterclockwise tail-to-tail DW pass through the ring. In addition, the simulation results indicated that the magnetic states at a circular ring were determined by the type and chirality of DW. We also studied the characteristics of domain wall motion in the same configuration, when the nano-ring was replaced with square and diamond structures. PMID:22121740
Axion domain wall baryogenesis
Daido, Ryuji; Kitajima, Naoya; Takahashi, Fuminobu
2015-07-28
We propose a new scenario of baryogenesis, in which annihilation of axion domain walls generates a sizable baryon asymmetry. Successful baryogenesis is possible for a wide range of the axion mass and decay constant, m≃10{sup 8}–10{sup 13} GeV and f≃10{sup 13}–10{sup 16} GeV. Baryonic isocurvature perturbations are significantly suppressed in our model, in contrast to various spontaneous baryogenesis scenarios in the slow-roll regime. In particular, the axion domain wall baryogenesis is consistent with high-scale inflation which generates a large tensor-to-scalar ratio within the reach of future CMB B-mode experiments. We also discuss the gravitational waves produced by the domain wall annihilation and its implications for the future gravitational wave experiments.
Interactions between domain walls and spin currents
NASA Astrophysics Data System (ADS)
Klaui, M.; Laufenberg, M.; Backes, D.; Buhrer, W.; Rudiger, U.; Vila, L.; Vouille, C.; Faini, G.
2006-03-01
A promising novel approach for switching magnetic nanostructures is current-induced domain wall propagation (CIDP), where due to a spin torque effect, electrons transfer angular momentum to a head-to-head domain wall and thereby push it in the direction of the electron flow without any externally applied fields. This effect has been observed with a variety of techniques including MFM [1] and spin polarized scanning electron microscopy [2] to directly observe current-induced domain wall propagation in ferromagnetic nanostructures and magnetoresistance measurements to systematically probe the critical current densities as a function of the geometry [3]. The observed wall velocities and critical current densities, where wall motion sets in at room temperature, do not agree well with theoretical 0K calculations [4]. We have therefore measured the critical current densities as a function of the sample temperature. We find that the spin torque effect becomes more efficient at low temperatures, which could account for some of the observed discrepancies between the 300K experiment and the 0K simulation. [1] A. Yamaguchi et al., Phys. Rev. Lett. 92, 77205 (2004); [2] M. Klaui et al., PRL 95, 26601 (2005); [3] M. Klaui et al., PRL 94, 106601 (2005); [4] A. Thiaville et al., EPL 69, 990 (2005); G. Tatara et al., APL 86, 252509 (2005);
Dynamical domain wall and localization
NASA Astrophysics Data System (ADS)
Toyozato, Yuta; Higuchi, Masafumi; Nojiri, Shin'ichi
2016-03-01
Based on the previous works (Toyozato et al., 2013 [24]; Higuchi and Nojiri, 2014 [25]), we investigate the localization of the fields on the dynamical domain wall, where the four-dimensional FRW universe is realized on the domain wall in the five-dimensional space-time. Especially we show that the chiral spinor can localize on the domain wall, which has not been succeeded in the past works as the seminal work in George et al. (2009) [23].
Mirror domain structures induced by interlayer magnetic wall coupling.
Lew, W S; Li, S P; Lopez-Diaz, L; Hatton, D C; Bland, J A C
2003-05-30
We have found that during giant magnetoresistance measurements in approximately 10 x 10 mm(2) NiFe/Cu/Co continuous film spin-valve structures, the resistance value suddenly drops to its absolute minimum during the NiFe reversal. The results reveal that the alignment of all magnetic domains in the NiFe film follow exactly that of corresponding domains in the Co film for an appropriate applied field strength. This phenomenon is caused by trapping of the NiFe domain walls through the magnetostatic interaction with the Co domain-wall stray fields. Consequently, the interlayer domain-wall coupling induces a mirror domain structure in the magnetic trilayer. PMID:12786582
Domain wall assisted GMR head with spin-Hall effect
NASA Astrophysics Data System (ADS)
Arun, R.; Sabareesan, P.; Daniel, M.
2016-05-01
We theoretically study the dynamics of a field induced domain wall in the Py/Pt bi-layer structure in the presence of spin-Hall effect (SHE) by solving the Landau-Lifshitz-Gilbert (LLG) equation along with the adiabatic, nonadiabatic and SHE spin-transfer torques (STTs). It is observed that a weak magnetic field moves the domain wall with high velocity in the presence of SHE and the direction of the velocity is changed by changing the direction of the weak field. The numerical results show that the magnetization of the ferromagnetic layer can be reversed quickly through domain wall motion by changing the direction of a weak external field in the presence of SHE while the direction of current is fixed. The SHE reduces the magnetization reversal time of 1000 nm length strip by 14.7 ns. This study is extended to model a domain wall based GMR (Giant Magnetoresistance) read head with SHE.
Asymmetric angular dependence of domain wall motion in magnetic nanowires.
Nam, Chunghee
2013-03-01
An angular dependence of domain wall (DW) motion is studied in a magnetic wire consisting of a giant-magnetoresistance spin-valve. A DW pinning site is formed by a single notch, where a conventional linear one and a specially designed tilted one are compared. The asymmetric angular dependence was found in the DW depinning behavior with the tilted notch. The geometry control of the pinning site can be useful for DW diode devices using a rotating magnetic field. PMID:23755619
Visualizing domain wall and reverse domain superconductivity.
Iavarone, M; Moore, S A; Fedor, J; Ciocys, S T; Karapetrov, G; Pearson, J; Novosad, V; Bader, S D
2014-08-28
In magnetically coupled, planar ferromagnet-superconductor (F/S) hybrid structures, magnetic domain walls can be used to spatially confine the superconductivity. In contrast to a superconductor in a uniform applied magnetic field, the nucleation of the superconducting order parameter in F/S structures is governed by the inhomogeneous magnetic field distribution. The interplay between the superconductivity localized at the domain walls and far from the walls leads to effects such as re-entrant superconductivity and reverse domain superconductivity with the critical temperature depending upon the location. Here we use scanning tunnelling spectroscopy to directly image the nucleation of superconductivity at the domain wall in F/S structures realized with Co-Pd multilayers and Pb thin films. Our results demonstrate that such F/S structures are attractive model systems that offer the possibility to control the strength and the location of the superconducting nucleus by applying an external magnetic field, potentially useful to guide vortices for computing application.
Visualizing domain wall and reverse domain superconductivity
Iavarone, M.; Moore, S. A.; Fedor, J.; Ciocys, S. T.; Karapetrov, G.; Pearson, J.; Novosad, V.; Bader, S. D.
2014-01-01
In magnetically coupled, planar ferromagnet-superconductor (F/S) hybrid structures, magnetic domain walls can be used to spatially confine the superconductivity. In contrast to a superconductor in a uniform applied magnetic field, the nucleation of the superconducting order parameter in F/S structures is governed by the inhomogeneous magnetic field distribution. The interplay between the superconductivity localized at the domain walls and far from the walls leads to effects such as re-entrant superconductivity and reverse domain superconductivity with the critical temperature depending upon the location. Here we use scanning tunnelling spectroscopy to directly image the nucleation of superconductivity at the domain wall in F/S structures realized with Co-Pd multilayers and Pb thin films. Our results demonstrate that such F/S structures are attractive model systems that offer the possibility to control the strength and the location of the superconducting nucleus by applying an external magnetic field, potentially useful to guide vortices for computing application. PMID:25164004
Functional domain walls in multiferroics
NASA Astrophysics Data System (ADS)
Meier, Dennis
2015-11-01
During the last decade a wide variety of novel and fascinating correlation phenomena has been discovered at domain walls in multiferroic bulk systems, ranging from unusual electronic conductance to inseparably entangled spin and charge degrees of freedom. The domain walls represent quasi-2D functional objects that can be induced, positioned, and erased on demand, bearing considerable technological potential for future nanoelectronics. Most of the challenges that remain to be solved before turning related device paradigms into reality, however, still fall in the field of fundamental condensed matter physics and materials science. In this topical review seminal experimental findings gained on electric and magnetic domain walls in multiferroic bulk materials are addressed. A special focus is put on the physical properties that emerge at so-called charged domain walls and the added functionality that arises from coexisting magnetic order. The research presented in this review highlights that we are just entering a whole new world of intriguing nanoscale physics that is yet to be explored in all its details. The goal is to draw attention to the persistent challenges and identify future key directions for the research on functional domain walls in multiferroics.
Dynamics of domain wall networks
Eto, Minoru; Fujimori, Toshiaki; Nagashima, Takayuki; Sakai, Norisuke; Nitta, Muneto; Ohashi, Keisuke
2007-12-15
Networks or webs of domain walls are admitted in Abelian or non-Abelian gauge theory coupled to fundamental Higgs fields with complex masses. We examine the dynamics of the domain wall loops by using the moduli approximation and find a phase rotation induces a repulsive force which can be understood as a Noether charge of Q-solitons. Non-Abelian gauge theory allows different types of loops which can be deformed to each other by changing a modulus. This admits the moduli geometry like a sandglass made by gluing the tips of the two cigar-(cone-)like metrics of a single triangle loop. We conclude that the sizes of all loops tend to grow for a late time in general models with complex Higgs masses, while the sizes are stabilized at some values once triplet masses are introduced for the Higgs fields. We also show that the stationary motion on the moduli space of the domain wall webs represents 1/4 Bogomol'nyi-Prasad-Sommerfield Q-webs of walls.
Current-induced three-dimensional domain wall propagation in cylindrical NiFe nanowires
NASA Astrophysics Data System (ADS)
Wong, D. W.; Purnama, I.; Lim, G. J.; Gan, W. L.; Murapaka, C.; Lew, W. S.
2016-04-01
We report on the magnetization configurations in single NiFe cylindrical nanowires grown by template-assisted electrodeposition. Angular anisotropic magnetoresistance measurements reveal that a three-dimensional helical domain wall is formed naturally upon relaxation from a saturated state. Micromagnetic simulations support the helical domain wall properties and its reversal process, which involves a splitting of the clockwise and anticlockwise vortices. When a pulsed current is applied to the nanowire, the helical domain wall propagation is observed with a minimum current density needed to overcome its intrinsic pinning.
Skyrmions from Instantons inside Domain Walls
NASA Astrophysics Data System (ADS)
Eto, Minoru; Nitta, Muneto; Ohashi, Keisuke; Tong, David
2005-12-01
Some years ago, Atiyah and Manton described a method to construct approximate Skyrmion solutions from Yang-Mills instantons. Here we present a dynamical realization of this construction using domain walls in a five-dimensional gauge theory. The non-Abelian gauge symmetry is broken in each vacuum but restored in the core of the domain wall, allowing instantons to nestle inside the wall. We show that the world volume dynamics of the wall is given by the Skyrme model, including the four-derivative term, and the instantons appear as domain wall Skyrmions.
Asymmetric counter propagation of domain walls
NASA Astrophysics Data System (ADS)
Andrade-Silva, I.; Clerc, M. G.; Odent, V.
2016-07-01
Far from equilibrium systems show different states and domain walls between them. These walls, depending on the type of connected equilibria, exhibit a rich spatiotemporal dynamics. Here, we investigate the asymmetrical counter propagation of domain walls in an in-plane-switching cell filled with a nematic liquid crystal. Experimentally, we characterize the shape and speed of the domain walls. Based on the molecular orientation, we infer that the counter propagative walls have different elastic deformations. These deformations are responsible of the asymmetric counter propagating fronts. Theoretically, based on symmetry arguments, we propose a simple bistable model under the influence of a nonlinear gradient, which qualitatively describes the observed dynamics.
Dzyaloshinskii-Moriya Domain Walls in Nanotubes
NASA Astrophysics Data System (ADS)
Tretiakov, Oleg; Goussev, Arseni; Robbins, J. M.; Slastikov, Valeriy
2015-03-01
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. We acknowledge support by the Grants-in-Aid for Scientific Research (No. 25800184 and No. 25247056) from the MEXT, Japan and SpinNet.
Okuda, Mitsunobu Miyamoto, Yasuyoshi; Miyashita, Eiichi; Hayashi, Naoto
2014-05-07
Current-driven magnetic domain wall motions in magnetic nanowires have attracted great interests for physical studies and engineering applications. The magnetic force microscope (MFM) is widely used for indirect verification of domain locations in nanowires, where relative magnetic force between the local domains and the MFM probe is used for detection. However, there is an occasional problem that the magnetic moments of MFM probe influenced and/or rotated the magnetic states in the low-moment nanowires. To solve this issue, the “magnetic domain scope for wide area with nano-order resolution (nano-MDS)” method has been proposed recently that could detect the magnetic flux distribution from the specimen directly by scanning of tunneling magnetoresistive field sensor. In this study, magnetic domain structure in nanowires was investigated by both MFM and nano-MDS, and the leakage magnetic flux density from the nanowires was measured quantitatively by nano-MDS. Specimen nanowires consisted from [Co (0.3)/Pd (1.2)]{sub 21}/Ru(3) films (units in nm) with perpendicular magnetic anisotropy were fabricated onto Si substrates by dual ion beam sputtering and e-beam lithography. The length and the width of the fabricated nanowires are 20 μm and 150 nm. We have succeeded to obtain not only the remanent domain images with the detection of up and down magnetizations as similar as those by MFM but also magnetic flux density distribution from nanowires directly by nano-MDS. The obtained value of maximum leakage magnetic flux by nano-MDS is in good agreement with that of coercivity by magneto-optical Kerr effect microscopy. By changing the protective diamond-like-carbon film thickness on tunneling magnetoresistive sensor, the three-dimensional spatial distribution of leakage magnetic flux could be evaluated.
Domain wall conduction in multiaxial ferroelectrics
Eliseev, E. A.; Morozovska, A. N.; Svechnikov, S. V.; Maksymovych, Petro; Kalinin, Sergei V
2012-01-01
The conductance of domain wall structures consisting of either stripes or cylindrical domains in multiaxial ferroelectric-semiconductors is analyzed. The effects of the flexoelectric coupling, domain size, wall tilt, and curvature on charge accumulation are analyzed using the Landau-Ginsburg Devonshire theory for polarization vector combined with the Poisson equation for charge distributions. The proximity and size effect of the electron and donor accumulation/depletion by thin stripe domains and cylindrical nanodomains are revealed. In contrast to thick domain stripes and wider cylindrical domains, in which the carrier accumulation (and so the static conductivity) sharply increases at the domain walls only, small nanodomains of radii less than 5-10 correlation lengths appeared conducting across the entire cross-section. Implications of such conductive nanosized channels may be promising for nanoelectronics.
Free-electron gas at charged domain walls in insulating BaTiO₃.
Sluka, Tomas; Tagantsev, Alexander K; Bednyakov, Petr; Setter, Nava
2013-01-01
Hetero interfaces between metal-oxides display pronounced phenomena such as semiconductor-metal transitions, magnetoresistance, the quantum hall effect and superconductivity. Similar effects at compositionally homogeneous interfaces including ferroic domain walls are expected. Unlike hetero interfaces, domain walls can be created, displaced, annihilated and recreated inside a functioning device. Theory predicts the existence of 'strongly' charged domain walls that break polarization continuity, but are stable and conduct steadily through a quasi-two-dimensional electron gas. Here we show this phenomenon experimentally in charged domain walls of the prototypical ferroelectric BaTiO₃. Their steady metallic-type conductivity, 10(9) times that of the parent matrix, evidence the presence of stable degenerate electron gas, thus adding mobility to functional interfaces.
Magnetoresistance and Phase Breaking Behavior of a Nitrogen Doped Multi-Walled Carbon Nanotube
NASA Astrophysics Data System (ADS)
Yuko Togashi,; Tetsuya Hatori,; Yoshihide Nakamura,; Nobuyuki Aoki,; Janathan P. Bird,; Mauricio Terrones,; Katsumi Kanako,; Yuichi Ochiai,
2010-02-01
The low temperature magnetoresistance (MR) has been studied in a nitrogen doped multi-walled carbon nanotube (CNxMWNT) with a four terminal resistance measurement. The phase coherent properties of electron transport in the CNxMWNT have been deduced from results of quantum-transport analysis. A zero-field peak of the weak localization can be observed in the low-temperature MR, however, there exhibits a clear boundary between the phase braking processes around 10 K. The phase coherence has been analyzed and the quasi-one-dimensional properties have been discussed in weakly localized metallic transport with a low temperature MR in terms of quantum interference.
Domain wall geometry controls conduction in ferroelectrics.
Vasudevan, R K; Morozovska, A N; Eliseev, E A; Britson, J; Yang, J-C; Chu, Y-H; Maksymovych, P; Chen, L Q; Nagarajan, V; Kalinin, S V
2012-11-14
A new paradigm of domain wall nanoelectronics has emerged recently, in which the domain wall in a ferroic is itself an active device element. The ability to spatially modulate the ferroic order parameter within a single domain wall allows the physical properties to be tailored at will and hence opens vastly unexplored device possibilities. Here, we demonstrate via ambient and ultrahigh-vacuum (UHV) scanning probe microscopy (SPM) measurements in bismuth ferrite that the conductivity of the domain walls can be modulated by up to 500% in the spatial dimension as a function of domain wall curvature. Landau-Ginzburg-Devonshire calculations reveal the conduction is a result of carriers or vacancies migrating to neutralize the charge at the formed interface. Phase-field modeling indicates that anisotropic potential distributions can occur even for initially uncharged walls, from polarization dynamics mediated by elastic effects. These results are the first proof of concept for modulation of charge as a function of domain wall geometry by a proximal probe, thereby expanding potential applications for oxide ferroics in future nanoscale electronics. PMID:22994244
Microwave background distortions from domain walls
NASA Technical Reports Server (NTRS)
Goetz, Guenter; Noetzold, Dirk
1990-01-01
Domain walls arising in a cosmic phase transition after decoupling were recently proposed as seeds for the formation of large scale structure. The distortion induced in the microwave background radiation is calculated in dependence of the wall thickness, surface density, scalar field potential, cosmic redshift and the velocity of the wall. It was found that the maximal redshift distortion for both spherical and planar walls is of the order pi G sigma H(sup -1)(sub 0), where sigma is the surface energy density and H(sup -1)(sub 0) the Hubble parameter. It was also found that, for a wall thickness smaller than the horizon, walls can be treated as infinitely thin, i.e., the redshift distortion is independent of the wall thickness and the specific form of the scalar potential. For planar walls moving with a Lorentz-factor gamma the redshift distortion is enhanced by gamma cubed.
Domain Wall structures in wide permalloy strips
NASA Astrophysics Data System (ADS)
Estevez, Virginia; Laurson, Lasse
2015-03-01
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.
Structural domain walls in polar hexagonal manganites
NASA Astrophysics Data System (ADS)
Kumagai, Yu
2014-03-01
The domain structure in the multiferroic hexagonal manganites is currently intensely investigated, motivated by the observation of intriguing sixfold topological defects at their meeting points [Choi, T. et al,. Nature Mater. 9, 253 (2010).] and nanoscale electrical conductivity at the domain walls [Wu, W. et al., Phys. Rev. Lett. 108, 077203 (2012).; Meier, D. et al., Nature Mater. 11, 284 (2012).], as well as reports of coupling between ferroelectricity, magnetism and structural antiphase domains [Geng, Y. et al., Nano Lett. 12, 6055 (2012).]. The detailed structure of the domain walls, as well as the origin of such couplings, however, was previously not fully understood. In the present study, we have used first-principles density functional theory to calculate the structure and properties of the low-energy structural domain walls in the hexagonal manganites [Kumagai, Y. and Spaldin, N. A., Nature Commun. 4, 1540 (2013).]. We find that the lowest energy domain walls are atomically sharp, with {210}orientation, explaining the orientation of recently observed stripe domains and suggesting their topological protection [Chae, S. C. et al., Phys. Rev. Lett. 108, 167603 (2012).]. We also explain why ferroelectric domain walls are always simultaneously antiphase walls, propose a mechanism for ferroelectric switching through domain-wall motion, and suggest an atomistic structure for the cores of the sixfold topological defects. This work was supported by ETH Zurich, the European Research Council FP7 Advanced Grants program me (grant number 291151), the JSPS Postdoctoral Fellowships for Research Abroad, and the MEXT Elements Strategy Initiative to Form Core Research Center TIES.
Moving Towards Domain Wall Devices in Ferroics
NASA Astrophysics Data System (ADS)
Gregg, Marty
Domain walls in ferroelectric, ferroelastic and multiferroic oxides are distinct functional materials in their own right. They can be conducting, or even superconducting, when surrounding domains are insulating; they can demonstrate magnetism when the surrounding bulk is non-magnetic and they can contain ordered electrical dipoles when the matrix containing them is non-polar. Since domain walls can also be created, destroyed, and controllably moved from place to place, there is an amazing opportunity for us to design new forms of devices in which functionality is actively and dynamically deployed (now you see it; now you don't). This is the essence of the emerging field known as ``domain wall nanoelectronics''. In time, this arena of research could change the way we think of nanoscale functional devices, moving increasingly towards agile circuitry and neuromorphic device architectures. While the control of domain wall injection, movement and annihilation has been developed rather well in the nanomagnetics community (in race-track and domain wall logic research), similar research has not been widely performed in nanoscale ferroelectrics, ferroelastics and multiferroics. This talk will discuss progress that has been made to date and the way in which nanomagnetics research can be used as a source of inspiration. Site-specific domain wall injection and motion control in both proper and improper ferroelectrics using inhomogeneous electric and elastic fields, as well as dielectric patterning in uniaxial ferroelectrics, will be specifically considered. As will be shown, sufficient control has been developed to allow the creation of a diode for domain wall motion in ferroelectrics, for example. The author acknowledges support from the Engineering and Physical Sciences Research Council (EPSRC).
Domain walls as probes of gravity
Dvali, Gia; Gabadadze, Gregory; Pujolas, Oriol; Rahman, Rakibur
2007-06-15
We show that domain walls are probes that enable one to distinguish large-distance modified gravity from general relativity (GR) at short distances. For example, low-tension domain walls are stealth in modified gravity, while they do produce global gravitational effects in GR. We demonstrate this by finding exact solutions for various domain walls in the DGP model. A wall with tension lower than the fundamental Planck scale does not inflate and has no gravitational effects on a 4D observer, since its 4D tension is completely screened by gravity itself. We argue that this feature remains valid in a generic class of models of infrared modified gravity. As a byproduct, we obtain exact solutions for supermassive codimension-2 branes.
On thick domain walls in general relativity
NASA Technical Reports Server (NTRS)
Goetz, Guenter; Noetzold, Dirk
1989-01-01
Planar scalar field configurations in general relativity differ considerably from those in flat space. It is shown that static domain walls of finite thickness in curved space-time do not possess a reflection symmetry. At infinity, the space-time tends to the Taub vacuum on one side of the wall and to the Minkowski vacuum (Rindler space-time) on the other. Massive test particles are always accelerated towards the Minkowski side, i.e., domain walls are attractive on the Taub side, but repulsive on the Minkowski side (Taub-vacuum cleaner). It is also proved that the pressure in all directions is always negative. Finally, a brief comment is made concerning the possibility of infinite, i.e., bigger than horizon size, domain walls in our universe. All of the results are independent of the form of the potential V(phi) greater than or equal to 0 of the scalar field phi.
Magnetic field asymmetry and high temperature magnetoresistance in single-walled carbon nanotubes
NASA Astrophysics Data System (ADS)
Cobden, David
2006-03-01
The length scales and scattering processes in the one-dimensional electron system in single-walled carbon nanotubes remain only partially understood. Measuring the magnetoresistance, in both linear and nonlinear response, is a way to investigate these processes. In disordered nanotubes with ballistic paths much shorter than the length, we observe magnetoresistance in the metallic regime which at low temperatures resembles the universal fluctuations and weak localization seen in higher dimensional metals. A parabolic magnetoresistance persists at room temperature, indicating a significant role for phase coherence and/or interactions at high temperatures. While the linear resistance of a two-terminal sample must be an even function of magnetic field B by Onsager's principle, the nonlinear resistance need not be. Importantly, the B-asymmetric nonlinear terms can in principle be used to infer the strength of electron-electron interactions in the sample [1]. We have therefore also measured in detail the lowest order B-asymmetric current contributions, with a focus on the B-linear term. This has apparently not been done before in any system. Consistent with general theory, at high temperatures the term is small and has a constant sign independent of Fermi energy. At low temperatures it grows and develops mesoscopic fluctuations. Although these result imply that interactions are involved in the transport, calculations specific to nanotubes are needed in order to extract interaction parameters. This work was done by the authors of Ref [2]. References: [1] E.L. Ivchenko and B. Spivak, Phys. Rev. B 66, 155404 (2002); [2] Jiang Wei, Michael Shimogawa, Zenghui Wang, Iuliana Radu, Robert Dormaier, and David H. Cobden, Phys. Rev. Lett. (Dec. 2005) (cond-mat/0506275).
NASA Astrophysics Data System (ADS)
Płomińska, Anna; Weymann, Ireneusz
2015-11-01
The spin-resolved transport properties of a single-wall carbon nanotube quantum dot, with an attached single molecular magnet, are studied theoretically. With the aid of the real-time diagrammatic technique in the lowest-order perturbation expansion with respect to the tunnel coupling, the current, differential conductance, and the tunnel magnetoresistance (TMR) are determined in both the linear and nonlinear response regimes. It is shown that transport properties depend greatly on both the shell filling sequence of the carbon nanotube and the type of exchange interaction between the molecular magnet and nanotube. This results in highly nontrivial behavior of the TMR, which is especially visible in the low bias voltage regime. Depending on the gate voltage and parameters of the system, we find transport regimes where either a greatly enhanced or negative TMR develops. The mechanism leading to such behavior is associated with nonequilibrium spin accumulation, which builds up in the antiparallel magnetic configuration of the device. We show that it is crucial whether the spin accumulation occurs in the highest-weight spin states or in states with lower spin values. While in the former case it leads to enhanced TMR, in the latter case it may result in negative tunnel magnetoresistance. In addition, we analyze how the above effects depend on the magnitude of the molecular magnet's spin, and show that this dependence is generally nonmonotonic.
Anomalous feedback and negative domain wall resistance
NASA Astrophysics Data System (ADS)
Cheng, Ran; Zhu, Jian-Gang; Xiao, Di
2016-11-01
Magnetic induction can be regarded as a negative feedback effect, where the motive-force opposes the change of magnetic flux that generates the motive-force. In artificial electromagnetics emerging from spintronics, however, this is not necessarily the case. By studying the current-induced domain wall dynamics in a cylindrical nanowire, we show that the spin motive-force exerting on electrons can either oppose or support the applied current that drives the domain wall. The switching into the anomalous feedback regime occurs when the strength of the dissipative torque β is about twice the value of the Gilbert damping constant α. The anomalous feedback manifests as a negative domain wall resistance, which has an analogy with the water turbine.
Seemann, K M; Garcia-Sanchez, F; Kronast, F; Miguel, J; Kákay, A; Schneider, C M; Hertel, R; Freimuth, F; Mokrousov, Y; Blügel, S
2012-02-17
We analyze the origin of the electrical resistance arising in domain walls of perpendicularly magnetized materials by considering a superposition of anisotropic magnetoresistance and the resistance implied by the magnetization chirality. The domain wall profiles of L1(0)-FePd and L1(0)-FePt are determined by micromagnetic simulations based on which we perform first-principles calculations to quantify electron transport through the core and closure region of the walls. The wall resistance, being twice as high in L1(0)-FePd than in L1(0)-FePt, is found to be clearly dominated in both cases by a high gradient of magnetization rotation, which agrees well with experimental observations.
Standing gravitational waves from domain walls
Gogberashvili, Merab; Myrzakul, Shynaray; Singleton, Douglas
2009-07-15
We construct a plane symmetric, standing gravitational wave for a domain wall plus a massless scalar field. The scalar field can be associated with a fluid which has the properties of 'stiff' matter, i.e., matter in which the speed of sound equals the speed of light. Although domain walls are observationally ruled out in the present era, the solution has interesting features which might shed light on the character of exact nonlinear wave solutions to Einstein's equations. Additionally this solution may act as a template for higher dimensional 'brane-world' model standing waves.
Voltage drop due to longitudinal spin accumulation across the ballistic domain wall
NASA Astrophysics Data System (ADS)
Fallahi, V.; Safaei, R.
2016-08-01
The ballistic magnetoresistance (MR) of a domain wall constricted in a nanocontact between two p -type semiconducting magnetic nanowires is studied theoretically using the Landauer-Büttiker approach. Our analysis is based on coherent scattering of the carriers by the spin-dependent potential associated with the wall structure. The transmission properties of coherent states are obtained by introducing an algorithm to solve the coupled spin channels Schrödinger equation with mixed Dirichlet-Neumann boundary conditions applied far from the domain wall. Then, the local accumulated spin densities along the nanowire produced by electrical spin injection at the nanocontact are numerically calculated. It is demonstrated that the induced voltage drop due to the longitudinal spin accumulation considerably increases in the case of the narrow domain walls. Furthermore, it is shown that two spin accumulation and mistracking effects give approximately equal contributions to the wall MR ratio in the limit of the sharp domain walls. However, the MR ratio is dominantly determined by the spin accumulation effect as the domain wall width increases.
Separated matter and antimatter domains with vanishing domain walls
Dolgov, A.D.; Godunov, S.I.; Rudenko, A.S.; Tkachev, I.I. E-mail: sgodunov@itep.ru E-mail: tkachev@ms2.inr.ac.ru
2015-10-01
We present a model of spontaneous (or dynamical) C and CP violation where it is possible to generate domains of matter and antimatter separated by cosmologically large distances. Such C(CP) violation existed only in the early universe and later it disappeared with the only trace of generated baryonic and/or antibaryonic domains. So the problem of domain walls in this model does not exist. These features are achieved through a postulated form of interaction between inflaton and a new scalar field, realizing short time C(CP) violation.
The dynamics of domain walls and strings
NASA Technical Reports Server (NTRS)
Gregory, Ruth; Haws, David; Garfinkle, David
1989-01-01
The leading order finite-width corrections to the equation of motion describing the motion of a domain wall are derived. The regime in which this equation of motion is invalid is discussed. Spherically and cylindrically symmetric solutions to this equation of motion are found. A misconception that has arisen in recent years regarding the rigidity (or otherwise) of cosmic strings is also clarified.
Antiferromagnetic Domain Wall Motion Driven by Spin-Orbit Torques.
Shiino, Takayuki; Oh, Se-Hyeok; Haney, Paul M; Lee, Seo-Won; Go, Gyungchoon; Park, Byong-Guk; Lee, Kyung-Jin
2016-08-19
We theoretically investigate the dynamics of antiferromagnetic domain walls driven by spin-orbit torques in antiferromagnet-heavy-metal bilayers. We show that spin-orbit torques drive antiferromagnetic domain walls much faster than ferromagnetic domain walls. As the domain wall velocity approaches the maximum spin-wave group velocity, the domain wall undergoes Lorentz contraction and emits spin waves in the terahertz frequency range. The interplay between spin-orbit torques and the relativistic dynamics of antiferromagnetic domain walls leads to the efficient manipulation of antiferromagnetic spin textures and paves the way for the generation of high frequency signals from antiferromagnets. PMID:27588878
Antiferromagnetic Domain Wall Motion Driven by Spin-Orbit Torques
NASA Astrophysics Data System (ADS)
Shiino, Takayuki; Oh, Se-Hyeok; Haney, Paul M.; Lee, Seo-Won; Go, Gyungchoon; Park, Byong-Guk; Lee, Kyung-Jin
2016-08-01
We theoretically investigate the dynamics of antiferromagnetic domain walls driven by spin-orbit torques in antiferromagnet-heavy-metal bilayers. We show that spin-orbit torques drive antiferromagnetic domain walls much faster than ferromagnetic domain walls. As the domain wall velocity approaches the maximum spin-wave group velocity, the domain wall undergoes Lorentz contraction and emits spin waves in the terahertz frequency range. The interplay between spin-orbit torques and the relativistic dynamics of antiferromagnetic domain walls leads to the efficient manipulation of antiferromagnetic spin textures and paves the way for the generation of high frequency signals from antiferromagnets.
Skyrmion domain wall collision and domain wall-gated skyrmion logic
NASA Astrophysics Data System (ADS)
Xing, Xiangjun; Pong, Philip W. T.; Zhou, Yan
2016-08-01
Skyrmions and domain walls are significant spin textures of great technological relevance to magnetic memory and logic applications, where they can be used as carriers of information. The unique topology of skyrmions makes them display emergent dynamical properties as compared with domain walls. Some studies have demonstrated that the two topologically inequivalent magnetic objects could be interconverted by using cleverly designed geometric structures. Here, we numerically address the skyrmion domain wall collision in a magnetic racetrack by introducing relative motion between the two objects based on a specially designed junction. An electric current serves as the driving force that moves a skyrmion toward a trapped domain wall pair. We see different types of collision dynamics depending on the driving parameters. Most importantly, the modulation of skyrmion transport using domain walls is realized in this system, allowing a set of domain wall-gated logical NOT, NAND, and NOR gates to be constructed. This work provides a skyrmion-based spin-logic architecture that is fully compatible with racetrack memories.
Stability of a pinned magnetic domain wall as a function of its internal configuration
NASA Astrophysics Data System (ADS)
Montaigne, F.; Duluard, A.; Briones, J.; Lacour, D.; Hehn, M.; Childress, J. R.
2015-01-01
It is shown that there are many stable configurations for a domain wall pinned by a notch along a magnetic stripe. The stability of several of these configurations is investigated numerically as a function of the thickness of the magnetic film. The depinning mechanism depends on the structure of the domain wall and on the thickness of the magnetic film. In the case of a spin-valve structure, it appears that the stray fields emerging from the hard layer at the notch location influence the stability of the micromagnetic configuration. Different depinning mechanisms are thus observed for the same film thickness depending on the magnetization orientation of the propagating domain. This conclusion qualitatively explains experimental magnetoresistance measurements.
Polar domain walls trigger magnetoelectric coupling
Fontcuberta, Josep; Skumryev, Vassil; Laukhin, Vladimir; Granados, Xavier; Salje, Ekhard K. H.
2015-01-01
Interface physics in oxides heterostructures is pivotal in material’s science. Domain walls (DWs) in ferroic systems are examples of naturally occurring interfaces, where order parameter of neighboring domains is modified and emerging properties may develop. Here we show that electric tuning of ferroelastic domain walls in SrTiO3 leads to dramatic changes of the magnetic domain structure of a neighboring magnetic layer (La1/2Sr1/2MnO3) epitaxially clamped on a SrTiO3 substrate. We show that the properties of the magnetic layer are intimately connected to the existence of polar regions at twin boundaries of SrTiO3, developing at , that can be electrically modulated. These findings illustrate that by exploiting the responsiveness of DWs nanoregions to external stimuli, even in absence of any domain contribution, prominent and adjustable macroscopic reactions of neighboring layers can be obtained. We conclude that polar DWs, known to exist in other materials, can be used to trigger tunable responses and may lead to new ways for the manipulation of interfacial emerging properties. PMID:26387597
Magnetoresistive polyaniline/multi-walled carbon nanotube nanocomposites with negative permittivity
NASA Astrophysics Data System (ADS)
Gu, Hongbo; Guo, Jiang; He, Qingliang; Jiang, Yuan; Huang, Yudong; Haldolaarachige, Neel; Luo, Zhiping; Young, David P.; Wei, Suying; Guo, Zhanhu
2013-12-01
Contrary to the observed positive giant magnetoresistance (GMR) in as-received multi-walled carbon nanotubes (MWNTs), pure polyaniline (PANI) synthesized with Cr(vi) as oxidant and MWNTs/PANI nanocomposites with ammonium persulfate (APS) as oxidant, a room temperature negative GMR of around -2% was reported in MWNTs/PANI nanocomposites with Cr(vi) as oxidant. Different from a frequency switch of permittivity from negative to positive in MWNTs/PANI nanocomposites with APS as oxidant, unique negative permittivity was observed in MWNTs/PANI nanocomposites with Cr(vi) as oxidant within the measured frequency range from 20 to 2 × 106 Hz. The obtained unique negative permittivity was explained by the plasma frequency from the Drude model, at which the permittivity changes from negative to positive and the material changes from a metamaterial to an ordinary dielectric medium. The observed positive and negative GMR behaviors in these disordered systems as verified by the temperature dependent resistivity exploration were well explained through a wave-function shrinkage model and orbital magnetoconductivity theory by calculating the changed localization length (a0).Contrary to the observed positive giant magnetoresistance (GMR) in as-received multi-walled carbon nanotubes (MWNTs), pure polyaniline (PANI) synthesized with Cr(vi) as oxidant and MWNTs/PANI nanocomposites with ammonium persulfate (APS) as oxidant, a room temperature negative GMR of around -2% was reported in MWNTs/PANI nanocomposites with Cr(vi) as oxidant. Different from a frequency switch of permittivity from negative to positive in MWNTs/PANI nanocomposites with APS as oxidant, unique negative permittivity was observed in MWNTs/PANI nanocomposites with Cr(vi) as oxidant within the measured frequency range from 20 to 2 × 106 Hz. The obtained unique negative permittivity was explained by the plasma frequency from the Drude model, at which the permittivity changes from negative to positive and the material
Domain wall motion in ferroelectrics: Barkhausen noise
NASA Astrophysics Data System (ADS)
Shur, V.; Rumyantsev, E.; Kozhevnikov, V.; Nikolaeva, E.; Shishkin, E.
2002-03-01
The switching current noise has been recorded during polarization reversal in single-crystalline gadolinium molybdate (GMO) and lithium tantalate (LT). Analysis of Barkhausen noise (BN) data allows to classify the noise types by determination of the critical indexes and fractal dimensions. BN is manifested as the short pulses during the polarization reversal. We have analyzed the BN data recorded in GMO and LT with various types of controlled domain structure. The data treatment in terms of probability distribution of duration, area and energy of individual pulses reveals the critical behavior typical for the fractal records in time. We used the Fourier transform and Hurst's rescaled range analysis for obtaining the Hurst factor, fractal dimension and classifying the noise types. We investigated by computer simulation the mechanism of sideways motion of 180O domain wall by nucleation at the wall taking into account the nuclei-nuclei interaction. It was shown that the moving domain walls display the fractal shape and their motion is accompanied by Flicker noise, which is in accord with experimental data. The research was made possible in part by Programs "Basic Research in Russian Universities" and "Priority Research in High School. Electronics", by Grant No. 01-02-17443 of RFBR, by Award No.REC-005 of CRDF.
Magnetic bead detection using domain wall-based nanosensor
Corte-León, H.; Krzysteczko, P.; Schumacher, H. W.; Manzin, A.; Cox, D.; Antonov, V.; Kazakova, O.
2015-05-07
We investigate the effect of a single magnetic bead (MB) on the domain wall (DW) pinning/depinning fields of a DW trapped at the corner of an L-shaped magnetic nanodevice. DW propagation across the device is investigated using magnetoresistance measurements. DW pinning/depinning fields are characterized in as-prepared devices and after placement of a 1 μm-sized MB (Dynabeads{sup ®} MyOne{sup ™}) at the corner. The effect of the MB on the DW dynamics is seen as an increase in the depinning field for specific orientations of the device with respect to the external magnetic field. The shift of the depinning field, ΔB{sub dep} = 4.5–27.0 mT, is highly stable and reproducible, being significantly above the stochastic deviation which is about 0.5 mT. The shift in the deppinning field is inversely proportional to the device width and larger for small negative angles between the device and the external magnetic field. Thus, we demonstrate that DW-based devices can be successfully used for detection of single micron size MB.
Correlation between spin structure oscillations and domain wall velocities
Bisig, André; Stärk, Martin; Mawass, Mohamad-Assaad; Moutafis, Christoforos; Rhensius, Jan; Heidler, Jakoba; Büttner, Felix; Noske, Matthias; Weigand, Markus; Eisebitt, Stefan; Tyliszczak, Tolek; Van Waeyenberge, Bartel; Stoll, Hermann; Schütz, Gisela; Kläui, Mathias
2013-01-01
Magnetic sensing and logic devices based on the motion of magnetic domain walls rely on the precise and deterministic control of the position and the velocity of individual magnetic domain walls in curved nanowires. Varying domain wall velocities have been predicted to result from intrinsic effects such as oscillating domain wall spin structure transformations and extrinsic pinning due to imperfections. Here we use direct dynamic imaging of the nanoscale spin structure that allows us for the first time to directly check these predictions. We find a new regime of oscillating domain wall motion even below the Walker breakdown correlated with periodic spin structure changes. We show that the extrinsic pinning from imperfections in the nanowire only affects slow domain walls and we identify the magnetostatic energy, which scales with the domain wall velocity, as the energy reservoir for the domain wall to overcome the local pinning potential landscape. PMID:23978905
Magnetic domain wall manipulation in (Ga,Mn)As nanostructures for spintronic applications
Wosinski, Tadeusz; Andrearczyk, Tomasz; Figielski, Tadeusz; Olender, Karolina; Wrobel, Jerzy
2014-02-21
Ring-shaped nanostructures have been designed and fabricated by electron-beam lithography patterning and chemical etching from thin epitaxial layers of the ferromagnetic semiconductor (Ga,Mn)As. The nanostructures, in a form of planar rings with a slit, were supplied with four electrical terminals and subjected to magneto-transport studies under planar weak magnetic field. Magnetoresistive effects caused by manipulation of magnetic domain walls and magnetization reversal in the nanostructures have been investigated and possible applications of the nanostructures as four-terminal spintronic devices are discussed.
PREFACE: Domain wall dynamics in nanostructures Domain wall dynamics in nanostructures
NASA Astrophysics Data System (ADS)
Marrows, C. H.; Meier, G.
2012-01-01
Domain structures in magnetic materials are ubiquitous and have been studied for decades. The walls that separate them are topological defects in the magnetic order parameter and have a wide variety of complex forms. In general, their investigation is difficult in bulk materials since only the domain structure on the surface of a specimen is visible. Cutting the sample to reveal the interior causes a rearrangement of the domains into a new form. As with many other areas of magnetism, the study of domain wall physics has been revitalised by the advent of nanotechnology. The ability to fabricate nanoscale structures has permitted the formation of simplified and controlled domain patterns; the development of advanced microscopy methods has permitted them to be imaged and then modelled; subjecting them to ultrashort field and current pulses has permitted their dynamics to be explored. The latest results from all of these advances are described in this special issue. Not only has this led to results of great scientific beauty, but also to concepts of great applicability to future information technologies. In this issue the reader will find the latest results for these domain wall dynamics and the high-speed processes of topological structures such as domain walls and magnetic vortices. These dynamics can be driven by the application of magnetic fields, or by flowing currents through spintronic devices using the novel physics of spin-transfer torque. This complexity has been studied using a wide variety of experimental techniques at the edge of the spatial and temporal resolution currently available, and can be described using sophisticated analytical theory and computational modelling. As a result, the dynamics can be engineered to give rise to finely controlled memory and logic devices with new functionality. Moreover, the field is moving to study not only the conventional transition metal ferromagnets, but also complex heterostructures, novel magnets and even other
Entropy production by domain wall decay in the NMSSM
NASA Astrophysics Data System (ADS)
Hattori, Hironori; Kobayashi, Tatsuo; Omoto, Naoya; Seto, Osamu
2015-11-01
We consider domain walls in the Z3 symmetric next-to-minimal supersymmetric standard model. The spontaneous Z3 discrete symmetry breaking produces domain walls, and the stable domain walls are problematic. Thus, we assume the Z3 symmetry is slightly but explicitly broken and the domain walls decay. Such a decay causes a large late-time entropy production. We study its cosmological implications on unwanted relics such as the moduli, gravitino, lightest superparticle, and axion.
Magnetoresistive polyaniline/multi-walled carbon nanotube nanocomposites with negative permittivity.
Gu, Hongbo; Guo, Jiang; He, Qingliang; Jiang, Yuan; Huang, Yudong; Haldolaarachige, Neel; Luo, Zhiping; Young, David P; Wei, Suying; Guo, Zhanhu
2014-01-01
Contrary to the observed positive giant magnetoresistance (GMR) in as-received multi-walled carbon nanotubes (MWNTs), pure polyaniline (PANI) synthesized with Cr(vi) as oxidant and MWNTs/PANI nanocomposites with ammonium persulfate (APS) as oxidant, a room temperature negative GMR of around -2% was reported in MWNTs/PANI nanocomposites with Cr(vi) as oxidant. Different from a frequency switch of permittivity from negative to positive in MWNTs/PANI nanocomposites with APS as oxidant, unique negative permittivity was observed in MWNTs/PANI nanocomposites with Cr(vi) as oxidant within the measured frequency range from 20 to 2 × 10(6) Hz. The obtained unique negative permittivity was explained by the plasma frequency from the Drude model, at which the permittivity changes from negative to positive and the material changes from a metamaterial to an ordinary dielectric medium. The observed positive and negative GMR behaviors in these disordered systems as verified by the temperature dependent resistivity exploration were well explained through a wave-function shrinkage model and orbital magnetoconductivity theory by calculating the changed localization length (a0). PMID:24226933
Domain-wall supergravities from sphere reduction
NASA Astrophysics Data System (ADS)
Cvetič , M.; Liu, James T.; Lü, H.; Pope, C. N.
1999-10-01
Kaluza-Klein sphere reductions of supergravities that admit Ads × Sphere vacuum solutions are believed to be consistent. The examples include the S4 and S7 reductions of eleven-dimensional supergravity, and the S5 reduction of ten-dimensional type IIB supergravity . In this paper we provide evidence that sphere reductions of supergravities that admit instead Domain-wallxSphere vacuum solutions are also consistent, where the background can be viewed as the near-horizon structure of a dilatonic p-brane of the theory. The resulting lower-dimensional theory is a gauged supergravity that admits a domain wall, rather than AdS, as a vacuum solution. We illustrate this consistency by taking the singular limits of certain modulus parameters, for which the original Sn compactifying spheres ( n = 4, 5 or 7) becomes Sp × Rq, with p = n - q < n. The consistency of the S4, S7 reductions then implies the consistency of the S p reductions of the lower-dimensional supergravities. In particular, we obtain explicit non-linear ansätze for the S3 reduction of type IIA and heterotic supergravities, restricting to the U(1) 2 subgroup of the SO(4) gauge group of S3. We also study the black-hole solutions in the lower-dimensional gauged supergravities with domain-wall backgrounds. We find new domain-wall black holes which are not the singular-modulus limits of the AdS black holes of the original theories, and we obtain their Killing spinors.
Low field domain wall dynamics in artificial spin-ice basis structure
Kwon, J.; Goolaup, S.; Lim, G. J.; Kerk, I. S.; Lew, W. S.; Chang, C. H.; Roy, K.
2015-10-28
Artificial magnetic spin-ice nanostructures provide an ideal platform for the observation of magnetic monopoles. The formation of a magnetic monopole is governed by the motion of a magnetic charge carrier via the propagation of domain walls (DWs) in a lattice. To date, most experiments have been on the static visualization of DW propagation in the lattice. In this paper, we report on the low field dynamics of DW in a unit spin-ice structure measured by magnetoresistance changes. Our results show that reversible DW propagation can be initiated within the spin-ice basis. The initial magnetization configuration of the unit structure strongly influences the direction of DW motion in the branches. Single or multiple domain wall nucleation can be induced in the respective branches of the unit spin ice by the direction of the applied field.
Strain-controlled magnetic domain wall propagation in hybrid piezoelectric/ferromagnetic structures
Lei, Na; Devolder, Thibaut; Agnus, Guillaume; Aubert, Pascal; Daniel, Laurent; Kim, Joo-Von; Zhao, Weisheng; Trypiniotis, Theodossis; Cowburn, Russell P.; Chappert, Claude; Ravelosona, Dafiné; Lecoeur, Philippe
2013-01-01
The control of magnetic order in nanoscale devices underpins many proposals for integrating spintronics concepts into conventional electronics. A key challenge lies in finding an energy-efficient means of control, as power dissipation remains an important factor limiting future miniaturization of integrated circuits. One promising approach involves magnetoelectric coupling in magnetostrictive/piezoelectric systems, where induced strains can bear directly on the magnetic anisotropy. While such processes have been demonstrated in several multiferroic heterostructures, the incorporation of such complex materials into practical geometries has been lacking. Here we demonstrate the possibility of generating sizeable anisotropy changes, through induced strains driven by applied electric fields, in hybrid piezoelectric/spin-valve nanowires. By combining magneto-optical Kerr effect and magnetoresistance measurements, we show that domain wall propagation fields can be doubled under locally applied strains. These results highlight the prospect of constructing low-power domain wall gates for magnetic logic devices. PMID:23340418
Strain-controlled magnetic domain wall propagation in hybrid piezoelectric/ferromagnetic structures.
Lei, Na; Devolder, Thibaut; Agnus, Guillaume; Aubert, Pascal; Daniel, Laurent; Kim, Joo-Von; Zhao, Weisheng; Trypiniotis, Theodossis; Cowburn, Russell P; Chappert, Claude; Ravelosona, Dafiné; Lecoeur, Philippe
2013-01-01
The control of magnetic order in nanoscale devices underpins many proposals for integrating spintronics concepts into conventional electronics. A key challenge lies in finding an energy-efficient means of control, as power dissipation remains an important factor limiting future miniaturization of integrated circuits. One promising approach involves magnetoelectric coupling in magnetostrictive/piezoelectric systems, where induced strains can bear directly on the magnetic anisotropy. While such processes have been demonstrated in several multiferroic heterostructures, the incorporation of such complex materials into practical geometries has been lacking. Here we demonstrate the possibility of generating sizeable anisotropy changes, through induced strains driven by applied electric fields, in hybrid piezoelectric/spin-valve nanowires. By combining magneto-optical Kerr effect and magnetoresistance measurements, we show that domain wall propagation fields can be doubled under locally applied strains. These results highlight the prospect of constructing low-power domain wall gates for magnetic logic devices. PMID:23340418
Boosting domain wall propagation by notches
NASA Astrophysics Data System (ADS)
Yuan, H. Y.; Wang, X. R.
2015-08-01
We report a counterintuitive finding that notches in an otherwise homogeneous magnetic nanowire can boost current-induced domain wall (DW) propagation. DW motion in notch-modulated wires can be classified into three phases: (1) A DW is pinned around a notch when the current density is below the depinning current density. (2) DW propagation velocity is boosted by notches above the depinning current density and when nonadiabatic spin-transfer torque strength β is smaller than the Gilbert damping constant α . The boost can be multifold. (3) DW propagation velocity is hindered when β >α . The results are explained by using the Thiele equation.
Magnetic domain wall motion by spin transfer
NASA Astrophysics Data System (ADS)
Grollier, Julie; Chanthbouala, A.; Matsumoto, R.; Anane, A.; Cros, V.; Nguyen van Dau, F.; Fert, Albert
2011-04-01
The discovery that a spin polarized current can exert a large torque on a ferromagnet through a transfusion of spin angular momentum, offers a new way to control a magnetization by simple current injection, without the help of an applied external field. Spin transfer can be used to induce magnetization reversals and oscillations, or to control the position of a magnetic domain wall. In this review, we focus on this last mechanism, which is today the subject of an extensive research, both because the microscopic details for its origin are still debated, but also because promising applications are at stake for non-volatile magnetic memories.
Constricted nanowire with stabilized magnetic domain wall
NASA Astrophysics Data System (ADS)
Sbiaa, R.; Al Bahri, M.
2016-08-01
Domain wall (DW)-based magnetic memory offers the possibility for increasing the storage capacity. However, stability of DW remains the major drawback of this scheme. In this letter, we propose a stepped nanowire for pinning DW in a desirable position. From micromagnetic simulation, the proposed design applied to in-plane magnetic anisotropy materials shows that by adjusting the nanowire step size and its width it is possible to stabilize DW for a desirable current density range. In contrast, only a movement of DW could be seen for conventional nanowire. An extension to a multi-stepped nanowire could be used for multi-bit per cell magnetic memory.
Polarization control at spin-driven ferroelectric domain walls
NASA Astrophysics Data System (ADS)
Leo, Naëmi; Bergman, Anders; Cano, Andres; Poudel, Narayan; Lorenz, Bernd; Fiebig, Manfred; Meier, Dennis
2015-04-01
Unusual electronic states arise at ferroelectric domain walls due to the local symmetry reduction, strain gradients and electrostatics. This particularly applies to improper ferroelectrics, where the polarization is induced by a structural or magnetic order parameter. Because of the subordinate nature of the polarization, the rigid mechanical and electrostatic boundary conditions that constrain domain walls in proper ferroics are lifted. Here we show that spin-driven ferroelectricity promotes the emergence of charged domain walls. This provides new degrees of flexibility for controlling domain-wall charges in a deterministic and reversible process. We create and position a domain wall by an electric field in Mn0.95Co0.05WO4. With a magnetic field we then rotate the polarization and convert neutral into charged domain walls, while its magnetic properties peg the wall to its location. Using atomistic Landau-Lifshitz-Gilbert simulations we quantify the polarization changes across the two wall types and highlight their general occurrence.
Polarization control at spin-driven ferroelectric domain walls.
Leo, Naëmi; Bergman, Anders; Cano, Andres; Poudel, Narayan; Lorenz, Bernd; Fiebig, Manfred; Meier, Dennis
2015-04-14
Unusual electronic states arise at ferroelectric domain walls due to the local symmetry reduction, strain gradients and electrostatics. This particularly applies to improper ferroelectrics, where the polarization is induced by a structural or magnetic order parameter. Because of the subordinate nature of the polarization, the rigid mechanical and electrostatic boundary conditions that constrain domain walls in proper ferroics are lifted. Here we show that spin-driven ferroelectricity promotes the emergence of charged domain walls. This provides new degrees of flexibility for controlling domain-wall charges in a deterministic and reversible process. We create and position a domain wall by an electric field in Mn0.95Co0.05WO4. With a magnetic field we then rotate the polarization and convert neutral into charged domain walls, while its magnetic properties peg the wall to its location. Using atomistic Landau-Lifshitz-Gilbert simulations we quantify the polarization changes across the two wall types and highlight their general occurrence.
A diode for ferroelectric domain-wall motion
Whyte, J.R.; Gregg, J.M.
2015-01-01
For over a decade, controlling domain-wall injection, motion and annihilation along nanowires has been the preserve of the nanomagnetics research community. Revolutionary technologies have resulted, like racetrack memory and domain-wall logic. Until recently, equivalent research in analogous ferroic materials did not seem important. However, with the discovery of sheet conduction, the control of domain walls in ferroelectrics has become vital for the future of what has been termed ‘domain-wall electronics'. Here we report the creation of a ferroelectric domain-wall diode, which allows a single direction of motion for all domain walls, irrespective of their polarity, under a series of alternating electric field pulses. The diode's sawtooth morphology is central to its function. Domain walls can move readily in the direction in which thickness increases gradually, but are prevented from moving in the other direction by the sudden thickness increase at the sawtooth edge. PMID:26059779
Inflationary power asymmetry from primordial domain walls
Jazayeri, Sadra; Akrami, Yashar; Firouzjahi, Hassan; Solomon, Adam R.; Wang, Yi E-mail: yashar.akrami@astro.uio.no E-mail: a.r.solomon@damtp.cam.ac.uk
2014-11-01
We study the asymmetric primordial fluctuations in a model of inflation in which translational invariance is broken by a domain wall. We calculate the corrections to the power spectrum of curvature perturbations; they are anisotropic and contain dipole, quadrupole, and higher multipoles with non-trivial scale-dependent amplitudes. Inspired by observations of these multipole asymmetries in terms of two-point correlations and variance in real space, we demonstrate that this model can explain the observed anomalous power asymmetry of the cosmic microwave background (CMB) sky, including its characteristic feature that the dipole dominates over higher multipoles. We test the viability of the model and place approximate constraints on its parameters by using observational values of dipole, quadrupole, and octopole amplitudes of the asymmetry measured by a local-variance estimator. We find that a configuration of the model in which the CMB sphere does not intersect the domain wall during inflation provides a good fit to the data. We further derive analytic expressions for the corrections to the CMB temperature covariance matrix, or angular power spectra, which can be used in future statistical analysis of the model in spherical harmonic space.
Chiral damping in magnetic domain walls dynamics
NASA Astrophysics Data System (ADS)
Jué, Emilie
Domain wall (DW) motion in materials with structural inversion asymmetry (SIA) and high spin-orbit coupling has attracted much interest in the recent years due to the discovery of unexpected physical mechanisms. Especially, it has been shown that the DW dynamics in such materials can be explained by chiral DWs with (partly or fully) Néel structure, whose stability derives from an interfacial Dzyaloshinskii-Moriya interaction (DMI). In this work, we show that DMI is not the only effect inducing chiral dynamics and demonstrate the existence of a chiral damping. This result is supported by the study of the asymmetry induced by an in-plane magnetic field on field induced domain wall motion in perpendicularly magnetized asymmetric Pt/Co/Pt trilayers. Using time reversal properties, we show that this asymmetry cannot be attributed to an effective field but originates from a purely dissipative mechanism. The observation of chiral damping, not only enriches the spectrum of physical phenomena engendered by the SIA, but since it can coexist with DMI it is essential for conceiving DW and skyrmion devices
Soliton-dependent plasmon reflection at bilayer graphene domain walls
NASA Astrophysics Data System (ADS)
Jiang, Lili; Shi, Zhiwen; Zeng, Bo; Wang, Sheng; Kang, Ji-Hun; Joshi, Trinity; Jin, Chenhao; Ju, Long; Kim, Jonghwan; Lyu, Tairu; Shen, Yuen-Ron; Crommie, Michael; Gao, Hong-Jun; Wang, Feng
2016-08-01
Layer-stacking domain walls in bilayer graphene are emerging as a fascinating one-dimensional system that features stacking solitons structurally and quantum valley Hall boundary states electronically. The interactions between electrons in the 2D graphene domains and the one-dimensional domain-wall solitons can lead to further new quantum phenomena. Domain-wall solitons of varied local structures exist along different crystallographic orientations, which can exhibit distinct electrical, mechanical and optical properties. Here we report soliton-dependent 2D graphene plasmon reflection at different 1D domain-wall solitons in bilayer graphene using near-field infrared nanoscopy. We observe various domain-wall structures in mechanically exfoliated graphene bilayers, including network-forming triangular lattices, individual straight or bent lines, and even closed circles. The near-field infrared contrast of domain-wall solitons arises from plasmon reflection at domain walls, and exhibits markedly different behaviours at the tensile- and shear-type domain-wall solitons. In addition, the plasmon reflection at domain walls exhibits a peculiar dependence on electrostatic gating. Our study demonstrates the unusual and tunable coupling between 2D graphene plasmons and domain-wall solitons.
Dynamics of domain wall driven by spin-transfer torque
Chureemart, P.; Evans, R. F. L.; Chantrell, R. W.
2011-05-01
Spin-torque switching of magnetic devices offers new technological possibilities for data storage and integrated circuits. We have investigated domain-wall motion in a ferromagnetic thin film driven by a spin-polarized current using an atomistic spin model with a modified Landau-Lifshitz-Gilbert equation including the effect of the spin-transfer torque. The presence of the spin-transfer torque is shown to create an out-of-plane domain wall, in contrast to the external-field-driven case where an in-plane wall is found. We have investigated the effect of the spin torque on domain-wall displacement, domain-wall velocity, and domain-wall width, as well as the equilibration time in the presence of the spin-transfer torque. We have shown that the minimum spin-current density, regarded as the critical value for domain-wall motion, decreases with increasing temperature.
Domain wall orientation and domain shape in KTiOPO4 crystals
NASA Astrophysics Data System (ADS)
Shur, V. Ya.; Vaskina, E. M.; Pelegova, E. V.; Chuvakova, M. A.; Akhmatkhanov, A. R.; Kizko, O. V.; Ivanov, M.; Kholkin, A. L.
2016-09-01
Domain shape evolution and domain wall motion have been studied in KTiOPO4 (KTP) ferroelectric single crystals using complementary experimental methods. The in situ visualization of domain kinetics has allowed revealing: (1) qualitative change of the domain shape, (2) dependence of the domain wall velocity on its orientation, (3) jump-like domain wall motion caused by domain merging, (4) effect of domain shape stability. The model of domain wall motion driven by generation of elementary steps (kink-pair nucleation) and subsequent kink motion is presented. The decrease in the relative velocity of the approaching parallel domain walls is attributed to electrostatic interaction. The effect of polarization reversal induced by chemical etching is observed. The obtained results are important for the development of domain engineering in the crystals of KTP family.
Magnetic moment softening and domain wall resistance in Ni nanowires.
Burton, J D; Sabirianov, R F; Jaswal, S S; Tsymbal, E Y; Mryasov, O N
2006-08-18
We perform ab initio calculations of the electronic structure and conductance of atomic-size Ni nanowires with domain walls only a few atomic lattice constants wide. We show that the hybridization between noncollinear spin states leads to a reduction of the magnetic moments in the domain wall resulting in the enhancement of the domain wall resistance. Experimental studies of the magnetic moment softening may be feasible with modern techniques such as scanning tunneling spectroscopy. PMID:17026271
Magnetic domain-wall dynamics in wide permalloy strips
NASA Astrophysics Data System (ADS)
Estévez, Virginia; Laurson, Lasse
2016-02-01
Domain walls in soft permalloy strips may exhibit various equilibrium micromagnetic structures depending on the width and thickness of the strip, ranging from the well-known transverse and vortex walls in narrow and thin strips to double and triple vortex walls recently reported in wider strips [V. Estévez and L. Laurson, Phys. Rev. B 91, 054407 (2015), 10.1103/PhysRevB.91.054407]. Here, we analyze the field driven dynamics of such domain walls in permalloy strips of widths from 240 nm up to 6 μ m , using the known equilibrium domain wall structures as initial configurations. Our micromagnetic simulations show that the domain wall dynamics in wide strips is very complex, and depends strongly on the geometry of the system, as well as on the magnitude of the driving field. We discuss in detail the rich variety of the dynamical behaviors found, including dynamic transitions between different domain wall structures, periodic dynamics of a vortex core close to the strip edge, transitions towards simpler domain wall structures of the multi-vortex domain walls controlled by vortex polarity, and the fact that for some combinations of the strip geometry and the driving field the system cannot support a compact domain wall.
Bent Ferroelectric Domain Walls as Reconfigurable Metallic-Like Channels.
Stolichnov, Igor; Feigl, Ludwig; McGilly, Leo J; Sluka, Tomas; Wei, Xian-Kui; Colla, Enrico; Crassous, Arnaud; Shapovalov, Konstantin; Yudin, Petr; Tagantsev, Alexander K; Setter, Nava
2015-12-01
Use of ferroelectric domain-walls in future electronics requires that they are stable, rewritable conducting channels. Here we demonstrate nonthermally activated metallic-like conduction in nominally uncharged, bent, rewritable ferroelectric-ferroelastic domain-walls of the ubiquitous ferroelectric Pb(Zr,Ti)O3 using scanning force microscopy down to a temperature of 4 K. New walls created at 4 K by pressure exhibit similar robust and intrinsic conductivity. Atomic resolution electron energy-loss spectroscopy confirms the conductivity confinement at the wall. This work provides a new concept in "domain-wall nanoelectronics".
Effective pinning energy landscape perturbations for propagating magnetic domain walls
Burn, D. M.; Atkinson, D.
2016-01-01
The interaction between a magnetic domain wall and a pinning site is explored in a planar nanowire using micromagnetics to reveal perturbations of the pinning energetics for propagating domain walls. Numerical simulations in the high damping ’quasi-static’ and low damping ’dynamic’ regimes are compared and show clear differences in de-pinning fields, indicating that dynamical micromagnetic models, which incorporate precessionally limited magnetization processes, are needed to understand domain wall pinning. Differences in the micromagnetic domain wall structure strongly influence the pinning and show periodic behaviour with increasing applied field associated with Walker breakdown. In the propagating regime pinning is complicated. PMID:27694953
Effective pinning energy landscape perturbations for propagating magnetic domain walls
NASA Astrophysics Data System (ADS)
Burn, D. M.; Atkinson, D.
2016-10-01
The interaction between a magnetic domain wall and a pinning site is explored in a planar nanowire using micromagnetics to reveal perturbations of the pinning energetics for propagating domain walls. Numerical simulations in the high damping ’quasi-static’ and low damping ’dynamic’ regimes are compared and show clear differences in de-pinning fields, indicating that dynamical micromagnetic models, which incorporate precessionally limited magnetization processes, are needed to understand domain wall pinning. Differences in the micromagnetic domain wall structure strongly influence the pinning and show periodic behaviour with increasing applied field associated with Walker breakdown. In the propagating regime pinning is complicated.
Hamilton-Jacobi method for curved domain walls and cosmologies
NASA Astrophysics Data System (ADS)
Skenderis, Kostas; Townsend, Paul K.
2006-12-01
We use Hamiltonian methods to study curved domain walls and cosmologies. This leads naturally to first-order equations for all domain walls and cosmologies foliated by slices of maximal symmetry. For Minkowski and AdS-sliced domain walls (flat and closed FLRW cosmologies) we recover a recent result concerning their (pseudo)supersymmetry. We show how domain-wall stability is consistent with the instability of AdS vacua that violate the Breitenlohner-Freedman bound. We also explore the relationship to Hamilton-Jacobi theory and compute the wave-function of a 3-dimensional closed universe evolving towards de Sitter spacetime.
Enhanced electromechanical response of ferroelectrics due to charged domain walls
Sluka, Tomas; Tagantsev, Alexander K.; Damjanovic, Dragan; Gureev, Maxim; Setter, Nava
2012-01-01
While commonly used piezoelectric materials contain lead, non-hazardous, high-performance piezoelectrics are yet to be discovered. Charged domain walls in ferroelectrics are considered inactive with regards to the piezoelectric response and, therefore, are largely ignored in this search. Here we demonstrate a mechanism that leads to a strong enhancement of the dielectric and piezoelectric properties in ferroelectrics with increasing density of charged domain walls. We show that an incomplete compensation of bound polarization charge at these walls creates a stable built-in depolarizing field across each domain leading to increased electromechanical response. Our model clarifies a long-standing unexplained effect of domain wall density on macroscopic properties of domain-engineered ferroelectrics. We show that non-toxic ferroelectrics like BaTiO3 with dense patterns of charged domain walls are expected to have strongly enhanced piezoelectric properties, thus suggesting a new route to high-performance, lead-free ferroelectrics. PMID:22434191
Chiral damping of magnetic domain walls
NASA Astrophysics Data System (ADS)
Jué, Emilie; Safeer, C. K.; Drouard, Marc; Lopez, Alexandre; Balint, Paul; Buda-Prejbeanu, Liliana; Boulle, Olivier; Auffret, Stephane; Schuhl, Alain; Manchon, Aurelien; Miron, Ioan Mihai; Gaudin, Gilles
2016-03-01
Structural symmetry breaking in magnetic materials is responsible for the existence of multiferroics, current-induced spin-orbit torques and some topological magnetic structures. In this Letter we report that the structural inversion asymmetry (SIA) gives rise to a chiral damping mechanism, which is evidenced by measuring the field-driven domain-wall (DW) motion in perpendicularly magnetized asymmetric Pt/Co/Pt trilayers. The DW dynamics associated with the chiral damping and those with Dzyaloshinskii-Moriya interaction (DMI) exhibit identical spatial symmetry. However, both scenarios are differentiated by their time reversal properties: whereas DMI is a conservative effect that can be modelled by an effective field, the chiral damping is purely dissipative and has no influence on the equilibrium magnetic texture. When the DW motion is modulated by an in-plane magnetic field, it reveals the structure of the internal fields experienced by the DWs, allowing one to distinguish the physical mechanism. The chiral damping enriches the spectrum of physical phenomena engendered by the SIA, and is essential for conceiving DW and skyrmion devices owing to its coexistence with DMI (ref. ).
Domain wall QCD with physical quark masses
NASA Astrophysics Data System (ADS)
Blum, T.; Boyle, P. A.; Christ, N. H.; Frison, J.; Garron, N.; Hudspith, R. J.; Izubuchi, T.; Janowski, T.; Jung, C.; Jüttner, A.; Kelly, C.; Kenway, R. D.; Lehner, C.; Marinkovic, M.; Mawhinney, R. D.; McGlynn, G.; Murphy, D. J.; Ohta, S.; Portelli, A.; Sachrajda, C. T.; Soni, A.; Rbc; Ukqcd Collaborations
2016-04-01
We present results for several light hadronic quantities (fπ , fK, BK, mu d, ms, t01 /2, w0) obtained from simulations of 2 +1 flavor domain wall lattice QCD with large physical volumes and nearly physical pion masses at two lattice spacings. We perform a short, O (3 )%, extrapolation in pion mass to the physical values by combining our new data in a simultaneous chiral/continuum "global fit" with a number of other ensembles with heavier pion masses. We use the physical values of mπ, mK and mΩ to determine the two quark masses and the scale—all other quantities are outputs from our simulations. We obtain results with subpercent statistical errors and negligible chiral and finite-volume systematics for these light hadronic quantities, including fπ=130.2 (9 ) MeV ; fK=155.5 (8 ) MeV ; the average up/down quark mass and strange quark mass in the MS ¯ scheme at 3 GeV, 2.997(49) and 81.64(1.17) MeV respectively; and the neutral kaon mixing parameter, BK, in the renormalization group invariant scheme, 0.750(15) and the MS ¯ scheme at 3 GeV, 0.530(11).
NASA Astrophysics Data System (ADS)
Zou, Xiaojing
We have fabricated, studied and compared the electrical and magnetic behavior of several sub-micron-sized polycrystalline and epitaxial chromium dioxide (CrO2) nanostructures, grown using selective-area growth technique. Magnetic domain structures were studied by magnetic force microscopy, and in-plane, lamellar domain structure with fragmented walls aligned along the magnetic easy axis direction have been observed, indicating the existence of a large magnetocrystalline anisotropy in epitaxial CrO2 nanostructures. Low-temperature transport measurements on nanowires have shown that the dc resistivity of polycrystalline CrO2 wires is strongly dependent on the linewidth. Below a critical temperature, a transition from a positive to a negative temperature coefficient of resistivity have been observed, which we attribute to a competition between the scattering of the conduction electrons inside the grains and scattering across the grain boundaries. Using a model based on grain boundary scattering, we estimate a mean transmission probability through the grain boundaries to be on the order of 10-1 . Furthermore, magnetoresistance (MR) measurement indicates that the MR behavior of polycrystalline CrO2 wires is dominated by the shape anisotropy; however, for epitaxial CrO2 wires, both the shape and magnetocrystalline anisotropy play important roles, and the resulting MR properties are found to be closely related to the orientation of the wire axis. By studying the MR curves, we inferred the internal magnetic domain structures in various single crystal CrO2 wires and found that the spin-dependent transport is much stronger across a grain boundary than a magnetic domain wall. We have also studied the magnetotransport properties of CrO2 nanoscale continuous contacts. Manipulating the domain walls using a large dc current in the contact area yields a magnetoresistance of up to 25%, which is the largest ever seen in a single ferromagnetic film. The single domain-wall
Asymmetric Domain Walls of Small Angle in Soft Ferromagnetic Films
NASA Astrophysics Data System (ADS)
Döring, Lukas; Ignat, Radu
2016-05-01
We focus on a special type of domain wall appearing in the Landau-Lifshitz theory for soft ferromagnetic films. These domain walls are divergence-free S^2-valued transition layers that connect two directions {m_θ^± in S^2} (differing by an angle {2θ}) and minimize the Dirichlet energy. Our main result is the rigorous derivation of the asymptotic structure and energy of such "asymmetric" domain walls in the limit {θ downarrow 0}. As an application, we deduce that a supercritical bifurcation causes the transition from symmetric to asymmetric walls in the full micromagnetic model.
Ferroelectric domain wall motion induced by polarized light.
Rubio-Marcos, Fernando; Del Campo, Adolfo; Marchet, Pascal; Fernández, Jose F
2015-03-17
Ferroelectric materials exhibit spontaneous and stable polarization, which can usually be reoriented by an applied external electric field. The electrically switchable nature of this polarization is at the core of various ferroelectric devices. The motion of the associated domain walls provides the basis for ferroelectric memory, in which the storage of data bits is achieved by driving domain walls that separate regions with different polarization directions. Here we show the surprising ability to move ferroelectric domain walls of a BaTiO₃ single crystal by varying the polarization angle of a coherent light source. This unexpected coupling between polarized light and ferroelectric polarization modifies the stress induced in the BaTiO₃ at the domain wall, which is observed using in situ confocal Raman spectroscopy. This effect potentially leads to the non-contact remote control of ferroelectric domain walls by light.
Thermal effects on transverse domain wall dynamics in magnetic nanowires
Leliaert, J.; Van de Wiele, B.; Vandermeulen, J.; Coene, A.; Dupré, L.; Vansteenkiste, A.; Waeyenberge, B. Van; Laurson, L.; Durin, G.
2015-05-18
Magnetic domain walls are proposed as data carriers in future spintronic devices, whose reliability depends on a complete understanding of the domain wall motion. Applications based on an accurate positioning of domain walls are inevitably influenced by thermal fluctuations. In this letter, we present a micromagnetic study of the thermal effects on this motion. As spin-polarized currents are the most used driving mechanism for domain walls, we have included this in our analysis. Our results show that at finite temperatures, the domain wall velocity has a drift and diffusion component, which are in excellent agreement with the theoretical values obtained from a generalized 1D model. The drift and diffusion component are independent of each other in perfect nanowires, and the mean square displacement scales linearly with time and temperature.
Ferroelectric domain wall motion induced by polarized light.
Rubio-Marcos, Fernando; Del Campo, Adolfo; Marchet, Pascal; Fernández, Jose F
2015-01-01
Ferroelectric materials exhibit spontaneous and stable polarization, which can usually be reoriented by an applied external electric field. The electrically switchable nature of this polarization is at the core of various ferroelectric devices. The motion of the associated domain walls provides the basis for ferroelectric memory, in which the storage of data bits is achieved by driving domain walls that separate regions with different polarization directions. Here we show the surprising ability to move ferroelectric domain walls of a BaTiO₃ single crystal by varying the polarization angle of a coherent light source. This unexpected coupling between polarized light and ferroelectric polarization modifies the stress induced in the BaTiO₃ at the domain wall, which is observed using in situ confocal Raman spectroscopy. This effect potentially leads to the non-contact remote control of ferroelectric domain walls by light. PMID:25779918
Mechanically driven domain wall movement in magnetoelastic nanomagnets
NASA Astrophysics Data System (ADS)
Mathurin, Théo; Giordano, Stefano; Dusch, Yannick; Tiercelin, Nicolas; Pernod, Philippe; Preobrazhensky, Vladimir
2016-07-01
Magnetic domain walls are fundamental objects arising in ferromagnetic materials, largely investigated both through micromagnetic simulations and experiments. While current- and field-based techniques for inducing domain wall propagation have been widely studied for fundamental understanding and application-oriented purposes, the possibility to manipulate domain walls using mechanical stress in magnetoelastic materials has only recently drawn interest. Here, a complete analytical model describing stress-induced transverse domain wall movement in ferromagnetic nanostripe with variable cross-section is presented. This approach yields a nonlinear integro-differential equation describing the magnetization field. Its numerical implementation, based on the nonlinear relaxation method, demonstrates the possibility to precisely control the position of a domain wall through mechanical action.
Moebius Algorithm for Domain Wall and GapDW Fermions
Ron Babich, Richard Brower, Kostas Orginos, Claudio Rebbi, David Schaich, Pavlos Vranas
2009-06-01
The M\\"obius domain wall action \\cite{Brower:2004xi} is a generalization of Shamir's action, which gives exactly the same overlap fermion lattice action as the separation ($L_s$) between the domain walls is taken to infinity. The performance advantages of the algorithm are presented for a small ensemble of quenched, full QCD domain wall and Gap domain wall lattices \\cite{Vranas:2006zk}. In particular, it is shown that at the larger lattice spacings relevant to current dynamical simulations M\\"obius fermions work well together with GapDWF reducing $L_s$ by more than a factor of two. It is noted that there is precise map between the domain wall and effective overlap action at finite quark mass including finite $L_s$ chiral violations so that the Ward-Takahashi identities for the axial and vector currents are exactly equivalent in both formulations.
Ferroelectric domain wall motion induced by polarized light
Rubio-Marcos, Fernando; Del Campo, Adolfo; Marchet, Pascal; Fernández, Jose F.
2015-01-01
Ferroelectric materials exhibit spontaneous and stable polarization, which can usually be reoriented by an applied external electric field. The electrically switchable nature of this polarization is at the core of various ferroelectric devices. The motion of the associated domain walls provides the basis for ferroelectric memory, in which the storage of data bits is achieved by driving domain walls that separate regions with different polarization directions. Here we show the surprising ability to move ferroelectric domain walls of a BaTiO3 single crystal by varying the polarization angle of a coherent light source. This unexpected coupling between polarized light and ferroelectric polarization modifies the stress induced in the BaTiO3 at the domain wall, which is observed using in situ confocal Raman spectroscopy. This effect potentially leads to the non-contact remote control of ferroelectric domain walls by light. PMID:25779918
Domain walls in Einstein-Gauss-Bonnet bulk
Mazharimousavi, S. Habib; Halilsoy, M.
2010-10-15
We investigate the dynamics of a n-dimensional domain wall in a n+1-dimensional Einstein-Gauss-Bonnet bulk. Exact effective potential induced by the Gauss-Bonnet (GB) term on the wall is derived. In the absence of the GB term we recover the familiar gravitational and antiharmonic oscillator potentials. Inclusion of the GB correction gives rise to a minimum radius of bounce for the Friedmann-Robertson-Walker universe expanding with a negative pressure on the domain wall.
Ballistic rectification of vortex domain wall chirality at nanowire corners
Omari, K.; Bradley, R. C.; Broomhall, T. J.; Hodges, M. P. P.; Hayward, T. J.; Rosamond, M. C.; Linfield, E. H.; Im, M.-Y.; Fischer, P.
2015-11-30
The interactions of vortex domain walls with corners in planar magnetic nanowires are probed using magnetic soft X-ray transmission microscopy. We show that when the domain walls are propagated into sharp corners using applied magnetic fields above a critical value, their chiralities are rectified to either clockwise or anticlockwise circulation depending on whether the corners turn left or right. Single-shot focused magneto-optic Kerr effect measurements are then used to demonstrate how, when combined with modes of domain propagation that conserve vortex chirality, this allows us to dramatically reduce the stochasticity of domain pinning at artificial defect sites. Our results provide a tool for controlling domain wall chirality and pinning behavior both in further experimental studies and in future domain wall-based memory, logic and sensor technologies.
Formation of charged ferroelectric domain walls with controlled periodicity
Bednyakov, Petr S.; Sluka, Tomas; Tagantsev, Alexander K.; Damjanovic, Dragan; Setter, Nava
2015-01-01
Charged domain walls in proper ferroelectrics were shown recently to possess metallic-like conductivity. Unlike conventional heterointerfaces, these walls can be displaced inside a dielectric by an electric field, which is of interest for future electronic circuitry. In addition, theory predicts that charged domain walls may influence the electromechanical response of ferroelectrics, with strong enhancement upon increased charged domain wall density. The existence of charged domain walls in proper ferroelectrics is disfavoured by their high formation energy and methods of their preparation in predefined patterns are unknown. Here we develop the theoretical background for the formation of charged domain walls in proper ferroelectrics using energy considerations and outline favourable conditions for their engineering. We experimentally demonstrate, in BaTiO3 single crystals the controlled build-up of high density charged domain wall patterns, down to a spacing of 7 μm with a predominant mixed electronic and ionic screening scenario, hinting to a possible exploitation of charged domain walls in agile electronics and sensing devices. PMID:26516026
Tong, Sheng; Jung, Il Woong; Choi, Yoon-Young; Hong, Seungbum; Roelofs, Andreas
2016-02-23
Advanced scanning probe microscopies (SPMs) open up the possibilities of the next-generation ferroic devices that utilize both domains and domain walls as active elements. However, current SPMs lack the capability of dynamically monitoring the motion of domains and domain walls in conjunction with the transport of the screening charges that lower the total electrostatic energy of both domains and domain walls. Charge gradient microscopy (CGM) is a strong candidate to overcome these shortcomings because it can map domains and domain walls at high speed and mechanically remove the screening charges. Yet the underlying mechanism of the CGM signals is not fully understood due to the complexity of the electrostatic interactions. Here, we designed a semiconductor-metal CGM tip, which can separate and quantify the ferroelectric domain and domain wall signals by simply changing its scanning direction. Our investigation reveals that the domain wall signals are due to the spatial change of polarization charges, while the domain signals are due to continuous removal and supply of screening charges at the CGM tip. In addition, we observed asymmetric CGM domain currents from the up and down domains, which are originated from the different debonding energies and the amount of the screening charges on positive and negative bound charges. We believe that our findings can help design CGM with high spatial resolution and lead to breakthroughs in information storage and energy-harvesting devices. PMID:26751281
Domain wall pinning in ultra-narrow electromigrated break junctions
NASA Astrophysics Data System (ADS)
Reeve, Robert M.; Loescher, André; Mawass, Mohamad-Assaad; Hoffmann-Vogel, Regina; Kläui, Mathias
2014-11-01
The study of magnetic domain walls in constrained geometries is an important topic, yet when dealing with extreme nanoscale magnetic systems artefacts can often dominate the measurements and obscure the effects of intrinsic magnetic origin. In this work we study the evolution of domain wall depinning in electromigrated ferromagnetic junctions which are both initially fabricated and subsequently tailored in-situ in clean ultra-high vacuum conditions. Carefully designed Ni80Fe20 (Permalloy) notched half-ring structures are fabricated and investigated as a function of constriction width by tailoring the size of the contact using controlled in-situ electromigration. It is found that the domain wall pinning strength is increased on reducing the contact size in line with a reduction of the wall energy in narrower constrictions. Furthermore, the angular dependency and symmetry of the depinning field is measured to determine the full pinning potential for a domain wall in a system with a narrow constriction.
Polarization control at spin-driven ferroelectric domain walls.
Leo, Naëmi; Bergman, Anders; Cano, Andres; Poudel, Narayan; Lorenz, Bernd; Fiebig, Manfred; Meier, Dennis
2015-01-01
Unusual electronic states arise at ferroelectric domain walls due to the local symmetry reduction, strain gradients and electrostatics. This particularly applies to improper ferroelectrics, where the polarization is induced by a structural or magnetic order parameter. Because of the subordinate nature of the polarization, the rigid mechanical and electrostatic boundary conditions that constrain domain walls in proper ferroics are lifted. Here we show that spin-driven ferroelectricity promotes the emergence of charged domain walls. This provides new degrees of flexibility for controlling domain-wall charges in a deterministic and reversible process. We create and position a domain wall by an electric field in Mn0.95Co0.05WO4. With a magnetic field we then rotate the polarization and convert neutral into charged domain walls, while its magnetic properties peg the wall to its location. Using atomistic Landau-Lifshitz-Gilbert simulations we quantify the polarization changes across the two wall types and highlight their general occurrence. PMID:25868608
Gapped domain walls, gapped boundaries, and topological degeneracy.
Lan, Tian; Wang, Juven C; Wen, Xiao-Gang
2015-02-20
Gapped domain walls, as topological line defects between (2+1)D topologically ordered states, are examined. We provide simple criteria to determine the existence of gapped domain walls, which apply to both Abelian and non-Abelian topological orders. Our criteria also determine which (2+1)D topological orders must have gapless edge modes, namely, which (1+1)D global gravitational anomalies ensure gaplessness. Furthermore, we introduce a new mathematical object, the tunneling matrix W, whose entries are the fusion-space dimensions W(ia), to label different types of gapped domain walls. By studying many examples, we find evidence that the tunneling matrices are powerful quantities to classify different types of gapped domain walls. Since a gapped boundary is a gapped domain wall between a bulk topological order and the vacuum, regarded as the trivial topological order, our theory of gapped domain walls inclusively contains the theory of gapped boundaries. In addition, we derive a topological ground state degeneracy formula, applied to arbitrary orientable spatial 2-manifolds with gapped domain walls, including closed 2-manifolds and open 2-manifolds with gapped boundaries.
Indirect localization of a magnetic domain wall mediated by quasi walls
Lacour, D.; Montaigne, F.; Rougemaille, N.; Belkhou, R.; Raabe, J.; Hehn, M.
2015-01-01
The manipulation of magnetic domain walls in thin films and nanostructures opens new opportunities for fundamental and applied research. But controlling reliably the position of a moving domain wall still remains challenging. So far, most of the studies aimed at understanding the physics of pinning and depinning processes in the magnetic layer in which the wall moves (active layer). In these studies, the role of other magnetic layers in the stack has been often ignored. Here, we report an indirect localization process of 180° domain walls that occurs in magnetic tunnel junctions, commonly used in spintronics. Combining Scanning Transmission X-Ray Microscopy and micromagnetic simulations, magnetic configurations in both layers are resolved. When nucleating a 180° domain wall in the active layer, a quasi wall is created in the reference layer, atop the wall. The wall and its quasi wall must then be moved or positioned together, as a unique object. As a mutual effect, a localized change of the magnetic properties in the reference layer induces a localized quasi wall in the active layer. The two types of quasi walls are shown to be responsible for an indirect localization process of the 180° domain wall in the active layer. PMID:26011004
NASA Astrophysics Data System (ADS)
Van de Wiele, Ben; Leliaert, Jonathan; Franke, Kévin J. A.; van Dijken, Sebastiaan
2016-03-01
Strong coupling of magnetic domain walls onto straight ferroelastic boundaries of a ferroelectric layer enables full and reversible electric-field control of magnetic domain wall motion. In this paper, the dynamics of this new driving mechanism is analyzed using micromagnetic simulations. We show that transverse domain walls with a near-180° spin structure are stabilized in magnetic nanowires and that electric fields can move these walls with high velocities. Above a critical velocity, which depends on material parameters, nanowire geometry and the direction of domain wall motion, the magnetic domain walls depin abruptly from the ferroelastic boundaries. Depinning evolves either smoothly or via the emission and annihilation of a vortex or antivortex core (Walker breakdown). In both cases, the magnetic domain wall slows down after depinning in an oscillatory fashion and eventually comes to a halt. The simulations provide design rules for hybrid ferromagnetic-ferroelectric domain-wall-based devices and indicate that material disorder and structural imperfections only influence Walker-breakdown-like depinning at high domain wall velocities.
Ferroelectricity of domain walls in rare earth iron garnet films.
Popov, A I; Zvezdin, K A; Gareeva, Z V; Mazhitova, F A; Vakhitov, R M; Yumaguzin, A R; Zvezdin, A K
2016-11-16
In this paper, we report on electric polarization arising in a vicinity of Bloch-like domain walls in rare-earth iron garnet films. The domain walls generate an intrinsic magnetic field that breaks an antiferroelectric structure formed in the garnets due to an exchange interaction between rare earth and iron sublattices. We explore 180° domain walls whose formation is energetically preferable in the films with perpendicular magnetic anisotropy. Magnetic and electric structures of the 180° quasi-Bloch domain walls have been simulated at various relations between system parameters. Singlet, doublet ground states of rare earth ions and strongly anisotropic rare earth Ising ions have been considered. Our results show that electric polarization appears in rare earth garnet films at Bloch domain walls, and the maximum of magnetic inhomogeneity is not always linked to the maximum of electric polarization. A number of factors including the temperature, the state of the rare earth ion and the type of a wall influence magnetically induced electric polarization. We show that the value of polarization can be enhanced by the shrinking of the Bloch domain wall width, decreasing the temperature, and increasing the deviations of magnetization from the Bloch rotation that are regulated by impacts given by magnetic anisotropies of the films. PMID:27620369
Ferroelectricity of domain walls in rare earth iron garnet films
NASA Astrophysics Data System (ADS)
Popov, A. I.; Zvezdin, K. A.; Gareeva, Z. V.; Mazhitova, F. A.; Vakhitov, R. M.; Yumaguzin, A. R.; Zvezdin, A. K.
2016-11-01
In this paper, we report on electric polarization arising in a vicinity of Bloch-like domain walls in rare-earth iron garnet films. The domain walls generate an intrinsic magnetic field that breaks an antiferroelectric structure formed in the garnets due to an exchange interaction between rare earth and iron sublattices. We explore 180° domain walls whose formation is energetically preferable in the films with perpendicular magnetic anisotropy. Magnetic and electric structures of the 180° quasi-Bloch domain walls have been simulated at various relations between system parameters. Singlet, doublet ground states of rare earth ions and strongly anisotropic rare earth Ising ions have been considered. Our results show that electric polarization appears in rare earth garnet films at Bloch domain walls, and the maximum of magnetic inhomogeneity is not always linked to the maximum of electric polarization. A number of factors including the temperature, the state of the rare earth ion and the type of a wall influence magnetically induced electric polarization. We show that the value of polarization can be enhanced by the shrinking of the Bloch domain wall width, decreasing the temperature, and increasing the deviations of magnetization from the Bloch rotation that are regulated by impacts given by magnetic anisotropies of the films.
Ferroelectricity of domain walls in rare earth iron garnet films.
Popov, A I; Zvezdin, K A; Gareeva, Z V; Mazhitova, F A; Vakhitov, R M; Yumaguzin, A R; Zvezdin, A K
2016-11-16
In this paper, we report on electric polarization arising in a vicinity of Bloch-like domain walls in rare-earth iron garnet films. The domain walls generate an intrinsic magnetic field that breaks an antiferroelectric structure formed in the garnets due to an exchange interaction between rare earth and iron sublattices. We explore 180° domain walls whose formation is energetically preferable in the films with perpendicular magnetic anisotropy. Magnetic and electric structures of the 180° quasi-Bloch domain walls have been simulated at various relations between system parameters. Singlet, doublet ground states of rare earth ions and strongly anisotropic rare earth Ising ions have been considered. Our results show that electric polarization appears in rare earth garnet films at Bloch domain walls, and the maximum of magnetic inhomogeneity is not always linked to the maximum of electric polarization. A number of factors including the temperature, the state of the rare earth ion and the type of a wall influence magnetically induced electric polarization. We show that the value of polarization can be enhanced by the shrinking of the Bloch domain wall width, decreasing the temperature, and increasing the deviations of magnetization from the Bloch rotation that are regulated by impacts given by magnetic anisotropies of the films.
Microwave conductance of ferroelectric domain walls in lead titanate
NASA Astrophysics Data System (ADS)
Tselev, Alexander; Cao, Ye; Yu, Pu; Kalinin, Sergei V.; Maksymovych, Petro
Numerous theoretical works predicted electronically conducting domain walls in otherwise insulating ferroelectric crystals. A number of recent experiments reported conducting walls, although conductivity itself and a conclusive proof of conductance mechanism remain elusive, largely due to the electrical contact problem. The latter can be overcome using high-frequency AC voltage. Here we will present our successful measurements of microwave conductance at 180o domain walls in lead titanate using microwave microscopy. AC conducting domain walls can be repeatably reconfigured and have extraordinary stability in time and temperature. AC conductivity is detected even when DC is not. Quantitative modeling reveals that the conductance of domain walls is comparable to doped silicon. We will also present a new and robust mechanism to create charged domain walls in any ferroelectric lattice. Overall, this sets the stage for a new generation of local experiments on conducting domain walls, and furthers the prospects of their application in fast electronic devices. AT, YC, SVK, PM supported by Division of Materials Sciences and Engineering, Office of Science, Basic Energy Sciences, U. S. DOE. PY supported by the National Basic Research Program of China (2015CB921700).
Topological valley transport at bilayer graphene domain walls
NASA Astrophysics Data System (ADS)
Ju, Long; Shi, Zhiwen; Nair, Nityan; Lv, Yinchuan; Jin, Chenhao; Velasco, Jairo; Ojeda-Aristizabal, Claudia; Bechtel, Hans A.; Martin, Michael C.; Zettl, Alex; Analytis, James; Wang, Feng
2015-04-01
Electron valley, a degree of freedom that is analogous to spin, can lead to novel topological phases in bilayer graphene. A tunable bandgap can be induced in bilayer graphene by an external electric field, and such gapped bilayer graphene is predicted to be a topological insulating phase protected by no-valley mixing symmetry, featuring quantum valley Hall effects and chiral edge states. Observation of such chiral edge states, however, is challenging because inter-valley scattering is induced by atomic-scale defects at real bilayer graphene edges. Recent theoretical work has shown that domain walls between AB- and BA-stacked bilayer graphene can support protected chiral edge states of quantum valley Hall insulators. Here we report an experimental observation of ballistic (that is, with no scattering of electrons) conducting channels at bilayer graphene domain walls. We employ near-field infrared nanometre-scale microscopy (nanoscopy) to image in situ bilayer graphene layer-stacking domain walls on device substrates, and we fabricate dual-gated field effect transistors based on the domain walls. Unlike single-domain bilayer graphene, which shows gapped insulating behaviour under a vertical electrical field, bilayer graphene domain walls feature one-dimensional valley-polarized conducting channels with a ballistic length of about 400 nanometres at 4 kelvin. Such topologically protected one-dimensional chiral states at bilayer graphene domain walls open up opportunities for exploring unique topological phases and valley physics in graphene.
Highly Efficient Domain Walls Injection in Perpendicular Magnetic Anisotropy Nanowire
NASA Astrophysics Data System (ADS)
Zhang, S. F.; Gan, W. L.; Kwon, J.; Luo, F. L.; Lim, G. J.; Wang, J. B.; Lew, W. S.
2016-04-01
Electrical injection of magnetic domain walls in perpendicular magnetic anisotropy nanowire is crucial for data bit writing in domain wall-based magnetic memory and logic devices. Conventionally, the current pulse required to nucleate a domain wall is approximately ~1012 A/m2. Here, we demonstrate an energy efficient structure to inject domain walls. Under an applied electric potential, our proposed Π-shaped stripline generates a highly concentrated current distribution. This creates a highly localized magnetic field that quickly initiates the nucleation of a magnetic domain. The formation and motion of the resulting domain walls can then be electrically detected by means of Ta Hall bars across the nanowire. Our measurements show that the Π-shaped stripline can deterministically write a magnetic data bit in 15 ns even with a relatively low current density of 5.34 × 1011 A/m2. Micromagnetic simulations reveal the evolution of the domain nucleation – first, by the formation of a pair of magnetic bubbles, then followed by their rapid expansion into a single domain. Finally, we also demonstrate experimentally that our injection geometry can perform bit writing using only about 30% of the electrical energy as compared to a conventional injection line.
Highly Efficient Domain Walls Injection in Perpendicular Magnetic Anisotropy Nanowire.
Zhang, S F; Gan, W L; Kwon, J; Luo, F L; Lim, G J; Wang, J B; Lew, W S
2016-01-01
Electrical injection of magnetic domain walls in perpendicular magnetic anisotropy nanowire is crucial for data bit writing in domain wall-based magnetic memory and logic devices. Conventionally, the current pulse required to nucleate a domain wall is approximately ~10(12) A/m(2). Here, we demonstrate an energy efficient structure to inject domain walls. Under an applied electric potential, our proposed Π-shaped stripline generates a highly concentrated current distribution. This creates a highly localized magnetic field that quickly initiates the nucleation of a magnetic domain. The formation and motion of the resulting domain walls can then be electrically detected by means of Ta Hall bars across the nanowire. Our measurements show that the Π-shaped stripline can deterministically write a magnetic data bit in 15 ns even with a relatively low current density of 5.34 × 10(11) A/m(2). Micromagnetic simulations reveal the evolution of the domain nucleation - first, by the formation of a pair of magnetic bubbles, then followed by their rapid expansion into a single domain. Finally, we also demonstrate experimentally that our injection geometry can perform bit writing using only about 30% of the electrical energy as compared to a conventional injection line. PMID:27098108
Highly Efficient Domain Walls Injection in Perpendicular Magnetic Anisotropy Nanowire
Zhang, S. F.; Gan, W. L.; Kwon, J.; Luo, F. L.; Lim, G. J.; Wang, J. B.; Lew, W. S.
2016-01-01
Electrical injection of magnetic domain walls in perpendicular magnetic anisotropy nanowire is crucial for data bit writing in domain wall-based magnetic memory and logic devices. Conventionally, the current pulse required to nucleate a domain wall is approximately ~1012 A/m2. Here, we demonstrate an energy efficient structure to inject domain walls. Under an applied electric potential, our proposed Π-shaped stripline generates a highly concentrated current distribution. This creates a highly localized magnetic field that quickly initiates the nucleation of a magnetic domain. The formation and motion of the resulting domain walls can then be electrically detected by means of Ta Hall bars across the nanowire. Our measurements show that the Π-shaped stripline can deterministically write a magnetic data bit in 15 ns even with a relatively low current density of 5.34 × 1011 A/m2. Micromagnetic simulations reveal the evolution of the domain nucleation – first, by the formation of a pair of magnetic bubbles, then followed by their rapid expansion into a single domain. Finally, we also demonstrate experimentally that our injection geometry can perform bit writing using only about 30% of the electrical energy as compared to a conventional injection line. PMID:27098108
Scalar triplet on a domain wall: an exact solution
NASA Astrophysics Data System (ADS)
Gani, Vakhid A.; Lizunova, Mariya A.; Radomskiy, Roman V.
2016-04-01
We study a model with a real scalar Higgs field and a scalar triplet field that allows existence of a topological defect — a domain wall. The wall breaks the global O(3) symmetry of the model, which gives rise to non-Abelian orientational degrees of freedom. We found an exact analytic solution that describes a domain wall with a localized configuration of the triplet field on it. This solution enables one to calculate contributions to the action from the orientational and translational degrees of freedom of the triplet field. We also study the linear stability of the domain wall with the triplet field switched off. We obtain that degrees of freedom localized on the wall can appear or do not appear depending on the parameters of the model.
BPS pion domain walls in the supersymmetric chiral Lagrangian
NASA Astrophysics Data System (ADS)
Gudnason, Sven Bjarke; Nitta, Muneto; Sasaki, Shin
2016-07-01
We construct exact solutions of BPS pion domain walls in the four-dimensional N =1 supersymmetric S U (N ) chiral Lagrangian with pion masses introduced via linear and quadratic superpotentials. The model admits N discrete vacua in the center of S U (N ) for the linear superpotential. In addition to the latter, new vacua appear for the quadratic superpotential. We find that the domain wall solutions of pions (Nambu-Goldstone bosons) that interpolate between a pair of (pion) vacua preserve half of supersymmetry. Contrary to our expectations, we have not been able to find domain walls involving the quasi-Nambu-Goldstone bosons present in the theory, which in turn has the consequence that not all vacua of the theory are connected by a BPS domain wall solution.
Effect of ac on current-induced domain wall motion
NASA Astrophysics Data System (ADS)
Kim, W. J.; Lee, T. D.; Choa, S. H.; Seo, S. M.; Lee, K. J.
2007-05-01
Saitoh et al. [Nature (London) 432, 203 (2004)] have reported the experimental result showing the interplay of a transverse domain wall with an electrical ac of megahertz-range frequencies. They observed a single peak of resistance in the frequency range and interpreted it with a nonadiabatic spin torque. It was argued that an ac current can induce a micrometer-range displacement of domain wall. We reconstructed the experiment in micromagnetic simulations considering the local nonzero nonadiabatic spin torque. We could not observe either an explicit single peak in the frequency-dependent resistance or an eventual displacement of domain wall by use of an ac. It indicates the local nonadiabatic torque is inappropriate to explain the experimental results of ac-induced domain wall motion. Other approaches such as the nonlocal nonadiabatic spin torque may be needed.
Domain wall formation in late-time phase transitions
NASA Technical Reports Server (NTRS)
Kolb, Edward W.; Wang, Yun
1992-01-01
We examine domain wall formulation in late time phase transitions. We find that in the invisible axion domain wall phenomenon, thermal effects alone are insufficient to drive different parts of the disconnected vacuum manifold. This suggests that domain walls do not form unless either there is some supplemental (but perhaps not unreasonable) dynamics to localize the scalar field responsible for the phase transition to the low temperature maximum (to an extraordinary precision) before the onset of the phase transition, or there is some non-thermal mechanism to produce large fluctuations in the scalar field. The fact that domain wall production is not a robust prediction of late time transitions may suggest future directions in model building.
Chirality-Dependent Transmission of Spin Waves through Domain Walls
NASA Astrophysics Data System (ADS)
Buijnsters, F. J.; Ferreiros, Y.; Fasolino, A.; Katsnelson, M. I.
2016-04-01
Spin-wave technology (magnonics) has the potential to further reduce the size and energy consumption of information-processing devices. In the submicrometer regime (exchange spin waves), topological defects such as domain walls may constitute active elements to manipulate spin waves and perform logic operations. We predict that spin waves that pass through a domain wall in an ultrathin perpendicular-anisotropy film experience a phase shift that depends on the orientation of the domain wall (chirality). The effect, which is absent in bulk materials, originates from the interfacial Dzyaloshinskii-Moriya interaction and can be interpreted as a geometric phase. We demonstrate analytically and by means of micromagnetic simulations that the phase shift is strong enough to switch between constructive and destructive interference. The two chirality states of the domain wall may serve as a memory bit or spin-wave switch in magnonic devices.
Characteristic microwave-background distortions from collapsing spherical domain walls
NASA Technical Reports Server (NTRS)
Goetz, Guenter; Notzold, Dirk
1990-01-01
The redshift distortion induced by collapsing spherical domain walls is calculated. The most frequent microwave background distortions are found to occur at large angles in the form of blue disks. This is the angular region currently measured by the COBE satellite. COBE could therefore detect signals predicted here for domain walls with surface energy density of the order of MeV. Such values for sigma are proposed in the late-time phase-transition scenario of Hill et al. (1989).
Direct observation of closure domain wall mediated spin waves
Mozooni, Babak McCord, Jeffrey
2015-07-27
The generation and guiding of spin waves from and by magnetic domain walls are demonstrated. The spin waves radiate from pinned and oscillating magnetic closure domain walls and propagate linearly along a narrow path formed by the surrounding 180° asymmetric Bloch domain walls. The propagating spin wave modes are directly visualized by time-resolved magneto-optical Kerr microscopy with picosecond temporal resolution. A linear relationship between excitation frequency, wavelength, and number of spin waves per domain exists. Independent of the field excitation frequency, a constant phase velocity of spin waves propagation is obtained. Spin waves characteristics can be tuned by varying the magnetic domain dynamics, allowing for variable spin wave characteristics with magnetic field characteristics and histories.
Direct observation of closure domain wall mediated spin waves
NASA Astrophysics Data System (ADS)
Mozooni, Babak; McCord, Jeffrey
2015-07-01
The generation and guiding of spin waves from and by magnetic domain walls are demonstrated. The spin waves radiate from pinned and oscillating magnetic closure domain walls and propagate linearly along a narrow path formed by the surrounding 180° asymmetric Bloch domain walls. The propagating spin wave modes are directly visualized by time-resolved magneto-optical Kerr microscopy with picosecond temporal resolution. A linear relationship between excitation frequency, wavelength, and number of spin waves per domain exists. Independent of the field excitation frequency, a constant phase velocity of spin waves propagation is obtained. Spin waves characteristics can be tuned by varying the magnetic domain dynamics, allowing for variable spin wave characteristics with magnetic field characteristics and histories.
NASA Astrophysics Data System (ADS)
Pertsev, N. A.; Kiselev, D. A.; Bdikin, I. K.; Kosec, M.; Kholkin, A. L.
2011-09-01
Direct measurements of the motion of domain walls in disordered ferroelectrics provide important information on their interaction with defects, which is crucial for the functioning of various ferroelectric devices such as high-K capacitors and ferroelectric-based memories. In this work, we report on the results of the nanoscale measurements of domain-wall velocity and static domain-wall roughness in disordered (Pb,La)(Zr,Ti)O3 (PLZT) ceramics prepared by hot press sintering. Relaxation of domain walls to their equilibrium configurations at short length scales yields the apparent roughness exponent ζ ≈ 0.67 in PLZT 9.5/65/35. At the same time, the dynamical exponent μ was found to be about 0.25 from the independent measurements of domain-wall creep under local application of electric field. An analysis of these two values points to the effective dimensionality deff = 1 for the domain walls in PLZT with high La content. This result is confirmed by the layer-by-layer polishing followed by the imaging of an artificially created domain. The origin of disorder and its dependence on La concentration in PLZT solid solutions are discussed.
Nonlinear dynamics of domain walls with cross-ties
NASA Astrophysics Data System (ADS)
Dubovik, M. N.; Zverev, V. V.; Filippov, B. N.
2016-07-01
The dynamic behavior of a domain wall with cross-ties is analyzed on the basis of micromagnetic simulation with exact allowance for all main (exchange, magnetoanisotropic, and magnetostatic) interactions in thin magnetically uniaxial ferromagnetic films with planar anisotropy. It is found that the peculiarities of motion of such domain walls are closely related to the behavior of topological defects in the magnetization distribution (generation, motion, and annihilation of vortex-antivortex pairs on the film surface and Bloch points). We observe three different regimes of motion (stationary, periodic, and turbulent regimes), each of which is realized in a certain range of fields oriented along the easy magnetization axis. It is shown that the experimentally observed dynamic bends of the walls with cross-ties are determined by the type of motion of vortices and antivortices. The velocities of domain walls in different regimes are calculated, and the dynamic configurations of the magnetization and existing dynamic transitions between them are investigated.
Spin waves and domain wall modes in curved magnetic nanowires.
Bocklage, Lars; Motl-Ziegler, Sandra; Topp, Jesco; Matsuyama, Toru; Meier, Guido
2014-07-01
The confinement of spin waves in inhomogeneous fields and spin wave interaction with domain walls has attracted interest due to possible applications in magnonics. We investigate spin waves in curved ferromagnetic nanowires. The field dispersion and localization of spin waves is revealed by comparison to known modes in stripes and taking into account the specific field reversal of the curved wire. In small wires we find a strongly altered mode spectrum in a certain field regime. Micromagnetic simulations show an extended domain wall within the wire in this field region. The domain wall shows several dynamic modes and changes the remaining spin wave modes. We find mode suppression as well as newly arising modes due to the strong inhomogenous internal field of the wall.
Evolution of thick domain walls in de Sitter universe
NASA Astrophysics Data System (ADS)
Dolgov, A. D.; Godunov, S. I.; Rudenko, A. S.
2016-10-01
We consider thick domain walls in a de Sitter universe following paper by Basu and Vilenkin. However, we are interested not only in stationary solutions found therein, but also investigate the general case of domain wall evolution with time. When the wall thickness parameter, δ0, is smaller than H‑1/√2, where H is the Hubble parameter in de Sitter space-time, then the stationary solutions exist, and initial field configurations tend with time to the stationary ones. However, there are no stationary solutions for δ0 >= H‑1/√2. We have calculated numerically the rate of the wall expansion in this case and have found that the width of the wall grows exponentially fast for δ0 gg H‑1. An explanation for the critical value δ0c = H‑1/√2 is also proposed.
Energy of domain walls in ferrite films
NASA Astrophysics Data System (ADS)
Gomez, M. E.; Prieto, P.; Mendoza, A.; Guzman, O.
2007-03-01
MnZn Ferrite films were deposited by RF sputtering on (001) single crystal MgO substrates. AFM images show an increment in grain size with the film thickness. Grains with diameter between φ ˜ 70 and 700 nm have been observed. The coercive field Hc as a function of the grain size reaches a maximum value of about 80 Oe for φc˜ 300 nm. The existence of a multidomain structure associated with a critical grain size was identified by Magneto-optical Kerr effect technique (MOKE). The transition of the one-domain regime to the two-domain regime was observed at a critical grain size of Dc˜ 530 nm. This value agree with values predicted previously. The Jiles-Atherton model (JAM) was used to discuss the experimental hysteresis loops. The k pinning parameter obtained from JAM shows a maximum value of k/μo = 67 Am^2 for grains with Lc˜ 529 nm. The total energy per unit area E was correlated with k and D. We found a simple phenomenological relationship given by E α kD; where D is the magnetic domain width.
Domain walls in supersymmetric QCD: The taming of the zoo
Binosi, Daniele; ter Veldhuis, Tonnis
2001-04-15
We provide a unified picture of the domain wall spectrum in supersymmetric QCD with N{sub c} colors and N{sub f} flavors of quarks in the (anti) fundamental representation. Within the framework of the Veneziano-Yankielowicz-Taylor effective Lagrangian, we consider domain walls connecting chiral symmetry breaking vacua, and we take the quark masses to be degenerate. For N{sub f}/N{sub c}<1/2, there is one BPS saturated domain wall for any value of the quark mass m. For 1/2{<=}N{sub f}/N{sub c}<1 there are two critical masses m{sub *} and m{sub **} which depend on the number of colors and flavors only through the ratio N{sub f}/N{sub c}. If m
Magnetoelectric domain wall dynamics and its implications for magnetoelectric memory
Belashchenko, K. D.; Tchernyshyov, O.; Kovalev, Alexey A.; Tretiakov, O. A.
2016-03-30
Domain wall dynamics in a magnetoelectric antiferromagnet is analyzed, and its implications for magnetoelectric memory applications are discussed. Cr2O3 is used in the estimates of the materials parameters. It is found that the domain wall mobility has a maximum as a function of the electric field due to the gyrotropic coupling induced by it. In Cr2O3, the maximal mobility of 0.1 m/(s Oe) is reached at E≈0.06 V/nm. Fields of this order may be too weak to overcome the intrinsic depinning field, which is estimated for B-doped Cr2O3. These major drawbacks for device implementation can be overcome by applying amore » small in-plane shear strain, which blocks the domain wall precession. Domain wall mobility of about 0.7 m/(s Oe) can then be achieved at E = 0.2 V/nm. Furthermore, a split-gate scheme is proposed for the domain-wall controlled bit element; its extension to multiple-gate linear arrays can offer advantages in memory density, programmability, and logic functionality.« less
Magnetoelectric domain wall dynamics and its implications for magnetoelectric memory
NASA Astrophysics Data System (ADS)
Belashchenko, K. D.; Tchernyshyov, O.; Kovalev, Alexey A.; Tretiakov, O. A.
2016-03-01
Domain wall dynamics in a magnetoelectric antiferromagnet is analyzed, and its implications for magnetoelectric memory applications are discussed. Cr2O3 is used in the estimates of the materials parameters. It is found that the domain wall mobility has a maximum as a function of the electric field due to the gyrotropic coupling induced by it. In Cr2O3, the maximal mobility of 0.1 m/(s Oe) is reached at E ≈0.06 V/nm. Fields of this order may be too weak to overcome the intrinsic depinning field, which is estimated for B-doped Cr2O3. These major drawbacks for device implementation can be overcome by applying a small in-plane shear strain, which blocks the domain wall precession. Domain wall mobility of about 0.7 m/(s Oe) can then be achieved at E = 0.2 V/nm. A split-gate scheme is proposed for the domain-wall controlled bit element; its extension to multiple-gate linear arrays can offer advantages in memory density, programmability, and logic functionality.
Majorana Fermion Rides on a Magnetic Domain Wall
NASA Astrophysics Data System (ADS)
Kim, Se Kwon; Tewari, Sumanta; Tserkovnyak, Yaroslav
Owing to the recent progress on endowing the electronic structure of magnetic nanowires with topological properties, the associated topological solitons in the magnetic texture--magnetic domain walls--appear as very natural hosts for exotic electronic excitations. Here, we propose to use the magnetic domain walls to engender Majorana fermions, which has several notable advantages compared to the existing approaches. First of all, the local tunneling density-of-states anomaly associated with the Majorana zero mode bound to a smooth magnetic soliton is immune to most of parasitic artifacts associated with the abrupt physical ends of a wire, which mar the existing experimental probes. Second, a viable route to move and braid Majorana fermions is offered by domain-wall motion. In particular, we envision the recently demonstrated heat-current induced motion of domain walls in insulating ferromagnets as a promising tool for nonintrusive displacement of Majorana modes. This leads us to propose a feasible scheme for braiding domain walls within a magnetic nanowire network, which manifests the nob-Abelian exchange statistics within the Majorana subspace. This work has been supported in part by the U.S. DOE-BES, FAME, and AFOSR grants.
Current-driven periodic domain wall creation in ferromagnetic nanowires
NASA Astrophysics Data System (ADS)
Sitte, Matthias; Everschor-Sitte, Karin; Valet, Thierry; Rodrigues, Davi R.; Sinova, Jairo; Abanov, Ar.
2016-08-01
We predict the electrical generation and injection of domain walls into a ferromagnetic nanowire without the need of an assisting magnetic field. Our analytical and numerical results show that above a critical current jc domain walls are injected into the nanowire with a period T ˜(j-jc) -1 /2 . Importantly, domain walls can be produced periodically even in a simple exchange ferromagnet with uniaxial anisotropy, without requiring any standard "twisting" interaction such as Dzyaloshinskii-Moriya or dipole-dipole interactions. We show analytically that this process and the period exponents are universal and do not depend on the peculiarities of the microscopic Hamiltonian. Finally we give a specific proposal for an experimental realization.
Ground state and constrained domain walls in Gd /Fe multilayers
NASA Astrophysics Data System (ADS)
Van Aken, Bas B.; Prieto, José L.; Mathur, Neil D.
2005-03-01
The magnetic ground state of antiferromagnetically coupled Gd /Fe multilayers and the evolution of in-plane domain walls is modeled with micromagnetics. The twisted state is characterized by a rapid decrease of the interface angle with increasing magnetic field. We found that for certain ratios MFe:MGd, the twisted state is already present at low fields. However, the magnetic ground state is not only determined by the ratio MFe:MGd but also by the thicknesses of the layers; that is by the total moments of the layer. The dependence of the magnetic ground state is explained by the amount of overlap of the domain walls at the interface. Thicker layers suppress the Fe-aligned and the Gd-aligned state in favor of the twisted state. On the other hand, ultrathin layers exclude the twisted state, since wider domain walls cannot form in these ultrathin layers.
Magnetic domain walls as reconfigurable spin-wave nanochannels
NASA Astrophysics Data System (ADS)
Wagner, K.; Kákay, A.; Schultheiss, K.; Henschke, A.; Sebastian, T.; Schultheiss, H.
2016-05-01
In the research field of magnonics, it is envisaged that spin waves will be used as information carriers, promoting operation based on their wave properties. However, the field still faces major challenges. To become fully competitive, novel schemes for energy-efficient control of spin-wave propagation in two dimensions have to be realized on much smaller length scales than used before. In this Letter, we address these challenges with the experimental realization of a novel approach to guide spin waves in reconfigurable, nano-sized magnonic waveguides. For this purpose, we make use of two inherent characteristics of magnetism: the non-volatility of magnetic remanence states and the nanometre dimensions of domain walls formed within these magnetic configurations. We present the experimental observation and micromagnetic simulations of spin-wave propagation inside nano-sized domain walls and realize a first step towards a reconfigurable domain-wall-based magnonic nanocircuitry.
Study of gravitational radiation from cosmic domain walls
Kawasaki, Masahiro; Saikawa, Ken'ichi E-mail: saikawa@icrr.u-tokyo.ac.jp
2011-09-01
In this paper, following the previous study, we evaluate the spectrum of gravitational wave background generated by domain walls which are produced if some discrete symmetry is spontaneously broken in the early universe. We apply two methods to calculate the gravitational wave spectrum: One is to calculate the gravitational wave spectrum directly from numerical simulations, and another is to calculate it indirectly by estimating the unequal time anisotropic stress power spectrum of the scalar field. Both analysises indicate that the slope of the spectrum changes at two characteristic frequencies corresponding to the Hubble radius at the decay of domain walls and the width of domain walls, and that the spectrum between these two characteristic frequencies becomes flat or slightly red tilted. The second method enables us to evaluate the GW spectrum for the frequencies which cannot be resolved in the finite box lattice simulations, but relies on the assumptions for the unequal time correlations of the source.
Epitaxial Engineering of Domain Walls and Distortions in Ferrite Heterostructures
NASA Astrophysics Data System (ADS)
Mundy, Julia
The defining feature of ferroics is the ability of an external stimulus--electric field, magnetic field, or stress--to move domain walls. These topological defects and their motion enables many useful attributes, e.g., memories that can be reversibly written between stable states as well as enhanced conductivity, permittivity, permeability, and piezoelectricity. Although methods are known to drastically increase their density, the placement of domain walls with atomic precision has until now evaded control. Here we engineer the location of domain walls with monolayer precision and exploit this ability to create a novel multiferroic in which ferroelectricity enhances magnetism at all relevant length scales. Starting with hexagonal LuFeO3, a geometric ferroelectric with the greatest known planar rumpling, we introduce individual extra monolayers of FeO during growth to construct formula-unit-thick syntactic layers of ferrimagnetic LuFe2O4 within the LuFeO3 matrix, i.e., (LuFeO3)m /(LuFe2O4)1 superlattices. The severe rumpling imposed by the neighboring LuFeO3 drives the ferrimagnetic LuFe2O4 into a simultaneously ferroelectric state and reduces the LuFe2O4 spin frustration. This increases the magnetic transition temperature significantly--to 281 K for the (LuFeO3)9 /(LuFe2O4)1 superlattice. Moreover, LuFeO3 can form charged ferroelectric domain walls, which we align to the LuFe2O4 bilayers with monolayer precision. Charge transfers to these domain walls to alleviate the otherwise electrostatically unstable polarization arrangement, further boosting the magnetic moment. Our results demonstrate the utility of combining ferroics at the atomic-layer level with attention to domain walls, geometric frustration and polarization doping to create multiferroics by design.
Model of bound interface dynamics for coupled magnetic domain walls
NASA Astrophysics Data System (ADS)
Politi, P.; Metaxas, P. J.; Jamet, J.-P.; Stamps, R. L.; Ferré, J.
2011-08-01
A domain wall in a ferromagnetic system will move under the action of an external magnetic field. Ultrathin Co layers sandwiched between Pt have been shown to be a suitable experimental realization of a weakly disordered 2D medium in which to study the dynamics of 1D interfaces (magnetic domain walls). The behavior of these systems is encapsulated in the velocity-field response v(H) of the domain walls. In a recent paper [P. J. Metaxas , Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.104.237206 104, 237206 (2010)] we studied the effect of ferromagnetic coupling between two such ultrathin layers, each exhibiting different v(H) characteristics. The main result was the existence of bound states over finite-width field ranges, wherein walls in the two layers moved together at the same speed. Here we discuss in detail the theory of domain wall dynamics in coupled systems. In particular, we show that a bound creep state is expected for vanishing H and we give the analytical, parameter free expression for its velocity which agrees well with experimental results.
Novel current driven domain wall dynamics in synthetic antiferromagnets
NASA Astrophysics Data System (ADS)
Yang, See-Hun
It was reported that the domain walls in nanowires can be moved efficiently by electrical currents by a new type of torque, chiral spin torque (CST), the combination of spin Hall effect and Dzyaloshinskii-Moriya interaction. Recently we domonstrated that ns-long current pulses can move domain walls at extraordinarily high speeds (up to ~750 m s -1) in synthetic antiferromagnetic (SAF) nanowires that have almost zero net magnetization, which is much more efficient compared with similar nanowires in which the sub-layers are coupled ferromagnetically (SF). This high speed is found to be due to a new type of powerful torque, exchange coupling torque (ECT) that is directly proportional to the strength of the antiferromagnetic exchange coupling between the two sub-layers, showing that the ECT is effective only in SAF not in SF. Moreover, it is found that the dependence of the wall velocity on the magnetic field applied along the nanowire is non-monotonic. Most recently we predict an Walker-breakdown-like domain wall precession in SAF nanowires in the presence of in-plane field based on the model we develop, and this extraordinary precession has been observed. In this talk I will discuss this in details by showing a unique characteristics of SAF sublayers' DW boost-and-drag mechanism along with CST and ECT. Novel current driven domain wall dynamics in synthetic antiferromagnets.
Runaway domain wall and space-time varying α
Chiba, Takeshi; Yamaguchi, Masahide E-mail: gucci@phys.titech.ac.jp
2011-03-01
Recently spatial as well as temporal variations of the fine structure constant α have been reported. We show that a ''runaway domain wall{sup ,} which arises for the scalar field potential without minima, can account for such variations simultaneously. The time variation is induced by a runaway potential and the spatial variation is induced by the formation of a domain wall. The model is consistent with the current cosmological data and can be tested by the future experiments to test the equivalence principle.
Thick domain walls in AdS black hole spacetimes
Moderski, Rafal; Rogatko, Marek
2006-08-15
Equations of motion for a real self-gravitating scalar field in the background of a black hole with negative cosmological constant were solved numerically. We obtain a sequence of static axisymmetric solutions representing thick domain wall cosmological black hole systems, depending on the mass of black hole, cosmological parameter and the parameter binding black hole mass with the width of the domain wall. For the case of extremal cosmological black hole the expulsion of scalar field from the black hole strongly depends on it.
Topological valley transport at bilayer graphene domain walls
NASA Astrophysics Data System (ADS)
Ju, Long; Shi, Zhiwen; Nair, Nityan; Lv, Yinchuan; Jin, Chenhao; Velasco, Jairo, Jr.; Ojeda-Aristizabal, Claudia; Bechtel, Hans; Martin, Michael; Zettl, Alex; Analytis, James; McEuen, Paul; Wang, Feng
Electron valley, a degree of freedom that is analogous to spin, can lead to novel topological phases in bilayer graphene. An external electric field can induce a tunable bandgap in bilayer graphene, and domain walls between AB- and BA-stacked bilayer graphene can support protected chiral edge states of quantum valley Hall insulators. In this talk, I will present our efforts on revealing the topologically protected edge states at AB-BA domain walls by combining near field infrared nanoscopy with electrical transport measurement. These one-dimensional valley-polarized conducting channels feature a ballistic length of about 400 nanometres at 4 kelvin.
Low energy electron imaging of domains and domain walls in magnesium-doped lithium niobate
NASA Astrophysics Data System (ADS)
Nataf, G. F.; Grysan, P.; Guennou, M.; Kreisel, J.; Martinotti, D.; Rountree, C. L.; Mathieu, C.; Barrett, N.
2016-09-01
The understanding of domain structures, specifically domain walls, currently attracts a significant attention in the field of (multi)-ferroic materials. In this article, we analyze contrast formation in full field electron microscopy applied to domains and domain walls in the uniaxial ferroelectric lithium niobate, which presents a large 3.8 eV band gap and for which conductive domain walls have been reported. We show that the transition from Mirror Electron Microscopy (MEM – electrons reflected) to Low Energy Electron Microscopy (LEEM – electrons backscattered) gives rise to a robust contrast between domains with upwards (Pup) and downwards (Pdown) polarization, and provides a measure of the difference in surface potential between the domains. We demonstrate that out-of-focus conditions of imaging produce contrast inversion, due to image distortion induced by charged surfaces, and also carry information on the polarization direction in the domains. Finally, we show that the intensity profile at domain walls provides experimental evidence for a local stray, lateral electric field.
Low energy electron imaging of domains and domain walls in magnesium-doped lithium niobate
NASA Astrophysics Data System (ADS)
Nataf, G. F.; Grysan, P.; Guennou, M.; Kreisel, J.; Martinotti, D.; Rountree, C. L.; Mathieu, C.; Barrett, N.
2016-09-01
The understanding of domain structures, specifically domain walls, currently attracts a significant attention in the field of (multi)-ferroic materials. In this article, we analyze contrast formation in full field electron microscopy applied to domains and domain walls in the uniaxial ferroelectric lithium niobate, which presents a large 3.8 eV band gap and for which conductive domain walls have been reported. We show that the transition from Mirror Electron Microscopy (MEM - electrons reflected) to Low Energy Electron Microscopy (LEEM - electrons backscattered) gives rise to a robust contrast between domains with upwards (Pup) and downwards (Pdown) polarization, and provides a measure of the difference in surface potential between the domains. We demonstrate that out-of-focus conditions of imaging produce contrast inversion, due to image distortion induced by charged surfaces, and also carry information on the polarization direction in the domains. Finally, we show that the intensity profile at domain walls provides experimental evidence for a local stray, lateral electric field.
Low energy electron imaging of domains and domain walls in magnesium-doped lithium niobate
Nataf, G. F.; Grysan, P.; Guennou, M.; Kreisel, J.; Martinotti, D.; Rountree, C. L.; Mathieu, C.; Barrett, N.
2016-01-01
The understanding of domain structures, specifically domain walls, currently attracts a significant attention in the field of (multi)-ferroic materials. In this article, we analyze contrast formation in full field electron microscopy applied to domains and domain walls in the uniaxial ferroelectric lithium niobate, which presents a large 3.8 eV band gap and for which conductive domain walls have been reported. We show that the transition from Mirror Electron Microscopy (MEM – electrons reflected) to Low Energy Electron Microscopy (LEEM – electrons backscattered) gives rise to a robust contrast between domains with upwards (Pup) and downwards (Pdown) polarization, and provides a measure of the difference in surface potential between the domains. We demonstrate that out-of-focus conditions of imaging produce contrast inversion, due to image distortion induced by charged surfaces, and also carry information on the polarization direction in the domains. Finally, we show that the intensity profile at domain walls provides experimental evidence for a local stray, lateral electric field. PMID:27608605
Low energy electron imaging of domains and domain walls in magnesium-doped lithium niobate.
Nataf, G F; Grysan, P; Guennou, M; Kreisel, J; Martinotti, D; Rountree, C L; Mathieu, C; Barrett, N
2016-01-01
The understanding of domain structures, specifically domain walls, currently attracts a significant attention in the field of (multi)-ferroic materials. In this article, we analyze contrast formation in full field electron microscopy applied to domains and domain walls in the uniaxial ferroelectric lithium niobate, which presents a large 3.8 eV band gap and for which conductive domain walls have been reported. We show that the transition from Mirror Electron Microscopy (MEM - electrons reflected) to Low Energy Electron Microscopy (LEEM - electrons backscattered) gives rise to a robust contrast between domains with upwards (Pup) and downwards (Pdown) polarization, and provides a measure of the difference in surface potential between the domains. We demonstrate that out-of-focus conditions of imaging produce contrast inversion, due to image distortion induced by charged surfaces, and also carry information on the polarization direction in the domains. Finally, we show that the intensity profile at domain walls provides experimental evidence for a local stray, lateral electric field. PMID:27608605
Light wave propagation through a dilaton-Maxwell domain wall
NASA Astrophysics Data System (ADS)
Morris, J. R.; Schulze-Halberg, A.
2015-10-01
We consider the propagation of electromagnetic waves through a dilaton-Maxwell domain wall of the type introduced by Gibbons and Wells [G. W. Gibbons and C. G. Wells, Classical and Quantum Gravity 11, 2499 (1994)]. It is found that if such a wall exists within our observable Universe, it would be absurdly thick, or else have a magnetic field in its core which is much stronger than observed intergalactic fields. We conclude that it is highly improbable that any such wall is physically realized.
Shang, Jianyu; Deng, Zhihong; Fu, Mengyin; Wang, Shunting
2016-01-01
Traditional artillery guidance can significantly improve the attack accuracy and overall combat efficiency of projectiles, which makes it more adaptable to the information warfare of the future. Obviously, the accurate measurement of artillery spin rate, which has long been regarded as a daunting task, is the basis of precise guidance and control. Magnetoresistive (MR) sensors can be applied to spin rate measurement, especially in the high-spin and high-g projectile launch environment. In this paper, based on the theory of a MR sensor measuring spin rate, the mathematical relationship model between the frequency of MR sensor output and projectile spin rate was established through a fundamental derivation. By analyzing the characteristics of MR sensor output whose frequency varies with time, this paper proposed the Chirp z-Transform (CZT) time-frequency (TF) domain analysis method based on the rolling window of a Blackman window function (BCZT) which can accurately extract the projectile spin rate. To put it into practice, BCZT was applied to measure the spin rate of 155 mm artillery projectile. After extracting the spin rate, the impact that launch rotational angular velocity and aspect angle have on the extraction accuracy of the spin rate was analyzed. Simulation results show that the BCZT TF domain analysis method can effectively and accurately measure the projectile spin rate, especially in a high-spin and high-g projectile launch environment. PMID:27322266
Shang, Jianyu; Deng, Zhihong; Fu, Mengyin; Wang, Shunting
2016-01-01
Traditional artillery guidance can significantly improve the attack accuracy and overall combat efficiency of projectiles, which makes it more adaptable to the information warfare of the future. Obviously, the accurate measurement of artillery spin rate, which has long been regarded as a daunting task, is the basis of precise guidance and control. Magnetoresistive (MR) sensors can be applied to spin rate measurement, especially in the high-spin and high-g projectile launch environment. In this paper, based on the theory of a MR sensor measuring spin rate, the mathematical relationship model between the frequency of MR sensor output and projectile spin rate was established through a fundamental derivation. By analyzing the characteristics of MR sensor output whose frequency varies with time, this paper proposed the Chirp z-Transform (CZT) time-frequency (TF) domain analysis method based on the rolling window of a Blackman window function (BCZT) which can accurately extract the projectile spin rate. To put it into practice, BCZT was applied to measure the spin rate of 155 mm artillery projectile. After extracting the spin rate, the impact that launch rotational angular velocity and aspect angle have on the extraction accuracy of the spin rate was analyzed. Simulation results show that the BCZT TF domain analysis method can effectively and accurately measure the projectile spin rate, especially in a high-spin and high-g projectile launch environment. PMID:27322266
Matter antimatter domains: A possible solution to the CP domain wall problem in the early universe
NASA Technical Reports Server (NTRS)
Mohanty, A. K.; Stecker, F. W.
1984-01-01
An SU(5) grand unified theory model is used to show how the degeneracy between vacua with different spontaneously broken charge parity can be dynamically lifted by a condensate of heavy fermion pairs. This drives a phase transition to a unique vacuum state with definite charge parity. The transition eliminates the domain walls in a matter antimatter symmetric domain cosmology.
Textural domain walls in superfluid 3He-B
NASA Astrophysics Data System (ADS)
Mizushima, Takeshi
Owing to the richness of symmetry, the superfluid 3He serves as a rich repository of topological quantum phenomena. This includes the emergence of surface Majorana fermions and their quantum mass acquisition at the topological critical point. Furthermore, the marriage of the prototype topological superfluid with nanofabrication techniques brings about a rich variety of spontaneous symmetry breaking, such as the formation of the stripe order and nontrivial domain walls. In this work, we examine the possible formation of textural domain walls in the superfluid 3He-B confined to a thin slab with a sub-micron thickness. When an applied magnetic field is much higher than the dipolar field, two nearly degenerate ground states appear, which are characterized by the Ising order associated with the spontaneous breaking of a magnetic order-two symmetry, lcirc;z = + 1 and - 1 . We here discuss the structure of the textural domain wall formed by the spatial modulation of the Ising order, such as low-lying quasiparticle excitations and spontaneous spin current. We also report bosonic modes bound to the textural domain wall.
Domain wall formation from level crossing in the axiverse
NASA Astrophysics Data System (ADS)
Daido, Ryuji; Kitajima, Naoya; Takahashi, Fuminobu
2015-09-01
We point out that domain wall formation is a more common phenomenon in the axiverse than previously thought. Level crossing could take place if there is a mixing between axions, and if some of the axions acquire a nonzero mass through nonperturbative effects as the corresponding gauge interactions become strong. The axion potential changes significantly during the level crossing, which affects the axion dynamics in various ways. We find that, if there is a mild hierarchy in the decay constants, the axion starts to run along the valley of the potential, passing through many crests and troughs, until it gets trapped in one of the minima: the axion roulette. The axion dynamics exhibits a chaotic behavior during the oscillations, and which minimum the axion is finally stabilized is highly sensitive to the initial misalignment angle. Therefore, the axion roulette is considered to be accompanied by domain wall formation. The cosmological domain wall problem can be avoided by introducing a small bias between the vacua. We discuss cosmological implications of the domain wall annihilation for baryogenesis and future gravitational wave experiments.
Spontaneously broken parity and consistent cosmology with transitory domain walls
Mishra, Sasmita; Yajnik, Urjit A.
2010-02-15
Domain wall structure which may form in theories with spontaneously broken parity is generically in conflict with standard cosmology. It has been argued that Planck scale suppressed effects can be sufficient for removing such domain walls. We study this possibility for three specific evolution scenarios for the domain walls, with evolution during a radiation dominated era, during a matter dominated era, and that accompanied by weak inflation. We determine the operators permitted by the supergravity formalism and find that the field content introduced to achieve desired spontaneous parity breaking makes possible Planck scale suppressed terms which can potentially remove the domain walls safely. However, the parity breaking scale, equivalently the Majorana mass scale M{sub R} of the right-handed neutrino, does get constrained in some of the cases, notably for the matter dominated evolution case which would be generic to string theory inspired models, giving rise to moduli fields. One left-right symmetric model with only triplets and bidoublets is found to be more constrained than another admitting a gauge singlet.
Domain wall mobility, stability and Walker breakdown in magnetic nanowires
NASA Astrophysics Data System (ADS)
Mougin, A.; Cormier, M.; Adam, J. P.; Metaxas, P. J.; Ferré, J.
2007-06-01
We present an analytical calculation of the velocity of a single 180° domain wall in a magnetic structure with reduced thickness and/or lateral dimension under the combined action of an external applied magnetic field and an electrical current. As for the case of field-induced domain wall propagation in thick films, two motion regimes with different mobilities are obtained, below and far above the so-called Walker field. Additionally, for the case of current induced motion, a Walker-like current density threshold is defined. The threshold field and current density, stating the wall's internal structure stability, differ from those in thick films; both are reduced by the same geometrical demagnetising factor which accounts for the confinement. This points out the fact that the velocity dependence over an extended field/current range and the knowledge of the Walker breakdown are mandatory to draw conclusions about the phenomenological Gilbert damping parameter tuning the magnetisation dynamics.
Non-volatile polarization switch of magnetic domain wall velocity
Huang, Z.; Stolichnov, I.; Setter, N.; Bernand-Mantel, A.; Schott, Marine; Pizzini, S.; Ranno, L.; Auffret, S.; Gaudin, G.
2015-12-21
Controlled propagation speed of individual magnetic domains in metal channels at the room temperature is obtained via the non-volatile field effect associated with the switchable polarization of P(VDF-TrFE) (polyvinylidene fluoride-trifluoroethylene) ferroelectric polymer. Polarization domains directly written using conducting atomic force microscope probe locally accelerate/decelerate the magnetic domains in the 0.6 nm thick Co film. The change of the magnetic domain wall velocity is consistent with the magnetic anisotropy energy modulation through the polarization upward/downward orientation. Excellent retention is observed. The demonstrated local non-destructive and reversible change of magnetic properties via rewritable patterning of ferroelectric domains could be attractive for exploring the ultimate limit of miniaturization in devices based on ferromagnetic/ferroelectric bilayers.
Detecting Domain Walls of Axionlike Models Using Terrestrial Experiments
NASA Astrophysics Data System (ADS)
Pospelov, M.; Pustelny, S.; Ledbetter, M. P.; Kimball, D. F. Jackson; Gawlik, W.; Budker, D.
2013-01-01
Stable topological defects of light (pseudo)scalar fields can contribute to the Universe’s dark energy and dark matter. Currently, the combination of gravitational and cosmological constraints provides the best limits on such a possibility. We take an example of domain walls generated by an axionlike field with a coupling to the spins of standard-model particles and show that, if the galactic environment contains a network of such walls, terrestrial experiments aimed at the detection of wall-crossing events are realistic. In particular, a geographically separated but time-synchronized network of sensitive atomic magnetometers can detect a wall crossing and probe a range of model parameters currently unconstrained by astrophysical observations and gravitational experiments.
Petitjean, Cyril; Luc, David; Waintal, Xavier
2012-09-14
Spins transverse to the magnetization of a ferromagnet only survive over a short distance. We develop a drift-diffusion approach that captures the main features of transverse spin effects in systems with arbitrary spin textures (e.g., vortices and domain walls) and generalizes the Valet-Fert theory. In addition to the standard characteristic lengths (mean free path for majority and minority electrons, and spin diffusion length), the theory introduces two length scales, the transverse spin coherence length ℓ(⊥) and the (Larmor) spin precession length ℓ(L). We show how ℓ(L) and ℓ(⊥) can be extracted from ab initio calculations or measured with giant magnetoresistance experiments. In long (adiabatic) domain walls, we provide an analytic formula that expresses the so-called "nonadiabatic" (or fieldlike) torque in terms of these length scales. However, this nonadiabatic torque is no longer a simple material parameter but depends on the actual spin texture: in thin (<10 nm) domain walls, we observe very significant deviations from the adiabatic limit. PMID:23005670
Rashba Torque Driven Domain Wall Motion in Magnetic Helices.
Pylypovskyi, Oleksandr V; Sheka, Denis D; Kravchuk, Volodymyr P; Yershov, Kostiantyn V; Makarov, Denys; Gaididei, Yuri
2016-01-01
Manipulation of the domain wall propagation in magnetic wires is a key practical task for a number of devices including racetrack memory and magnetic logic. Recently, curvilinear effects emerged as an efficient mean to impact substantially the statics and dynamics of magnetic textures. Here, we demonstrate that the curvilinear form of the exchange interaction of a magnetic helix results in an effective anisotropy term and Dzyaloshinskii-Moriya interaction with a complete set of Lifshitz invariants for a one-dimensional system. In contrast to their planar counterparts, the geometrically induced modifications of the static magnetic texture of the domain walls in magnetic helices offer unconventional means to control the wall dynamics relying on spin-orbit Rashba torque. The chiral symmetry breaking due to the Dzyaloshinskii-Moriya interaction leads to the opposite directions of the domain wall motion in left- or right-handed helices. Furthermore, for the magnetic helices, the emergent effective anisotropy term and Dzyaloshinskii-Moriya interaction can be attributed to the clear geometrical parameters like curvature and torsion offering intuitive understanding of the complex curvilinear effects in magnetism.
Rashba Torque Driven Domain Wall Motion in Magnetic Helices
NASA Astrophysics Data System (ADS)
Pylypovskyi, Oleksandr V.; Sheka, Denis D.; Kravchuk, Volodymyr P.; Yershov, Kostiantyn V.; Makarov, Denys; Gaididei, Yuri
2016-03-01
Manipulation of the domain wall propagation in magnetic wires is a key practical task for a number of devices including racetrack memory and magnetic logic. Recently, curvilinear effects emerged as an efficient mean to impact substantially the statics and dynamics of magnetic textures. Here, we demonstrate that the curvilinear form of the exchange interaction of a magnetic helix results in an effective anisotropy term and Dzyaloshinskii–Moriya interaction with a complete set of Lifshitz invariants for a one-dimensional system. In contrast to their planar counterparts, the geometrically induced modifications of the static magnetic texture of the domain walls in magnetic helices offer unconventional means to control the wall dynamics relying on spin-orbit Rashba torque. The chiral symmetry breaking due to the Dzyaloshinskii–Moriya interaction leads to the opposite directions of the domain wall motion in left- or right-handed helices. Furthermore, for the magnetic helices, the emergent effective anisotropy term and Dzyaloshinskii–Moriya interaction can be attributed to the clear geometrical parameters like curvature and torsion offering intuitive understanding of the complex curvilinear effects in magnetism.
Dissipative dynamics of composite domain walls in magnetic nanostrips
NASA Astrophysics Data System (ADS)
Tretiakov, O.; Bazaliy, Ya. B.; Tchernyshyov, O.
2007-03-01
We describe the dynamics of domain walls in thin magnetic nanostrips of submicron width under the action of magnetic field. Once the fast precession of magnetization is averaged out, the dynamics reduces to purely dissipative motion where the system follows the direction of the local energy gradient (Glauber's model A) [1]. We then apply the method of collective coordinates [2] to our variational model of the domain wall [3] reducing the dynamics to the evolution of two collective coordinates (the location of the vortex core). In weak magnetic fields the wall moves steadily. The calculated velocity is in good agreement with the results of numerical simulations (no adjustable parameters were used). In higher fields the steady motion breaks down and acquires an oscillatory character caused by periodic creation and annihilation of topological defects comprising the domain wall [3]. Numerical simulations uncover at least two different modes of oscillation. [1] C. J. Garc'ia-Cervera and W. E, J. Appl. Phys. 90, 370 (2001). [2] A. S'anchez and A. R. Bishop, SIAM Rev. 40, 579 (1998). [3] Preceding talk by O. Tchernyshyov.
Rashba Torque Driven Domain Wall Motion in Magnetic Helices
Pylypovskyi, Oleksandr V.; Sheka, Denis D.; Kravchuk, Volodymyr P.; Yershov, Kostiantyn V.; Makarov, Denys; Gaididei, Yuri
2016-01-01
Manipulation of the domain wall propagation in magnetic wires is a key practical task for a number of devices including racetrack memory and magnetic logic. Recently, curvilinear effects emerged as an efficient mean to impact substantially the statics and dynamics of magnetic textures. Here, we demonstrate that the curvilinear form of the exchange interaction of a magnetic helix results in an effective anisotropy term and Dzyaloshinskii–Moriya interaction with a complete set of Lifshitz invariants for a one-dimensional system. In contrast to their planar counterparts, the geometrically induced modifications of the static magnetic texture of the domain walls in magnetic helices offer unconventional means to control the wall dynamics relying on spin-orbit Rashba torque. The chiral symmetry breaking due to the Dzyaloshinskii–Moriya interaction leads to the opposite directions of the domain wall motion in left- or right-handed helices. Furthermore, for the magnetic helices, the emergent effective anisotropy term and Dzyaloshinskii–Moriya interaction can be attributed to the clear geometrical parameters like curvature and torsion offering intuitive understanding of the complex curvilinear effects in magnetism. PMID:27008975
Whyte, J. R.; McQuaid, R. G. P.; Einsle, J. F.; Gregg, J. M.; Ashcroft, C. M.; Canalias, C.; Gruverman, A.
2014-08-14
Simple meso-scale capacitor structures have been made by incorporating thin (∼300 nm) single crystal lamellae of KTiOPO{sub 4} (KTP) between two coplanar Pt electrodes. The influence that either patterned protrusions in the electrodes or focused ion beam milled holes in the KTP have on the nucleation of reverse domains during switching was mapped using piezoresponse force microscopy imaging. The objective was to assess whether or not variations in the magnitude of field enhancement at localised “hot-spots,” caused by such patterning, could be used to both control the exact locations and bias voltages at which nucleation events occurred. It was found that both the patterning of electrodes and the milling of various hole geometries into the KTP could allow controlled sequential injection of domain wall pairs at different bias voltages; this capability could have implications for the design and operation of domain wall electronic devices, such as memristors, in the future.
Faster motion of double 360° domain walls system induced by spin-polarized current
Zhang, S. F.; Zhu, Q. Y.; Mu, C. P.; Zheng, Q.; Liu, X. Y.; Liu, Q. F.; Wang, J. B.
2014-05-07
By micromagnetic simulation, we investigated a double 360° domain walls system in two parallel nanowires. Two domain walls are coupled to each other via magnetostatic interaction. When a spin-polarized current is applied to only one nanowire or both nanowires with the same direction, the two domain walls propagate along nanowires together. The critical velocity of such system is obviously higher than that of a single 360° domain wall. The interaction between the two domain walls can be modeled as two bodies that connected by a spring, and we analyzed the coupling characteritics of the double 360° domain walls at last.
Domain-wall spin dynamics in kagome antiferromagnets.
Lhotel, E; Simonet, V; Ortloff, J; Canals, B; Paulsen, C; Suard, E; Hansen, T; Price, D J; Wood, P T; Powell, A K; Ballou, R
2011-12-16
We report magnetization and neutron scattering measurements down to 60 mK on a new family of Fe based kagome antiferromagnets, in which a strong local spin anisotropy combined with a low exchange path network connectivity lead to domain walls intersecting the kagome planes through strings of free spins. These produce unfamiliar slow spin dynamics in the ordered phase, evolving from exchange-released spin flips towards a cooperative behavior on decreasing the temperature, probably due to the onset of long-range dipolar interaction. A domain structure of independent magnetic grains is obtained that could be generic to other frustrated magnets.
Localization and chiral symmetry in three flavor domain wall QCD
Antonio, David J.; Bowler, Kenneth C.; Boyle, Peter A.; Hart, Alistair; Kenway, Richard D.; Tweedie, Robert J.; Christ, Norman H.; Cohen, Saul D.; Li, Shu; Lin, Meifeng; Mawhinney, Robert D.; Clark, Michael A.; Dawson, Chris; Joo, Balint; Jung, Chulwoo; Maynard, Christopher M.; Ohta, Shigemi; Yamaguchi, Azusa
2008-01-01
We present results for the dependence of the residual mass of domain wall fermions on the size of the fifth dimension and its relation to the density and localization properties of low-lying eigenvectors of the corresponding Hermitian Wilson Dirac operator in three flavor domain wall QCD. Using the DBW2 and Iwasaki gauge actions, we generate ensembles of configurations with a 16{sup 3}x32 space-time volume and an extent of 8 in the fifth dimension for the sea quarks. We demonstrate the existence of a regime where the degree of locality, the size of chiral symmetry breaking, and the rate of topology change can be acceptable for inverse lattice spacings a{sup -1}{>=}1.6 GeV, enabling a programme of simulations of 2+1 flavor QCD to be conducted safely in this region of parameter space.
Single particle demultiplexer based on domain wall conduits
NASA Astrophysics Data System (ADS)
Torti, A.; Mondiali, V.; Cattoni, A.; Donolato, M.; Albisetti, E.; Haghiri-Gosnet, A. M.; Vavassori, Paolo; Bertacco, R.
2012-10-01
The remote manipulation of micro and nano-sized magnetic particles carrying molecules or biological entities over a chip surface is of paramount importance for future on-chip applications in biology and medicine. In this paper, we present a method for the on-chip demultiplexing of individual magnetic particles using bifurcated magnetic nano-conduits for the propagation of constrained domain walls (DWs). We demonstrate that the controlled injection and propagation of a domain wall in a bifurcation allow capturing, transporting, and sorting a single magnetic particle between two predefined paths. The cascade of n levels of such building blocks allows for the implementation of a variety of complex sorting devices as, e.g., a demultiplexer for the controlled sorting among 2n paths.
Bounds on curved domain walls in 5D gravity
Kachru, Shamit; Schulz, Michael; Silverstein, Eva
2000-10-15
We discuss maximally symmetric curved deformations of the flat domain wall solutions of five-dimensional dilaton gravity that appeared in a recent approach to the cosmological constant problem. By analyzing the bulk field configurations and the boundary conditions at a four-dimensional maximally symmetric curved domain wall, we obtain constraints on such solutions. For a special dilaton coupling to the brane tension that appeared in recent works, we find no curved deformations, confirming and extending slightly a result of Arkani-Hamed which was argued using a Z{sub 2} symmetry of the solution. For more general dilaton-dependent brane tension, we find that the curvature is bounded by the Kaluza-Klein scale in the fifth dimension.
Magnetoresistance of nanosized magnetic configurations in single nanowires
NASA Astrophysics Data System (ADS)
Wegrowe, J.-E.; Gilbert, S.; Doudin, B.; Ansermet, J.-Ph.
1998-03-01
The problem of studying spin configurations at nanoscopic level is that magnetic measurements at this scale cannot be performed using usual magnetometers. We have shown that anisotropic magnetoresistance (AMR) measured with micro-contacts allows spin configurations of a single nanowire to be studied in details. The nanowires are diameter 50 nm and length 6000 nm and are produced by a combination of electrodeposition in track-etched membrane templates and sputtering technics. Magnetoresistance of well-defined spin configurations in single nanowires, like Curling magnetization reversal modes or domain wall, are measured.
Analysis of ultra-narrow ferromagnetic domain walls
Jenkins, Catherine; Paul, David
2012-01-10
New materials with high magnetic anisotropy will have domains separated by ultra-narrow ferromagnetic walls with widths on the order of a few unit cells, approaching the limit where the elastic continuum approximation often used in micromagnetic simulations is accurate. The limits of this approximation are explored, and the static and dynamic interactions with intrinsic crystalline defects and external driving elds are modeled. The results developed here will be important when considering the stability of ultra-high-density storage media.
Domain-wall motion in random potential and hysteresis modeling
Pasquale, M.; Basso, V.; Bertotti, G.; Jiles, D.C.; Bi, Y.
1998-06-01
Two different approaches to hysteresis modeling are compared using a common ground based on energy relations, defined in terms of dissipated and stored energy. Using the Preisach model and assuming that magnetization is mainly due to domain-wall motion, one can derive the expression of magnetization along a major loop typical of the Jiles{endash}Atherton model and then extend its validity to cases where mean-field effects and reversible contributions are present. {copyright} {ital 1998 American Institute of Physics.}
Study of ferroelectric domain switching by domain wall induced light scattering
NASA Astrophysics Data System (ADS)
Volk, T.; Isakov, D.; Ivanov, N.; Ivleva, L.; Betzler, K.; Tunyagi, A.; Wöhlecke, M.
2005-04-01
The 90°-light scattering on domain walls was probed in various strontium barium niobate (SBN) crystals for studies of the ferroelectric switching under pulsed fields. The validity of this optical method is proved by a good agreement of the switching parameters deduced from optical scattering data with those obtained with electric methods. Scanning of the scattering over the crystal bulk revealed local specialities of the switching, particularly, a marked distribution of the domain wall density D along the polar axis with a maximum close to the negative electrode. In compliance with these in situ observations, the electro-optic coefficient rc reveals a position dependence in all SBN crystals poled in the ferroelectric phase, rc decreasing from the positive to negative electrode. This regularity is interpreted in terms of the domain density distribution D(z ) and accounted for by an asymmetry of the domain nucleation.
Before sailing on a domain-wall sea
Golterman, Maarten; Shamir, Yigal
2005-02-01
We discuss the very different roles of the valence-quark and the sea-quark residual masses (m{sub res}{sup v} and m{sub res}{sup s}) in dynamical domain-wall fermions simulations. Focusing on matrix elements of the effective weak Hamiltonian containing a power divergence, we find that m{sub res}{sup v} can be a source of a much bigger systematic error. To keep all systematic errors due to residual masses at the 1% level, we estimate that one needs am{sub res}{sup s} < or approx. 10{sup -3} and am{sub res}{sup v} < or approx. 10{sup -5}, at a lattice spacing a{approx}0.1 fm. The practical implications are that (1) optimal use of computer resources calls for a mixed scheme with different domain-wall fermion actions for the valence and sea quarks; (2) better domain-wall fermion actions are needed for both the sea and the valence sectors.
Symmetry-protected topological phases from decorated domain walls.
Chen, Xie; Lu, Yuan-Ming; Vishwanath, Ashvin
2014-03-26
Symmetry-protected topological phases generalize the notion of topological insulators to strongly interacting systems of bosons or fermions. A sophisticated group cohomology approach has been used to classify bosonic symmetry-protected topological phases, which however does not transparently predict their properties. Here we provide a physical picture that leads to an intuitive understanding of a large class of symmetry-protected topological phases in d=1,2,3 dimensions. Such a picture allows us to construct explicit models for the symmetry-protected topological phases, write down ground state wave function and discover topological properties of symmetry defects both in the bulk and on the edge of the system. We consider symmetries that include a Z2 subgroup, which allows us to define domain walls. While the usual disordered phase is obtained by proliferating domain walls, we show that symmetry-protected topological phases are realized when these domain walls are decorated, that is, are themselves symmetry-protected topological phases in one lower dimension. This construction works both for unitary Z2 and anti-unitary time reversal symmetry.
Domain wall and isocurvature perturbation problems in axion models
Kawasaki, Masahiro; Yoshino, Kazuyoshi; Yanagida, Tsutomu T. E-mail: tsutomu.tyanagida@ipmu.jp
2013-11-01
Axion models have two serious cosmological problems, domain wall and isocurvature perturbation problems. In order to solve these problems we investigate the Linde's model in which the field value of the Peccei-Quinn (PQ) scalar is large during inflation. In this model the fluctuations of the PQ field grow after inflation through the parametric resonance and stable axionic strings may be produced, which results in the domain wall problem. We study formation of axionic strings using lattice simulations. It is found that in chaotic inflation the axion model is free from both the domain wall and the isocurvature perturbation problems if the initial misalignment angle θ{sub a} is smaller than O(10{sup −2}). Furthermore, axions can also account for the dark matter for the breaking scale v ≅ 10{sup 12−16} GeV and the Hubble parameter during inflation H{sub inf}∼<10{sup 11−12} GeV in general inflation models.
Reconfigurable logic via gate controlled domain wall trajectory in magnetic network structure
Murapaka, C.; Sethi, P.; Goolaup, S.; Lew, W. S.
2016-01-01
An all-magnetic logic scheme has the advantages of being non-volatile and energy efficient over the conventional transistor based logic devices. In this work, we present a reconfigurable magnetic logic device which is capable of performing all basic logic operations in a single device. The device exploits the deterministic trajectory of domain wall (DW) in ferromagnetic asymmetric branch structure for obtaining different output combinations. The programmability of the device is achieved by using a current-controlled magnetic gate, which generates a local Oersted field. The field generated at the magnetic gate influences the trajectory of the DW within the structure by exploiting its inherent transverse charge distribution. DW transformation from vortex to transverse configuration close to the output branch plays a pivotal role in governing the DW chirality and hence the output. By simply switching the current direction through the magnetic gate, two universal logic gate functionalities can be obtained in this device. Using magnetic force microscopy imaging and magnetoresistance measurements, all basic logic functionalities are demonstrated. PMID:26839036
Reconfigurable logic via gate controlled domain wall trajectory in magnetic network structure
NASA Astrophysics Data System (ADS)
Murapaka, C.; Sethi, P.; Goolaup, S.; Lew, W. S.
2016-02-01
An all-magnetic logic scheme has the advantages of being non-volatile and energy efficient over the conventional transistor based logic devices. In this work, we present a reconfigurable magnetic logic device which is capable of performing all basic logic operations in a single device. The device exploits the deterministic trajectory of domain wall (DW) in ferromagnetic asymmetric branch structure for obtaining different output combinations. The programmability of the device is achieved by using a current-controlled magnetic gate, which generates a local Oersted field. The field generated at the magnetic gate influences the trajectory of the DW within the structure by exploiting its inherent transverse charge distribution. DW transformation from vortex to transverse configuration close to the output branch plays a pivotal role in governing the DW chirality and hence the output. By simply switching the current direction through the magnetic gate, two universal logic gate functionalities can be obtained in this device. Using magnetic force microscopy imaging and magnetoresistance measurements, all basic logic functionalities are demonstrated.
Third type of domain wall in soft magnetic nanostrips
NASA Astrophysics Data System (ADS)
Nguyen, V. D.; Fruchart, O.; Pizzini, S.; Vogel, J.; Toussaint, J.-C.; Rougemaille, N.
2015-07-01
Magnetic domain walls (DWs) in nanostructures are low-dimensional objects that separate regions with uniform magnetisation. Since they can have different shapes and widths, DWs are an exciting playground for fundamental research, and became in the past years the subject of intense works, mainly focused on controlling, manipulating, and moving their internal magnetic configuration. In nanostrips with in-plane magnetisation, two DWs have been identified: in thin and narrow strips, transverse walls are energetically favored, while in thicker and wider strips vortex walls have lower energy. The associated phase diagram is now well established and often used to predict the low-energy magnetic configuration in a given magnetic nanostructure. However, besides the transverse and vortex walls, we find numerically that another type of wall exists in permalloy nanostrips. This third type of DW is characterised by a three-dimensional, flux closure micromagnetic structure with an unusual length and three internal degrees of freedom. Magnetic imaging on lithographically-patterned permalloy nanostrips confirms these predictions and shows that these DWs can be moved with an external magnetic field of about 1 mT. An extended phase diagram describing the regions of stability of all known types of DWs in permalloy nanostrips is provided.
Propagating and reflecting of spin wave in permalloy nanostrip with 360° domain wall
Zhang, Senfu; Mu, Congpu; Zhu, Qiyuan; Zheng, Qi; Liu, Xianyin; Wang, Jianbo; Liu, Qingfang
2014-01-07
By micromagnetic simulation, we investigated the interaction between propagating spin wave (or magnonic) and a 360° domain wall in a nanostrip. It is found that propagating spin wave can drive a 360° domain wall motion, and the velocity and direction are closely related to the transmission coefficient of the spin wave of the domain wall. When the spin wave passes through the domain wall completely, the 360° domain wall moves toward the spin wave source. When the spin wave is reflected by the domain wall, the 360° domain wall moves along the spin wave propagation direction. Moreover, when the frequency of the spin wave is coincident with that of the 360° domain wall normal mode, the 360° domain wall velocity will be resonantly enhanced no matter which direction the 360 DW moves along. On the other hand, when the spin wave is reflected from the moving 360° domain wall, we observed the Doppler effect clearly. After passing through a 360° domain wall, the phase of the spin wave is changed, and the phase shift is related to the frequency. Nevertheless, phase shift could be manipulated by the number of 360° domain walls that spin wave passing through.
Controlled motion of domain walls in submicron amorphous wires
NASA Astrophysics Data System (ADS)
Ťibu, Mihai; Lostun, Mihaela; Allwood, Dan A.; Rotǎrescu, Cristian; Atiťoaie, Alexandru; Lupu, Nicoleta; Óvári, Tibor-Adrian; Chiriac, Horia
2016-05-01
Results on the control of the domain wall displacement in cylindrical Fe77.5Si7.5B15 amorphous glass-coated submicron wires prepared by rapid quenching from the melt are reported. The control methods have relied on conical notches with various depths, up to a few tens of nm, made in the glass coating and in the metallic nucleus using a focused ion beam (FIB) system, and on the use of small nucleation coils at one of the sample ends in order to apply magnetic field pulses aimed to enhance the nucleation of reverse domains. The notch-based method is used for the first time in the case of cylindrical ultrathin wires. The results show that the most efficient technique of controlling the domain wall motion in this type of samples is the simultaneous use of notches and nucleation coils. Their effect depends on wire diameter, notch depth, its position on the wire length, and characteristics of the applied pulse.
Magnetic domain walls of relic fermions as Dark Energy
Yajnik, Urjit A.
2005-12-02
We show that relic fermions of the Big Bang can enter a ferromagnetic state if they possess a magnetic moment and satisfy the requirements of Stoner theory of itinerant ferromagnetism. The domain walls of this ferromagnetism can successfully simulate Dark Energy over the observable epoch spanning {approx} 10 billion years. We obtain conditions on the anomalous magnetic moment of such fermions and their masses. Known neutrinos fail to satisfy the requirements thus pointing to the possibility of a new ultralight sector in Particle Physics.
Longitudinal domain wall formation in elongated assemblies of ferromagnetic nanoparticles
Varón, Miriam; Beleggia, Marco; Jordanovic, Jelena; Schiøtz, Jakob; Kasama, Takeshi; Puntes, Victor F.; Frandsen, Cathrine
2015-01-01
Through evaporation of dense colloids of ferromagnetic ~13 nm ε-Co particles onto carbon substrates, anisotropic magnetic dipolar interactions can support formation of elongated particle structures with aggregate thicknesses of 100–400 nm and lengths of up to some hundred microns. Lorenz microscopy and electron holography reveal collective magnetic ordering in these structures. However, in contrast to continuous ferromagnetic thin films of comparable dimensions, domain walls appear preferentially as longitudinal, i.e., oriented parallel to the long axis of the nanoparticle assemblies. We explain this unusual domain structure as the result of dipolar interactions and shape anisotropy, in the absence of inter-particle exchange coupling. PMID:26416297
Magnetic Hardening from the Suppression of Domain Walls by Nonmagnetic Particles
Hu, Shenyang Y.; Li, Yulan; McCloy, John S.; Montgomery, Robert O.; Henager, Charles H.
2013-03-07
Magnetic domain switching and hysteresis loops in a single crystal α-iron with and without nonmagnetic particles were simulated based on the magnetization dynamics of the Landau–Lifshitz–Gilbert equation. It is found that the 360o Bloch domain wall is the easiest nucleation site for an anti-direction domain. The nucleation occurs by splitting the 360o Bloch domain wall into two 180o domain walls. However, the existence of nonmagnetic particles destroys the 180o domain walls and prevents the formation of 360o Bloch domain walls. Simulation results demonstrate that the impact of nonmagnetic particle on the formation of the 360o Bloch domain wall is a magnetic hardening mechanism.
Magnetic domain wall induced ferroelectricity in double perovskites
Zhou, Hai Yang; Zhao, Hong Jian E-mail: xmchen59@zju.edu.cn; Chen, Xiang Ming E-mail: xmchen59@zju.edu.cn; Zhang, Wen Qing
2015-04-13
Recently, a magnetically induced ferroelectricity occurring at magnetic domain wall of double perovskite Lu{sub 2}CoMnO{sub 6} has been reported experimentally. However, there exists a conflict whether the electric polarization is along b or c direction. Here, by first-principles calculations, we show that the magnetic domain wall (with ↑↑↓↓ spin configuration) can lead to the ferroelectric displacements of R{sup 3+}, Ni{sup 2+}, Mn{sup 4+}, and O{sup 2−} ions in double perovskites R{sub 2}NiMnO{sub 6} (R = rare earth ion) via exchange striction. The resulted electric polarization is along b direction with the P2{sub 1} symmetry. We further reveal the origin of the ferroelectric displacements as that: (1) on a structural point of view, such displacements make the two out-of-plane Ni-O-Mn bond angles as well as Ni-Mn distance unequal, and (2) on an energy point of view, such displacements weaken the out-of-plane Ni-Mn super-exchange interaction obviously. Finally, our calculations show that such a kind of ferroelectric order is general in ferromagnetic double perovskites.
Domain wall motion in sub-100 nm magnetic wire
NASA Astrophysics Data System (ADS)
Siddiqui, Saima; Dutta, Sumit; Currivan, Jean Anne; Ross, Caroline; Baldo, Marc
2015-03-01
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 μm 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.
Honeycomb and triangular domain wall networks in heteroepitaxial systems
NASA Astrophysics Data System (ADS)
Elder, K. R.; Chen, Z.; Elder, K. L. M.; Hirvonen, P.; Mkhonta, S. K.; Ying, S.-C.; Granato, E.; Huang, Zhi-Feng; Ala-Nissila, T.
2016-05-01
A comprehensive study is presented for the influence of misfit strain, adhesion strength, and lattice symmetry on the complex Moiré patterns that form in ultrathin films of honeycomb symmetry adsorbed on compact triangular or honeycomb substrates. The method used is based on a complex Ginzburg-Landau model of the film that incorporates elastic strain energy and dislocations. The results indicate that different symmetries of the heteroepitaxial systems lead to distinct types of domain wall networks and phase transitions among various surface Moiré patterns and superstructures. More specifically, the results show a dramatic difference between the phase diagrams that emerge when a honeycomb film is adsorbed on substrates of honeycomb versus triangular symmetry. It is also shown that in the small deformation limit, the complex Ginzburg-Landau model reduces to a two-dimensional sine-Gordon free energy form. This free energy can be solved exactly for one dimensional patterns and reveals the role of domains walls and their crossings in determining the nature of the phase diagrams.
Rise of Racetrack Memory! Domain Wall Spin-Orbitronics
NASA Astrophysics Data System (ADS)
Parkin, Stuart
Memory-storage devices based on the current controlled motion of a series of domain walls (DWs) in magnetic racetracks promise performance and reliability beyond that of conventional magnetic disk drives and solid state storage devices (1). Racetracks that are formed from atomically thin, perpendicularly magnetized nano-wires, interfaced with adjacent metal layers with high spin-orbit coupling, give rise to domain walls that exhibit a chiral Néel structure (2). These DWs can be moved very efficiently with current via chiral spin-orbit torques (2,3). Record-breaking current-induced DW speeds exceeding 1,000 m/sec are found in synthetic antiferromagnetic structures (3) in which the net magnetization of the DWs is tuned to almost zero, making them ``invisible''. Based on these recent discoveries, Racetrack Memory devices have the potential to operate on picosecond timescales and at densities more than 100 times greater than other memory technologies. (1) S.S.P. Parkin et al., Science 320, 5873 (2008); S.S.P. Parkin and S.-H. Yang, Nat. Nano. 10, 195 (2015). (2) K.-S. Ryu metal. Nat. Nano. 8, 527 (2013). (3) S.-H. Yang, K.-S. Ryu and S.S.P. Parkin, Nat. Nano. 10, 221 (2015). (4). S.S.P. Parkin, Phys. Rev. Lett. 67, 3598 (1991).
Oscillatory dependence of current-driven magnetic domain wall motion on current pulse length
NASA Astrophysics Data System (ADS)
Thomas, Luc; Hayashi, Masamitsu; Jiang, Xin; Moriya, Rai; Rettner, Charles; Parkin, Stuart S. P.
2006-09-01
Magnetic domain walls, in which the magnetization direction varies continuously from one direction to another, have long been objects of considerable interest. New concepts for devices based on such domain walls are made possible by the direct manipulation of the walls using spin-polarized electrical current through the phenomenon of spin momentum transfer. Most experiments to date have considered the current-driven motion of domain walls under quasi-static conditions, whereas for technological applications, the walls must be moved on much shorter timescales. Here we show that the motion of domain walls under nanosecond-long current pulses is surprisingly sensitive to the pulse length. In particular, we find that the probability of dislodging a domain wall, confined to a pinning site in a permalloy nanowire, oscillates with the length of the current pulse, with a period of just a few nanoseconds. Using an analytical model and micromagnetic simulations, we show that this behaviour is connected to a current-induced oscillatory motion of the domain wall. The period is determined by the wall's mass and the slope of the confining potential. When the current is turned off during phases of the domain wall motion when it has enough momentum, the domain wall is driven out of the confining potential in the opposite direction to the flow of spin angular momentum. This dynamic amplification effect could be exploited in magnetic nanodevices based on domain wall motion.
X-ray imaging of extended magnetic domain walls in Ni80Fe20 wires
Basu, S.; Fry, P. W.; Allwood, D. A.; Bryan, M. T.; Gibbs, M. R. J.; Schrefl, T.; Im, M.-Y.; Fischer, P.
2009-06-20
We have used magnetic transmission X-ray microscopy to image magnetization configurations in 700 nm wide Ni{sub 80}Fe{sub 20} planar wires attached to 'nucleation' pads Domain walls were observed to inject only across half of the wire width but extend to several micrometers in length. Magnetostatic interactions with adjacent wires caused further unusual domain wall behavior. Micromagnetic modeling suggests the extended walls have Neel-like structure along their length and indicates weaker exchange coupling than is often assumed. These observations explain previous measurements of domain wall injection and demonstrate that magnetic domain walls in larger nanowires cannot always be considered as localized entities.
NASA Astrophysics Data System (ADS)
Chen, Hong-Bo; Li, You-Quan
2016-07-01
We theoretically study the dynamics of a magnetic domain wall controlled by an electric field in the presence of the spin flexoelectric interaction. We reveal that this interaction generates an effective spin torque and results in significant changes in the current-driven domain wall motion. In particular, the electric field can stabilize the domain wall motion, leading to strong suppression of the current-induced Walker breakdown and thus allowing a higher maximum wall velocity. We can furthermore use this electric-field control to efficiently switch the chirality of a moving domain wall in the steady regime.
NASA Astrophysics Data System (ADS)
Burn, David M.; Atkinson, Del
2013-06-01
The control of individual magnetic domain walls has potential for future spintronic memory and data processing applications. The speed and reliability of such devices are determined by the dynamic properties of the domain walls. Typically, spin precession limitations lead to Walker breakdown, limiting wall velocity resulting in low mobility. Here, we show the suppression of Walker breakdown by the careful design of small amplitude periodic nanowire structuring to match the periodicity of domain wall spin structure transformations. This opens up a channel for energy dissipation via spin wave emission, allowing a domain wall to maintain its spin structure during propagation.
Efficient stopping of current-driven domain wall using a local Rashba field
NASA Astrophysics Data System (ADS)
Tatara, Gen; Saarikoski, Henri; Mitsumata, Chiharu
2016-10-01
We show theoretically that a locally embedded Rashba interaction acts as a strong pinning center for current-driven domain walls and demonstrate efficient capturing and depinning of the wall using a weak Rashba interaction of the order of 0.01 eV Å. Our discovery is expected to be useful for highly reliable control of domain walls in racetrack memories.
NASA Astrophysics Data System (ADS)
Trützschler, Julia; Sentosun, Kadir; Mozooni, Babak; Mattheis, Roland; McCord, Jeffrey
2016-08-01
High density magnetic domain wall gratings are imprinted in ferromagnetic-antiferromagnetic thin films by local ion irradiation by which alternating head-to-tail-to-head-to-tail and head-to-head-to-tail-to-tail spatially overlapping domain wall networks are formed. Unique magnetic domain processes result from the interaction of anchored domain walls. Non-linear magnetization response is introduced by the laterally distributed magnetic anisotropy phases. The locally varying magnetic charge distribution gives rise to localized and guided magnetization spin-wave modes directly constrained by the narrow domain wall cores. The exchange coupled multiphase material structure leads to unprecedented static and locally modified dynamic magnetic material properties.
Magnetic Damping: Domain Wall Dynamics versus Local Ferromagnetic Resonance
NASA Astrophysics Data System (ADS)
Weindler, T.; Bauer, H. G.; Islinger, R.; Boehm, B.; Chauleau, J.-Y.; Back, C. H.
2014-12-01
Magnetic relaxation is one of the dominating features of magnetization dynamics. Depending on the magnetic structure and the experimental approach, different magnitudes of the damping parameter are reported even for a given material. In this study, we experimentally address this issue by accessing the damping parameter in the same magnetic nanotracks using different approaches: local ferromagnetic resonance (α =0.0072 ) and field-driven domain wall dynamics (α =0.023 ). The experimental results cannot fully be accounted for by modeling only roughness in micromagnetic simulations. Consequently, we have included nonlocal texture induced damping to the micromagnetic code. We find excellent agreement with the observed increased damping in the vortex structures for the same input Gilbert alpha when texture-induced nonlocal damping is included.
Depinning transition of a domain wall in ferromagnetic films
Xi, Bin; Luo, Meng -Bo; Vinokur, Valerii M.; Hu, Xiao
2015-09-14
We report first principle numerical study of domain wall (DW) depinning in two-dimensional magnetic film, which is modeled by 2D random-field Ising system with the dipole-dipole interaction. We observe non-conventional activation-type motion of DW and reveal the fractal structure of DW near the depinning transition. We determine scaling functions describing critical dynamics near the transition and obtain universal exponents establishing connection between thermal softening of pinning potential and critical dynamics. In addition, we observe that tuning the strength of the dipole-dipole interaction switches DW dynamics between two different universality classes, corresponding to two distinct dynamic regimes characterized by non-Arrhenius andmore » conventional Arrhenius-type DW motions.« less
Chaotic dynamics of magnetic domain walls in nanowires
NASA Astrophysics Data System (ADS)
Pivano, A.; Dolocan, V. O.
2016-04-01
The nonlinear dynamics of a transverse domain wall (TDW) in permalloy and nickel nanostrips with two artificially patterned pinning centers is studied numerically up to rf frequencies. The phase diagram frequency-driving amplitude shows a rich variety of dynamical behaviors depending on the material parameters and the type and shape of pinning centers. We find that T-shaped traps (antinotches) create a classical double well Duffing potential that leads to a small chaotic region in the case of nickel and a large one for Py. In contrast, the rectangular constrictions (notches) create an exponential potential that leads to larger chaotic regions interspersed with periodic windows for both Py and Ni. The influence of temperature manifests itself by enlarging the chaotic region and activating thermal jumps between the pinning sites while reducing the depinning field at low frequency in the notched strips.
Depinning Transition of a Domain Wall in Ferromagnetic Films.
Xi, Bin; Luo, Meng-Bo; Vinokur, Valerii M; Hu, Xiao
2015-01-01
We report first principle numerical study of domain wall (DW) depinning in two-dimensional magnetic film, which is modeled by 2D random-field Ising system with the dipole-dipole interaction. We observe nonconventional activation-type motion of DW and reveal the fractal structure of DW near the depinning transition. We determine scaling functions describing critical dynamics near the transition and obtain universal exponents establishing connection between thermal softening of pinning potential and critical dynamics. We observe that tuning the strength of the dipole-dipole interaction switches DW dynamics between two different universality classes, corresponding to two distinct dynamic regimes characterized by non-Arrhenius and conventional Arrhenius-type DW motions.
Domain wall oscillations induced by spin torque in magnetic nanowires
Sbiaa, R.; Chantrell, R. W.
2015-02-07
Using micromagnetic simulations, the effects of the non-adiabatic spin torque (β) and the geometry of nanowires on domain wall (DW) dynamics are investigated. For the case of in-plane anisotropy nanowire, it is observed that the type of DW and its dynamics depends on its dimension. For a fixed length, the critical switching current decreases almost exponentially with the width W, while the DW speed becomes faster for larger W. For the case of perpendicular anisotropy nanowire, it was observed that DW dynamics depends strongly on β. For small values of β, oscillations of DW around the center of nanowire were revealed even after the current is switched off. In addition to nanowire geometry and intrinsic material properties, β could provide a way to control DW dynamics.
Coupled domain wall oscillations in magnetic cylindrical nanowires
Murapaka, Chandrasekhar; Goolaup, S.; Purnama, I.; Lew, W. S.
2015-02-07
We report on transverse domain wall (DW) dynamics in two closely spaced cylindrical nanowires. The magnetostatically coupled DWs are shown to undergo an intrinsic oscillatory motion along the nanowire length in addition to their default rotational motion. In the absence of external forces, the amplitude of the DW oscillation is governed by the change in the frequency of the DW rotation. It is possible to sustain the DW oscillations by applying spin-polarized current to the nanowires to balance the repulsive magnetostatic coupling. The current density required to sustain the DW oscillation is found to be in the order of 10{sup 5 }A/cm{sup 2}. Morover, our analysis of the oscillation reveals that the DWs in cylindrical nanowires possess a finite mass.
Investigation of dominant spin wave modes by domain walls collision
Ramu, M.; Purnama, I.; Goolaup, S.; Chandra Sekhar, M.; Lew, W. S.
2014-06-28
Spin wave emission due to field-driven domain wall (DW) collision has been investigated numerically and analytically in permalloy nanowires. The spin wave modes generated are diagonally symmetric with respect to the collision point. The non-propagating mode has the highest amplitude along the middle of the width. The frequency of this mode is strongly correlated to the nanowire geometrical dimensions and is independent of the strength of applied field within the range of 0.1 mT to 1 mT. For nanowire with film thickness below 5 nm, a second spin wave harmonic mode is observed. The decay coefficient of the spin wave power suggests that the DWs in a memory device should be at least 300 nm apart for them to be free of interference from the spin waves.
Depinning transition of a domain wall in ferromagnetic films
Xi, Bin; Luo, Meng -Bo; Vinokur, Valerii M.; Hu, Xiao
2015-09-14
We report first principle numerical study of domain wall (DW) depinning in two-dimensional magnetic film, which is modeled by 2D random-field Ising system with the dipole-dipole interaction. We observe non-conventional activation-type motion of DW and reveal the fractal structure of DW near the depinning transition. We determine scaling functions describing critical dynamics near the transition and obtain universal exponents establishing connection between thermal softening of pinning potential and critical dynamics. In addition, we observe that tuning the strength of the dipole-dipole interaction switches DW dynamics between two different universality classes, corresponding to two distinct dynamic regimes characterized by non-Arrhenius and conventional Arrhenius-type DW motions.
Depinning Transition of a Domain Wall in Ferromagnetic Films
Xi, Bin; Luo, Meng-Bo; Vinokur, Valerii M.; Hu, Xiao
2015-01-01
We report first principle numerical study of domain wall (DW) depinning in two-dimensional magnetic film, which is modeled by 2D random-field Ising system with the dipole-dipole interaction. We observe nonconventional activation-type motion of DW and reveal the fractal structure of DW near the depinning transition. We determine scaling functions describing critical dynamics near the transition and obtain universal exponents establishing connection between thermal softening of pinning potential and critical dynamics. We observe that tuning the strength of the dipole-dipole interaction switches DW dynamics between two different universality classes, corresponding to two distinct dynamic regimes characterized by non-Arrhenius and conventional Arrhenius-type DW motions. PMID:26365753
Head-to-head domain wall structures in wide permalloy strips
NASA Astrophysics Data System (ADS)
Estévez, Virginia; Laurson, Lasse
2015-02-01
We analyze 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 walls, vortex wall) also double vortex and triple vortex domain walls for large enough strip widths and thicknesses. Also several metastable domain wall structures are found for wide and/or thick strips. We discuss the details of the relaxation process from random magnetization initial states towards the stable domain wall structure and show that our results are robust with respect to changes of, e.g., the magnitude of the Gilbert damping constant and details of the initial conditions.
High domain wall velocities via spin transfer torque using vertical current injection
Metaxas, Peter J.; Sampaio, Joao; Chanthbouala, André; Matsumoto, Rie; Anane, Abdelmadjid; Fert, Albert; Zvezdin, Konstantin A.; Yakushiji, Kay; Kubota, Hitoshi; Fukushima, Akio; Yuasa, Shinji; Nishimura, Kazumasa; Nagamine, Yoshinori; Maehara, Hiroki; Tsunekawa, Koji; Cros, Vincent; Grollier, Julie
2013-01-01
Domain walls, nanoscale transition regions separating oppositely oriented ferromagnetic domains, have significant promise for use in spintronic devices for data storage and memristive applications. The state of these devices is related to the wall position and thus rapid operation will require a controllable onset of domain wall motion and high speed wall displacement. These processes are traditionally driven by spin transfer torque due to lateral injection of spin polarized current through a ferromagnetic nanostrip. However, this geometry is often hampered by low maximum wall velocities and/or a need for prohibitively high current densities. Here, using time-resolved magnetotransport measurements, we show that vertical injection of spin currents through a magnetic tunnel junction can drive domain walls over hundreds of nanometers at ~500 m/s using current densities on the order of 6 MA/cm2. Moreover, these measurements provide information about the stochastic and deterministic aspects of current driven domain wall mediated switching. PMID:23670402
High domain wall velocities via spin transfer torque using vertical current injection.
Metaxas, Peter J; Sampaio, Joao; Chanthbouala, André; Matsumoto, Rie; Anane, Abdelmadjid; Fert, Albert; Zvezdin, Konstantin A; Yakushiji, Kay; Kubota, Hitoshi; Fukushima, Akio; Yuasa, Shinji; Nishimura, Kazumasa; Nagamine, Yoshinori; Maehara, Hiroki; Tsunekawa, Koji; Cros, Vincent; Grollier, Julie
2013-01-01
Domain walls, nanoscale transition regions separating oppositely oriented ferromagnetic domains, have significant promise for use in spintronic devices for data storage and memristive applications. The state of these devices is related to the wall position and thus rapid operation will require a controllable onset of domain wall motion and high speed wall displacement. These processes are traditionally driven by spin transfer torque due to lateral injection of spin polarized current through a ferromagnetic nanostrip. However, this geometry is often hampered by low maximum wall velocities and/or a need for prohibitively high current densities. Here, using time-resolved magnetotransport measurements, we show that vertical injection of spin currents through a magnetic tunnel junction can drive domain walls over hundreds of nanometers at ~500 m/s using current densities on the order of 6 MA/cm(2). Moreover, these measurements provide information about the stochastic and deterministic aspects of current driven domain wall mediated switching. PMID:23670402
High domain wall velocities via spin transfer torque using vertical current injection
NASA Astrophysics Data System (ADS)
Metaxas, Peter J.; Sampaio, Joao; Chanthbouala, André; Matsumoto, Rie; Anane, Abdelmadjid; Fert, Albert; Zvezdin, Konstantin A.; Yakushiji, Kay; Kubota, Hitoshi; Fukushima, Akio; Yuasa, Shinji; Nishimura, Kazumasa; Nagamine, Yoshinori; Maehara, Hiroki; Tsunekawa, Koji; Cros, Vincent; Grollier, Julie
2013-05-01
Domain walls, nanoscale transition regions separating oppositely oriented ferromagnetic domains, have significant promise for use in spintronic devices for data storage and memristive applications. The state of these devices is related to the wall position and thus rapid operation will require a controllable onset of domain wall motion and high speed wall displacement. These processes are traditionally driven by spin transfer torque due to lateral injection of spin polarized current through a ferromagnetic nanostrip. However, this geometry is often hampered by low maximum wall velocities and/or a need for prohibitively high current densities. Here, using time-resolved magnetotransport measurements, we show that vertical injection of spin currents through a magnetic tunnel junction can drive domain walls over hundreds of nanometers at ~500 m/s using current densities on the order of 6 MA/cm2. Moreover, these measurements provide information about the stochastic and deterministic aspects of current driven domain wall mediated switching.
NASA Astrophysics Data System (ADS)
Komine, Takashi; Aono, Tomosuke
2016-05-01
We demonstrate current-induced domain wall motion in bilayer nanowire with synthetic antiferromagnetic (SAF) coupling by modeling two body problems for motion equations of domain wall. The influence of interlayer exchange coupling and magnetostatic interactions on current-induced domain wall motion in SAF nanowires was also investigated. By assuming the rigid wall model for translational motion, the interlayer exchange coupling and the magnetostatic interaction between walls and domains in SAF nanowires enhances domain wall speed without any spin-orbit-torque. The enhancement of domain wall speed was discussed by energy distribution as a function of wall angle configuration in bilayer nanowires.
Cosmic bubble and domain wall instabilities II: fracturing of colliding walls
Braden, Jonathan; Bond, J. Richard; Mersini-Houghton, Laura
2015-08-26
We study collisions between nearly planar domain walls including the effects of small initial nonplanar fluctuations. These perturbations represent the small fluctuations that must exist in a quantum treatment of the problem. In a previous paper, we demonstrated that at the linear level a subset of these fluctuations experience parametric amplification as a result of their coupling to the planar symmetric background. Here we study the full three-dimensional nonlinear dynamics using lattice simulations, including both the early time regime when the fluctuations are well described by linear perturbation theory as well as the subsequent stage of fully nonlinear evolution. We find that the nonplanar fluctuations have a dramatic effect on the overall evolution of the system. Specifically, once these fluctuations begin to interact nonlinearly the split into a planar symmetric part of the field and the nonplanar fluctuations loses its utility. At this point the colliding domain walls dissolve, with the endpoint of this being the creation of a population of oscillons in the collision region. The original (nearly) planar symmetry has been completely destroyed at this point and an accurate study of the system requires the full three-dimensional simulation.
Dynamic effects of quenched disorder on domain wall motion in magnetic nanowires
NASA Astrophysics Data System (ADS)
He, Y. Y.; Zheng, B.; Zhou, N. J.
2016-10-01
The domain wall dynamics in magnetic nanowires is numerically studied with the Landau-Lifshitz-Gilbert equation. Below the Walker breakdown threshold, the domain wall presents a stable propagation, while above the threshold where the retrograde mode dominates, the oscillation period is controlled by the external field and anisotropy. More importantly, the dynamic effects of quenched disorder on the domain wall motion are explored. A continuous pinning-depinning phase transition is detected. The dynamic scaling form is analyzed with the data collapse of the domain wall velocity, and both the static and dynamic critical exponents are extracted.
Domain wall dynamics of periodic magnetic domain patterns in Co2MnGe-Heusler microstripes
NASA Astrophysics Data System (ADS)
Gross, K.; Westerholt, K.; Zabel, H.
2016-03-01
Highly symmetric periodic domain patterns were obtained in Co2MnGe-Heusler microstripes as a result of the competition between growth-induced in-plane magnetic anisotropy and shape anisotropy. Zero field magnetic configurations and magnetic field-induced domain wall (DW) motion were studied by magnetic force microscopy-image technique for two different cases: dominant uniaxial- and dominant cubic in-plane anisotropy. We implemented a magneto-optical Kerr effect susceptometer to investigate the DW dynamics of periodic domain structures by measuring the in-phase and out-of-phase components of the Kerr signal as a function of magnetic field frequency and amplitude. The DW dynamics for fields applied transversally to the long stripe axis was found to be dominated by viscous slide motion. We used the inherent symmetry/periodicity properties of the magnetic domain structure to fit the experimental results with a theoretical model allowing to extract the DW mobility for the case of transverse DWs (μ TDW = 1.1 m s-1 Oe-1) as well as for vortex-like DWs (μ VDW = 8.7 m s-1 Oe-1). Internal spin structure transformations may cause a reduction of DW mobility in TDWs as observed by OMMFF simulations.
NASA Astrophysics Data System (ADS)
Metaxas, Peter; Zermatten, Pierre-Jean; Novak, Rafael; Jamet, Jean-Pierre; Weil, Raphael; Rohart, Stanislas; Ferre, Jacques; Mougin, Alexandra; Stamps, Robert; Baltz, Vincent; Rodmacq, Bernard; Gaudin, Gilles
2012-02-01
The stray magnetic field of an array of ferromagnetic nanodots is used to generate a spatially periodic pinning potential for domain walls moving through a physically separate, weakly disordered, magnetic layer lying beneath the array. This technique represents a non-destructive method to create tunable and localised pinning sites for domain walls which are consequently subject to co-existing (but independent) periodic and disordered pinning potentials. Beyond the fundamentally attractive application of creating a model experimental system to study interface motion through multiple co-existing pinning potentials, our system interestingly exhibits many characteristics that are normally associated with exchange bias. This is a direct result of the fact that pinning effects induced by the periodic pinning potential depend upon the polarity of the applied magnetic field which drives the domain wall motion, a phenomenon which manifests itself in field-polarity-dependent domain wall mobilities and profiles.
Persistent conductive footprints of 109° domain walls in bismuth ferrite films
Stolichnov, I.; Iwanowska, M.; Colla, E.; Setter, N.; Ziegler, B.; Gaponenko, I.; Paruch, P.; Huijben, M.; Rijnders, G.
2014-03-31
Using conductive and piezoforce microscopy, we reveal a complex picture of electronic transport at weakly conductive 109° domain walls in bismuth ferrite films. Even once initial ferroelectric stripe domains are changed/erased, persistent conductive paths signal the original domain wall position. The conduction at such domain wall “footprints” is activated by domain movement and decays rapidly with time, but can be re-activated by opposite polarity voltage. The observed phenomena represent true leakage conduction rather than merely displacement currents. We propose a scenario of hopping transport in combination with thermionic injection over interfacial barriers controlled by the ferroelectric polarization.
Time-resolved imaging of current-induced domain-wall oscillations
Bocklage, Lars; Krueger, Benjamin; Eiselt, Rene; Bolte, Markus; Fischer, Peter; Meier, Guido
2008-10-07
Current-induced domain-wall dynamics is investigated via high-resolution soft x-ray transmission microscopy by a stroboscopic pump-and-probe measurement scheme at a temporal resolution of 200 ps. A 180{sup o} domain wall in a restoring potential of a permalloy microstructure is displaced from its equilibrium position by nanosecond current pulses leading to oscillations with velocities up to 325 m/s. The motion of the wall is described with an analytical model of a rigid domain wall in a nonharmonic potential allowing one to determine the mass of the domain wall. We show that Oersted fields dominate the domain-wall dynamics in our geometry.
The increase of the spin-transfer torque threshold current density in coupled vortex domain walls.
Lepadatu, S; Mihai, A P; Claydon, J S; Maccherozzi, F; Dhesi, S S; Kinane, C J; Langridge, S; Marrows, C H
2012-01-18
We have studied the dependence on the domain wall structure of the spin-transfer torque current density threshold for the onset of wall motion in curved, Gd-doped Ni(80)Fe(20) nanowires with no artificial pinning potentials. For single vortex domain walls, for both 10% and 1% Gd-doping concentrations, the threshold current density is inversely proportional to the wire width and significantly lower compared to the threshold current density measured for transverse domain walls. On the other hand for high Gd concentrations and large wire widths, double vortex domain walls are formed which require an increase in the threshold current density compared to single vortex domain walls at the same wire width. We suggest that this is due to the coupling of the vortex cores, which are of opposite chirality, and hence will be acted on by opposing forces arising through the spin-transfer torque effect.
Correlated Switching Dynamics in the Nanoscale Proximity of 90∘ Ferroelectric Domain Walls
NASA Astrophysics Data System (ADS)
Lei, Shiming; Wang, Xueyun; Cheong, S. W.; Chen, L. Q.; Kalinin, Sergei; Gopalan, Venkatraman
2015-03-01
Ferroelectrics are materials which have a built in polarization in their crystal structure even in the absence of an electric field. Domain walls themselves can possess dramatically different properties than the bulk ferroelectrics themselves. Previously we discovered that the universally present 180° walls have an order of magnitude lower domain switching threshold field than the bulk. This effect extends up to many microns around a wall, though the wall itself is unit cell thick. Here we present new results on 90° walls in PbTiO3 single crystals that show similar proximity effect and correlated switching. Our SSPFM imaging across the a / c / a domain walls suggests a strong correlated switching behavior in the proximity of the inclined 90° domain walls, even at a small AC driving voltage of 1V without DC bias on the tip. Consistent with phase-field modeling results, the inclined extended domain walls is found to act as nucleation sites in ferroelectric materials, and give rise to the domain wall asymmetrical broadening across the domain wall.
Domain wall QCD with near-physical pions
NASA Astrophysics Data System (ADS)
Arthur, R.; Blum, T.; Boyle, P. A.; Christ, N. H.; Garron, N.; Hudspith, R. J.; Izubuchi, T.; Jung, C.; Kelly, C.; Lytle, A. T.; Mawhinney, R. D.; Murphy, D.; Ohta, S.; Sachrajda, C. T.; Soni, A.; Yu, J.; Zanotti, J. M.
2013-05-01
We present physical results for a variety of light hadronic quantities obtained via a combined analysis of three 2+1 flavour domain wall fermion ensemble sets. For two of our ensemble sets we used the Iwasaki gauge action with β=2.13 (a-1=1.75(4)GeV) and β=2.25 (a-1=2.31(4)GeV) and lattice sizes of 243×64 and 323×64 respectively, with unitary pion masses in the range 293(5)-417(10) MeV. The extent Ls for the 5th dimension of the domain wall fermion formulation is Ls=16 in these ensembles. In this analysis we include a third ensemble set that makes use of the novel Iwasaki+DSDR (dislocation suppressing determinant ratio) gauge action at β=1.75 (a-1=1.37(1)GeV) with a lattice size of 323×64 and Ls=32 to reach down to partially-quenched pion masses as low as 143(1) MeV and a unitary pion mass of 171(1) MeV, while retaining good chiral symmetry and topological tunneling. We demonstrate a significant improvement in our control over the chiral extrapolation, resulting in much improved continuum predictions for the above quantities. The main results of this analysis include the pion and kaon decay constants, fπ=127(3)stat(3)sysMeV and fK=152(3)stat(2)sysMeV respectively (fK/fπ=1.199(12)stat(14)sys); the average up/down quark mass and the strange-quark mass in the MS¯-scheme at 3 GeV, mud(MS¯,3GeV)=3.05(8)stat(6)sysMeV and ms(MS¯,3GeV)=83.5(1.7)stat(1.1)sys; the neutral kaon mixing parameter in the MS¯-scheme at 3 GeV, BK(MS¯,3GeV)=0.535(8)stat(13)sys, and in the RGI scheme, B^K=0.758(11)stat(19)sys; and the Sommer scales r1=0.323(8)stat(4)sysfm and r0=0.480(10)stat(4)sys (r1/r0=0.673(11)stat(3)sys). We also obtain values for the SU(2) chiral perturbation theory effective couplings, l3¯=2.91(23)stat(7)sys and l4¯=3.99(16)stat(9)sys.
Transverse field-induced nucleation pad switching modes during domain wall injection
Bryan, M. T.; Fry, P. W.; Schrefl, T.; Gibbs, M. R. J.; Allwood, D. A.; Im, M.-Y.; Fischer, P.
2010-03-12
We have used magnetic transmission X-ray microscopy (M-TXM) to image in-field magnetization configurations of patterned Ni{sub 80}Fe{sub 20} domain wall 'injection pads' and attached planar nanowires. Comparison with micromagnetic simulations suggests that the evolution of magnetic domains in rectangular injection pads depends on the relative orientation of closure domains in the remanent state. The magnetization reversal pathway is also altered by the inclusion of transverse magnetic fields. These different modes explain previous results of domain wall injection into nanowires. Even more striking was the observation of domain walls injecting halfway across the width of wider (>400 nm wide) wires but over wire lengths of several micrometers. These extended Neel walls can interact with adjacent nanowires and cause a switching in the side of the wire undergoing reversal as the domain wall continues to expand.
Depinning of domain walls in permalloy nanowires with asymmetric notches.
Gao, Y; You, B; Ruan, X Z; Liu, M Y; Yang, H L; Zhan, Q F; Li, Z; Lei, N; Zhao, W S; Pan, D F; Wan, J G; Wu, J; Tu, H Q; Wang, J; Zhang, W; Xu, Y B; Du, J
2016-01-01
Effective control of the domain wall (DW) motion along the magnetic nanowires is of great importance for fundamental research and potential application in spintronic devices. In this work, a series of permalloy nanowires with an asymmetric notch in the middle were fabricated with only varying the width (d) of the right arm from 200 nm to 1000 nm. The detailed pinning and depinning processes of DWs in these nanowires have been studied by using focused magneto-optic Kerr effect (FMOKE) magnetometer, magnetic force microscopy (MFM) and micromagnetic simulation. The experimental results unambiguously exhibit the presence of a DW pinned at the notch in a typical sample with d equal to 500 nm. At a certain range of 200 nm < d < 500 nm, both the experimental and simulated results show that the DW can maintain or change its chirality randomly during passing through the notch, resulting in two DW depinning fields. Those two depinning fields have opposite d dependences, which may be originated from different potential well/barrier generated by the asymmetric notch with varying d. PMID:27600627
Depinning of domain walls in permalloy nanowires with asymmetric notches
NASA Astrophysics Data System (ADS)
Gao, Y.; You, B.; Ruan, X. Z.; Liu, M. Y.; Yang, H. L.; Zhan, Q. F.; Li, Z.; Lei, N.; Zhao, W. S.; Pan, D. F.; Wan, J. G.; Wu, J.; Tu, H. Q.; Wang, J.; Zhang, W.; Xu, Y. B.; Du, J.
2016-09-01
Effective control of the domain wall (DW) motion along the magnetic nanowires is of great importance for fundamental research and potential application in spintronic devices. In this work, a series of permalloy nanowires with an asymmetric notch in the middle were fabricated with only varying the width (d) of the right arm from 200 nm to 1000 nm. The detailed pinning and depinning processes of DWs in these nanowires have been studied by using focused magneto-optic Kerr effect (FMOKE) magnetometer, magnetic force microscopy (MFM) and micromagnetic simulation. The experimental results unambiguously exhibit the presence of a DW pinned at the notch in a typical sample with d equal to 500 nm. At a certain range of 200 nm < d < 500 nm, both the experimental and simulated results show that the DW can maintain or change its chirality randomly during passing through the notch, resulting in two DW depinning fields. Those two depinning fields have opposite d dependences, which may be originated from different potential well/barrier generated by the asymmetric notch with varying d.
Depinning of domain walls in permalloy nanowires with asymmetric notches.
Gao, Y; You, B; Ruan, X Z; Liu, M Y; Yang, H L; Zhan, Q F; Li, Z; Lei, N; Zhao, W S; Pan, D F; Wan, J G; Wu, J; Tu, H Q; Wang, J; Zhang, W; Xu, Y B; Du, J
2016-09-07
Effective control of the domain wall (DW) motion along the magnetic nanowires is of great importance for fundamental research and potential application in spintronic devices. In this work, a series of permalloy nanowires with an asymmetric notch in the middle were fabricated with only varying the width (d) of the right arm from 200 nm to 1000 nm. The detailed pinning and depinning processes of DWs in these nanowires have been studied by using focused magneto-optic Kerr effect (FMOKE) magnetometer, magnetic force microscopy (MFM) and micromagnetic simulation. The experimental results unambiguously exhibit the presence of a DW pinned at the notch in a typical sample with d equal to 500 nm. At a certain range of 200 nm < d < 500 nm, both the experimental and simulated results show that the DW can maintain or change its chirality randomly during passing through the notch, resulting in two DW depinning fields. Those two depinning fields have opposite d dependences, which may be originated from different potential well/barrier generated by the asymmetric notch with varying d.
Evidence of domain wall pinning in aluminum substituted cobalt ferrites
NASA Astrophysics Data System (ADS)
Maurya, J. C.; Janrao, P. S.; Datar, A. A.; Kanhe, N. S.; Bhoraskar, S. V.; Mathe, V. L.
2016-08-01
In the present work spinel structured cobalt ferrites with aluminum substitution having composition CoAlxFe2-xO4 (x=0.0, 0.1, 0.2 and 0.3) have been synthesized using chemical co-precipitation method. Their microstructural, magnetic, magnetostriction and magnetoimpedance properties have been investigated. The piezomagnetic coefficient (dλ/dH) obtained from magnetostriction data is found to enhance with 0.1 Al substitutions in place of iron which decreases with further increase of Al content. It is noticed that 0.3 Al substitutions in place of Fe introduces domain wall pinning as evidenced from magnetostriction, magnetoimpedance and dc magnetization data. It is noted that ferrites so prepared using a simple procedure are magnetostrictive in good measure and with the addition of very small amount of non-magnetic aluminum their magnetostriction has shown saturation at relatively low magnetic fields. Such magnetostrictive ferrites find their applications in magnetic sensors and actuators.
Depinning of domain walls in permalloy nanowires with asymmetric notches
Gao, Y.; You, B.; Ruan, X. Z.; Liu, M. Y.; Yang, H. L.; Zhan, Q. F.; Li, Z.; Lei, N.; Zhao, W. S.; Pan, D. F.; Wan, J. G.; Wu, J.; Tu, H. Q.; Wang, J.; Zhang, W.; Xu, Y. B.; Du, J.
2016-01-01
Effective control of the domain wall (DW) motion along the magnetic nanowires is of great importance for fundamental research and potential application in spintronic devices. In this work, a series of permalloy nanowires with an asymmetric notch in the middle were fabricated with only varying the width (d) of the right arm from 200 nm to 1000 nm. The detailed pinning and depinning processes of DWs in these nanowires have been studied by using focused magneto-optic Kerr effect (FMOKE) magnetometer, magnetic force microscopy (MFM) and micromagnetic simulation. The experimental results unambiguously exhibit the presence of a DW pinned at the notch in a typical sample with d equal to 500 nm. At a certain range of 200 nm < d < 500 nm, both the experimental and simulated results show that the DW can maintain or change its chirality randomly during passing through the notch, resulting in two DW depinning fields. Those two depinning fields have opposite d dependences, which may be originated from different potential well/barrier generated by the asymmetric notch with varying d. PMID:27600627
Sustained chiral magnetic domain wall motion driven by spin-orbit torques under the tilted current
NASA Astrophysics Data System (ADS)
He, Peng-Bin; Yan, Han; Cai, Meng-Qiu; Li, Zai-Dong
2016-06-01
We theoretically investigate the steady magnetic domain wall driven by spin-orbit torques in the heavy-metal/magnet bilayers with perpendicular anisotropy. Based on collective coordinates method and stability analysis, we analyze the effects of tilted current and Dzyaloshinskii-Moriya interaction on the wall. We find that the wall acquires a sustained motion in the high-current regime by deviating the current from the wall track. Also, a persistent motion can be supported by the competition between spin-orbit torques and Dzyaloshinskii-Moriya interaction in transforming wall type. In the low-current regime, there exist a switching of wall chirality and a reversal of wall motion.
Lequeux, Steven; Sampaio, Joao; Bortolotti, Paolo; Cros, Vincent; Grollier, Julie; Matsumoto, Rie; Yakushiji, Kay; Kubota, Hitoshi; Fukushima, Akio; Yuasa, Shinji; Nishimura, Kazumasa; Nagamine, Yoshinori; Tsunekawa, Koji
2015-11-02
Spin torque resonance has been used to simultaneously probe the dynamics of a magnetic domain wall and of magnetic domains in a nanostripe magnetic tunnel junction. Due to the large associated resistance variations, we are able to analyze quantitatively the resonant properties of these single nanoscale magnetic objects. In particular, we find that the magnetic damping of both the domains and the domain wall is doubled compared to the damping value of the host magnetic layer. We estimate the contributions to the damping arising from the dipolar couplings between the different layers in the junction and from the intralayer spin pumping effect, and find that they cannot explain the large damping enhancement that we observe. We conclude that the measured increased damping is intrinsic to large amplitudes excitations of spatially localized modes or solitons such as vibrating or propagating domain walls.
NASA Astrophysics Data System (ADS)
Lequeux, Steven; Sampaio, Joao; Bortolotti, Paolo; Devolder, Thibaut; Matsumoto, Rie; Yakushiji, Kay; Kubota, Hitoshi; Fukushima, Akio; Yuasa, Shinji; Nishimura, Kazumasa; Nagamine, Yoshinori; Tsunekawa, Koji; Cros, Vincent; Grollier, Julie
2015-11-01
Spin torque resonance has been used to simultaneously probe the dynamics of a magnetic domain wall and of magnetic domains in a nanostripe magnetic tunnel junction. Due to the large associated resistance variations, we are able to analyze quantitatively the resonant properties of these single nanoscale magnetic objects. In particular, we find that the magnetic damping of both the domains and the domain wall is doubled compared to the damping value of the host magnetic layer. We estimate the contributions to the damping arising from the dipolar couplings between the different layers in the junction and from the intralayer spin pumping effect, and find that they cannot explain the large damping enhancement that we observe. We conclude that the measured increased damping is intrinsic to large amplitudes excitations of spatially localized modes or solitons such as vibrating or propagating domain walls.
Nucleon Structure with Domain Wall Fermions at a = 0.086 fm
Syritsyn, Sergey; Bratt, Jonathan; Lin, Meifeng; Meyer, Harvey; Negele, John; Pochinsky, Andrew; Procura, M.; Edwards, Robert; Orginos, Konstantinos; Richards, David; Engelhardt, Michael; Fleming, George; Haegler, Philipp; Musch, Bernhard; Renner, Dru; Schroers, Wolfram
2008-12-01
We present initial calculations of nucleon matrix elements of twist-two operators with 2+1 flavors of domain wall fermions at a lattice spacing a = 0.084 fm for pion masses down to 300 MeV. We also compare the results with the domain wall calculations on a coarser lattice.
Spin-wave-driven high-speed domain-wall motions in soft magnetic nanotubes
Yang, Jaehak; Yoo, Myoung-Woo; Kim, Sang-Koog
2015-10-28
We report on a micromagnetic simulation study of interactions between propagating spin waves and a head-to-head domain wall in geometrically confined magnetic nanotubes. We found that incident spin waves of specific frequencies can lead to sufficiently high-speed (on the order of a few hundreds of m/s or higher) domain-wall motions in the same direction as that of the incident spin-waves. The domain-wall motions and their speed vary remarkably with the frequency and the amplitude of the incident spin-waves. High-speed domain-wall motions originate from the transfer torque of spin waves' linear momentum to the domain wall, through the partial or complete reflection of the incident spin waves from the domain wall. This work provides a fundamental understanding of the interaction of the spin waves with a domain wall in the magnetic nanotubes as well as a route to all-magnetic control of domain-wall motions in the magnetic nanoelements.
Dynamics of superparamagnetic microbead transport along magnetic nanotracks by magnetic domain walls
NASA Astrophysics Data System (ADS)
Rapoport, Elizabeth; Beach, Geoffrey S. D.
2012-02-01
The dynamics of fluid-borne superparamagnetic bead transport by field-driven domain walls in submicrometer ferromagnetic tracks is studied experimentally together with numerical and analytical modeling. Experiments show that nanotrack-guided domain walls can propel individual trapped beads through an aqueous medium at speeds approaching 1000 μm/s, 10 to 100 times faster than through any previously demonstrated mechanism.
Deterministic Domain Wall Motion Orthogonal To Current Flow Due To Spin Orbit Torque
Bhowmik, Debanjan; Nowakowski, Mark E.; You, Long; Lee, OukJae; Keating, David; Wong, Mark; Bokor, Jeffrey; Salahuddin, Sayeef
2015-01-01
Spin-polarized electrons can move a ferromagnetic domain wall through the transfer of spin angular momentum when current flows in a magnetic nanowire. Such current induced control of a domain wall is of significant interest due to its potential application for low power ultra high-density data storage. In previous reports, it has been observed that the motion of the domain wall always happens parallel to the current flow – either in the same or opposite direction depending on the specific nature of the interaction. In contrast, here we demonstrate deterministic control of a ferromagnetic domain wall orthogonal to current flow by exploiting the spin orbit torque in a perpendicularly polarized Ta/CoFeB/MgO heterostructure in presence of an in-plane magnetic field. Reversing the polarity of either the current flow or the in-plane field is found to reverse the direction of the domain wall motion. Notably, such orthogonal motion with respect to current flow is not possible from traditional spin transfer torque driven domain wall propagation even in presence of an external magnetic field. Therefore the domain wall motion happens purely due to spin orbit torque. These results represent a completely new degree of freedom in current induced control of a ferromagnetic domain wall. PMID:26139349
Current-driven vortex domain wall motion in wire-tube nanostructures
Espejo, A. P.; Vidal-Silva, N.; López-López, J. A.; Goerlitz, D.; Nielsch, K.; Escrig, J.
2015-03-30
We have investigated the current-driven domain wall motion in nanostructures comprised of a pair of nanotube and nanowire segments. Under certain values of external magnetic fields, it is possible to pin a vortex domain wall in the transition zone between the wire and tube segments. We explored the behavior of this domain wall under the action of an electron flow applied in the opposite direction to the magnetic field. Thus, for a fixed magnetic field, it is possible to release a domain wall pinned simply by increasing the intensity of the current density, or conversely, for a fixed current density, it is possible to release the domain wall simply decreasing the magnetic external field. When the domain wall remains pinned due to the competition between the current density and the magnetic external field, it exhibits a oscillation frequency close to 8 GHz. The amplitude of the oscillations increases with the current density and decreases over time. On the other hand, when the domain wall is released and propagated through the tube segment, this shows the standard separation between a steady and a precessional regime. The ability to pin and release a domain wall by varying the geometric parameters, the current density, or the magnetic field transforms these wire-tube nanostructures in an interesting alternative as an on/off switch nano-transistor.
Modulated Magnetic Nanowires for Controlling Domain Wall Motion: Toward 3D Magnetic Memories.
Ivanov, Yurii P; Chuvilin, Andrey; Lopatin, Sergei; Kosel, Jurgen
2016-05-24
Cylindrical magnetic nanowires are attractive materials for next generation data storage devices owing to the theoretically achievable high domain wall velocity and their efficient fabrication in highly dense arrays. In order to obtain control over domain wall motion, reliable and well-defined pinning sites are required. Here, we show that modulated nanowires consisting of alternating nickel and cobalt sections facilitate efficient domain wall pinning at the interfaces of those sections. By combining electron holography with micromagnetic simulations, the pinning effect can be explained by the interaction of the stray fields generated at the interface and the domain wall. Utilizing a modified differential phase contrast imaging, we visualized the pinned domain wall with a high resolution, revealing its three-dimensional vortex structure with the previously predicted Bloch point at its center. These findings suggest the potential of modulated nanowires for the development of high-density, three-dimensional data storage devices. PMID:27138460
Athermal domain-wall creep near a ferroelectric quantum critical point.
Kagawa, Fumitaka; Minami, Nao; Horiuchi, Sachio; Tokura, Yoshinori
2016-02-16
Ferroelectric domain walls are typically stationary because of the presence of a pinning potential. Nevertheless, thermally activated, irreversible creep motion can occur under a moderate electric field, thereby underlying rewritable and non-volatile memory applications. Conversely, as the temperature decreases, the occurrence of creep motion becomes less likely and eventually impossible under realistic electric-field magnitudes. Here we show that such frozen ferroelectric domain walls recover their mobility under the influence of quantum fluctuations. Nonlinear permittivity and polarization-retention measurements of an organic charge-transfer complex reveal that ferroelectric domain-wall creep occurs via an athermal process when the system is tuned close to a pressure-driven ferroelectric quantum critical point. Despite the heavy masses of material building blocks such as molecules, the estimated effective mass of the domain wall is comparable to the proton mass, indicating the realization of a ferroelectric domain wall with a quantum-particle nature near the quantum critical point.
Direct imaging of thermally driven domain wall motion in magnetic insulators.
Jiang, Wanjun; Upadhyaya, Pramey; Fan, Yabin; Zhao, Jing; Wang, Minsheng; Chang, Li-Te; Lang, Murong; Wong, Kin L; Lewis, Mark; Lin, Yen-Ting; Tang, Jianshi; Cherepov, Sergiy; Zhou, Xuezhi; Tserkovnyak, Yaroslav; Schwartz, Robert N; Wang, Kang L
2013-04-26
Thermally induced domain wall motion in a magnetic insulator was observed using spatiotemporally resolved polar magneto-optical Kerr effect microscopy. The following results were found: (i) the domain wall moves towards hot regime; (ii) a threshold temperature gradient (5 K/mm), i.e., a minimal temperature gradient required to induce domain wall motion; (iii) a finite domain wall velocity outside of the region with a temperature gradient, slowly decreasing as a function of distance, which is interpreted to result from the penetration of a magnonic current into the constant temperature region; and (iv) a linear dependence of the average domain wall velocity on temperature gradient, beyond a threshold thermal bias. Our observations can be qualitatively explained using a magnonic spin transfer torque mechanism, which suggests the utility of magnonic spin transfer torque for controlling magnetization dynamics. PMID:23679764
Modulated Magnetic Nanowires for Controlling Domain Wall Motion: Toward 3D Magnetic Memories.
Ivanov, Yurii P; Chuvilin, Andrey; Lopatin, Sergei; Kosel, Jurgen
2016-05-24
Cylindrical magnetic nanowires are attractive materials for next generation data storage devices owing to the theoretically achievable high domain wall velocity and their efficient fabrication in highly dense arrays. In order to obtain control over domain wall motion, reliable and well-defined pinning sites are required. Here, we show that modulated nanowires consisting of alternating nickel and cobalt sections facilitate efficient domain wall pinning at the interfaces of those sections. By combining electron holography with micromagnetic simulations, the pinning effect can be explained by the interaction of the stray fields generated at the interface and the domain wall. Utilizing a modified differential phase contrast imaging, we visualized the pinned domain wall with a high resolution, revealing its three-dimensional vortex structure with the previously predicted Bloch point at its center. These findings suggest the potential of modulated nanowires for the development of high-density, three-dimensional data storage devices.
Athermal domain-wall creep near a ferroelectric quantum critical point
Kagawa, Fumitaka; Minami, Nao; Horiuchi, Sachio; Tokura, Yoshinori
2016-01-01
Ferroelectric domain walls are typically stationary because of the presence of a pinning potential. Nevertheless, thermally activated, irreversible creep motion can occur under a moderate electric field, thereby underlying rewritable and non-volatile memory applications. Conversely, as the temperature decreases, the occurrence of creep motion becomes less likely and eventually impossible under realistic electric-field magnitudes. Here we show that such frozen ferroelectric domain walls recover their mobility under the influence of quantum fluctuations. Nonlinear permittivity and polarization-retention measurements of an organic charge-transfer complex reveal that ferroelectric domain-wall creep occurs via an athermal process when the system is tuned close to a pressure-driven ferroelectric quantum critical point. Despite the heavy masses of material building blocks such as molecules, the estimated effective mass of the domain wall is comparable to the proton mass, indicating the realization of a ferroelectric domain wall with a quantum-particle nature near the quantum critical point. PMID:26880041
Suppression of the intrinsic stochastic pinning of domain walls in magnetic nanostripes.
Muñoz, Manuel; Prieto, José L
2011-01-01
Nanofabrication has allowed the development of new concepts such as magnetic logic and race-track memory, both of which are based on the displacement of magnetic domain walls on magnetic nanostripes. One of the issues that has to be solved before devices can meet the market demands is the stochastic behaviour of the domain wall movement in magnetic nanostripes. Here we show that the stochastic nature of the domain wall motion in permalloy nanostripes can be suppressed at very low fields (0.6-2.7 Oe). We also find different field regimes for this stochastic motion that match well with the domain wall propagation modes. The highest pinning probability is found around the precessional mode and, interestingly, it does not depend on the external field in this regime. These results constitute an experimental evidence of the intrinsic nature of the stochastic pinning of domain walls in soft magnetic nanostripes.
Pinning induced by inter-domain wall interactions in planar magnetic nanowires
Hayward, T.J.; Bryan, M.T.; Fry, P.W.; Fundi, P.M.; Gibbs, M.R.J.; Allwood, D.A.; Im, M.-Y.; Fischer, P.
2009-10-30
We have investigated pinning potentials created by inter-domain wall magnetostatic interactions in planar magnetic nanowires. We show that these potentials can take the form of an energy barrier or an energy well depending on the walls' relative monopole moments, and that the applied magnetic fields required to overcome these potentials are significant. Both transverse and vortex wall pairs are investigated and it is found that transverse walls interact more strongly due to dipolar coupling between their magnetization structures. Simple analytical models which allow the effects of inter-domain wall interactions to be estimated are also presented.
Dzyaloshinskii-Moriya domain wall resonance in ferromagnetic nanowires with a spin-transfer torque
Li, Zai-Dong; Liu, Fei; Li, Qiu-Yan; He, P. B.
2015-05-07
We theoretically investigate the current-induced domain wall resonance in ferromagnetic nanowires with a Dzyaloshinskii-Moriya interaction. The adiabatic and nonadiabatic torques distort the wall's internal structure and exert a global pressure on the wall. An effective Newton's equation is obtained analytically for a domain wall moving in one-dimensional potential and subject to a viscous friction and a driving force. Our results demonstrate that the Dzyaloshinskii-Moriya interaction affects the critical current density for depinning the wall, resonance frequency, and amplitude.
Controlling the stability of both the structure and velocity of domain walls in magnetic nanowires
NASA Astrophysics Data System (ADS)
Brandão, J.; Atkinson, D.
2016-08-01
For magnetic nanowire devices, the precise control of both domain wall (DW) motion and pinning behaviour is essential for reliable functional performance. The domain wall velocity and wall structure are typically sensitive to the driving field or spin-polarized current, and the pinning behaviour depends on the walls' structure and chirality, leading to variability in behaviour. Here, a systematic study combining experimental measurements and micromagnetic simulations of planar nanowires with small fixed-angle structural modulations on both edges was undertaken to study the domain wall reversal regime. A phase diagram for the reversal field as a function of modulation amplitude was obtained that shows that three DW reversal regime. A range of field and modulation amplitudes were identified in which stable DW reversal occurs, where the wall velocity is constant as a function of field and the wall structure is stable, which is well suited to applications.
Impedance and domain wall mass determination in cylindrical wire with circular anisotropy
NASA Astrophysics Data System (ADS)
Ziman, J.; Kladivová, M.; Šuhajová, V.
2015-11-01
A study of single magnetic domain wall contribution to impedance due to its oscillation in the intermediate frequency region (100 kHz to a few MHz) is presented for a domain wall between circular domains. A simple theoretical model of the wall trapped in a quadratic potential well is proposed, for which the possible influence of skin effect is tested using a scalar permeability model. From this model, for parameters of the Co68.2Fe4.3Si12.5B15 wire used in the experiment, it follows that the frequency dependence of domain wall contribution to impedance exhibits a single maximum at the frequency of an ac current equal to the natural frequency ω0 of the domain wall moving in the quadratic potential well. Experimental dependence confirmed the existence of this maximum, and it made it possible to obtain the value of natural frequency ω0. From the theoretical model it follows that this parameter depends on inertial domain wall mass. Additional experimental procedures are proposed to measure parameters of the quadratic potential well in which the wall is trapped, and the value of domain wall mass per unit area 1.64 ×10-9 kgm-2 was obtained.
Physical results from 2+1 flavor domain wall QCD
Scholz,E.E.
2008-07-14
We review recent results for the chiral behavior of meson masses and decay constants and the determination of the light quark masses by the RBC and UKQCD collaborations. We find that one-loop SU(2) chiral perturbation theory represents the behavior of our lattice data better than one-loop SU(3) chiral perturbation theory in both the pion and kaon sectors. The simulations have been performed using the Iwasaki gauge action at two different lattice spacings with the physical spatial volume held approximately fixed at (2.7fm){sup 3}. The Domain Wall fermion formulation was used for the 2+1 dynamical quark flavors: two (mass degenerate) light flavors with masses as light as roughly 1/5 the mass of the physical strange quark mass and one heavier quark flavor at approximately the value of the physical strange quark mass, On the ensembles generated with the coarser lattice spacing, we obtain for the physical average up- and down-quark and strange quark masses m{sub ud}{sup {ovr MS}} (2 GeV) = 3.72(0.16){sub stat}(0.33){sub ren}(0.18){sub syst}MeV and m{sub s}{sup {ovr MS}} (2 GeV) = 107.3(4.4){sub stat}(9.7){sub ren}(4.9){sub syst} MeV, respectively, while they find for the pion and kaon decay constants f{sub {pi}} = 124.1(3.6){sub stat}(6.9){sub syst}MeV, f{sub K} = 149.6(3.6){sub stat}(6.3){sub syst} MeV. The analysis for the finer lattice spacing has not been fully completed yet, but we already present some first (preliminary) results.
Domain-wall depinning dominated by the Spin Hall effect
NASA Astrophysics Data System (ADS)
Swagten, Henk
2013-03-01
Current induced domain wall motion (CIDWM) in perpendicular materials is believed to be very efficient. We will show that the Spin Hall effect (SHE) provides a radically new mechanism for CIDWM in these systems. Using focused-ion-beam irradiation we are able to stabilize and pin two DWs in a Pt/Co/Pt nanowire. By depinning the DWs under the application of a perpendicular field as well as an injected charge current and in-plane magnetic field, we are able to disentangle the contributions to DW motion originating from (1) conventional spin transfer torques that act on magnetization gradients and (2) from the hitherto unexplored SHE torques. The fact the perpendicular depinning field H as a function of charge current J for the two DWs has equal slope dH/dJ, as well as a sign change of the slope when we change the polarity of the DWs, directly proves the dominance of the SHE contribution. To further proof that the SHE is governing the depinning process, we have tuned the internal spin structure of the DW from Bloch to Néel, by varying the in-plane field parallel to the current, and find that the influence of current on the depinning is highest when the DW has the Néel structure. This behavior is verified by macrospin simulations, which can quantitatively explain our data. As a final compelling evidence, we have varied the thickness of the bottom and top Pt, showing that we are able to tune the spin Hall currents originating from the nonmagnetic Pt layers. The work is part of the research programme of the Foundation for Fundamental Research on Matter (FOM), which is part of the Netherlands Organisation for Scientific Research (NWO).
Kim, June-Seo; Mawass, Mohamad-Assaad; Bisig, André; Krüger, Benjamin; Reeve, Robert M.; Schulz, Tomek; Büttner, Felix; Yoon, Jungbum; You, Chun-Yeol; Weigand, Markus; Stoll, Hermann; Schütz, Gisela; Swagten, Henk J. M.; Koopmans, Bert; Eisebitt, Stefan; Kläui, Mathias
2014-01-01
Magnetic storage and logic devices based on magnetic domain wall motion rely on the precise and synchronous displacement of multiple domain walls. The conventional approach using magnetic fields does not allow for the synchronous motion of multiple domains. As an alternative method, synchronous current-induced domain wall motion was studied, but the required high-current densities prevent widespread use in devices. Here we demonstrate a radically different approach: we use out-of-plane magnetic field pulses to move in-plane domains, thus combining field-induced magnetization dynamics with the ability to move neighbouring domain walls in the same direction. Micromagnetic simulations suggest that synchronous permanent displacement of multiple magnetic walls can be achieved by using transverse domain walls with identical chirality combined with regular pinning sites and an asymmetric pulse. By performing scanning transmission X-ray microscopy, we are able to experimentally demonstrate in-plane magnetized domain wall motion due to out-of-plane magnetic field pulses. PMID:24663150
Domain wall kinetics of lithium niobate single crystals near the hexagonal corner
Choi, Ju Won; Ko, Do-Kyeong; Yu, Nan Ei E-mail: jhro@pnu.edu; Kitamura, Kenji; Ro, Jung Hoon E-mail: jhro@pnu.edu
2015-03-09
A mesospheric approach based on a simple microscopic 2D Ising model in a hexagonal lattice plane is proposed to explain macroscopic “asymmetric in-out domain wall motion” observation in the (0001) plane of MgO-doped stoichiometric lithium niobate. Under application of an electric field that was higher than the conventional coercive field (E{sub c}) to the ferroelectric crystal, a natural hexagonal domain was obtained with walls that were parallel to the Y-axis of the crystal. When a fraction of the coercive field of around 0.1E{sub c} is applied in the reverse direction, this hexagonal domain is shrunk (moved inward) from the corner site into a shape with a corner angle of around 150° and 15° wall slopes to the Y-axis. A flipped electric field of 0.15E{sub c} is then applied to recover the natural hexagonal shape, and the 150° corner shape changes into a flat wall with 30° slope (moved outward). The differences in corner domain shapes between inward and outward domain motion were analyzed theoretically in terms of corner and wall site energies, which are described using the domain corner angle and wall slope with respect to the crystal Y-axis, respectively. In the inward domain wall motion case, the energy levels of the evolving 150° domain corner and 15° slope walls are most competitive, and could co-exist. In the outward case, the energy levels of corners with angles >180° are highly stable when compared with the possible domain walls; only a flat wall with 30° slope to the Y-axis is possible during outward motion.
Hydrodynamics of domain walls in ferroelectrics and multiferroics: Impact on memory devices
NASA Astrophysics Data System (ADS)
Scott, J. F.; Evans, D. M.; Gregg, J. M.; Gruverman, A.
2016-07-01
The standard "Kittel Law" for the thickness and shape of ferroelectric, ferroelastic, or ferromagnet domains assumes mechanical equilibrium. The present paper shows that such domains may be highly nonequilibrium, with unusual thicknesses and shapes. In lead germanate and multiferroic lead zirconate titanate iron tantalate domain wall instabilities resemble hydrodynamics (Richtmyer-Meshkov and Helfrich-Hurault, respectively).
Nanoscale imaging and control of domain-wall hopping with a nitrogen-vacancy center microscope.
Tetienne, J-P; Hingant, T; Kim, J-V; Diez, L Herrera; Adam, J-P; Garcia, K; Roch, J-F; Rohart, S; Thiaville, A; Ravelosona, D; Jacques, V
2014-06-20
The control of domain walls in magnetic wires underpins an emerging class of spintronic devices. Propagation of these walls in imperfect media requires defects that pin them to be characterized on the nanoscale. Using a magnetic microscope based on a single nitrogen-vacancy (NV) center in diamond, we report domain-wall imaging on a 1-nanometer-thick ferromagnetic nanowire and directly observe Barkhausen jumps between two pinning sites spaced 50 nanometers apart. We further demonstrate in situ laser control of these jumps, which allows us to drag the domain wall along the wire and map the pinning landscape. Our work demonstrates the potential of NV microscopy to study magnetic nano-objects in complex media, whereas controlling domain walls with laser light may find an application in spintronic devices.
Domain wall in a quantum anomalous Hall insulator as a magnetoelectric piston
NASA Astrophysics Data System (ADS)
Upadhyaya, Pramey; Tserkovnyak, Yaroslav
2016-07-01
We theoretically study the magnetoelectric coupling in a quantum anomalous Hall insulator state induced by interfacing a dynamic magnetization texture to a topological insulator. In particular, we propose that the quantum anomalous Hall insulator with a magnetic configuration of a domain wall, when contacted by electrical reservoirs, acts as a magnetoelectric piston. A moving domain wall pumps charge current between electrical leads in a closed circuit, while applying an electrical bias induces reciprocal domain-wall motion. This pistonlike action is enabled by a finite reflection of charge carriers via chiral modes imprinted by the domain wall. Moreover, we find that, when compared with the recently discovered spin-orbit torque-induced domain-wall motion in heavy metals, the reflection coefficient plays the role of an effective spin-Hall angle governing the efficiency of the proposed electrical control of domain walls. Quantitatively, this effective spin-Hall angle is found to approach a universal value of 2, providing an efficient scheme to reconfigure the domain-wall chiral interconnects for possible memory and logic applications.
Trützschler, Julia; Sentosun, Kadir; Mozooni, Babak; Mattheis, Roland; McCord, Jeffrey
2016-01-01
High density magnetic domain wall gratings are imprinted in ferromagnetic-antiferromagnetic thin films by local ion irradiation by which alternating head-to-tail-to-head-to-tail and head-to-head-to-tail-to-tail spatially overlapping domain wall networks are formed. Unique magnetic domain processes result from the interaction of anchored domain walls. Non-linear magnetization response is introduced by the laterally distributed magnetic anisotropy phases. The locally varying magnetic charge distribution gives rise to localized and guided magnetization spin-wave modes directly constrained by the narrow domain wall cores. The exchange coupled multiphase material structure leads to unprecedented static and locally modified dynamic magnetic material properties. PMID:27487941
Domain wall conductivity in semiconducting hexagonal ferroelectric TbMnO3 thin films.
Kim, D J; Connell, J G; Seo, S S A; Gruverman, A
2016-04-15
Although enhanced conductivity of ferroelectric domain boundaries has been found in BiFeO3 and Pb(Zr,Ti)O3 films as well as hexagonal rare-earth manganite single crystals, the mechanism of the domain wall conductivity is still under debate. Using conductive atomic force microscopy, we observe enhanced conductance at the electrically-neutral domain walls in semiconducting hexagonal ferroelectric TbMnO3 thin films where the structure and polarization direction are strongly constrained along the c-axis. This result indicates that domain wall conductivity in ferroelectric rare-earth manganites is not limited to charged domain walls. We show that the observed conductivity in the TbMnO3 films is governed by a single conduction mechanism, namely, the back-to-back Schottky diodes tuned by the segregation of defects. PMID:26933770
Charge-order domain walls with enhanced conductivity in a layered manganite
NASA Astrophysics Data System (ADS)
Ma, Eric Yue; Bryant, Benjamin; Tokunaga, Yusuke; Aeppli, Gabriel; Tokura, Yoshinori; Shen, Zhi-Xun
2015-07-01
Interfaces and boundaries in condensed-matter systems often have electronic properties distinct from the bulk material and thus have become a topic of both fundamental scientific interest and technological importance. Here we identify, using microwave impedance microscopy, enhanced conductivity of charge-order domain walls in the layered manganite Pr(Sr0.1Ca0.9)2Mn2O7. We obtain a complete mesoscopic map of surface topography, crystalline orientation and electronic phase, and visualize the thermal phase transition between two charge-ordered phases. In both phases, charge-order domains occur with domain walls showing enhanced conductivity likely due to local lifting of the charge order. Finite element analysis shows that the resolved domain walls can be as narrow as few nanometres. The domain walls are stabilized by structural twins and have a strong history dependence, suggesting that they may be manipulated to create novel devices.
Trützschler, Julia; Sentosun, Kadir; Mozooni, Babak; Mattheis, Roland; McCord, Jeffrey
2016-01-01
High density magnetic domain wall gratings are imprinted in ferromagnetic-antiferromagnetic thin films by local ion irradiation by which alternating head-to-tail-to-head-to-tail and head-to-head-to-tail-to-tail spatially overlapping domain wall networks are formed. Unique magnetic domain processes result from the interaction of anchored domain walls. Non-linear magnetization response is introduced by the laterally distributed magnetic anisotropy phases. The locally varying magnetic charge distribution gives rise to localized and guided magnetization spin-wave modes directly constrained by the narrow domain wall cores. The exchange coupled multiphase material structure leads to unprecedented static and locally modified dynamic magnetic material properties. PMID:27487941
Domain walls in two-component dynamical lattices.
Kevrekidis, P G; Malomed, Boris A; Frantzeskakis, D J; Bishop, A R
2003-03-01
We introduce domain-wall (DW) states in the bimodal discrete nonlinear Schrödinger equation, in which the modes are coupled by cross-phase modulation (XPM). The results apply to an array of nonlinear optical waveguides carrying two different polarizations of light, or two different wavelengths, with anomalous intrinsic diffraction controlled by direction of the light beam, and to a string of drops of a binary Bose-Einstein condensate, trapped in an optical lattice. By means of continuation from various initial patterns taken in the anticontinuum (AC) limit, we find a number of different solutions of the DW type, for which different stability scenarios are identified. In the case of strong-XPM coupling, DW configurations contain a single mode at each end of the chain. The most fundamental solution of this type is found to be always stable. Another solution, which is generated by a different AC pattern, demonstrates behavior which is unusual for nonlinear dynamical lattices: it is unstable for small values of the coupling constant C (which measures the ratio of the nonlinearity and coupling lengths), and becomes stable at larger C. Stable bound states of DWs are also found. DW configurations generated by more sophisticated AC patterns are identified as well, but they are either completely unstable, or are stable only at small values of C. In the case of weak XPM, a natural DW solution is the one which contains a combination of both polarizations, with the phase difference between them 0 and pi at the opposite ends of the lattice. This solution is unstable at all values of C, but the instability is very weak for large C, indicating stabilization as the continuum limit is approached. The stability of DWs is also verified by direct simulations, and the evolution of unstable DWs is simulated too; in particular, it is found that, in the weak-XPM system, the instability may give rise to a moving DW. The DW states can be observed experimentally in the same parameter range
Multi-scalar tachyon potential on non-BPS domain walls
NASA Astrophysics Data System (ADS)
Brito, F. A.; Jesuíno, H. S.
2010-07-01
We have considered the multi-scalar and multi-tachyon fields living on a 3d domain wall embedded in a 5d dimensional Minkowski spacetime. The effective action for such a domain wall can be found by integrating out the normal m odes as vibrating modes around the domain wall solution of a truncated 5d supergravity action. The multi-scalar tachyon potential is good enough to modeling assisted inflation scenario with multi-tachyon fields. The tachyon condensation is also briefly addressed.
Domain wall creation in nanostructures driven by a spin-polarized current.
Ravelosona, D; Mangin, S; Lemaho, Y; Katine, J A; Terris, B D; Fullerton, Eric E
2006-05-12
We report on current-driven magnetization reversal in nanopillars with elements having perpendicular magnetic anisotropy. Whereas only the two uniform magnetization states are available under the action of a magnetic field, we observed current-induced Bloch domain walls in pillars as small as 50 x 100 nm(2). This domain wall state can be further controlled by current to restore the uniform states. The ability to nucleate and manipulate domain walls by a current gives insight into the reversal mechanisms of small nanoelements and provides new prospects for ultrahigh density spintronic devices. PMID:16712386
Domain wall motion driven by spin Hall effect—Tuning with in-plane magnetic anisotropy
Rushforth, A. W.
2014-04-21
This letter investigates the effects of in-plane magnetic anisotropy on the current induced motion of magnetic domain walls in systems with dominant perpendicular magnetic anisotropy, where accumulated spins from the spin Hall effect in an adjacent heavy metal layer are responsible for driving the domain wall motion. It is found that that the sign and magnitude of the domain wall velocity in the uniform flow regime can be tuned significantly by the in-plane magnetic anisotropy. These effects are sensitive to the ratio of the adiabatic and non-adiabatic spin transfer torque parameters and are robust in the presence of pinning and thermal fluctuations.
NASA Astrophysics Data System (ADS)
Ding, Hu; Wenliang, Zhang; Yuan, Wei; Xiaotian, Zhang; Cong, Ren; Lei, Shan; Yi-feng, Ya; Huiqian, Luo; Shiliang, Li
2016-05-01
We have studied the angular magnetoresistance of iron pnictides BaFe2-x Ni x As2, which shows clear 180 degree periodicity as fitted by a cosine function. In the x = 0.065 sample, the phase of the two-fold symmetry changes 90 degrees above the tetragonal-to-orthorhombic structural transition temperature T s. Since the phase at low temperature is associated with the rotation of orthorhombic domains by magnetic field, we show that even vacuum grease can push the presence of orthorhombic domains at temperatures much higher than T s. Our results suggest that residual stress may have significant effects in studying the nematic orders and its fluctuations in iron pnictides. Project supported by the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDB07020300), the National Basic Research Program of China (Grant Nos. 2012CB821400 and 2011CBA00110), and the National Natural Science Foundation of China (Grant Nos. 11374011, 11374346, and 11305257).
Domain wall spin structures in mesoscopic Fe rings probed by high resolution SEMPA
NASA Astrophysics Data System (ADS)
Krautscheid, Pascal; Reeve, Robert M.; Lauf, Maike; Krüger, Benjamin; Kläui, Mathias
2016-10-01
We present a combined theoretical and experimental study of the energetic stability and accessibility of different domain wall spin configurations in mesoscopic magnetic iron rings. The evolution is investigated as a function of the width and thickness in a regime of relevance to devices, while Fe is chosen as a material due to its simple growth in combination with attractive magnetic properties including high saturation magnetization and low intrinsic anisotropy. Micromagnetic simulations are performed to predict the lowest energy states of the domain walls, which can be either the transverse or vortex wall spin structure, in good agreement with analytical models, with further simulations revealing the expected low temperature configurations observable on relaxation of the magnetic structure from saturation in an external field. In the latter case, following the domain wall nucleation process, transverse domain walls are found at larger widths and thicknesses than would be expected by just comparing the competing energy terms demonstrating the importance of metastability of the states. The simulations are compared to high spatial resolution experimental images of the magnetization using scanning electron microscopy with polarization analysis to provide a phase diagram of the various spin configurations. In addition to the vortex and simple symmetric transverse domain wall, a significant range of geometries are found to exhibit highly asymmetric transverse domain walls with properties distinct from the symmetric transverse wall. Simulations of the asymmetric walls reveal an evolution of the domain wall tilting angle with ring thickness which can be understood from the thickness dependencies of the contributing energy terms. Analysis of all the data reveals that in addition to the geometry, the influence of materials properties, defects and thermal activation all need to be taken into account in order to understand and reliably control the experimentally accessible
Time evolution of temperature and entropy of various collapsing domain walls
Halstead, Evan
2013-08-01
We investigate the time evolution of the temperature and entropy of gravitationally collapsing shells of matter, represented by domain walls, as seen by an asymptotic observer. In particular, we seek to understand how topology and the addition of a cosmological constant affect the gravitational collapse. Previous work has shown that the entropy of a spherically symmetric collapsing domain approaches a constant. In this paper, we reproduce these results, using both a fully quantum and a semi-classical approach, then we repeat the process for a de Sitter Schwarzschild domain wall (spherical with cosmological constant) and a (3+1) BTZ domain wall (cylindrical). We do this by coupling a scalar field to the background of the domain wall and analyzing the spectrum of radiation as a function of time. We find that the spectrum is quasi-thermal, with the degree of thermality increasing as the domain wall approaches the horizon. The thermal distribution allows for the determination of the temperature as a function of time, and we find that the late time temperature is consistent with the Hawking temperature. From the temperature we find the entropy. Since the collapsing domain wall is what forms a black hole, we can compare the results to those of the standard entropy-area relation. We find that the entropy does in fact approach a constant that is consistent with the Hawking entropy. However, both the de Sitter Schwarzschild domain wall and the (3+1) BTZ domain wall show periods of decreasing entropy, which suggests that spontaneous collapse may be prevented.
Laccases Direct Lignification in the Discrete Secondary Cell Wall Domains of Protoxylem1[W][OPEN
Schuetz, Mathias; Benske, Anika; Smith, Rebecca A.; Watanabe, Yoichiro; Tobimatsu, Yuki; Ralph, John; Demura, Taku; Ellis, Brian; Samuels, A. Lacey
2014-01-01
Plants precisely control lignin deposition in spiral or annular secondary cell wall domains during protoxylem tracheary element (TE) development. Because protoxylem TEs function to transport water within rapidly elongating tissues, it is important that lignin deposition is restricted to the secondary cell walls in order to preserve the plasticity of adjacent primary wall domains. The Arabidopsis (Arabidopsis thaliana) inducible VASCULAR NAC DOMAIN7 (VND7) protoxylem TE differentiation system permits the use of mutant backgrounds, fluorescent protein tagging, and high-resolution live-cell imaging of xylem cells during secondary cell wall development. Enzymes synthesizing monolignols, as well as putative monolignol transporters, showed a uniform distribution during protoxylem TE differentiation. By contrast, the oxidative enzymes LACCASE4 (LAC4) and LAC17 were spatially localized to secondary cell walls throughout protoxylem TE differentiation. These data support the hypothesis that precise delivery of oxidative enzymes determines the pattern of cell wall lignification. This view was supported by lac4lac17 mutant analysis demonstrating that laccases are necessary for protoxylem TE lignification. Overexpression studies showed that laccases are sufficient to catalyze ectopic lignin polymerization in primary cell walls when exogenous monolignols are supplied. Our data support a model of protoxylem TE lignification in which monolignols are highly mobile once exported to the cell wall, and in which precise targeting of laccases to secondary cell wall domains directs lignin deposition. PMID:25157028
Tunable short-wavelength spin wave excitation from pinned magnetic domain walls.
Van de Wiele, Ben; Hämäläinen, Sampo J; Baláž, Pavel; Montoncello, Federico; van Dijken, Sebastiaan
2016-02-17
Miniaturization of magnonic devices for wave-like computing requires emission of short-wavelength spin waves, a key feature that cannot be achieved with microwave antennas. In this paper, we propose a tunable source of short-wavelength spin waves based on highly localized and strongly pinned magnetic domain walls in ferroelectric-ferromagnetic bilayers. When driven into oscillation by a microwave spin-polarized current, the magnetic domain walls emit spin waves with the same frequency as the excitation current. The amplitude of the emitted spin waves and the range of attainable excitation frequencies depend on the availability of domain wall resonance modes. In this respect, pinned domain walls in magnetic nanowires are particularly attractive. In this geometry, spin wave confinement perpendicular to the nanowire axis produces a multitude of domain wall resonances enabling efficient spin wave emission at frequencies up to 100 GHz and wavelengths down to 20 nm. At high frequency, the emission of spin waves in magnetic nanowires becomes monochromatic. Moreover, pinning of magnetic domain wall oscillators onto the same ferroelectric domain boundary in parallel nanowires guarantees good coherency between spin wave sources, which opens perspectives towards the realization of Mach-Zehnder type logic devices and sensors.
NASA Astrophysics Data System (ADS)
Gomonay, O.; Kläui, M.; Sinova, J.
2016-10-01
Future applications of antiferromagnets (AFs) in many spintronics devices rely on the precise manipulation of domain walls. The conventional approach using static magnetic fields is inefficient due to the low susceptibility of AFs. Recently proposed electrical manipulation with spin-orbit torques is restricted to metals with a specific crystal structure. Here, we propose an alternative, broadly applicable approach: using asymmetric magnetic field pulses to induce controlled ratchet motion of AF domain walls. The efficiency of this approach is based on three peculiarities of AF dynamics. First, a time-dependent magnetic field couples with an AF order parameter stronger than a static magnetic field, which leads to higher mobility of the domain walls. Second, the rate of change of the magnetic field couples with the spatial variation of the AF order parameter inside the domain, and this enables a synchronous motion of multiple domain walls with the same structure. Third, tailored asymmetric field pulses in combination with static friction can prevent backward motion of domain walls and thus lead to the desired controlled ratchet effect. The proposed use of an external field, rather than internal spin-orbit torques, avoids any restrictions on size, conductivity, and crystal structure of the AF material. We believe that our approach paves a way for the development of AF-based devices based on the controlled motion of AF domain walls.
Tunable short-wavelength spin wave excitation from pinned magnetic domain walls
Van de Wiele, Ben; Hämäläinen, Sampo J.; Baláž, Pavel; Montoncello, Federico; van Dijken, Sebastiaan
2016-01-01
Miniaturization of magnonic devices for wave-like computing requires emission of short-wavelength spin waves, a key feature that cannot be achieved with microwave antennas. In this paper, we propose a tunable source of short-wavelength spin waves based on highly localized and strongly pinned magnetic domain walls in ferroelectric-ferromagnetic bilayers. When driven into oscillation by a microwave spin-polarized current, the magnetic domain walls emit spin waves with the same frequency as the excitation current. The amplitude of the emitted spin waves and the range of attainable excitation frequencies depend on the availability of domain wall resonance modes. In this respect, pinned domain walls in magnetic nanowires are particularly attractive. In this geometry, spin wave confinement perpendicular to the nanowire axis produces a multitude of domain wall resonances enabling efficient spin wave emission at frequencies up to 100 GHz and wavelengths down to 20 nm. At high frequency, the emission of spin waves in magnetic nanowires becomes monochromatic. Moreover, pinning of magnetic domain wall oscillators onto the same ferroelectric domain boundary in parallel nanowires guarantees good coherency between spin wave sources, which opens perspectives towards the realization of Mach-Zehnder type logic devices and sensors. PMID:26883893
Inertia-Free Thermally Driven Domain-Wall Motion in Antiferromagnets.
Selzer, Severin; Atxitia, Unai; Ritzmann, Ulrike; Hinzke, Denise; Nowak, Ulrich
2016-09-01
Domain-wall motion in antiferromagnets triggered by thermally induced magnonic spin currents is studied theoretically. It is shown by numerical calculations based on a classical spin model that the wall moves towards the hotter regions, as in ferromagnets. However, for larger driving forces the so-called Walker breakdown-which usually speeds down the wall-is missing. This is due to the fact that the wall is not tilted during its motion. For the same reason antiferromagnetic walls have no inertia and, hence, no acceleration phase leading to higher effective mobility. PMID:27636489
Inertia-Free Thermally Driven Domain-Wall Motion in Antiferromagnets.
Selzer, Severin; Atxitia, Unai; Ritzmann, Ulrike; Hinzke, Denise; Nowak, Ulrich
2016-09-01
Domain-wall motion in antiferromagnets triggered by thermally induced magnonic spin currents is studied theoretically. It is shown by numerical calculations based on a classical spin model that the wall moves towards the hotter regions, as in ferromagnets. However, for larger driving forces the so-called Walker breakdown-which usually speeds down the wall-is missing. This is due to the fact that the wall is not tilted during its motion. For the same reason antiferromagnetic walls have no inertia and, hence, no acceleration phase leading to higher effective mobility.
Domain-wall theory and nonstationarity in driven flow with exclusion
NASA Astrophysics Data System (ADS)
Stinchcombe, R. B.; de Queiroz, S. L. A.
2016-07-01
We study the dynamical evolution toward steady state of the stochastic nonequilibrium model known as the totally asymmetric simple exclusion process, in both uniform and nonuniform (staggered) one-dimensional systems with open boundaries. Domain-wall theory and numerical simulations are used and, where pertinent, their results are compared to existing mean-field predictions and exact solutions where available. For uniform chains we find that the inclusion of fluctuations inherent to the domain-wall formulation plays a crucial role in providing good agreement with simulations, which is severely lacking in the corresponding mean-field predictions. For alternating-bond chains the domain-wall predictions for the features of the phase diagram in the parameter space of injection and ejection rates turn out to be realized only in an incipient and quantitatively approximate way. Nevertheless, significant quantitative agreement can be found between several additional domain-wall theory predictions and numerics.
Direct imaging of topological edge states at a bilayer graphene domain wall
NASA Astrophysics Data System (ADS)
Yin, Long-Jing; Jiang, Hua; Qiao, Jia-Bin; He, Lin
2016-06-01
The AB-BA domain wall in gapped graphene bilayers is a rare naked structure hosting topological electronic states. Although it has been extensively studied in theory, a direct imaging of its topological edge states is still missing. Here we image the topological edge states at the graphene bilayer domain wall by using scanning tunnelling microscope. The simultaneously obtained atomic-resolution images of the domain wall provide us unprecedented opportunities to measure the spatially varying edge states within it. The one-dimensional conducting channels are observed to be mainly located around the two edges of the domain wall, which is reproduced quite well by our theoretical calculations. Our experiment further demonstrates that the one-dimensional topological states are quite robust even in the presence of high magnetic fields. The result reported here may raise hopes of graphene-based electronics with ultra-low dissipation.
Mobile metallic domain walls in an all-in-all-out magnetic insulator.
Ma, Eric Yue; Cui, Yong-Tao; Ueda, Kentaro; Tang, Shujie; Chen, Kai; Tamura, Nobumichi; Wu, Phillip M; Fujioka, Jun; Tokura, Yoshinori; Shen, Zhi-Xun
2015-10-30
Magnetic domain walls are boundaries between regions with different configurations of the same magnetic order. In a magnetic insulator, where the magnetic order is tied to its bulk insulating property, it has been postulated that electrical properties are drastically different along the domain walls, where the order is inevitably disturbed. Here we report the discovery of highly conductive magnetic domain walls in a magnetic insulator, Nd2Ir2O7, that has an unusual all-in-all-out magnetic order, via transport and spatially resolved microwave impedance microscopy. The domain walls have a virtually temperature-independent sheet resistance of ~1 kilohm per square, show smooth morphology with no preferred orientation, are free from pinning by disorders, and have strong thermal and magnetic field responses that agree with expectations for all-in-all-out magnetic order.
Universal charge and current on magnetic domain walls in Weyl semimetals
NASA Astrophysics Data System (ADS)
Araki, Yasufumi; Yoshida, Akihide; Nomura, Kentaro
2016-09-01
Domain walls in three-dimensional Weyl semimetals, formed by localized magnetic moments, are investigated. There appear bound states around the domain wall with the discrete spectrum, among which we find "Fermi arc" states with the linear dispersion. The Fermi arc modes contribute to the electric charge and current localized at the domain wall, which reveal a universal behavior depending only on chemical potential and the splitting of the Weyl nodes. This equilibrium current can be traced back to the chiral magnetic effect, or the edge counterpart of the anomalous Hall effect in the bulk. We propose a way to manipulate the motion of the domain wall, accompanied with the localized charge, by applying an external electric field.
Direct imaging of topological edge states at a bilayer graphene domain wall.
Yin, Long-Jing; Jiang, Hua; Qiao, Jia-Bin; He, Lin
2016-01-01
The AB-BA domain wall in gapped graphene bilayers is a rare naked structure hosting topological electronic states. Although it has been extensively studied in theory, a direct imaging of its topological edge states is still missing. Here we image the topological edge states at the graphene bilayer domain wall by using scanning tunnelling microscope. The simultaneously obtained atomic-resolution images of the domain wall provide us unprecedented opportunities to measure the spatially varying edge states within it. The one-dimensional conducting channels are observed to be mainly located around the two edges of the domain wall, which is reproduced quite well by our theoretical calculations. Our experiment further demonstrates that the one-dimensional topological states are quite robust even in the presence of high magnetic fields. The result reported here may raise hopes of graphene-based electronics with ultra-low dissipation. PMID:27312315
Domain wall model in the galactic Bose-Einstein condensate halo
Souza, J.C.C. de; Pires, M.O.C. E-mail: marcelo.pires@ufabc.edu.br
2013-05-01
We assume that the galactic dark matter halo, considered composed of an axionlike particles Bose-Einstein condensate [1], can present topological defects, namely domain walls, arising as the dark soliton solution for the Gross-Pitaevskii equation in a self-graviting potential. We investigate the influence that such substructures would have in the gravitational interactions within a galaxy. We find that, for the simple domain wall model proposed, the effects are too small to be identified, either by means of a local measurement of the gradient of the gravitational field or by analysing galaxy rotation curves. In the first case, the gradient of the gravitational field in the vicinity of the domain wall would be 10{sup −31} (m/s{sup 2})/m. In the second case, the ratio of the tangential velocity correction of a star due to the presence of the domain wall to the velocity in the spherical symmetric case would be 10{sup −8}.
Analytical modelling and x-ray imaging of oscillations of a single magnetic domain wall
Bocklage, Lars; Kruger, Benjamin; Fischer, Peter; Meier, Guido
2009-07-10
Domain-wall oscillation in a pinnig potential is described analytically in a one dimensional model for the feld-driven case. For a proper description the pinning potential has to be extended by nonharmonic contributions. Oscillations of a domain wall are observed on its genuine time scale by magnetic X-ray microscopy. It is shown that the nonharmonic terms are present in real samples with a strong restoring potential. In the framework of our model we gain deep insight into the domain-wall motion by looking at different phase spaces. The corrections of the harmonic potential can change the motion of the domain wall significantly. The damping parameter of permalloy is determined via the direct imaging technique.
Adiabatic spin-transfer-torque-induced domain wall creep in a magnetic metal
NASA Astrophysics Data System (ADS)
Duttagupta, S.; Fukami, S.; Zhang, C.; Sato, H.; Yamanouchi, M.; Matsukura, F.; Ohno, H.
2016-04-01
The dynamics of elastic interfaces is a general field of interest in statistical physics, where magnetic domain wall has served as a prototypical example. Domain wall `creep’ under the action of sub-threshold driving forces with thermal activation is known to be described by a scaling law with a certain universality class, which represents the mechanism of the interaction of domain walls with the applied forces over the disorder of the system. Here we show different universality classes depending on the driving forces, magnetic field or spin-polarized current, in a metallic system, which have hitherto been seen only in a magnetic semiconductor. We reveal that an adiabatic spin-transfer torque plays a major role in determining the universality class of current-induced creep, which does not depend on the intricacies of material disorder. Our results shed light on the physics of the creep motion of domain walls and other elastic systems.
Temperature change effect on BaTiO3 single crystal surface potential around domain walls
NASA Astrophysics Data System (ADS)
He, D. Y.; Xing, X. R.; Qiao, L. J.; Volinsky, Alex A.
2014-08-01
Temperature dependence of the surface potential distribution on the BaTiO3 (0 0 1) single crystal ferroelectric domain walls was investigated by the scanning Kelvin probe microscopy. After decreasing the single crystal temperature below the Curie point (TC), high potential (∼600 mV) stripes were immediately observed near the 90° a-c domain wall surface. The potential stripes were not stable and decayed with time. The adjacent c domain surface screening charges and their mobility play a dominant role in this experiment. The corrugation topography at the 90° a-c domain wall acts as a natural charge trap and should not be neglected. Besides, the polarization and the strain variations across the wall induce large physical changes of the material.
Domain-wall theory and nonstationarity in driven flow with exclusion.
Stinchcombe, R B; de Queiroz, S L A
2016-07-01
We study the dynamical evolution toward steady state of the stochastic nonequilibrium model known as the totally asymmetric simple exclusion process, in both uniform and nonuniform (staggered) one-dimensional systems with open boundaries. Domain-wall theory and numerical simulations are used and, where pertinent, their results are compared to existing mean-field predictions and exact solutions where available. For uniform chains we find that the inclusion of fluctuations inherent to the domain-wall formulation plays a crucial role in providing good agreement with simulations, which is severely lacking in the corresponding mean-field predictions. For alternating-bond chains the domain-wall predictions for the features of the phase diagram in the parameter space of injection and ejection rates turn out to be realized only in an incipient and quantitatively approximate way. Nevertheless, significant quantitative agreement can be found between several additional domain-wall theory predictions and numerics. PMID:27575075
Multiple integral representation for the trigonometric SOS model with domain wall boundaries
NASA Astrophysics Data System (ADS)
Galleas, W.
2012-05-01
Using the dynamical Yang-Baxter algebra we derive a functional equation for the partition function of the trigonometric SOS model with domain wall boundary conditions. The solution of the equation is given in terms of a multiple contour integral.
Direct observation of stochastic domain-wall depinning in magnetic nanowires
Im, Mi-Young; Bocklage, Lars; Fischer, Peter; Meier, Guido
2008-11-01
The stochastic field-driven depinning of a domain wall pinned at a notch in a magnetic nanowire is directly observed using magnetic X-ray microscopy with high lateral resolution down to 15 nm. The depinning-field distribution in Ni{sub 80}Fe{sub 20} nanowires considerably depends on the wire width and the notch depth. The difference in the multiplicity of domain-wall types generated in the vicinity of a notch is responsible for the observed dependence of the stochastic nature of the domain wall depinning field on the wire width and the notch depth. Thus the random nature of the domain wall depinning process is controllable by an appropriate design of the nanowire.
Huang, Hao-Ting; Lai, Mei-Feng; Hou, Yun-Fang; Wei, Zung-Hang
2015-05-13
We investigated the influence of magnetic domain walls and magnetic fields on the thermal conductivity of suspended magnetic nanowires. The thermal conductivity of the nanowires was obtained using steady-state Joule heating to measure the change in resistance caused by spontaneous heating. The results showed that the thermal conductivity coefficients of straight and wavy magnetic nanowires decreased with an increase in the magnetic domain wall number, implying that the scattering between magnons and domain walls hindered the heat transport process. In addition, we proved that the magnetic field considerably reduced the thermal conductivity of a magnetic nanowire. The influence of magnetic domain walls and magnetic fields on the thermal conductivity of polycrystalline magnetic nanowires can be attributed to the scattering of long-wavelength spin waves mediated by intergrain exchange coupling.
Direct imaging of topological edge states at a bilayer graphene domain wall
Yin, Long-Jing; Jiang, Hua; Qiao, Jia-Bin; He, Lin
2016-01-01
The AB–BA domain wall in gapped graphene bilayers is a rare naked structure hosting topological electronic states. Although it has been extensively studied in theory, a direct imaging of its topological edge states is still missing. Here we image the topological edge states at the graphene bilayer domain wall by using scanning tunnelling microscope. The simultaneously obtained atomic-resolution images of the domain wall provide us unprecedented opportunities to measure the spatially varying edge states within it. The one-dimensional conducting channels are observed to be mainly located around the two edges of the domain wall, which is reproduced quite well by our theoretical calculations. Our experiment further demonstrates that the one-dimensional topological states are quite robust even in the presence of high magnetic fields. The result reported here may raise hopes of graphene-based electronics with ultra-low dissipation. PMID:27312315
Coupling between Current and Dynamic Magnetization : from Domain Walls to Spin Waves
NASA Astrophysics Data System (ADS)
Lucassen, M. E.
2012-05-01
So far, we have derived some general expressions for domain-wall motion and the spin motive force. We have seen that the β parameter plays a large role in both subjects. In all chapters of this thesis, there is an emphasis on the determination of this parameter. We also know how to incorporate thermal fluctuations for rigid domain walls, as shown above. In Chapter 2, we study a different kind of fluctuations: shot noise. This noise is caused by the fact that an electric current consists of electrons, and therefore has fluctuations. In the process, we also compute transmission and reflection coefficients for a rigid domain wall, and from them the linear momentum transfer. More work on fluctuations is done in Chapter 3. Here, we consider a (extrinsically pinned) rigid domain wall under the influence of thermal fluctuations that induces a current via spin motive force. We compute how the resulting noise in the current is related to the β parameter. In Chapter 4 we look into in more detail into the spin motive forces from field driven domain walls. Using micro magnetic simulations, we compute the spin motive force due to vortex domain walls explicitly. As mentioned before, this gives qualitatively different results than for a rigid domain wall. The final subject in Chapter 5 is the application of the general expression for spin motive forces to magnons. Although this might seem to be unrelated to domain-wall motion, this calculation allows us to relate the β parameter to macroscopic transport coefficients. This work was supported by Stichting voor Fundamenteel Onderzoek der Materie (FOM), the Netherlands Organization for Scientific Research (NWO), and by the European Research Council (ERC) under the Seventh Framework Program (FP7).
Elementary depinning processes of magnetic domain walls under fields and currents
NASA Astrophysics Data System (ADS)
Nguyen, V. D.; Torres, W. Savero; Laczkowski, P.; Marty, A.; Jamet, M.; Beigné, C.; Notin, L.; Vila, L.; Attané, J. P.
2014-10-01
The probability laws associated to domain wall depinning under fields and currents have been studied in NiFe and FePt nanowires. Three basic domain wall depinning processes, associated to different potential landscapes, are found to appear identically in those systems with very different anisotropies. We show that these processes constitute the building blocks of any complex depinning mechanism. A Markovian analysis is proposed, that provides a unified picture of the depinning mechanism and an insight into the pinning potential landscape.
Nucleation, imaging, and motion of magnetic domain walls in cylindrical nanowires
NASA Astrophysics Data System (ADS)
Da, S., Col; Jamet, S.; StaÅo, M.; Trapp, B.; Le Denmat, S.; Cagnon, L.; Toussaint, J. C.; Fruchart, O.
2016-08-01
We report several procedures for the robust nucleation of magnetic domain walls in cylindrical permalloy nanowires. Specific features of the magnetic force microscopy (MFM) contrast of such wires are discussed, to avoid the misinterpretation of the magnetization states. The domain walls moved under quasistatic magnetic fields in the range 0.1-10 mT, as evidenced by MFM at remanence at different stages of their motion.
Electrical effects of spin density wave quantization and magnetic domain walls in chromium
Kummamuru, Ravi K.; Soh, Yeong-Ah
2008-05-05
The role of magnetic domains (and the walls between domains) in determining the electrical properties of ferromagnetic materials has been investigated in great detail for many years, not least because control over domains offers a means of manipulating electron spin to control charge transport in 'spintronic' devices. In contrast, much less attention has been paid to the effects of domains and domain walls on the electrical properties of antiferromagnets: antiferromagnetic domains show no net external magnetic moment, and so are difficult to manipulate or probe. Here we describe electrical measurements on chromium -- a simple metal and quintessential spin density wave antiferromagnet -- that show behaviour directly related to spin density wave formation and the presence of antiferromagnetic domains. Two types of thermal hysteresis are seen in both longitudinal and Hall resistivity: the first can be explained by the quantization of spin density waves due to the finite film thickness (confirmed by X-ray diffraction measurements) and the second by domain-wall scattering of electrons. We also observe the striking influence of the electrical lead configuration (a mesoscopic effect) on the resistivity of macroscopic samples in the spin density wave state. Our results are potentially of practical importance, in that they reveal tunable electrical effects of film thickness and domain walls that are as large as the highest seen for ferromagnets.
Electrical effects of spin density wave quantization and magnetic domain walls in chromium.
Kummamuru, Ravi K; Soh, Yeong-Ah
2008-04-17
The role of magnetic domains (and the walls between domains) in determining the electrical properties of ferromagnetic materials has been investigated in great detail for many years, not least because control over domains offers a means of manipulating electron spin to control charge transport in 'spintronic' devices. In contrast, much less attention has been paid to the effects of domains and domain walls on the electrical properties of antiferromagnets: antiferromagnetic domains show no net external magnetic moment, and so are difficult to manipulate or probe. Here we describe electrical measurements on chromium--a simple metal and quintessential spin density wave antiferromagnet--that show behaviour directly related to spin density wave formation and the presence of antiferromagnetic domains. Two types of thermal hysteresis are seen in both longitudinal and Hall resistivity: the first can be explained by the quantization of spin density waves due to the finite film thickness (confirmed by X-ray diffraction measurements) and the second by domain-wall scattering of electrons. We also observe the striking influence of the electrical lead configuration (a mesoscopic effect) on the resistivity of macroscopic samples in the spin density wave state. Our results are potentially of practical importance, in that they reveal tunable electrical effects of film thickness and domain walls that are as large as the highest seen for ferromagnets.
Artificial chemical and magnetic structure at the domain walls of an epitaxial oxide.
Farokhipoor, S; Magén, C; Venkatesan, S; Íñiguez, J; Daumont, C J M; Rubi, D; Snoeck, E; Mostovoy, M; de Graaf, C; Müller, A; Döblinger, M; Scheu, C; Noheda, B
2014-11-20
Progress in nanotechnology requires new approaches to materials synthesis that make it possible to control material functionality down to the smallest scales. An objective of materials research is to achieve enhanced control over the physical properties of materials such as ferromagnets, ferroelectrics and superconductors. In this context, complex oxides and inorganic perovskites are attractive because slight adjustments of their atomic structures can produce large physical responses and result in multiple functionalities. In addition, these materials often contain ferroelastic domains. The intrinsic symmetry breaking that takes place at the domain walls can induce properties absent from the domains themselves, such as magnetic or ferroelectric order and other functionalities, as well as coupling between them. Moreover, large domain wall densities create intense strain gradients, which can also affect the material's properties. Here we show that, owing to large local stresses, domain walls can promote the formation of unusual phases. In this sense, the domain walls can function as nanoscale chemical reactors. We synthesize a two-dimensional ferromagnetic phase at the domain walls of the orthorhombic perovskite terbium manganite (TbMnO3), which was grown in thin layers under epitaxial strain on strontium titanate (SrTiO3) substrates. This phase is yet to be created by standard chemical routes. The density of the two-dimensional sheets can be tuned by changing the film thickness or the substrate lattice parameter (that is, the epitaxial strain), and the distance between sheets can be made as small as 5 nanometres in ultrathin films, such that the new phase at domain walls represents up to 25 per cent of the film volume. The general concept of using domain walls of epitaxial oxides to promote the formation of unusual phases may be applicable to other materials systems, thus giving access to new classes of nanoscale materials for applications in nanoelectronics and
Artificial chemical and magnetic structure at the domain walls of an epitaxial oxide
NASA Astrophysics Data System (ADS)
Farokhipoor, S.; Magén, C.; Venkatesan, S.; Íñiguez, J.; Daumont, C. J. M.; Rubi, D.; Snoeck, E.; Mostovoy, M.; de Graaf, C.; Müller, A.; Döblinger, M.; Scheu, C.; Noheda, B.
2014-11-01
Progress in nanotechnology requires new approaches to materials synthesis that make it possible to control material functionality down to the smallest scales. An objective of materials research is to achieve enhanced control over the physical properties of materials such as ferromagnets, ferroelectrics and superconductors. In this context, complex oxides and inorganic perovskites are attractive because slight adjustments of their atomic structures can produce large physical responses and result in multiple functionalities. In addition, these materials often contain ferroelastic domains. The intrinsic symmetry breaking that takes place at the domain walls can induce properties absent from the domains themselves, such as magnetic or ferroelectric order and other functionalities, as well as coupling between them. Moreover, large domain wall densities create intense strain gradients, which can also affect the material's properties. Here we show that, owing to large local stresses, domain walls can promote the formation of unusual phases. In this sense, the domain walls can function as nanoscale chemical reactors. We synthesize a two-dimensional ferromagnetic phase at the domain walls of the orthorhombic perovskite terbium manganite (TbMnO3), which was grown in thin layers under epitaxial strain on strontium titanate (SrTiO3) substrates. This phase is yet to be created by standard chemical routes. The density of the two-dimensional sheets can be tuned by changing the film thickness or the substrate lattice parameter (that is, the epitaxial strain), and the distance between sheets can be made as small as 5 nanometres in ultrathin films, such that the new phase at domain walls represents up to 25 per cent of the film volume. The general concept of using domain walls of epitaxial oxides to promote the formation of unusual phases may be applicable to other materials systems, thus giving access to new classes of nanoscale materials for applications in nanoelectronics and
Domain wall pinning in FeCoCu bamboo-like nanowires
NASA Astrophysics Data System (ADS)
Berganza, Eider; Bran, Cristina; Jaafar, Miriam; Vázquez, Manuel; Asenjo, Agustina
2016-07-01
The three dimensional nature of cylindrical magnetic nanowires has opened a new way to control the domain configuration as well as the magnetization reversal process. The pinning effect of the periodic diameter modulations on the domain wall propagation in FeCoCu individual nanowires is determined by Magnetic Force Microscopy, MFM. A main bistable magnetic configuration is firstly concluded from MFM images characterized by the spin reversal between two nearly single domain states with opposite axial magnetization. Complementary micromagnetic simulations confirm a vortex mediated magnetization reversal process. A non-standard variable field MFM imaging procedure allows us to observe metastable magnetic states where the propagating domain wall is pinned at certain positions with enlarged diameter. Moreover, it is demonstrated that it is possible to control the position of the pinned domain walls by an external magnetic field.
Domain wall pinning in FeCoCu bamboo-like nanowires.
Berganza, Eider; Bran, Cristina; Jaafar, Miriam; Vázquez, Manuel; Asenjo, Agustina
2016-01-01
The three dimensional nature of cylindrical magnetic nanowires has opened a new way to control the domain configuration as well as the magnetization reversal process. The pinning effect of the periodic diameter modulations on the domain wall propagation in FeCoCu individual nanowires is determined by Magnetic Force Microscopy, MFM. A main bistable magnetic configuration is firstly concluded from MFM images characterized by the spin reversal between two nearly single domain states with opposite axial magnetization. Complementary micromagnetic simulations confirm a vortex mediated magnetization reversal process. A non-standard variable field MFM imaging procedure allows us to observe metastable magnetic states where the propagating domain wall is pinned at certain positions with enlarged diameter. Moreover, it is demonstrated that it is possible to control the position of the pinned domain walls by an external magnetic field. PMID:27406891
Domain wall pinning in FeCoCu bamboo-like nanowires.
Berganza, Eider; Bran, Cristina; Jaafar, Miriam; Vázquez, Manuel; Asenjo, Agustina
2016-07-11
The three dimensional nature of cylindrical magnetic nanowires has opened a new way to control the domain configuration as well as the magnetization reversal process. The pinning effect of the periodic diameter modulations on the domain wall propagation in FeCoCu individual nanowires is determined by Magnetic Force Microscopy, MFM. A main bistable magnetic configuration is firstly concluded from MFM images characterized by the spin reversal between two nearly single domain states with opposite axial magnetization. Complementary micromagnetic simulations confirm a vortex mediated magnetization reversal process. A non-standard variable field MFM imaging procedure allows us to observe metastable magnetic states where the propagating domain wall is pinned at certain positions with enlarged diameter. Moreover, it is demonstrated that it is possible to control the position of the pinned domain walls by an external magnetic field.
Domain wall pinning in FeCoCu bamboo-like nanowires
Berganza, Eider; Bran, Cristina; Jaafar, Miriam; Vázquez, Manuel; Asenjo, Agustina
2016-01-01
The three dimensional nature of cylindrical magnetic nanowires has opened a new way to control the domain configuration as well as the magnetization reversal process. The pinning effect of the periodic diameter modulations on the domain wall propagation in FeCoCu individual nanowires is determined by Magnetic Force Microscopy, MFM. A main bistable magnetic configuration is firstly concluded from MFM images characterized by the spin reversal between two nearly single domain states with opposite axial magnetization. Complementary micromagnetic simulations confirm a vortex mediated magnetization reversal process. A non-standard variable field MFM imaging procedure allows us to observe metastable magnetic states where the propagating domain wall is pinned at certain positions with enlarged diameter. Moreover, it is demonstrated that it is possible to control the position of the pinned domain walls by an external magnetic field. PMID:27406891
Direct imaging of domain wall interactions in Ni80Fe20 planar nanowires
Hayward, T. J.; Bryan, M. T.; Fry, P. W.; Fundi, P. M.; Gibbs, M. R. J.; Allwood, D. A.; Im, M.-Y.; Fischer, P.
2010-01-18
We have investigated magnetostatic interactions between domain walls in Ni{sub 80}Fe{sub 20} planar nanowires using magnetic soft x-ray microscopy and micromagnetic simulations. In addition to significant monopole-like attraction and repulsion effects we observe that there is coupling of the magnetization configurations of the walls. This is explained in terms of an interaction energy that depends not only on the distance between the walls, but also upon their internal magnetization structure.
Pirro, P.; Sebastian, T.; Leven, B.; Hillebrands, B.; Koyama, T.; Brächer, T.
2015-06-08
The interaction of propagating dipolar spin waves with magnetic domain walls is investigated in square-shaped microstructures patterned from the Heusler compound Co{sub 2}Mn{sub 0.6}Fe{sub 0.4}Si. Using magnetic force microscopy, the reversible preparation of a Landau state with four magnetic domains separated by Néel domain walls is confirmed. A local spin-wave excitation using a microstructured antenna is realized in one of the domains. It is shown by Brillouin light scattering microscopy that the domain structure in the remanence state has a strong influence on the spin-wave excitation and propagation. The domain walls strongly reflect the spin waves and can be used as spin-wave reflectors. A comparison with micromagnetic simulations shows that the strong reflection is due to the long-range dipolar interaction which has important implications for the use of these spin waves for exerting an all-magnonic spin-transfer torque.
Movement of magnetic domain walls induced by single femtosecond laser pulses
NASA Astrophysics Data System (ADS)
Sandig, O.; Shokr, Y. A.; Vogel, J.; Valencia, S.; Kronast, F.; Kuch, W.
2016-08-01
We present a microscopic investigation of how the magnetic domain structure in ultrathin films changes after direct excitation by single ultrashort laser pulses. Using photoelectron emission microscopy in combination with x-ray magnetic circular dichroism in the resonant absorption of soft x rays, we find that individual laser pulses of ≈60 fs duration and a central wavelength of 800 nm lead to clear changes in the domain structure of a Co layer of three atomic monolayers thickness in an epitaxial Co/Cu/Ni trilayer on a Cu(001) single-crystal substrate. A relatively small enhancement of the sample base temperature by 40 K is sufficient to lower the threshold of laser fluence for domain wall motion by about a factor of two. Pump-probe measurements with a laser fluence just below this threshold indicate that the laser-induced demagnetization of the sample is far from complete in these experiments. Although the domain wall motion appears similar to thermal domain wall fluctuations, quantitatively it cannot be explained by pure thermal activation of domain wall motion by the transient rise of sample temperature after the laser pulse, but it is likely to be triggered by a laser-induced depinning of domain walls.
Shevchenko, A B; Barabash, M Yu
2015-12-01
It is shown that at low temperatures, quantum oscillations of nanoscale structural inhomogeneities (the vertical Bloch line and the Bloch point) occur in the domain walls of cylindrical magnetic domains formed in a uniaxial magnetic film with strong magnetic anisotropy. The conditions for the excitation of these oscillations are determined.
Time Variation of the Fine Structure Constant in the Spacetime of a Cosmic Domain Wall
NASA Astrophysics Data System (ADS)
Campanelli, L.; Cea, P.; Tedesco, L.
The gravitational field produced by a domain wall acts as a medium with spacetime-dependent permittivity ɛ. Therefore, the fine structure constant α=e2/4πɛ will be a time-dependent function at fixed position. The most stringent constraint on the time-variation of α comes from the natural reactor Oklo and gives |˙ α /α | < few × 10-17 yr-1. This limit constrains the tension of a cosmic domain wall to be less than σ ≲ 10-2 MeV3, and then represents the most severe limit on the energy density of a cosmic wall stretching our Universe.
Interaction Energy of Domain Walls in a Nonlocal Ginzburg-Landau Type Model from Micromagnetics
NASA Astrophysics Data System (ADS)
Ignat, Radu; Moser, Roger
2016-07-01
We study a variational model from micromagnetics involving a nonlocal Ginzburg-Landau type energy for {S1}-valued vector fields. These vector fields form domain walls, called Néel walls, that correspond to one-dimensional transitions between two directions within the unit circle {S1}. Due to the nonlocality of the energy, a Néel wall is a two length scale object, comprising a core and two logarithmically decaying tails. Our aim is to determine the energy differences leading to repulsion or attraction between Néel walls. In contrast to the usual Ginzburg-Landau vortices, we obtain a renormalised energy for Néel walls that shows both a tail-tail interaction and a core-tail interaction. This is a novel feature for Ginzburg-Landau type energies that entails attraction between Néel walls of the same sign and repulsion between Néel walls of opposite signs.
Controlled creation and displacement of charged domain walls in ferroelectric thin films.
Feigl, L; Sluka, T; McGilly, L J; Crassous, A; Sandu, C S; Setter, N
2016-08-10
Charged domain walls in ferroelectric materials are of high interest due to their potential use in nanoelectronic devices. While previous approaches have utilized complex scanning probe techniques or frustrative poling here we show the creation of charged domain walls in ferroelectric thin films during simple polarization switching using either a conductive probe tip or patterned top electrodes. We demonstrate that ferroelectric switching is accompanied - without exception - by the appearance of charged domain walls and that these walls can be displaced and erased reliably. We ascertain from a combination of scanning probe microscopy, transmission electron microscopy and phase field simulations that creation of charged domain walls is a by-product of, and as such is always coupled to, ferroelectric switching. This is due to the (110) orientation of the tetragonal (Pb,Sr)TiO3 thin films and the crucial role played by the limited conduction of the LSMO bottom electrode layer used in this study. This work highlights that charged domain walls, far from being exotic, unstable structures, as might have been assumed previously, can be robust, stable easily-controlled features in ferroelectric thin films.
Controlled creation and displacement of charged domain walls in ferroelectric thin films
Feigl, L.; Sluka, T.; McGilly, L. J.; Crassous, A.; Sandu, C. S.; Setter, N.
2016-01-01
Charged domain walls in ferroelectric materials are of high interest due to their potential use in nanoelectronic devices. While previous approaches have utilized complex scanning probe techniques or frustrative poling here we show the creation of charged domain walls in ferroelectric thin films during simple polarization switching using either a conductive probe tip or patterned top electrodes. We demonstrate that ferroelectric switching is accompanied - without exception - by the appearance of charged domain walls and that these walls can be displaced and erased reliably. We ascertain from a combination of scanning probe microscopy, transmission electron microscopy and phase field simulations that creation of charged domain walls is a by-product of, and as such is always coupled to, ferroelectric switching. This is due to the (110) orientation of the tetragonal (Pb,Sr)TiO3 thin films and the crucial role played by the limited conduction of the LSMO bottom electrode layer used in this study. This work highlights that charged domain walls, far from being exotic, unstable structures, as might have been assumed previously, can be robust, stable easily-controlled features in ferroelectric thin films. PMID:27507433
Controlled creation and displacement of charged domain walls in ferroelectric thin films
NASA Astrophysics Data System (ADS)
Feigl, L.; Sluka, T.; McGilly, L. J.; Crassous, A.; Sandu, C. S.; Setter, N.
2016-08-01
Charged domain walls in ferroelectric materials are of high interest due to their potential use in nanoelectronic devices. While previous approaches have utilized complex scanning probe techniques or frustrative poling here we show the creation of charged domain walls in ferroelectric thin films during simple polarization switching using either a conductive probe tip or patterned top electrodes. We demonstrate that ferroelectric switching is accompanied - without exception - by the appearance of charged domain walls and that these walls can be displaced and erased reliably. We ascertain from a combination of scanning probe microscopy, transmission electron microscopy and phase field simulations that creation of charged domain walls is a by-product of, and as such is always coupled to, ferroelectric switching. This is due to the (110) orientation of the tetragonal (Pb,Sr)TiO3 thin films and the crucial role played by the limited conduction of the LSMO bottom electrode layer used in this study. This work highlights that charged domain walls, far from being exotic, unstable structures, as might have been assumed previously, can be robust, stable easily-controlled features in ferroelectric thin films.
Controlled creation and displacement of charged domain walls in ferroelectric thin films.
Feigl, L; Sluka, T; McGilly, L J; Crassous, A; Sandu, C S; Setter, N
2016-01-01
Charged domain walls in ferroelectric materials are of high interest due to their potential use in nanoelectronic devices. While previous approaches have utilized complex scanning probe techniques or frustrative poling here we show the creation of charged domain walls in ferroelectric thin films during simple polarization switching using either a conductive probe tip or patterned top electrodes. We demonstrate that ferroelectric switching is accompanied - without exception - by the appearance of charged domain walls and that these walls can be displaced and erased reliably. We ascertain from a combination of scanning probe microscopy, transmission electron microscopy and phase field simulations that creation of charged domain walls is a by-product of, and as such is always coupled to, ferroelectric switching. This is due to the (110) orientation of the tetragonal (Pb,Sr)TiO3 thin films and the crucial role played by the limited conduction of the LSMO bottom electrode layer used in this study. This work highlights that charged domain walls, far from being exotic, unstable structures, as might have been assumed previously, can be robust, stable easily-controlled features in ferroelectric thin films. PMID:27507433
In situ atom scale visualization of domain wall dynamics in VO2 insulator-metal phase transition.
He, Xinfeng; Xu, Tao; Xu, Xiaofeng; Zeng, Yijie; Xu, Jing; Sun, Litao; Wang, Chunrui; Xing, Huaizhong; Wu, Binhe; Lu, Aijiang; Liu, Dingquan; Chen, Xiaoshuang; Chu, Junhao
2014-10-08
A domain wall, as a device, can bring about a revolution in developing manipulation of semiconductor heterostructures devices at the atom scale. However, it is a challenge for these new devices to control domain wall motion through insulator-metal transition of correlated-electron materials. To fully understand and harness this motion, it requires visualization of domain wall dynamics in real space. Here, domain wall dynamics in VO2 insulator-metal phase transition was observed directly by in situ TEM at atom scale. Experimental results depict atom scale evolution of domain morphologies and domain wall exact positions in (202) and (040) planes referring to rutile structure at 50°C. In addition, microscopic mechanism of domain wall dynamics and accurate lattice basis vector relationship of two domains were investigated with the assistance of X-ray diffraction, ab initio calculations and image simulations. This work offers a route to atom scale tunable heterostructure device application.
In Situ Atom Scale Visualization of Domain Wall Dynamics in VO2 Insulator-Metal Phase Transition
He, Xinfeng; Xu, Tao; Xu, Xiaofeng; Zeng, Yijie; Xu, Jing; Sun, Litao; Wang, Chunrui; Xing, Huaizhong; Wu, Binhe; Lu, Aijiang; Liu, Dingquan; Chen, Xiaoshuang; Chu, Junhao
2014-01-01
A domain wall, as a device, can bring about a revolution in developing manipulation of semiconductor heterostructures devices at the atom scale. However, it is a challenge for these new devices to control domain wall motion through insulator-metal transition of correlated-electron materials. To fully understand and harness this motion, it requires visualization of domain wall dynamics in real space. Here, domain wall dynamics in VO2 insulator-metal phase transition was observed directly by in situ TEM at atom scale. Experimental results depict atom scale evolution of domain morphologies and domain wall exact positions in (202) and (040) planes referring to rutile structure at 50°C. In addition, microscopic mechanism of domain wall dynamics and accurate lattice basis vector relationship of two domains were investigated with the assistance of X-ray diffraction, ab initio calculations and image simulations. This work offers a route to atom scale tunable heterostructure device application. PMID:25292447
Simulations of super-structure domain walls in two dimensional assemblies of magnetic nanoparticles
Jordanovic, J.; Frandsen, C.; Beleggia, M.; Schiøtz, J.
2015-07-28
We simulate the formation of domain walls in two-dimensional assemblies of magnetic nanoparticles. Particle parameters are chosen to match recent electron holography and Lorentz microscopy studies of almost monodisperse cobalt nanoparticles assembled into regular, elongated lattices. As the particles are small enough to consist of a single magnetic domain each, their magnetic interactions can be described by a spin model in which each particle is assigned a macroscopic “superspin.” Thus, the magnetic behaviour of these lattices may be compared to magnetic crystals with nanoparticle superspins taking the role of the atomic spins. The coupling is, however, different. The superspins interact only by dipolar interactions as exchange coupling between individual nanoparticles may be neglected due to interparticle spacing. We observe that it is energetically favorable to introduce domain walls oriented along the long dimension of nanoparticle assemblies rather than along the short dimension. This is unlike what is typically observed in continuous magnetic materials, where the exchange interaction introduces an energetic cost proportional to the area of the domain walls. Structural disorder, which will always be present in realistic assemblies, pins longitudinal domain walls when the external field is reversed, and makes a gradual reversal of the magnetization by migration of longitudinal domain walls possible, in agreement with previous experimental results.
Correlated polarization switching in the proximity of a 180 degrees domain wall
Aravind, Vasudeva Rao; Morozovska, A. N.; Bhattacharya, S.; Lee, Dongwa; Jesse, Stephen; Grinberg, I; Li, Y L; Choudhury, S; Wu, P; Seal, Katyayani; Rappe, Andrew M; Rar, Andrei; Svechnikov, S. V.; Eliseev, Eugene; Phillpot, S. R.; Chen, L. Q.; Gopalana, V.; Kalinin, Sergei V
2010-01-01
Domain-wall dynamics in ferroic materials underpins functionality of data storage and information technology devices. Using localized electric field of a scanning probe microscopy tip, we experimentally demonstrate a surprisingly rich range of polarization reversal behaviors in the vicinity of the initially flat 180 degrees ferroelectric domain wall. The nucleation bias is found to increase by an order of magnitude from a two-dimensional (2D) nucleus at the wall to three-dimensional nucleus in the bulk. The wall is thus significantly ferroelectrically softer than the bulk. The wall profoundly affects switching on length scales on the order of micrometers. The mechanism of correlated switching is analyzed using analytical theory and phase-field modeling. The long-range effect is ascribed to wall bending under the influence of a tip with bias that is well below the bulk nucleation level at large distances from the wall. These studies provide an experimental link between the macroscopic and mesoscopic physics of domain walls in ferroelectrics and atomistic models of 2D nucleation.
Evolution of domain walls in the early universe. Ph.D. Thesis - Chicago Univ.
NASA Technical Reports Server (NTRS)
Kawano, Lawrence
1989-01-01
The evolution of domain walls in the early universe is studied via 2-D computer simulation. The walls are initially configured on a triangular lattice and then released from the lattice, their evolution driven by wall curvature and by the universal expansion. The walls attain an average velocity of about 0.3c and their surface area per volume (as measured in comoving coordinates) goes down with a slope of -1 with respect to conformal time, regardless of whether the universe is matter or radiation dominated. The additional influence of vacuum pressure causes the energy density to fall away from this slope and steepen, thus allowing a situation in which domain walls can constitute a significant portion of the energy density of the universe without provoking an unacceptably large perturbation upon the microwave background.
All-in-all-out magnetic domain wall conduction in a pyrochlore iridate heterointerface
NASA Astrophysics Data System (ADS)
Fujita, T. C.; Uchida, M.; Kozuka, Y.; Sano, W.; Tsukazaki, A.; Arima, T.; Kawasaki, M.
2016-02-01
Pyrochlore oxides possessing "all-in-all-out" spin ordering have attracted burgeoning interest as a rich ground of emergent states. This ordering has two distinct types of magnetic domains (all-in-all-out or all-out-all-in) with broken time-reversal symmetry, and a nontrivial metallic surface state has been theoretically demonstrated to appear at their domain wall. Here, we report on the observation of this metallic conduction at the single all-in-all-out/all-out-all-in magnetic domain wall formed at the heterointerface of two pyrochlore iridates. By utilizing the different magnetoresponses of them with different lanthanide ions, the domain wall is controllably inserted at the heterointerface, the surface state being detected as an anomalous conduction enhancement with a ferroic hysteresis. Our establishment paves the way for further investigation and manipulation of this new type of surface transport.
Schaab, J.; Meier, D.; Krug, I. P.; Nickel, F.; Gottlob, D. M.; Doğanay, H.; Schneider, C. M.; Cano, A.; Hentschel, M.; Yan, Z.; Bourret, E.; Ramesh, R.
2014-06-09
High-resolution X-ray photoemission electron microscopy (X-PEEM) is a well-established method for imaging ferroelectric domain structures. Here, we expand the scope of application of X-PEEM and demonstrate its capability for imaging and investigating domain walls in ferroelectrics with high spatial resolution. Using ErMnO{sub 3} as test system, we show that ferroelectric domain walls can be visualized based on photo-induced charging effects and local variations in their electronic conductance can be mapped by analyzing the energy distribution of photoelectrons. Our results open the door for non-destructive, contact-free, and element-specific studies of the electronic and chemical structure at domain walls in ferroelectrics.
Inertia-Free Thermally Driven Domain-Wall Motion in Antiferromagnets
NASA Astrophysics Data System (ADS)
Selzer, Severin; Atxitia, Unai; Ritzmann, Ulrike; Hinzke, Denise; Nowak, Ulrich
2016-09-01
Domain-wall motion in antiferromagnets triggered by thermally induced magnonic spin currents is studied theoretically. It is shown by numerical calculations based on a classical spin model that the wall moves towards the hotter regions, as in ferromagnets. However, for larger driving forces the so-called Walker breakdown—which usually speeds down the wall—is missing. This is due to the fact that the wall is not tilted during its motion. For the same reason antiferromagnetic walls have no inertia and, hence, no acceleration phase leading to higher effective mobility.
Suppression of stochastic pinning in magnetic nanowire devices using “virtual” domain walls
Hodges, M. P. P.; Hayward, T. J.; Bryan, M. T.; Fry, P. W.; Im, M.-Y.; Fischer, P.
2014-09-28
We have investigated the pinning and depinning of “virtual” domain walls in planar magnetic nanowires. Such virtual walls are created when a conventional domain wall becomes annihilated at a narrow gap between two segments of a discontinuous nanowire. By using focused magneto-optical Kerr effect magnetometry to study the repeatability of their depinning, we show that virtual walls exhibit single-mode depinning distributions, characterized by remarkably low, sub-Oersted standard deviations. This is in stark contrast to the depinning of domain walls from conventional notch-shaped defects, which typically exhibit multi-mode depinning field distributions spanning tens to hundreds of Oersteds. High-resolution magnetic soft x-ray microscopy measurements are used to reveal that this high level of repeatability is the result of a simple mediated-nucleation process, which decouples the depinning mechanism from structure of the initially injected DWs. Our work serves as an example of how the complex and dynamical stochastic behaviors exhibited by domain walls in nanowires can be controlled.
Modulation of domain wall dynamics in TbFeCo single layer nanowire
NASA Astrophysics Data System (ADS)
Ngo, Duc-The; Ikeda, Kotaro; Awano, Hiroyuki
2012-04-01
We demonstrate the possibility to write and modulate the magnetic domain walls in a TbFeCo single layer nanowire (300 nm width, 150 μm length). To realize this, a tiny magnetic domain was nucleated by an Oersted field produced by a 1.6 MHz pulse current (35 mA in amplitude, 5-40 ns in length) crossed the wire. To write the wall to the wire, a DC current was used to drive the nucleated domain (with two walls in two sides) to the wire in accordance with spin-transfer torque mechanism. A critical current density of Jc = 3.5 × 1010 Am-2 was required to control the motion of the walls in the wire. It was found that the size of the domain moving in the wire could be adjusted by either external field or the length of the nucleated pulse current. This could be considered as an important note for writing process in domain wall spin-torque devices, especially, memory elements.
Proposal for a Domain Wall Nano-Oscillator driven by Non-uniform Spin Currents
NASA Astrophysics Data System (ADS)
Sharma, Sanchar; Muralidharan, Bhaskaran; Tulapurkar, Ashwin
2015-09-01
We propose a new mechanism and a related device concept for a robust, magnetic field tunable radio-frequency (rf) oscillator using the self oscillation of a magnetic domain wall subject to a uniform static magnetic field and a spatially non-uniform vertical dc spin current. The self oscillation of the domain wall is created as it translates periodically between two unstable positions, one being in the region where both the dc spin current and the magnetic field are present, and the other, being where only the magnetic field is present. The vertical dc spin current pushes it away from one unstable position while the magnetic field pushes it away from the other. We show that such oscillations are stable under noise and can exhibit a quality factor of over 1000. A domain wall under dynamic translation, not only being a source for rich physics, is also a promising candidate for advancements in nanoelectronics with the actively researched racetrack memory architecture, digital and analog switching paradigms as candidate examples. Devising a stable rf oscillator using a domain wall is hence another step towards the realization of an all domain wall logic scheme.
Current-induced domain wall motion in permalloy nanowires with a rectangular cross-section
Ai, J. H.; Miao, B. F.; Sun, L.; You, B.; Hu, An; Ding, H. F.
2011-11-01
We performed micromagnetic simulations of the current-induced domain wall motion in permalloy nanowires with rectangular cross-section. In the absence of the nonadiabatic spin-transfer term, a threshold current, J{sub c} is required to drive the domain wall moving continuously. We find that J{sub c} is proportional to the maximum cross product of the demagnetization field and magnetization orientation of the domain wall and the domain wall width. With varying both the wire thickness and width, a minimum threshold current in the order of 10{sup 6} A/cm{sup 2} is obtained when the thickness is equivalent to the wire width. With the nonadiabatic spin-transfer term, the calculated domain wall velocity {nu} equals to the adiabatic spin transfer velocity u when the current is far above the Walker limit J{sub w}. Below J{sub w}, {nu}=({beta}/{alpha})u, where {beta} is the nonadiabatic parameter and {alpha} is the damping factor. For different {beta}, we find the Walker limit can be scaled as J{sub w}=({alpha}/{beta}-{alpha})J{sub c}. Our simulations agree well with the one dimensional analytical calculation, suggesting the findings are the general behaviors of the systems in this particular geometry.
Proposal for a Domain Wall Nano-Oscillator driven by Non-uniform Spin Currents
Sharma, Sanchar; Muralidharan, Bhaskaran; Tulapurkar, Ashwin
2015-01-01
We propose a new mechanism and a related device concept for a robust, magnetic field tunable radio-frequency (rf) oscillator using the self oscillation of a magnetic domain wall subject to a uniform static magnetic field and a spatially non-uniform vertical dc spin current. The self oscillation of the domain wall is created as it translates periodically between two unstable positions, one being in the region where both the dc spin current and the magnetic field are present, and the other, being where only the magnetic field is present. The vertical dc spin current pushes it away from one unstable position while the magnetic field pushes it away from the other. We show that such oscillations are stable under noise and can exhibit a quality factor of over 1000. A domain wall under dynamic translation, not only being a source for rich physics, is also a promising candidate for advancements in nanoelectronics with the actively researched racetrack memory architecture, digital and analog switching paradigms as candidate examples. Devising a stable rf oscillator using a domain wall is hence another step towards the realization of an all domain wall logic scheme. PMID:26420544
A compact model of domain wall propagation for logic and memory design
NASA Astrophysics Data System (ADS)
Zhao, W. S.; Duval, J.; Ravelosona, D.; Klein, J.-O.; Kim, J. V.; Chappert, C.
2011-04-01
Current-driven domain wall motion is very promising for low-power, high-density, and high-speed circuits. By combining this shifting scheme with magnetic tunnel junction (MTJ) for reading and writing processes, it opens new routes for nonvolatile logic and memory applications that are crucial for the future of spintronics. This paper reports on a compact model for domain wall-MTJ-based circuit design, simulation, and evaluation. It integrates spin transfer torque mechanism for magnetization reversal and domain wall nucleation, current-driven domain wall pinning/motion behaviors, and tunnel resistance theory of MTJ nanopillar, in which the free layer is one storage element of magnetic stripe. This model is programmed with a very flexible structure to achieve the best simulation precision and efficiency, and provide easy parameter configuration interface. It is compatible with classical computer-aided design environment and can be cosimulated directly with CMOS design kits. By using the compact model, we have successfully simulated a domain wall propagation shift register.
Detection of ferromagnetic domain wall pinning and depinning with a semiconductor device
Malec, Chris E.; Bennett, Brian R.; Johnson, Mark B.
2015-12-21
We demonstrate the detection of a ferromagnetic domain wall using a nanoscale Hall cross. A narrow permalloy wire is defined lithographically on top of a Hall cross fabricated from an InAs quantum well. The width of the Hall cross (500 nm–1 μm) is similar to the width of the ferromagnetic wire (200–500 nm), and a geometric pinning site is fabricated in the ferromagnetic wire to trap a domain wall within the area of the Hall cross. The devices provide a signal that is often the same order of magnitude as the offset Hall voltage when a domain wall is located above the Hall cross, and may be useful for memory applications. Different geometries for the Hall cross and ferromagnetic wire are tested, and radiofrequency pulses are sent into the wire to demonstrate current driven domain wall motion. Further changes to the Hall bar geometry with respect to the wire geometry are investigated by numerical computation. A large gain in signal is seen for Hall bars only slightly wider than the ferromagnetic wires as compared to those twice as wide, as well as a larger sensitivity to the exact position of the domain wall with respect to the center of the Hall cross.
Chiba, D; Kawaguchi, M; Fukami, S; Ishiwata, N; Shimamura, K; Kobayashi, K; Ono, T
2012-06-06
Controlling the displacement of a magnetic domain wall is potentially useful for information processing in magnetic non-volatile memories and logic devices. A magnetic domain wall can be moved by applying an external magnetic field and/or electric current, and its velocity depends on their magnitudes. Here we show that the applying an electric field can change the velocity of a magnetic domain wall significantly. A field-effect device, consisting of a top-gate electrode, a dielectric insulator layer, and a wire-shaped ferromagnetic Co/Pt thin layer with perpendicular anisotropy, was used to observe it in a finite magnetic field. We found that the application of the electric fields in the range of ± 2-3 MV cm(-1) can change the magnetic domain wall velocity in its creep regime (10(6)-10(3) m s(-1)) by more than an order of magnitude. This significant change is due to electrical modulation of the energy barrier for the magnetic domain wall motion.
NASA Astrophysics Data System (ADS)
Mokrý, Pavel; Sluka, Tomáš
2016-02-01
The motion of ferroelectric domain walls greatly contributes to the macroscopic dielectric and piezoelectric response of ferroelectric materials. The domain-wall motion through the ferroelectric material is, however, hindered by pinning on crystal defects, which substantially reduces these contributions. Here, using thermodynamic models based on the Landau-Ginzburg-Devonshire theory, we find a relation between the microscopic reversible motion of nonferroelastic 180∘ domain walls interacting with a periodic array of pinning centers and the nonlinear macroscopic permittivity. We show that the reversible motion of domain walls can be split into two basic modes: first, the bending of a domain wall between pinning centers, and, second, the uniform movement of the domain-wall plane. We show that their respective contributions may change when the distribution of pinning centers is rearranged during the material aging. We demonstrate that it is possible to indicate which mechanism of the domain-wall motion is affected during material aging. This allows one to judge whether the defects only homogeneously accumulate at domain walls or prefer to align in certain directions inside the domain-wall plane. We suggest that this information can be obtained using simple macroscopic dielectric measurements and a proper analysis of the nonlinear response. Our results may therefore serve as a simple and useful tool to obtain details on domain-wall pinning in an aging process.
Néel-like domain walls in ferroelectric Pb(Zr,Ti)O3 single crystals
Wei, Xian-Kui; Jia, Chun-Lin; Sluka, Tomas; Wang, Bi-Xia; Ye, Zuo-Guang; Setter, Nava
2016-01-01
In contrast to the flexible rotation of magnetization direction in ferromagnets, the spontaneous polarization in ferroelectric materials is highly confined along the symmetry-allowed directions. Accordingly, chirality at ferroelectric domain walls was treated only at the theoretical level and its real appearance is still a mystery. Here we report a Néel-like domain wall imaged by atom-resolved transmission electron microscopy in Ti-rich ferroelectric Pb(Zr1−xTix)O3 crystals, where nanometre-scale monoclinic order coexists with the tetragonal order. The formation of such domain walls is interpreted in the light of polarization discontinuity and clamping effects at phase boundaries between the nesting domains. Phase-field simulation confirms that the coexistence of both phases as encountered near the morphotropic phase boundary promotes the polarization to rotate in a continuous manner. Our results provide a further insight into the complex domain configuration in ferroelectrics, and establish a foundation towards exploring chiral domain walls in ferroelectrics. PMID:27539075
Néel-like domain walls in ferroelectric Pb(Zr,Ti)O3 single crystals
NASA Astrophysics Data System (ADS)
Wei, Xian-Kui; Jia, Chun-Lin; Sluka, Tomas; Wang, Bi-Xia; Ye, Zuo-Guang; Setter, Nava
2016-08-01
In contrast to the flexible rotation of magnetization direction in ferromagnets, the spontaneous polarization in ferroelectric materials is highly confined along the symmetry-allowed directions. Accordingly, chirality at ferroelectric domain walls was treated only at the theoretical level and its real appearance is still a mystery. Here we report a Néel-like domain wall imaged by atom-resolved transmission electron microscopy in Ti-rich ferroelectric Pb(Zr1-xTix)O3 crystals, where nanometre-scale monoclinic order coexists with the tetragonal order. The formation of such domain walls is interpreted in the light of polarization discontinuity and clamping effects at phase boundaries between the nesting domains. Phase-field simulation confirms that the coexistence of both phases as encountered near the morphotropic phase boundary promotes the polarization to rotate in a continuous manner. Our results provide a further insight into the complex domain configuration in ferroelectrics, and establish a foundation towards exploring chiral domain walls in ferroelectrics.
Néel-like domain walls in ferroelectric Pb(Zr,Ti)O3 single crystals.
Wei, Xian-Kui; Jia, Chun-Lin; Sluka, Tomas; Wang, Bi-Xia; Ye, Zuo-Guang; Setter, Nava
2016-01-01
In contrast to the flexible rotation of magnetization direction in ferromagnets, the spontaneous polarization in ferroelectric materials is highly confined along the symmetry-allowed directions. Accordingly, chirality at ferroelectric domain walls was treated only at the theoretical level and its real appearance is still a mystery. Here we report a Néel-like domain wall imaged by atom-resolved transmission electron microscopy in Ti-rich ferroelectric Pb(Zr1-xTix)O3 crystals, where nanometre-scale monoclinic order coexists with the tetragonal order. The formation of such domain walls is interpreted in the light of polarization discontinuity and clamping effects at phase boundaries between the nesting domains. Phase-field simulation confirms that the coexistence of both phases as encountered near the morphotropic phase boundary promotes the polarization to rotate in a continuous manner. Our results provide a further insight into the complex domain configuration in ferroelectrics, and establish a foundation towards exploring chiral domain walls in ferroelectrics. PMID:27539075
A Tunable Magnetic Domain Wall Conduit Regulating Nanoparticle Diffusion.
Tierno, Pietro; Johansen, Tom H; Sancho, José M
2016-08-10
We demonstrate a general and robust method to confine on a plane strongly diffusing nanoparticles in water by using size tunable magnetic channels. These virtual conduits are realized with pairs of movable Bloch walls located within an epitaxially grown ferrite garnet film. We show that once inside the magnetic conduit the particles experience an effective local parabolic potential in the transverse direction, while freely diffusing along the conduit. The stiffness of the magnetic potential is determined as a function of field amplitude that varies the width of the magnetic channel. Precise control of the degree of confinement is demonstrated by tuning the applied field. The magnetic conduit is then used to realize single files of nonpassing particles and to induce periodic condensation of an ensemble of particles into parallel stripes in a completely controllable and reversible manner.
A Tunable Magnetic Domain Wall Conduit Regulating Nanoparticle Diffusion.
Tierno, Pietro; Johansen, Tom H; Sancho, José M
2016-08-10
We demonstrate a general and robust method to confine on a plane strongly diffusing nanoparticles in water by using size tunable magnetic channels. These virtual conduits are realized with pairs of movable Bloch walls located within an epitaxially grown ferrite garnet film. We show that once inside the magnetic conduit the particles experience an effective local parabolic potential in the transverse direction, while freely diffusing along the conduit. The stiffness of the magnetic potential is determined as a function of field amplitude that varies the width of the magnetic channel. Precise control of the degree of confinement is demonstrated by tuning the applied field. The magnetic conduit is then used to realize single files of nonpassing particles and to induce periodic condensation of an ensemble of particles into parallel stripes in a completely controllable and reversible manner. PMID:27434042
NASA Astrophysics Data System (ADS)
Hoelbling, Christian; Zielinski, Christian
2016-07-01
We follow up on a suggestion by Adams and construct explicit domain wall fermion operators with staggered kernels. We compare different domain wall formulations, namely the standard construction as well as Boriçi's modified and Chiu's optimal construction, utilizing both Wilson and staggered kernels. In the process, we generalize the staggered kernels to arbitrary even dimensions and introduce both truncated and optimal staggered domain wall fermions. Some numerical investigations are carried out in the (1 +1 )-dimensional setting of the Schwinger model, where we explore spectral properties of the bulk, effective and overlap Dirac operators in the free-field case, on quenched thermalized gauge configurations and on smooth topological configurations. We compare different formulations using the effective mass, deviations from normality and violations of the Ginsparg-Wilson relation as measures of chirality.
Griggio, Flavio; Jesse, Stephen; Kumar, Amit; Ovchinnikov, Oleg S; Kim, H.; Jackson, T. N.; Damjanovic, Dragan; Kalinin, Sergei V; Trolier-Mckinstry, Susan E
2012-01-01
The role of long-range strain interactions on domain wall dynamics is explored through macroscopic and local measurements of nonlinear behavior in mechanically clamped and released polycrystalline lead zirconate-titanate (PZT) films. Released films show a dramatic change in the global dielectric nonlinearity and its frequency dependence as a function of mechanical clamping. Furthermore, we observe a transition from strong clustering of the nonlinear response for the clamped case to almost uniform nonlinearity for the released film. This behavior is ascribed to increased mobility of domain walls. These results suggest the dominant role of collective strain interactions mediated by the local and global mechanical boundary conditions on the domain wall dynamics. The work presented in this Letter demonstrates that measurements on clamped films may considerably underestimate the piezoelectric coefficients and coupling constants of released structures used in microelectromechanical systems, energy harvesting systems, and microrobots.
Highly asymmetric magnetic domain wall propagation due to coupling to a periodic pinning potential
NASA Astrophysics Data System (ADS)
Novak, R. L.; Metaxas, P. J.; Jamet, J.-P.; Weil, R.; Ferré, J.; Mougin, A.; Rohart, S.; Stamps, R. L.; Zermatten, P.-J.; Gaudin, G.; Baltz, V.; Rodmacq, B.
2015-06-01
Magneto-optical microscopy and magnetometry have been used to study magnetization reversal in an ultrathin magnetically soft (Pt/Co)2 ferromagnetic film coupled to an array of magnetically harder (Co/Pt)4 nanodots via a predominantly dipolar interaction across a 3 nm Pt spacer. This interaction generates a spatially periodic pinning potential for domain walls propagating through the continuous magnetic film. When reversing the applied field with respect to the static nanodot array magnetization orientation, strong asymmetries in the wall velocity and switching fields are observed. Asymmetric switching fields mean that hysteresis of the film is characterized by a large bias field of dipolar origin which is linked to the wall velocity asymmetry. This latter asymmetry, though large at low fields, vanishes at high fields where the domains become round and compact. A field-polarity-controlled transition from dendritic to compact faceted domain structures is also seen at intermediate fields and a model is proposed to interpret the transition.
NASA Astrophysics Data System (ADS)
Mathurin, Théo; Giordano, Stefano; Dusch, Yannick; Tiercelin, Nicolas; Pernod, Philippe; Preobrazhensky, Vladimir
2016-02-01
The motion of a ferromagnetic domain wall in nanodevices is usually induced by means of external magnetic fields or polarized currents. Here, we demonstrate the possibility to reversibly control the position of a Néel domain wall in a ferromagnetic nanostripe through a uniform mechanical stress. The latter is generated by an electro-active substrate combined with the nanostripe in a multiferroic heterostructure. We develop a model describing the magnetization distribution in the ferromagnetic material, properly taking into account the magnetoelectric coupling. Through its numerical implementation, we obtain the relationship between the electric field applied to the piezoelectric substrate and the position of the magnetic domain wall in the nanostripe. As an example, we analyze a structure composed of a PMN-PT substrate and a TbCo2/FeCo composite nanostripe.
Field-driven sense elements for chirality-dependent domain wall detection and storage
Bowden, S. R.; Unguris, J.
2013-12-14
A method for locally sensing and storing data of transverse domain wall chirality in planar nanowire logic and memory systems is presented. Patterned elements, in close proximity to the nanowires, respond to the asymmetry in the stray field from the domain wall to produce a chirality-dependent response. When a bias field is applied, a stray field-assisted reversal of the element magnetization results in a reversed remanent state, measurable by scanning electron microscopy with polarization analysis (SEMPA). The elements are designed as triangles with tips pointing toward the nanowire, allowing the shape anisotropy to be dominated by the base but having a portion with lower volume and lower energy barrier closest to the domain wall. Micromagnetic modeling assists in the design of the nanowire-triangle systems and experiments using SEMPA confirm the importance of aspect ratio and spacing given a constant bias field magnitude.
Stress-induced phase transition in ferroelectric domain walls of BaTiO3.
Stepkova, V; Marton, P; Hlinka, J
2012-05-30
The seminal paper by Zhirnov (1958 Zh. Eksp. Teor. Fiz. 35 1175-80) explained why the structure of domain walls in ferroelectrics and ferromagnets is drastically different. Here we show that the antiparallel ferroelectric walls in rhombohedral ferroelectric BaTiO(3) can be switched between the Ising-like state (typical for ferroelectrics) and a Bloch-like state (unusual for ferroelectric walls but typical for magnetic ones). Phase-field simulations using a Ginzburg-Landau-Devonshire model suggest that this symmetry-breaking transition can be induced by a compressive epitaxial stress. The strain-tunable chiral properties of these domain walls promise a range of novel phenomena in epitaxial ferroelectric thin films.
NASA Astrophysics Data System (ADS)
Garzarella, Anthony; Wu, Dong; Shinn, Mannix
Under small, externally-applied magnetic fields, the Faraday rotation in magneto-optic material containing ferromagnetic domains is driven primarily by two principal mechanisms: domain wall motion and coherent domain rotations. Domain wall motion yields a larger Faraday responsivity but is limited by magnetically induced optical incoherence and by damping effects. Coherent domain rotation yields smaller Faraday rotations, but exhibits a flatter and broader frequency response. The two mechanisms occur along orthogonal principal axes and may be probed independently. However, when probed along an oblique angle to the principal axes, the relationship between the Faraday rotation and the external field changes from linear to tensorial. Although this may lead to more complicated phenomena (e.g. a sensitivity axis that depends on RF frequency), the interplay of domain rotation and domain wall motion can be exploited to improve responsivity or bandwidth. The detailed experimental data can be understood in terms of a quantitative model for the magnitude and direction of the responsivity vector. Applications to magnetic field sensors based on arrayed bismuth doped iron garnet films will be emphasized in this presentation.
Magnetostatic dipolar domain-wall pinning in chains of permalloy triangular rings.
Vavassori, P.; Bisero, D.; Bonanni, V.; Busato, A.; Grimsditch, M.; Lebecki, K. M.; Metlushko, V.; Ilic, B.; Materials Science Division; CIC nanoGUNE Consolider; Univ. di Ferrara; CNR-INFM National Research Centre; Polish Academy of Science; Univ. of Illinois at Chicago; Cornell Univ.
2008-01-01
In a combined experimental and numerical study, we investigated the details of the motion and pinning of domain walls in isolated and interacting permalloy triangular rings (side 2 {micro}m, width 250 nm, and thickness 25 nm). To induce interaction between the rings, they were arranged either in vertical chains with an apex of each triangle in proximity to the edge center of the triangle above it or in horizontal chains where the proximity is between the adjacent corners of the triangles. Using longitudinal and diffraction magneto-optic Kerr effects, magnetic force microscopy, and micromagnetic simulations, we determined the field dependence of the spin structure in the rings. In all cases the remnant state of each ring is an 'onion' state characterized by two domain walls - one head to head the other tail to tail - pinned at the apexes. In isolated rings the magnetization reversal occurs between two onion states via the formation of an intermediate vortex state, which arises from the motion and annihilation of the two domain walls. In the case of the horizontal chains the reversal mechanism is unchanged except that the dipolar interaction affects the field range in which the rings are in the vortex state. In the case of vertical chains an additional intermediate state is observed during reversal. The new state involves a domain wall pinned at the center of the edge that is in close proximity to the apex of its neighbor. We show that the domain-wall motion in this last case can be modeled by a triple potential well. Because the new state requires that a domain wall be pinned at the neighboring apex, our observations can be viewed as a very elementary form of magnetic logic.
Highly mobile ferroelastic domain walls in compositionally graded ferroelectric thin films
Damodaran, Anoop; Okatan, M. B.; Kacher, J.; Gammer, C.; Vasudevan, Rama; Pandya, S.; Dedon, L. R.; Mangalam, R. V.; Jesse, Stephen; Balke, Nina; et al
2016-02-15
Domains and domain walls are critical in determining the response of ferroelectrics, and the ability to controllably create, annihilate, or move domains is essential to enable a range of next-generation devices. Whereas electric-field control has been demonstrated for ferroelectric 180° domain walls, similar control of ferroelastic domains has not been achieved. Here, using controlled composition and strain gradients, we demonstrate deterministic control of ferroelastic domains that are rendered highly mobile in a controlled and reversible manner. Through a combination of thin-film growth, transmission-electron-microscopy-based nanobeam diffraction and nanoscale band-excitation switching spectroscopy, we show that strain gradients in compositionally graded PbZr1-xTixO3 heterostructuresmore » stabilize needle-like ferroelastic domains that terminate inside the film. These needle-like domains are highly labile in the out-of-plane direction under applied electric fields, producing a locally enhanced piezoresponse. This work demonstrates the efficacy of novel modes of epitaxy in providing new modalities of domain engineering and potential for as-yet-unrealized nanoscale functional devices.« less
Highly mobile ferroelastic domain walls in compositionally graded ferroelectric thin films
NASA Astrophysics Data System (ADS)
Agar, J. C.; Damodaran, A. R.; Okatan, M. B.; Kacher, J.; Gammer, C.; Vasudevan, R. K.; Pandya, S.; Dedon, L. R.; Mangalam, R. V. K.; Velarde, G. A.; Jesse, S.; Balke, N.; Minor, A. M.; Kalinin, S. V.; Martin, L. W.
2016-05-01
Domains and domain walls are critical in determining the response of ferroelectrics, and the ability to controllably create, annihilate, or move domains is essential to enable a range of next-generation devices. Whereas electric-field control has been demonstrated for ferroelectric 180° domain walls, similar control of ferroelastic domains has not been achieved. Here, using controlled composition and strain gradients, we demonstrate deterministic control of ferroelastic domains that are rendered highly mobile in a controlled and reversible manner. Through a combination of thin-film growth, transmission-electron-microscopy-based nanobeam diffraction and nanoscale band-excitation switching spectroscopy, we show that strain gradients in compositionally graded PbZr1-xTixO3 heterostructures stabilize needle-like ferroelastic domains that terminate inside the film. These needle-like domains are highly labile in the out-of-plane direction under applied electric fields, producing a locally enhanced piezoresponse. This work demonstrates the efficacy of novel modes of epitaxy in providing new modalities of domain engineering and potential for as-yet-unrealized nanoscale functional devices.
NASA Astrophysics Data System (ADS)
Richter, Kornel; Krone, Andrea; Mawass, Mohamad-Assaad; Krüger, Benjamin; Weigand, Markus; Stoll, Hermann; Schütz, Gisela; Kläui, Mathias
2016-07-01
We report time-resolved observations of field-induced domain wall nucleation in asymmetric ferromagnetic rings using single direction field pulses and rotating fields. We show that the asymmetric geometry of a ring allows for controlling the position of nucleation events, when a domain wall is nucleated by a rotating magnetic field. Direct observation by scanning transmission x-ray microscopy (STXM) reveals that the nucleation of domain walls occurs through the creation of transient ripplelike structures. This magnetization state is found to exhibit a surprisingly high reproducibility even at room temperature and we determine the combinations of field strengths and field directions that allow for reliable nucleation of domain walls and directly quantify the stability of the magnetic states. Our analysis of the processes occurring during field induced domain wall nucleation shows how the effective fields determine the nucleation location reproducibly, which is a key prerequisite toward using domain walls for spintronic devices.
Spatially periodic domain wall pinning potentials: Asymmetric pinning and dipolar biasing
NASA Astrophysics Data System (ADS)
Metaxas, P. J.; Zermatten, P.-J.; Novak, R. L.; Rohart, S.; Jamet, J.-P.; Weil, R.; Ferré, J.; Mougin, A.; Stamps, R. L.; Gaudin, G.; Baltz, V.; Rodmacq, B.
2013-02-01
Domain wall propagation has been measured in continuous, weakly disordered, quasi-two-dimensional, Ising-like magnetic layers that are subject to spatially periodic domain wall pinning potentials. The potentials are generated non-destructively using the stray magnetic field of ordered arrays of magnetically hard [Co/Pt]m nanoplatelets, which are patterned above and are physically separated from the continuous magnetic layer. The effect of the periodic pinning potentials on thermally activated domain wall creep dynamics is shown to be equivalent, at first approximation, to that of a uniform, effective retardation field, Hret, which acts against the applied field, H. We show that Hret depends not only on the array geometry but also on the relative orientation of H and the magnetization of the nanoplatelets. A result of the latter dependence is that wall-mediated hysteresis loops obtained for a set nanoplatelet magnetization exhibit many properties that are normally associated with ferromagnet/antiferromagnet exchange bias systems. These include a switchable bias, coercivity enhancement, and domain wall roughness that is dependent on the applied field polarity.
Elementary depinning processes of magnetic domain walls under fields and currents.
Nguyen, V D; Torres, W Savero; Laczkowski, P; Marty, A; Jamet, M; Beigné, C; Notin, L; Vila, L; Attané, J P
2014-01-01
The probability laws associated to domain wall depinning under fields and currents have been studied in NiFe and FePt nanowires. Three basic domain wall depinning processes, associated to different potential landscapes, are found to appear identically in those systems with very different anisotropies. We show that these processes constitute the building blocks of any complex depinning mechanism. A Markovian analysis is proposed, that provides a unified picture of the depinning mechanism and an insight into the pinning potential landscape. PMID:25270773
Gravitational waves from domain walls in the next-to-minimal supersymmetric standard model
Kadota, Kenji; Kawasaki, Masahiro; Saikawa, Ken’ichi
2015-10-16
The next-to-minimal supersymmetric standard model predicts the formation of domain walls due to the spontaneous breaking of the discrete Z{sub 3}-symmetry at the electroweak phase transition, and they collapse before the epoch of big bang nucleosynthesis if there exists a small bias term in the potential which explicitly breaks the discrete symmetry. Signatures of gravitational waves produced from these unstable domain walls are estimated and their parameter dependence is investigated. It is shown that the amplitude of gravitational waves becomes generically large in the decoupling limit, and that their frequency is low enough to be probed in future pulsar timing observations.
NASA Astrophysics Data System (ADS)
Rapoport, Elizabeth; Beach, Geoffrey S. D.
2012-04-01
Magnetic domain walls in ferromagnetic tracks can be used to trap and transport superparamagnetic beads for lab-on-a-chip applications. Here it is shown that the magnetostatic binding between a domain wall and a superparamagnetic bead suspended in a host fluid leads to a distinct magneto-mechanical resonance under application of a sinusoidal driving field. The characteristic resonant frequency depends on the ratio of the magnetostatic binding force to the viscous drag on the bead. This resonance has been experimentally detected for a single trapped superparamagnetic bead using an optical detection technique.
Atomistic simulation study of transverse domain wall in hexagonal YMnO3
NASA Astrophysics Data System (ADS)
Jiang, Ning; Zhang, X.
2015-11-01
Using atomistic simulation method, we developed a set of interatomic potential parameters which accurately reproduced the complex atomic structure of multiferroic hexagonal manganite YMnO3. We then demonstrated a systematic study of intrinsic defects, and the fine atomic configurations and local structural distortions of two types of transverse domain wall. Moreover, the energy and structure details of transverse domain walls in oxygen deficient YMnO3 were revealed. Insights into the conductance enhancement was obtained. The present study sheds light on the understanding of structure-property relation in YMnO3.
Microwave a.c. conductivity of domain walls in ferroelectric thin films
NASA Astrophysics Data System (ADS)
Tselev, Alexander; Yu, Pu; Cao, Ye; Dedon, Liv R.; Martin, Lane W.; Kalinin, Sergei V.; Maksymovych, Petro
2016-05-01
Ferroelectric domain walls are of great interest as elementary building blocks for future electronic devices due to their intrinsic few-nanometre width, multifunctional properties and field-controlled topology. To realize the electronic functions, domain walls are required to be electrically conducting and addressable non-destructively. However, these properties have been elusive because conducting walls have to be electrically charged, which makes them unstable and uncommon in ferroelectric materials. Here we reveal that spontaneous and recorded domain walls in thin films of lead zirconate and bismuth ferrite exhibit large conductance at microwave frequencies despite being insulating at d.c. We explain this effect by morphological roughening of the walls and local charges induced by disorder with the overall charge neutrality. a.c. conduction is immune to large contact resistance enabling completely non-destructive walls read-out. This demonstrates a technological potential for harnessing a.c. conduction for oxide electronics and other materials with poor d.c. conduction, particularly at the nanoscale.
Microwave a.c. conductivity of domain walls in ferroelectric thin films
Tselev, Alexander; Yu, Pu; Cao, Ye; Dedon, Liv R.; Martin, Lane W.; Kalinin, Sergei V.; Maksymovych, Petro
2016-01-01
Ferroelectric domain walls are of great interest as elementary building blocks for future electronic devices due to their intrinsic few-nanometre width, multifunctional properties and field-controlled topology. To realize the electronic functions, domain walls are required to be electrically conducting and addressable non-destructively. However, these properties have been elusive because conducting walls have to be electrically charged, which makes them unstable and uncommon in ferroelectric materials. Here we reveal that spontaneous and recorded domain walls in thin films of lead zirconate and bismuth ferrite exhibit large conductance at microwave frequencies despite being insulating at d.c. We explain this effect by morphological roughening of the walls and local charges induced by disorder with the overall charge neutrality. a.c. conduction is immune to large contact resistance enabling completely non-destructive walls read-out. This demonstrates a technological potential for harnessing a.c. conduction for oxide electronics and other materials with poor d.c. conduction, particularly at the nanoscale. PMID:27240997
Wall mechanics and exocytosis define the shape of growth domains in fission yeast
Abenza, Juan F.; Couturier, Etienne; Dodgson, James; Dickmann, Johanna; Chessel, Anatole; Dumais, Jacques; Salas, Rafael E. Carazo
2015-01-01
The amazing structural variety of cells is matched only by their functional diversity, and reflects the complex interplay between biochemical and mechanical regulation. How both regulatory layers generate specifically shaped cellular domains is not fully understood. Here, we report how cell growth domains are shaped in fission yeast. Based on quantitative analysis of cell wall expansion and elasticity, we develop a model for how mechanics and cell wall assembly interact and use it to look for factors underpinning growth domain morphogenesis. Surprisingly, we find that neither the global cell shape regulators Cdc42-Scd1-Scd2 nor the major cell wall synthesis regulators Bgs1-Bgs4-Rgf1 are reliable predictors of growth domain geometry. Instead, their geometry can be defined by cell wall mechanics and the cortical localization pattern of the exocytic factors Sec6-Syb1-Exo70. Forceful re-directioning of exocytic vesicle fusion to broader cortical areas induces proportional shape changes to growth domains, demonstrating that both features are causally linked. PMID:26455310
Current induced domain wall motion in GaMnAs close to the Curie temperature.
Jeudy, V; Curiale, J; Adam, J-P; Thiaville, A; Lemaître, A; Faini, G
2011-11-01
Domain wall dynamics produced by spin transfer torques is investigated in (Ga, Mn)As ferromagnetic semiconducting tracks with perpendicular anisotropy, close to the Curie temperature. The domain wall velocities are found to follow a linear flow regime which only slightly varies with temperature. Using the Döring inequality, boundaries of the spin polarization of the current are deduced. A comparison with the predictions of the mean field k·p theory leads to an estimation of the carrier density whose value is compatible with results published in the literature. The spin polarization of the current and the magnetization of the magnetic atoms present similar temperature variations. This leads to a weak temperature dependence of the spin drift velocity and thus of the domain wall velocity. A combined study of field- and current-driven motion and deformation of magnetic domains reveals a motion of domain walls in the steady state regime without transition to the precessional regime. The ratio between the non-adiabatic torque β and the Gilbert damping factor α is shown to remain close to unity.
An exact solution for a thick domain wall in general relativity
NASA Technical Reports Server (NTRS)
Goetz, Guenter; Noetzold, Dirk
1989-01-01
An exact solution of the Einstein equations for a static, planar domain wall with finite thickness is presented. At infinity, density and pressure vanish and the space-time tends to the Minkowski vacuum on one side of the wall and to the Taub vacuum on the other side. A surprising feature of this solution is that the density and pressure distribution are symmetric about the central plane of the wall whereas the space-time metric and therefore also the gravitational field experienced by a test particle is asymmetric.
NASA Astrophysics Data System (ADS)
Bryan, M. T.; Fry, P. W.; Fischer, P. J.; Allwood, D. A.
2008-04-01
Magnetic transmission x-ray microscopy (M-TXM) is used to image domain walls in magnetic ring structures formed by a 300nm wide, 24nm thick Ni81Fe19 nanowire. Both transverse- and vortex-type domain walls are observed after application of different field sequences. Domain walls can be observed by comparing images obtained from opposite field sequences or else domain wall propagation observed by comparing successive images in a particular field sequence. This demonstrates the potential use of M-TXM in developing and understanding planar magnetic nanowire behavior.
Bryan, M. T.; Fry, P. W.; Fischer, P.; Allwood, D. A.
2007-12-01
Magnetic transmission X-ray microscopy (M-TXM) is used to image domain walls in magnetic ring structures formed by a 300 nm wide, 24 nm thick Ni{sub 81}Fe{sub 19} nanowire. Both transverse and vortex type domain walls are observed after application of different field sequences. Domain walls can be observed by comparing images obtained from opposite field sequences, or else domain wall propagation observed by comparing successive images in a particular field sequence. This demonstrates the potential use of M-TXM in developing and understanding planar magnetic nanowire behavior.
Miyamoto, S; Miura, T; Watanabe, S; Nagase, K; Hirayama, Y
2016-03-01
We present fractional quantum Hall domain walls confined in a gate-defined wire structure. Our experiments utilize spatial oscillation of domain walls driven by radio frequency electric fields to cause nuclear magnetic resonance. The resulting spectra are discussed in terms of both large quadrupole fields created around the wire and hyperfine fields associated with the oscillating domain walls. This provides the experimental fact that the domain walls survive near the confined geometry despite of potential deformation, by which a localized magnetic resonance is allowed in electrical means. PMID:26885703
Revealing and understanding the behavior of structural domain walls from first principles
NASA Astrophysics Data System (ADS)
Iniguez, Jorge
2015-03-01
Ferroelectric and ferroelastic domain walls (DWs) are becoming the focus of renewed excitement. Modern experimental techniques permit an unprecedented control on domain structures, and it is now possible to produce materials with a large volume fraction occupied by the DWs themselves. Also, recent experiments show that DWs can display distinct properties not present in the domains, which suggests the possibility of using the walls themselves as the functional material in nano-devices. In this talk I will review recent projects in which we have used theory and first-principles simulation to reveal and explain a variety of DW-related effects. The presentation will include the formation of novel two-dimensional crystals at the DWs of a ferroelastic material, the occurrence of ferroic orders (ferroelectric, ferromagnetic) confined at the DWs of various compounds, and cases in which peculiar (and useful) response and switching properties relie on existence of a multi-domain state. I will also summarize experimental evidence for most of these incredible findings, which clearly ratify domain and domain-wall engineering as a powerful strategy to obtain novel functional nano-materials. // Work done in collaboration with many researchers, the main ones being: J.C. Wojdeł (ICMAB-CSIC), C. Magén (INA at U. Zaragoza), M. Mostovoy (U. Groningen), P. Zubko (U. College London), as well as the groups of Beatriz Noheda (U. Groningen), R. Ramesh (UC Berkeley) and J.-M. Triscone (U. Geneva). Supported by MINECO-Spain.
Tian, Lei; Wang, Yumei Ge, Binghui; Zhang, Xiangqun; Zhang, Zhihua
2015-03-16
Using the advanced spherical aberration-corrected high angle annular dark field scanning transmission electron microscope imaging techniques, we investigated atomic-scale structural features of domain walls and domain patterns in YMnO{sub 3} single crystal. Three different types of interlocked ferroelectric-antiphase domain walls and two abnormal topological four-state vortex-like domain patterns are identified. Each ferroelectric domain wall is accompanied by a translation vector, i.e., 1/6[210] or −1/6[210], demonstrating its interlocked nature. Different from the four-state vortex domain patterns caused by a partial edge dislocation, two four-state vortex-like domain configurations have been obtained at atomic level. These observed phenomena can further extend our understanding of the fascinating vortex domain patterns in multiferroic hexagonal rare-earth manganites.
NASA Astrophysics Data System (ADS)
Sánchez-Tejerina, L.; Alejos, Ó.; Martínez, E.; Muñoz, J. M.
2016-07-01
The dynamics of domain walls in ultrathin ferromagnetic strips with perpendicular magnetic anisotropy is studied from both numerical and analytical micromagnetics. The influence of a moderate interfacial Dzyaloshinskii-Moriya interaction associated to a bi-layer strip arrangement has been considered, giving rise to the formation of Dzyaloshinskii domain walls. Such walls possess under equilibrium conditions an inner magnetization structure defined by a certain orientation angle that make them to be considered as intermediate configurations between Bloch and Néel walls. Two different dynamics are considered, a field-driven and a current-driven dynamics, in particular, the one promoted by the spin torque due to the spin-Hall effect. Results show an inherent asymmetry associated with the rotation of the domain wall magnetization orientation before reaching the stationary regime, characterized by a constant terminal speed. For a certain initial DW magnetization orientation at rest, the rotation determines whether the reorientation of the DW magnetization prior to reach stationary motion is smooth or abrupt. This asymmetry affects the DW motion, which can even reverse for a short period of time. Additionally, it is found that the terminal speed in the case of the current-driven dynamics may depend on either the initial DW magnetization orientation at rest or the sign of the longitudinally injected current.
Magnetic domain wall creep in the presence of an effective interlayer coupling field
NASA Astrophysics Data System (ADS)
Metaxas, P. J.; Jamet, J. P.; Ferré, J.; Rodmacq, B.; Dieny, B.; Stamps, R. L.
We investigate thermally activated domain wall creep in a system consisting of two ultrathin Co layers with perpendicular anisotropy coupled antiferromagnetically through a 4 nm thick Pt spacer layer. The field driven dynamics of domain walls in the softer Co layer have been measured while keeping the harder Co layer negatively saturated. The effect of the interlayer interaction on the soft layer is interpreted in terms of an effective coupling field, HJ, which results in an asymmetry between the domain wall speeds measured under positive and negative driving fields. We show that creep theory remains valid to describe the observed wall motion when the effective coupling field is included in the creep velocity law as a component of the total field acting on the wall. Using the resultant modified creep expression, we determine a value for the effective coupling field which is consistent with that measured from the shift of the soft layer's minor hysteresis loop. The net antiferromagnetic coupling is attributed to a combination of RKKY and orange-peel coupling.
Internal friction due to domain-wall motion in martensitically transformed A15 compounds
Snead, C.L. Jr.; Welch, D.O.
1985-01-01
A lattice instability in A15 materials in some cases leads to a cubic-to-tetragonal martensitic transformation at low temperatures. The transformed material orients in lamellae with c axes alternately aligned along the <100> directions producing domain walls between the lamellae. An internal-friction (delta) feature below T/sub m/ is attributed to stress-induced domain-wall motion. The magnitude of the friction increases as temperature is lowered below T/sub m/ as (1-c/a) increases, and behaves as (1-c/a)/sup 2/ from T/sub m/ down to the superconducting critical temperature where the increasing tetragonality is inhibited. The effect of strain in the lattice is to decrease the domain-wall internal friction, but not affect T/sub m/. Neutron-induced disorder and the addition of some third-elements in alloying decrease both delta and T/sub m/, with some elements reducing only the former. Less than 1 at. % H is seen to completely suppress both delta and T/sub m. Martensitically transformed V/sub 2/Zr demonstrates low-temperature internal-friction and modulus behavior consists with easy ..beta../m wall motion relative to the easy m/m motion of the A15's. For the V/sub 2/Zr, a peak in delta is observed, qualitatively in agreement with expected ..beta../m wall motion.
Ballistic conductivity of graphene channel with p-n junction at ferroelectric domain wall
NASA Astrophysics Data System (ADS)
Morozovska, Anna N.; Eliseev, Eugene A.; Strikha, Maksym V.
2016-06-01
The influence of a ferroelectric domain wall on the ballistic conductance of a single-layer graphene channel in the graphene/physical gap/ferroelectric film heterostructure has been studied in the Wentzel-Kramers-Brillouin approximation. The self-consistent numerical simulation of the electric field and the space charge dynamics in the heterostructure, as well as the approximate analytical theory, show that the contact between the domain wall and the surface creates a p-n junction in the graphene channel. We calculated that the carrier concentration induced in graphene by uncompensated ferroelectric dipoles originated from the abrupt spontaneous polarization change near the surface can reach values of about 1019 m-2, which are two orders of magnitude higher than those obtained for the graphene on non-ferroelectric substrates. Therefore, we predict that the graphene channel with the p-n junction caused by the ferroelectric domain wall would be characterized by rather a high ballistic conductivity. Moreover, the graphene p-n junction at the ferroelectric domain wall can be an excellent rectifier with a conductivity ratio of about 10 between the direct and reverse polarities of the applied voltage.
NMR study of domain wall pinning in a magnetically ordered material
NASA Astrophysics Data System (ADS)
Pleshakov, I. V.; Popov, P. S.; Kuz'min, Yu. I.; Dudkin, V. I.
2016-01-01
The use of nuclear magnetic resonance in the form of spin echo in combination with magnetic field pulses applied to a magnetically ordered material sample offers a convenient tool for studying characteristics of the centers of domain-wall pinning. Possibilities of this method have been demonstrated in experiments with lithium-zinc ferrite.
A small cellulose binding domain protein in Phytophtora is cell wall localized
Technology Transfer Automated Retrieval System (TEKTRAN)
Cellulose binding domains (CBD) are structurally conserved regions linked to catalytic regions of cellulolytic enzymes. While widespread amongst saprophytic fungi that subsist on plant cell wall polysaccharides, they are not generally present in plant pathogenic fungi. A genome wide survey of CBDs w...
Axionic domain wall number related to U(1)anom global symmetry
NASA Astrophysics Data System (ADS)
Kim, Jihn E.
2016-08-01
The QCD axion with fa at an intermediate scale, 109 GeV ∼1012 GeV, seems in conflict with the gravity spoil of global symmetries and may face the axionic domain wall problem. We point out that the string compactifications with an anomalous U(1) gauge symmetry, allowing desirable chiral matter spectra, circumvent these two problems simultaneously.
Frequency-Induced Bulk Magnetic Domain-Wall Freezing Visualized by Neutron Dark-Field Imaging
NASA Astrophysics Data System (ADS)
Betz, B.; Rauscher, P.; Harti, R. P.; Schäfer, R.; Van Swygenhoven, H.; Kaestner, A.; Hovind, J.; Lehmann, E.; Grünzweig, C.
2016-08-01
We use neutron dark-field imaging to visualize and interpret the response of bulk magnetic domain walls to static and dynamic magnetic excitations in (110)-Goss textured iron silicon high-permeability steel alloy. We investigate the domain-wall motion under the influence of an external alternating sinusoidal magnetic field. In particular, we perform scans combining varying levels of dcoffset (0 - 30 A /m ) , oscillation amplitude Aac (0 - 1500 A /m ) , and frequency fac ((0 - 200 Hz ) . By increasing amplitude Aac while maintaining constant values of dcoffset and fac , we record the transition from a frozen domain-wall structure to a mobile one. Vice versa, increasing fac while keeping Aac and dcoffset constant led to the reverse transition from a mobile domain-wall structure into a frozen one. We show that varying both Aac and fac shifts the position of the transition region. Furthermore, we demonstrate that higher frequencies require higher oscillation amplitudes to overcome the freezing phenomena. The fundamental determination and understanding of the frequency-induced freezing process in high-permeability steel alloys is of high interest to the further development of descriptive models for bulk macromagnetic phenomena. Likewise, the efficiency of transformers can be improved based on our results, since these alloys are used as transformer core material.
Dynamics of domain-wall Dirac fermions on a topological insulator: A chiral fermion beam splitter
NASA Astrophysics Data System (ADS)
Hammer, René; Pötz, Walter
2013-12-01
The intersection of two ferromagnetic domain walls placed on the surface of topological insulators provides a one-way beam splitter for domain-wall Dirac fermions. Based on an analytic expression for a static two-soliton magnetic texture we perform a systematic numerical study of the propagation of Dirac wave packets along such intersections. A single-cone staggered-grid finite difference lattice scheme is employed in the numerical analysis. It is shown that the angle of intersection plays a decisive role in determining the splitting ratio of the fermion beam. For a nonrectangular intersection, the width and, to a lesser extent, the type of domain walls, e.g., Bloch or Néel, determine the properties of the splitter. As the ratio between domain-wall width and transverse localization length of the Dirac fermion is increased its propagation behavior changes from quantum-mechanical (wavelike) to classical ballistic (particlelike). An electric gate placed near the intersection offers a dynamic external control knob for adjusting the splitting ratio.
Some properties of domain wall solution in the Randall-Sundrum model
NASA Astrophysics Data System (ADS)
Ichinose, Shoichi
2001-12-01
Properties of the domain wall (kink) solution in the five-dimensional Randall-Sundrum model are examined both analytically and numerically. The configuration is derived by the bulk Higgs mechanism. We focus on (1) the convergence property of the solution, (2) the stablity of the solution, (3) the non-singular property of the Riemann curvature and (4) the behaviours of the warp factor and the Higgs field. It is found that the bulk curvature changes the sign around the surface of the wall. We also present some exact solutions for two simple cases: (a) the no-potential case, (b) the cosmological term-dominated case. Both solutions have the (naked) curvature singularity. We can regard the domain wall solution as a singularity resolution of the exact solutions.
Accomodation of the speed distribution of magnetic domain walls to their eddy current interactions
NASA Astrophysics Data System (ADS)
Bishop, J. E. L.
1990-05-01
The eddy interaction of Pry & Bean type domain walls, distributed randomly across a lamination, is investigated by Monte Carlo simulation supported, for large mean domain width/lamination thickness ratio overlineW/D , by analysis. When all walls are constrained to make equal flux rate contributions, the eddy loss exceeds the "classical" (uniform dB/ dt ) loss Λ c by a factor η R = η O + 1 where η O = 1.628 overlineW/D is the corresponding factor without eddy overlap. This confirms earlier work. Howe ver, when each wall adjusts its rate to balance eddy drag and applied field pressure, a lower ratio η A = η O + Δη A results with 0.7 < Δη A < 1. This is contrary to Bertotti's rule that independent random eddy interactions contribute Λ c while correlated interactions make a higher contribution.
NASA Astrophysics Data System (ADS)
Metaxas, Peter J.; Albert, Maximilian; Lequeux, Steven; Cros, Vincent; Grollier, Julie; Bortolotti, Paolo; Anane, Abdelmadjid; Fangohr, Hans
2016-02-01
We study resonant translational, breathing, and twisting modes of transverse magnetic domain walls pinned at notches in ferromagnetic nanostrips. We demonstrate that a mode's sensitivity to notches depends strongly on the mode's characteristics. For example, the frequencies of modes that involve lateral motion of the wall are the most sensitive to changes in the notch intrusion depth, especially at the narrow, more strongly confined end of the domain wall. In contrast, the breathing mode, whose dynamics are concentrated away from the notches is relatively insensitive to changes in the notches' sizes. We also demonstrate a sharp drop in the translational mode's frequency towards zero when approaching depinning which is confirmed, using a harmonic oscillator model, to be consistent with a reduction in the local slope of the notch-induced confining potential at its edge.
Pectin Modification in Cell Walls of Ripening Tomatoes Occurs in Distinct Domains.
Steele, N. M.; McCann, M. C.; Roberts, K.
1997-05-01
The class of cell wall polysaccharides that undergoes the most extensive modification during tomato (Lycopersicon esculentum) fruit ripening is pectin. De-esterification of the polygalacturonic acid backbone by pectin methylesterase facilitates the depolymerization of pectins by polygalacturonase II (PGII). To investigate the spatial aspects of the de-esterification of cell wall pectins and the subsequent deposition of PGII, we have used antibodies to relatively methylesterified and nonesterified pectic epitopes and to the PGII protein on thin sections of pericarp tissue at different developmental stages. De-esterification of pectins and deposition of PGII protein occur in block-like domains within the cell wall. The boundaries of these domains are distinct and persistent, implying strict, spatial regulation of enzymic activities. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of proteins strongly associated with cell walls of pericarp tissue at each stage of fruit development show ripening-related changes in this protein population. Western blots of these gels with anti-PGII antiserum demonstrate that PGII expression is ripening-related. The PGII co-extracts with specific pectic fractions extracted with imidazole or with Na2CO3 at 0[deg]C from the walls of red-ripe pericarp tissue, indicating that the strong association between PGII and the cell wall involves binding to particular pectic polysaccharides.
Evolution of light domain walls interacting with dark matter, part 1
NASA Technical Reports Server (NTRS)
Massarotti, Alessandro
1990-01-01
The evolution of domain walls generated in the early Universe is discussed considering an interaction between the walls and a major gaseous component of the dark matter. The walls are supposed able to reflect the particles elastically and with a reflection coefficient of unity. A toy Lagrangian that could give rise to such a phenomenon is discussed. In the simple model studied, highly non-relativistic and slowly varying speeds are obtained for the domain walls (approximately 10 (exp -2)(1+z)(exp -1)) and negligible distortions of the microwave background. In addition, these topological defects may provide a mechanism of forming the large scale structure of the Universe, by creating fluctuations in the dark matter (delta rho/rho approximately O(1)) on a scale comparable with the distance the walls move from the formation (in the model d less than 20 h(exp -1) Mpc). The characteristic scale of the wall separation can be easily chosen to be of the order of 100 Mpc instead of being restricted to the horizon scale, as usually obtained.
NASA Astrophysics Data System (ADS)
Guo, Lili; Jiang, Limei; Zhou, Yichun
2016-09-01
The effect of interface misfit strain on the movement and tilt angles of the domain wall in ferroelectric thin film is investigated with a multicoupling finite element model. Since this theoretical model is developed based on the phase field method and is solved using the finite element method, it can effectively predict the electromechanical coupling behavior of materials that have complicated boundary conditions. The simulated results demonstrate that the position, tilt angles, strain gradient and energy density of the domain wall can be modulated by misfit compressive strain at the interface of ferroelectric nanostructures. A larger interface misfit compressive strain will lead to the movement of domain wall towards the direction which allows the a domain to possess a larger volume. The difference of the tilt angles of domain walls on both sides of the a domain becomes larger as the interface misfit strain increases, implying a transition of the shape of the a domain from parallelogram to wedge.
Time evolution of domain-wall motion induced by nanosecond laser pulses
NASA Astrophysics Data System (ADS)
Gerasimov, M. V.; Logunov, M. V.; Spirin, A. V.; Nozdrin, Yu. N.; Tokman, I. D.
2016-07-01
The time evolution of the magnetization normal component change in a garnet film with a labyrinthine domain structure under the action of circularly and linearly polarized laser pump pulses (the pulse duration is 5 ns; the wavelength is 527 nm) has been studied. The dynamic state of the magnetic film was registered using an induction method with a time resolution of 1 ns. It was found that for the initial state of the magnetic film with an equilibrium domain structure, the form of the photomagnetization pulse reflects the time evolution of a domain-wall motion. The domain-wall motion initiated by the circularly polarized laser pump pulse continues in the same direction for a time more than an order of magnitude exceeding the laser pulse duration. In general, the time evolution of the domain-wall movement occurs in three stages. The separation of the contributions to the photomagnetization from the polarization-dependent and polarization-independent effects was carried out. The photomagnetization pulses that reflect the contributions by the aforementioned effects differ by form, and more than two orders of magnitude by duration. Their form doesn't change under a magnetic bias field change, only the photomagnetization pulse amplitude does: for the polarization-dependent contribution, it's an even function of the field, and for the polarization-independent contribution, it's an odd function. The interconnection between the polarization-dependent and polarization-independent effects, on the one hand, and the domain-wall displacement and the change of the film's saturation magnetization, on the other hand, was identified and described.
Atomic-scale mechanisms of ferroelastic domain-wall-mediated ferroelectric switching
NASA Astrophysics Data System (ADS)
Gao, Peng; Britson, Jason; Jokisaari, Jacob R.; Nelson, Christopher T.; Baek, Seung-Hyub; Wang, Yiran; Eom, Chang-Beom; Chen, Long-Qing; Pan, Xiaoqing
2013-11-01
Polarization switching in ferroelectric thin films occurs via nucleation and growth of 180° domains through a highly inhomogeneous process in which the kinetics are largely controlled by defects, interfaces and pre-existing domain walls. Here we present the first real-time, atomic-scale observations and phase-field simulations of domain switching dominated by pre-existing, but immobile, ferroelastic domains in Pb(Zr0.2Ti0.8)O3 thin films. Our observations reveal a novel hindering effect, which occurs via the formation of a transient layer with a thickness of several unit cells at an otherwise charged interface between a ferroelastic domain and a switched domain. This transient layer possesses a low-magnitude polarization, with a dipole glass structure, resembling the dead layer. The present study provides an atomic level explanation of the hindering of ferroelectric domain motion by ferroelastic domains. Hindering can be overcome either by applying a higher bias or by removing the as-grown ferroelastic domains in fabricated nanostructures.
High Antiferromagnetic Domain Wall Velocity Induced by Néel Spin-Orbit Torques
NASA Astrophysics Data System (ADS)
Gomonay, O.; Jungwirth, T.; Sinova, J.
2016-07-01
We demonstrate the possibility to drive an antiferromagnetic domain wall at high velocities by fieldlike Néel spin-orbit torques. Such torques arise from current-induced local fields that alternate their orientation on each sublattice of the antiferromagnet and whose orientation depends primarily on the current direction, giving them their fieldlike character. The domain wall velocities that can be achieved by this mechanism are 2 orders of magnitude greater than the ones in ferromagnets. This arises from the efficiency of the staggered spin-orbit fields to couple to the order parameter and from the exchange-enhanced phenomena in antiferromagnetic texture dynamics, which leads to a low domain wall effective mass and the absence of a Walker breakdown limit. In addition, because of its nature, the staggered spin-orbit field can lift the degeneracy between two 180° rotated states in a collinear antiferromagnet, and it provides a force that can move such walls and control the switching of the states.
NASA Astrophysics Data System (ADS)
Liao, Zhaoliang; Huijben, Mark; Koster, Gertjan; Rijnders, Guus
2014-09-01
La2/3Sr1/3MnO3 films with uniaxial magnetic anisotropy were coherently grown on NdGaO3 (110) substrates. The uniaxial anisotropy has strong effect on magnetoresistance (MR). A positive MR was observed when the current is along magnetic easy axis under the current-field perpendicular geometry. In contrast, no positive MR is observed when current is along the magnetic hard axis regardless of the field direction. Our analysis indicates that the anomalous anisotropic MR effect arises from the uniaxial magnetic anisotropy caused stripe domains which contribute to strong anisotropic domain wall resistivity.
NASA Astrophysics Data System (ADS)
Sturma, M.; Bellegarde, C.; Toussaint, J.-C.; Gusakova, D.
2016-09-01
In this paper, we use simulations to study current-induced domain wall dynamics by simultaneously resolving the spin transport and micromagnetic equations for a three-dimensional ferromagnetic strip. In contrast to local approaches, which neglect mutual interaction between spins and magnetic moments, our approach recalculates the spin distribution at each time step using the generalized drift diffusion model, which takes the transverse spin absorption phenomenon into account. We quantified the differences between a local approach and treatment based on a self-consistent method by plotting the domain wall velocity as a function of the domain wall width. We also characterized the domain wall velocity and the Walker breakdown condition as a function of the transverse spin absorption length l⊥, which plays a crucial role in domain wall dynamics.
Tunneling decay of false domain walls: The silence of the lambs
NASA Astrophysics Data System (ADS)
Haberichter, Mareike; MacKenzie, Richard; Paranjape, M. B.; Ung, Yvan
2016-04-01
We study the decay of "false" domain walls, that is, metastable states of the quantum theory where the true vacuum is trapped inside the wall with the false vacuum outside. We consider a theory with two scalar fields, a shepherd field and a field of sheep. The shepherd field serves to herd the solitons of the sheep field so that they are nicely bunched together. However, quantum tunnelling of the shepherd field releases the sheep to spread out uncontrollably. We show how to calculate the tunnelling amplitude for such a disintegration.
Light domain walls, massive neutrinos and the large scale structure of the Universe
NASA Technical Reports Server (NTRS)
Massarotti, Alessandro
1991-01-01
Domain walls generated through a cosmological phase transition are considered, which interact nongravitationally with light neutrinos. At a redshift z greater than or equal to 10(exp 4), the network grows rapidly and is virtually decoupled from the matter. As the friction with the matter becomes dominant, a comoving network scale close to that of the comoving horizon scale at z of approximately 10(exp 4) gets frozen. During the later phases, the walls produce matter wakes of a thickness d of approximately 10h(exp -1)Mpc, that may become seeds for the formation of the large scale structure observed in the Universe.
Optimized cobalt nanowires for domain wall manipulation imaged by in situ Lorentz microscopy
Rodriguez, L. A.; Magen, C.; Snoeck, E.; Gatel, C.; Serrano-Ramon, L.; and others
2013-01-14
Direct observation of domain wall (DW) nucleation and propagation in focused electron beam induced deposited Co nanowires as a function of their dimensions was carried out by Lorentz microscopy (LTEM) upon in situ application of magnetic field. Optimal dimensions favoring the unambiguous DW nucleation/propagation required for applications were found in 500-nm-wide and 13-nm-thick Co nanowires, with a maximum nucleation field and the largest gap between nucleation and propagation fields. The internal DW structures were resolved using the transport-of-intensity equation formalism in LTEM images and showed that the optimal nanowire dimensions correspond to the crossover between the nucleation of transverse and vortex walls.
Douglas, A. M.; Kumar, A.; Gregg, J. M.; Whatmore, R. W.
2015-10-26
Conducting atomic force microscopy images of bulk semiconducting BaTiO{sub 3} surfaces show clear stripe domain contrast. High local conductance correlates with strong out-of-plane polarization (mapped independently using piezoresponse force microscopy), and current-voltage characteristics are consistent with dipole-induced alterations in Schottky barriers at the metallic tip-ferroelectric interface. Indeed, analyzing current-voltage data in terms of established Schottky barrier models allows relative variations in the surface polarization, and hence the local domain structure, to be determined. Fitting also reveals the signature of surface-related depolarizing fields concentrated near domain walls. Domain information obtained from mapping local conductance appears to be more surface-sensitive than that from piezoresponse force microscopy. In the right materials systems, local current mapping could therefore represent a useful complementary technique for evaluating polarization and local electric fields with nanoscale resolution.
NASA Astrophysics Data System (ADS)
Meng, Qingping; Han, Myung-Geun; Tao, Jing; Xu, Guangyong; Welch, David O.; Zhu, Yimei
2015-02-01
The motion of domain walls (DWs) is critical to switching kinetics in ferroelectric (FE) materials. Merz's law, dependent only on the applied electric field, cannot explain recent experimental observations in FE thin films because these experiments showed that the DW velocity depends not only on the strength of the applied electric field but also on size of the reversal domain. In this paper, we derive a model to understand the dominant factors controlling the velocity of FE DWs. Our calculations reveal that the DW velocities are not only a function of the strength of the electric field but also decay exponentially with the increasing characteristic time of the measurement or the size of the growing domain. Our observations can naturally explain the gigantic variation reported in the literature, over 15 orders of magnitude, in the experimentally measured DW velocities and the formation of the stripe shape of FE domains.
NASA Astrophysics Data System (ADS)
Kim, Sungwon
Ferroelectric LiNbO3 and LiTaO3 crystals have developed, over the last 50 years as key materials for integrated and nonlinear optics due to their large electro-optic and nonlinear optical coefficients and a broad transparency range from 0.4 mum-4.5 mum wavelengths. Applications include high speed optical modulation and switching in 40GHz range, second harmonic generation, optical parametric amplification, pulse compression and so on. Ferroelectric domain microengineering has led to electro-optic scanners, dynamic focusing lenses, total internal reflection switches, and quasi-phase matched (QPM) frequency doublers. Most of these applications have so far been on non-stoichiometric compositions of these crystals. Recent breakthroughs in crystal growth have however opened up an entirely new window of opportunity from both scientific and technological viewpoint. The growth of stoichiometric composition crystals has led to the discovery of many fascinating effects arising from the presence or absence of atomic defects, such as an order of magnitude changes in coercive fields, internal fields, domain backswitching and stabilization phenomenon. On the nanoscale, unexpected features such as the presence of wide regions of optical contrast and strain have been discovered at 180° domain walls. Such strong influence of small amounts of nonstoichiometric defects on material properties has led to new device applications, particularly those involving domain patterning and shaping such as QPM devices in thick bulk crystals and improved photorefractive damage compositions. The central focus of this dissertation is to explore the role of nonstoichiometry and its precise influence on macroscale and nanoscale properties in lithium niobate and tantalate. Macroscale properties are studied using a combination of in-situ and high-speed electro-optic imaging microscopy and electrical switching experiments. Local static and dynamic strain properties at individual domain walls is studied
Domain Wall Motion Across Various Grain Boundaries in Ferroelectric Thin Films
Marincel, Daniel M.; Zhang, Huairuo; Jesse, Stephen; Belianinov, Alex; Okatan, Mahmut B.; Kalinin, Sergei V.; Rainforth, W. Mark; Reaney, Ian M.; Randall, Clive A.; Trolier-McKinstry, Susan
2015-03-21
Domain wall movement at and near engineered 10°, 15°, and 24° tilt and 10° and 30° twist grain boundaries was measured by band excitation piezoresponse force microscopy for Pb(Zr,Ti)O3 films with Zr/Ti ratio of 45/55 and 52/48. A minimum in nonlinear response was observed at the grain boundary for the highest angle twist and tilt grain boundaries, while a maximum in nonlinear response was observed at the 10° tilt grain boundaries. Lastly, the observed nonlinear response was correlated to the domain structure imaged in cross section by transmission electron microscopy.
Domain Wall Motion Across Various Grain Boundaries in Ferroelectric Thin Films
Marincel, Daniel M.; Zhang, Huairuo; Jesse, Stephen; Belianinov, Alex; Okatan, Mahmut B.; Kalinin, Sergei V.; Rainforth, W. Mark; Reaney, Ian M.; Randall, Clive A.; Trolier-McKinstry, Susan
2015-03-21
Domain wall movement at and near engineered 10°, 15°, and 24° tilt and 10° and 30° twist grain boundaries was measured by band excitation piezoresponse force microscopy for Pb(Zr,Ti)O_{3} films with Zr/Ti ratio of 45/55 and 52/48. A minimum in nonlinear response was observed at the grain boundary for the highest angle twist and tilt grain boundaries, while a maximum in nonlinear response was observed at the 10° tilt grain boundaries. Lastly, the observed nonlinear response was correlated to the domain structure imaged in cross section by transmission electron microscopy.
NASA Astrophysics Data System (ADS)
Ghosh, Dipankar; Bah, Abubakarr; Carman, Gregory P.; Ravichandran, Guruswami
2016-01-01
This paper describes experimental data on a polycrystalline nickel subjected to compressive loads induced in a split Hopkinson pressure bar test. A perpendicular bias magnetic field with respect to the loading direction is used to orient the domains and a pick-up coil measures the magnetic response of the sample during loading. Utilizing this experimental configuration, this study investigated the coupled effects of the magnetic and mechanical fields on domain wall motion in a polycrystalline magnetostrictive material (Ni) during the high-rate elastic loading. The experimental measurements reveal that the magnitude of the stress-induced magnetization change is dependent upon bias magnetic field.
Switching local magnetization by electric-field-induced domain wall motion
NASA Astrophysics Data System (ADS)
Kakizakai, Haruka; Ando, Fuyuki; Koyama, Tomohiro; Yamada, Kihiro; Kawaguchi, Masashi; Kim, Sanghoon; Kim, Kab-Jin; Moriyama, Takahiro; Chiba, Daichi; Ono, Teruo
2016-06-01
Electric field effect on magnetism is an appealing technique for manipulating magnetization at a low energy cost. Here, we show that the local magnetization of an ultrathin Co film can be switched by simply applying a gate electric field without the assistance of any external magnetic field or current flow. The local magnetization switching is explained by nucleation and annihilation of magnetic domains through domain wall motion induced by the electric field. Our results lead to external-field-free and ultralow-energy spintronic applications.
Xu, Qingping; Liu, Xueqian W.; Patin, Delphine; Farr, Carol L.; Grant, Joanna C.; Chiu, Hsiu-Ju; Jaroszewski, Lukasz; Knuth, Mark W.; Godzik, Adam; Lesley, Scott A.; Elsliger, Marc-André; Deacon, Ashley M.
2015-01-01
ABSTRACT Bacterial SH3 (SH3b) domains are commonly fused with papain-like Nlp/P60 cell wall hydrolase domains. To understand how the modular architecture of SH3b and NlpC/P60 affects the activity of the catalytic domain, three putative NlpC/P60 cell wall hydrolases were biochemically and structurally characterized. These enzymes all have γ-d-Glu-A2pm (A2pm is diaminopimelic acid) cysteine amidase (or dl-endopeptidase) activities but with different substrate specificities. One enzyme is a cell wall lysin that cleaves peptidoglycan (PG), while the other two are cell wall recycling enzymes that only cleave stem peptides with an N-terminal l-Ala. Their crystal structures revealed a highly conserved structure consisting of two SH3b domains and a C-terminal NlpC/P60 catalytic domain, despite very low sequence identity. Interestingly, loops from the first SH3b domain dock into the ends of the active site groove of the catalytic domain, remodel the substrate binding site, and modulate substrate specificity. Two amino acid differences at the domain interface alter the substrate binding specificity in favor of stem peptides in recycling enzymes, whereas the SH3b domain may extend the peptidoglycan binding surface in the cell wall lysins. Remarkably, the cell wall lysin can be converted into a recycling enzyme with a single mutation. PMID:26374125
Localization and chiral symmetry in 2+1 flavor domain wall QCD
David J. Antonio; Kenneth C. Bowler; Peter A. Boyle; Norman H. Christ; Michael A. Clark; Saul D. Cohen; Chris Dawson; Alistair Hart; Balint Joó; Chulwoo Jung; Richard D. Kenway; Shu Li; Meifeng Lin; Robert D. Mawhinney; Christopher M. Maynard; Shigemi Ohta; Robert J. Tweedie; Azusa Yamaguchi
2008-01-01
We present results for the dependence of the residual mass of domain wall fermions (DWF) on the size of the fifth dimension and its relation to the density and localization properties of low-lying eigenvectors of the corresponding hermitian Wilson Dirac operator relevant to simulations of 2+1 flavor domain wall QCD. Using the DBW2 and Iwasaki gauge actions, we generate ensembles of configurations with a $16^3\\times 32$ space-time volume and an extent of 8 in the fifth dimension for the sea quarks. We demonstrate the existence of a regime where the degree of locality, the size of chiral symmetry breaking and the rate of topology change can be acceptable for inverse lattice spacings $a^{-1} \\ge 1.6$ GeV.
Quenched domain wall QCD with DBW2 gauge action toward nucleon decay matrix element calculation
NASA Astrophysics Data System (ADS)
Aoki, Yasumichi
2001-10-01
The domain wall fermion action is a promising way to control chiral symmetry in lattice gauge theory. By the good chiral symmetry of this approach even at finite lattice spacing, one is able to extract hadronic matrix elements, like kaon weak matrix elements, for which the symmetry is extremely important. Ordinary fermions with poor chiral symmetry make calculation difficult because of the large mixing of operators with different chiral structure. Even though the domain wall fermion action with the simple Wilson gauge action has a good chiral symmetry, one can further improve the symmetry by using a different gauge action. We take a non-perturbatively improved action, the DBW2 action of the QCD Taro group. Hadron masses are systematically examined for a range of parameters. Application to nucleon decay matrix element is also discussed.
360° domain walls: stability, magnetic field and electric current effects
NASA Astrophysics Data System (ADS)
Zhang, Jinshuo; Siddiqui, Saima A.; Ho, Pin; Currivan-Incorvia, Jean Anne; Tryputen, Larysa; Lage, Enno; Bono, David C.; Baldo, Marc A.; Ross, Caroline A.
2016-05-01
The formation of 360° magnetic domain walls (360DWs) in Co and Ni80Fe20 thin film wires was demonstrated experimentally for different wire widths, by successively injecting two 180° domain walls (180DWs) into the wire. For narrow wires (≤50 nm wide for Co), edge roughness prevented the combination of the 180DWs into a 360DW, and for wide wires (200 nm for Co) the 360DW was unstable and annihilated spontaneously, but over an intermediate range of wire widths, reproducible 360DW formation occurred. The annihilation and dissociation of 360DWs was demonstrated by applying a magnetic field parallel to the wire, showing that annihilation fields were several times higher than dissociation fields in agreement with micromagnetic modeling. The annihilation of a 360DW by current pulsing was demonstrated.
On the estimation of gravitational wave spectrum from cosmic domain walls
Hiramatsu, Takashi; Kawasaki, Masahiro; Saikawa, Ken'ichi E-mail: kawasaki@icrr.u-tokyo.ac.jp
2014-02-01
We revisit the production of gravitational waves from unstable domain walls analyzing their spectrum by the use of field theoretic lattice simulations with grid size 1024{sup 3}, which is larger than the previous study. We have recognized that there exists an error in the code used in the previous study, and the correction of the error leads to the suppression of the spectrum of gravitational waves at high frequencies. The peak of the spectrum is located at the scale corresponding to the Hubble radius at the time of the decay of domain walls, and its amplitude is consistent with the naive estimation based on the quadrupole formula. Using the numerical results, the magnitude and the peak frequency of gravitational waves at the present time are estimated. It is shown that for some choices of parameters the signal of gravitational waves is strong enough to be probed in the future gravitational wave experiments.
Logic circuit prototypes for three-terminal magnetic tunnel junctions with mobile domain walls
NASA Astrophysics Data System (ADS)
Currivan-Incorvia, J. A.; Siddiqui, S.; Dutta, S.; Evarts, E. R.; Zhang, J.; Bono, D.; Ross, C. A.; Baldo, M. A.
2016-01-01
Spintronic computing promises superior energy efficiency and nonvolatility compared to conventional field-effect transistor logic. But, it has proven difficult to realize spintronic circuits with a versatile, scalable device design that is adaptable to emerging material physics. Here we present prototypes of a logic device that encode information in the position of a magnetic domain wall in a ferromagnetic wire. We show that a single three-terminal device can perform inverter and buffer operations. We demonstrate one device can drive two subsequent gates and logic propagation in a circuit of three inverters. This prototype demonstration shows that magnetic domain wall logic devices have the necessary characteristics for future computing, including nonlinearity, gain, cascadability, and room temperature operation.
Logic circuit prototypes for three-terminal magnetic tunnel junctions with mobile domain walls
Currivan-Incorvia, J. A.; Siddiqui, S.; Dutta, S.; Evarts, E. R.; Zhang, J.; Bono, D.; Ross, C. A.; Baldo, M. A.
2016-01-01
Spintronic computing promises superior energy efficiency and nonvolatility compared to conventional field-effect transistor logic. But, it has proven difficult to realize spintronic circuits with a versatile, scalable device design that is adaptable to emerging material physics. Here we present prototypes of a logic device that encode information in the position of a magnetic domain wall in a ferromagnetic wire. We show that a single three-terminal device can perform inverter and buffer operations. We demonstrate one device can drive two subsequent gates and logic propagation in a circuit of three inverters. This prototype demonstration shows that magnetic domain wall logic devices have the necessary characteristics for future computing, including nonlinearity, gain, cascadability, and room temperature operation. PMID:26754412
Depinning of the ferroelectric domain wall in congruent LiNbO3
NASA Astrophysics Data System (ADS)
Lee, Donghwa; Gopalan, Venkatraman; Phillpot, Simon R.
2016-08-01
The high coercive field, Ec, of congruent LiNbO3 can be reduced by doping with Mg or Zn atoms, or by increasing the temperature above a threshold value. The physical origin for this reduction is not currently understood. Here, density functional theory calculations illustrate the atomic origin of the change in the switching field of the congruent LiNbO3. They show that the high Ec in the congruent LiNbO3 is a result of niobium antisite atoms on the lithium sublattice, pinning the motion of the domain walls. Thus, the healing of antisites by diffusion can significantly reduce the coercive field. In addition, this work demonstrates that the migration of these niobium antisites can be enhanced by doping or by changing the temperature. Thus, the depinning process of the congruent LiNbO3 is understood by the migration of the niobium antisite defect across the domain wall.
Universal magnetic domain wall dynamics in the presence of weak disorder
NASA Astrophysics Data System (ADS)
Ferré, Jacques; Metaxas, Peter J.; Mougin, Alexandra; Jamet, Jean-Pierre; Gorchon, Jon; Jeudy, Vincent
2013-10-01
The motion of elastic interfaces in disordered media is a broad topic relevant to many branches of physics. Field-driven magnetic domain wall motion in ultrathin ferromagnetic Pt/Co/Pt films can be well interpreted within the framework of theories developed to describe elastic interface dynamics in the presence of weak disorder. Indeed, the three theoretically predicted dynamic regimes of creep, depinning, and flow have all been directly evidenced in this model experimental system. We discuss these dynamic regimes and demonstrate how field-driven creep can be controlled not only by temperature and pinning, but also via interactions with magnetic entities located inside or outside the magnetic layer. Consequences of confinement effects in nano-devices are briefly reviewed, as some recent results on domain wall motion driven by an electric current or assisted by an electric field. Finally new theoretical developments and perspectives are discussed.
Perterbative O(asa) matching in static heavy and domain-wall light quark system
Ishikawa,T.
2008-07-14
We discuss the perturbative O(a{sub s}a) matching in the static heavy and domain-wall light quark system. The gluon action is the Iwasaki action and the link smearing is performed in the static heavy action. The chiral symmetry of the light quark realized by using the domain-wall fermion formulation does not prohibit the mixing of the operators at O(a). The application of O(a) improvement to the actual data shows that the B meson decay constant f{sub B}, the matrix elements M{sub B} and the B parameter B{sub B} have non-negligible effects, while the effect on the SU(3) breaking ratio {zeta} is small.
NASA Astrophysics Data System (ADS)
Kameni Ntichi, Abelin; Modave, Axel; Boubekeur, Mohamed; Preault, Valentin; Pichon, Lionel; Geuzaine, Christophe
2013-11-01
This article presents a time domain discontinuous Galerkin method applied for solving the con-servative form of Maxwells' equations and computing the radiated fields in electromagnetic compatibility problems. The results obtained in homogeneous media for the transverse magnetic waves are validated in two cases. We compare our solution to an analytical solution of Maxwells' equations based on characteristic method. Our results on shielding effectiveness of a conducting wall are same as those obtained from analytical expression in frequency domain. The propagation in heterogeneous medium is explored. The shielding effectiveness of a composite wall partially filled by circular conductives inclusions is computed. The proposed results are in conformity with the classical predictive homogenization rules. Contribution to the Topical Issue "Numelec 2012", Edited by Adel Razek.
The Stability of Fake Flat Domain Walls on Kähler Manifold
NASA Astrophysics Data System (ADS)
Akbar, F. T.; Wijaya, R. N.; Gunara, B. E.
2016-08-01
In this paper, we study the stability of flat fake domain walls solution of fake N = 1 supergravity in d + 1 dimensions with Kahler surface as the sigma model. We start with Lagrangian for N = 1 fake supergravity which is coupling between gravity and complex scalar in d + 1 dimensions with scalar potential turned on. Then, as in supergravity theory, we demand that the scalar fields span the Kahler manifold. The equations of motion for fields can be reduced into first order equations by defining the superpotential and the resulting equations are called the projection equation and the fake BPS equation. Finally, we discuss about the stability of flat fake domain walls by investigating the critical points of the superpotential and the scalar potential.
Domain wall interactions due to vacuum Dirac field fluctuations in 2 +1 dimensions
NASA Astrophysics Data System (ADS)
Fosco, C. D.; Mazzitelli, F. D.
2016-07-01
We evaluate quantum effects due to a two-component Dirac field in 2 +1 spacetime dimensions, coupled to domain-wall-like defects with a smooth shape. We show that these effects induce nontrivial contributions to the (shape-dependent) energy of the domain walls. For a single defect, we study the divergences in the corresponding self-energy, and also consider the role of the massless zero mode—corresponding to the Callan-Harvey mechanism—by coupling the Dirac field to an external gauge field. For two defects, we show that the Dirac field induces a nontrivial, Casimir-like effect between them, and we provide an exact expression for that interaction in the case of two straight-line parallel defects. As is the case for the Casimir interaction energy, the result is finite and unambiguous.
NASA Astrophysics Data System (ADS)
Lai, Y. W.; Scheerbaum, N.; Hinz, D.; Gutfleisch, O.; Schäfer, R.; Schultz, L.; McCord, J.
2007-05-01
A detailed study of twin boundary motion in NiMnGa single crystals together with in situ magnetic domain observation is presented. Optical polarization microscopy in connection with a magneto-optical indicator film technique was used to investigate the reorganization of the magnetic domains during twin boundary motion over a wide magnetic field range. Images at different field strengths demonstrate that no magnetic domain wall motion within the twins takes place, even during the structural reorientation by twin boundary movement. This absence of interaction of magnetic and structural domains is different from currently proposed models, which assume domain wall movement under an external field.
Swift thermal steering of domain walls in ferromagnetic MnBi stripes.
Sukhov, Alexander; Chotorlishvili, Levan; Ernst, Arthur; Zubizarreta, Xabier; Ostanin, Sergey; Mertig, Ingrid; Gross, Eberhard K U; Berakdar, Jamal
2016-01-01
We predict a fast domain wall (DW) motion induced by a thermal gradient across a nanoscopic ferromagnetic stripe of MnBi. The driving mechanism is an exchange torque fueled by magnon accumulation at the DWs. Depending on the thickness of the sample, both hot-to-cold and cold-to-hot DW motion directions are possible. The finding unveils an energy efficient way to manipulate DWs as an essential element in magnetic information processing such as racetrack memory. PMID:27076097
Hadron spectrum with domain-wall valence quarks on an improved staggered sea
Richards, David; Edwards, Robert; Orginos, Konstantinos
2006-07-23
The hadron spectrum is computed in full QCD using domain-wall valence fermions on an improved staggered sea, for pion masses down to around $350{approx}(/rm MeV)$. Emphasis is laid on the low-lying baryon spectrum. All possible baryon correlators obtainable from local and quasi-local quark sources are computed, using lattice group-theory methods Results are presented for the lowest-lying states in each isospin channel.
Hadronic physics with domain-wall valence and improved staggered sea quarks
D. B. Renner; W. Schroers; R. Edwards; G. T. Fleming; Ph. Hagler; J. W. Negele; K. Orginos; A. V. Pochinski; D. Richards
2004-06-01
With the advent of chiral fermion formulations, the simulation of light valence quarks has finally become realistic for numerical simulations of lattice QCD. The simulation of light dynamical quarks, however, remains one of the major challenges and is still an obstacle to realistic simulations. We attempt to meet this challenge using a hybrid combination of Asqtad sea quarks and domain-wall valence quarks. Initial results for the proton form factor and the nucleon axial coupling are presented.
Universal Pinning Energy Barrier for Driven Domain Walls in Thin Ferromagnetic Films.
Jeudy, V; Mougin, A; Bustingorry, S; Savero Torres, W; Gorchon, J; Kolton, A B; Lemaître, A; Jamet, J-P
2016-07-29
We report a comparative study of magnetic field driven domain wall motion in thin films made of different magnetic materials for a wide range of field and temperature. The full thermally activated creep motion, observed below the depinning threshold, is shown to be described by a unique universal energy barrier function. Our findings should be relevant for other systems whose dynamics can be modeled by elastic interfaces moving on disordered energy landscapes. PMID:27517790
Bottom hadrons from lattice QCD with domain wall and NRQCD fermions
Stefan Meinel, William Detmold, C.-J. David Lin, Matthew Wingate
2009-07-01
Dynamical 2+1 flavor lattice QCD is used to calculate the masses of bottom hadrons, including B mesons, singly and doubly bottom baryons, and for the first time also the triply-bottom baryon Omega{sub bbb}. The domain wall action is used for the up-, down-, and strange quarks (both valence and sea), while the bottom quark is implemented with non-relativistic QCD. A calculation of the bottomonium spectrum is also presented.
BLUM,T.; SONI,A.
2007-03-15
The workshop was held to mark the 10th anniversary of the first numerical simulations of QCD using domain wall fermions initiated at BNL. It is very gratifying that in the intervening decade widespread use of domain wall and overlap fermions is being made. It therefore seemed appropriate at this stage for some ''communal introspection'' of the progress that has been made, hurdles that need to be overcome, and physics that can and should be done with chiral fermions. The meeting was very well attended, drawing about 60 registered participants primarily from Europe, Japan and the US. It was quite remarkable that pioneers David Kaplan, Herbert Neuberger, Rajamani Narayanan, Yigal Shamir, Sinya Aoki, and Pavlos Vranas all attended the workshop. Comparisons between domain wall and overlap formulations, with their respective advantages and limitations, were discussed at length, and a broad physics program including pion and kaon physics, the epsilon regime, nucleon structure, and topology, among others, emerged. New machines and improved algorithms have played a key role in realizing realistic dynamical fermion lattice simulations (small quark mass, large volume, and so on), so much in fact that measurements are now as costly. Consequently, ways to make the measurements more efficient were also discussed. We were very pleased to see the keen and ever growing interest in chiral fermions in our community and the significant strides our colleagues have made in bringing chiral fermions to the fore of lattice QCD calculations. Their contributions made the workshop a success, and we thank them deeply for sharing their time and ideas. Finally, we must especially acknowledge Norman Christ and Bob Mawhinney for their early and continued collaboration without which the success of domain wall fermions would not have been possible.
Integral formula for elliptic SOS models with domain walls and a reflecting end
NASA Astrophysics Data System (ADS)
Lamers, Jules
2015-12-01
In this paper we extend previous work of Galleas and the author to elliptic SOS models. We demonstrate that the dynamical reflection algebra can be exploited to obtain a functional equation characterizing the partition function of an elliptic SOS model with domain-wall boundaries and one reflecting end. Special attention is paid to the structure of the functional equation. Through this approach we find a novel multiple-integral formula for that partition function.
Swift thermal steering of domain walls in ferromagnetic MnBi stripes
Sukhov, Alexander; Chotorlishvili, Levan; Ernst, Arthur; Zubizarreta, Xabier; Ostanin, Sergey; Mertig, Ingrid; Gross, Eberhard K. U.; Berakdar, Jamal
2016-01-01
We predict a fast domain wall (DW) motion induced by a thermal gradient across a nanoscopic ferromagnetic stripe of MnBi. The driving mechanism is an exchange torque fueled by magnon accumulation at the DWs. Depending on the thickness of the sample, both hot-to-cold and cold-to-hot DW motion directions are possible. The finding unveils an energy efficient way to manipulate DWs as an essential element in magnetic information processing such as racetrack memory. PMID:27076097
Bbb ZN domain walls in hot Script N = 4 SYM at weak and strong coupling
NASA Astrophysics Data System (ADS)
Armoni, Adi; Kumar, S. Prem; Ridgway, Jefferson M.
2009-01-01
We study the tensions of domain walls in the deconfined phase of Script N = 4 SUSY Yang-Mills theory on Bbb R3 × S1, at weak and strong coupling. We calculate the k-wall tension at one-loop order and find that it is proportional to k(N-k) (Casimir scaling). The two-loops analysis suggests that Casimir scaling persists to this order. The strong coupling calculation is performed by using the AdS/CFT correspondence. We argue that the k-wall should be identified with an NS5-brane wrapping an S4 inside S5 in the AdS-Schwarzschild × S5 background in Type IIB string theory. The tension at strong coupling is compared with the weak coupling result. We also compare our results with those from lattice simulations in pure Yang-Mills theory.
Domain wall of a ferromagnet on a three-dimensional topological insulator
Wakatsuki, Ryohei; Ezawa, Motohiko; Nagaosa, Naoto
2015-01-01
Topological insulators (TIs) show rich phenomena and functions which can never be realized in ordinary insulators. Most of them come from the peculiar surface or edge states. Especially, the quantized anomalous Hall effect (QAHE) without an external magnetic field is realized in the two-dimensional ferromagnet on a three-dimensional TI which supports the dissipationless edge current. Here we demonstrate theoretically that the domain wall of this ferromagnet, which carries edge current, is charged and can be controlled by the external electric field. The chirality and relative stability of the Neel wall and Bloch wall depend on the position of the Fermi energy as well as the form of the coupling between the magnetic moments and orbital of the host TI. These findings will pave a path to utilize the magnets on TI for the spintronics applications. PMID:26323943
Influence of Joule heating on current-induced domain wall depinning
NASA Astrophysics Data System (ADS)
Moretti, Simone; Raposo, Victor; Martinez, Eduardo
2016-06-01
The domain wall depinning from a notch in a Permalloy nanostrip on top of a SiO2/Si substrate is studied theoretically under application of static magnetic fields and the injection of short current pulses. The influence of Joule heating on current-induced domain wall depinning is explored self-consistently by coupling the magnetization dynamics in the ferromagnetic strip to the heat transport throughout the system. Our results indicate that Joule heating plays a remarkable role in these processes, resulting in a reduction in the critical depinning field and/or in a temporary destruction of the ferromagnetic order for typically injected current pulses. In agreement with experimental observations, similar pinning-depinning phase diagrams can be deduced for both current polarities when the Joule heating is taken into account. These observations, which are incompatible with the sole contribution of spin transfer torques, provide a deeper understanding of the physics underlying these processes and establish the real scope of the spin transfer torque. They are also relevant for technological applications based on current-induced domain-wall motion along soft strips.
Anomalous Dielectric Loss at Ferroelectric Domain Walls Revealed by Microwave Impedance Microscopy
NASA Astrophysics Data System (ADS)
Wu, Xiaoyu; Ren, Yuan; Hu, Rongwei; Cheong, Sang-Wook; Lai, Keji
2015-03-01
Domain walls (DWs) in multiferroic materials, within which the ferroic order parameter changes its orientation, may possess emergent properties that are absent in the bulk domains. Combining the standard piezo-force microscopy (PFM), conductive atomic-force microscopy (C-AFM), and a novel microwave impedance microscopy (MIM) technique, we observed strong dielectric loss at the domain walls and vortex cores on the (001) charge neutral surface of hexagonal manganite YMnO3. The DW contrast was detected for a broad frequency range between 100MHz and 3GHz. The equivalent DW conductivity inferred from the MIM signals is estimated to be five orders of magnitude higher than that of the bulk YMnO3, which cannot be explained within the existing theoretical framework. By applying a DC bias on the MIM probe, we have also observed the transition from DW contrast to domain contrast in the impedance images. The MIM technique provides a unique opportunity to probe the nanoscale electronic anomalies in various topological defects, which will be crucial for future device applications of multiferroics.
Domain Walls, near-BPS Bubbles and Probabilities in the Landscape
Ceresole, Anna; Dall'Agata, Gianguido; Giryavets, Alexander; Kallosh, Renata; Linde, Andrei; /Stanford U., Phys. Dept.
2006-06-27
We develop a theory of static BPS domain walls in stringy landscape and present a large family of BPS walls interpolating between different supersymmetric vacua. Examples include KKLT models, STU models, type IIB multiple flux vacua, and models with several Minkowski and AdS vacua. After the uplifting, some of the vacua become dS, whereas some others remain AdS. The near-BPS walls separating these vacua may be seen as bubble walls in the theory of vacuum decay. As an outcome of our investigation of the BPS walls, we found that the decay rate of dS vacua to a collapsing space with a negative vacuum energy can be quite large. The parts of space that experience a decay to a collapsing space, or to a Minkowski vacuum, never return back to dS space. The channels of irreversible vacuum decay serve as sinks for the probability flow. The existence of such sinks is a distinguishing feature of the landscape. We show that it strongly affects the probability distributions in string cosmology.
NASA Astrophysics Data System (ADS)
Krishnia, S.; Purnama, I.; Lew, W. S.
2016-12-01
In a patterned Co honeycomb spin ice structure, we show that violation in the ice-rule or magnetic monopoles, can be observed during a magnetization reversal process in 430 Oe≤H≤760 Oe magnetic field (H) range. The monopoles are shown to originate from the nucleation of domain walls at the edges, and they hop towards the other edge via the propagation of magnetic domain walls. The paths that the domain walls traveled or the Dirac strings, are shown to increase in length with magnetic fields increment and no random flipping of the bars are observed in the structure.
Quantum shock waves and domain walls in the real-time dynamics of a superfluid unitary Fermi gas.
Bulgac, Aurel; Luo, Yuan-Lung; Roche, Kenneth J
2012-04-13
We show that in the collision of two superfluid fermionic atomic clouds one observes the formation of quantum shock waves as discontinuities in the number density and collective flow velocity. Domain walls, which are topological excitations of the superfluid order parameter, are also generated and exhibit abrupt phase changes by π and slower motion than the shock waves. The domain walls are distinct from the gray soliton train or number density ripples formed in the wake of the shock waves and observed in the collisions of superfluid bosonic atomic clouds. Domain walls with opposite phase jumps appear to collide elastically.
Periodic magnetic domains in single-crystalline cobalt filament arrays
NASA Astrophysics Data System (ADS)
Chen, Fei; Wang, Fan; Jia, Fei; Li, Jingning; Liu, Kai; Huang, Sunxiang; Luan, Zhongzhi; Wu, Di; Chen, Yanbin; Zhu, Jianmin; Peng, Ru-Wen; Wang, Mu
2016-02-01
Magnetic structures with controlled domain wall pattern may be applied as potential building blocks for three-dimensional magnetic memory and logic devices. Using a unique electrochemical self-assembly method, we achieve regular single-crystalline cobalt filament arrays with specific geometric profile and crystallographic orientation, and the magnetic domain configuration can be conveniently tailored. We report the transition of periodic antiparallel magnetic domains to compressed vortex magnetic domains depending on the ratio of height to width of the wires. A "phase diagram" is obtained to describe the dependence of the type of magnetic domain and the geometrical profiles of the wires. Magnetoresistance of the filaments demonstrates that the contribution of a series of 180∘ domain walls is over 0.15 % of the zero-field resistance ρ (H =0 ) . These self-assembled magnetic nanofilaments, with controlled periodic domain patterns, offer an interesting platform to explore domain-wall-based memory and logic devices.
Néel walls between tailored parallel-stripe domains in IrMn/CoFe exchange bias layers
Ueltzhöffer, Timo Schmidt, Christoph; Ehresmann, Arno; Krug, Ingo; Nickel, Florian; Gottlob, Daniel
2015-03-28
Tailored parallel-stripe magnetic domains with antiparallel magnetizations in adjacent domains along the long stripe axis have been fabricated in an IrMn/CoFe Exchange Bias thin film system by 10 keV He{sup +}-ion bombardment induced magnetic patterning. Domain walls between these domains are of Néel type and asymmetric as they separate domains of different anisotropies. X-ray magnetic circular dichroism asymmetry images were obtained by x-ray photoelectron emission microscopy at the Co/Fe L{sub 3} edges at the synchrotron radiation source BESSY II. They revealed Néel-wall tail widths of 1 μm in agreement with the results of a model that was modified in order to describe such walls. Similarly obtained domain core widths show a discrepancy to values estimated from the model, but could be explained by experimental broadening. The rotation senses in adjacent walls were determined, yielding unwinding domain walls with non-interacting walls in this layer system.
The dynamics of field and current-driven magnetic domain wall depinning
NASA Astrophysics Data System (ADS)
Beach, Geoffrey; Knutson, Carl; Tsoi, Maxim; Erskine, James
2008-03-01
The depinning of a magnetic domain wall from a well-defined potential well was studied experimentally on timescales ranging from minutes down to tens of nanoseconds. At longer timescales, the behavior follows the classical Neel-Brown model of thermal activation, one of the few observations of this process for the ideal case of a single energy barrier. Below one microsecond, however, the depinning rate becomes independent of the activation volume and assumes a more universal behavior. This transition is due to a vanishing of the energy barrier at a critical field, beyond which the rate of depinning depends primarily on the torque supplied by the field and spin current. A dc spin-polarized current flowing across the domain wall has the effect of lowering the energy barrier by an amount that is predominantly quadratic in current, independent of its direction. This is seen to arise from a shift of the wall in the energy potential due to the adiabatic component of spin-transfer torque.
Burn, D. M. Atkinson, D.
2014-10-28
Understanding domain wall pinning and propagation in nanowires are important for future spintronics and nanoparticle manipulation technologies. Here, the effects of microscopic local modification of the magnetic properties, induced by focused-ion-beam intermixing, in NiFe/Au bilayer nanowires on the pinning behavior of domain walls was investigated. The effects of irradiation dose and the length of the irradiated features were investigated experimentally. The results are considered in the context of detailed quasi-static micromagnetic simulations, where the ion-induced modification was represented as a local reduction of the saturation magnetization. Simulations show that domain wall pinning behavior depends on the magnitude of the magnetization change, the length of the modified region, and the domain wall structure. Comparative analysis indicates that reduced saturation magnetisation is not solely responsible for the experimentally observed pinning behavior.
The stability of steady motion of magnetic domain wall: Role of higher-order spin-orbit torques
He, Peng-Bin Yan, Han; Cai, Meng-Qiu; Li, Zai-Dong
2015-12-14
The steady motion of magnetic domain wall driven by spin-orbit torques is investigated analytically in the heavy/ferromagnetic metal nanowires for three cases with a current transverse to the in-plane and perpendicular easy axis, and along the in-plane easy axis. By the stability analysis of Walker wall profile, we find that if including the higher-order spin-orbit torques, the Walker breakdown can be avoided in some parameter regions of spin-orbit torques with a current transverse to or along the in-plane easy axis. However, in the case of perpendicular anisotropy, even considering the higher-order spin-orbit torques, the velocity of domain wall cannot be efficiently enhanced by the current. Furthermore, the direction of wall motion is dependent on the configuration and chirality of domain wall with a current along the in-plane easy axis or transverse to the perpendicular one. Especially, the direction of motion can be controlled by the initial chirality of domain wall. So, if only involving the spin-orbit mechanism, it is preferable to adopt the scheme of a current along the in-plane easy axis for enhancing the velocity and controlling the direction of domain wall.
Scaling behavior of domain walls at the T = 0 ferromagnet to spin-glass transition
NASA Astrophysics Data System (ADS)
Melchert, O.; Hartmann, A. K.
2009-01-01
Using mappings to combinatorial optimization problems, one can often study physical systems better by means of sophisticated algorithms from computer science. Here, we study the geometric properties of domain-wall excitations in a two-dimensional random-bond Ising spin system, where each realization of the disorder consists of a random fraction ρ of ferromagnetic bonds and a fraction (1-ρ) of bonds drawn from a Gaussian distribution with zero mean and unit width. We formulate an auxiliary graph theoretical problem in which domain walls are given by undirected shortest paths with possibly negative distances [O. Melchert and A.K. Hartmann Phys. Rev. B 76, 174411 (2007)]. Due to the details of the mapping, standard shortest path algorithms (e.g. the Dijkstra algorithm) cannot be applied. To solve such shortest path problems it requires minimum weight perfect matching algorithms. We first locate the critical point ρc, where the ferromagnet (large ρ) to spin-glass transition occurs. For certain values of ρ close to the critical point we investigate the stiffness exponent θ and the fractal dimension df that describe the scaling of the average domain-wall energy and length, respectively. Performing a finite-size scaling analysis we find that both exponents remain constant in the spin-glass phase, i.e. θ~-0.28 and df~1.275. This is consistent with conformal field theory, where it seems to be possible [C. Amoruso et al. Phys. Rev. Lett. 97, 267202 (2006)] to relate the exponents via df-1 = 3/[4(3+θ)].
Improving ferrite MIG head read-back distortions caused by domain walls and granularity (abstract)
NASA Astrophysics Data System (ADS)
Argyle, B. E.; Schäfer, R.; Trouilloud, P. L.; Re, M. E.; Praino, A. P.; Takayama, S.; Dingley, D.
1994-05-01
Ferrite MiG heads intended for narrow track (≲10 μm) digital recording were recently investigated in the critical pole-tip region at the air-bearing-surface using micro-ellipsometry, Kerr microscopy, and electron back-scatter diffraction from individual grains,1 and using magnetic force microscopy to detect air-gap remanent fields.2 Comparison of these direct observations with readback-after-write waveforms from written test tracks, and consideration of granularity influences on bulk permeability and domain size, indicate that waveform instability and asymmetry from polycrystalline ferrite (PCF) heads would be diminished by suitable size and orientation of the grains.1 The use of single-crystal ferrite3 (SCF) for advanced laser enhanced etch definition3 of narrow pole MiGs can avoid this type of distortion. However, secondary signals4 often appear as weak pulses separated in time from the main gap pulse. We have associated this effect with a zig-zag shaped wall seen nucleated and propagated from the pole tips by a write pulse.4 This wall and its underlying domains lie remanent in the stressed ABS material and evidently react to the bit fields during the read cycle. The secondary read-back response, though similar to the pseudo-gap effect, differs in origin. Its timing depends on the distance of the zig-zag wall to the gap, not the fixed position of the sendust-ferrite interface. Our results indicate that suitable grain oriented ferrite would reduce PCF MiG head read-back asymmetry and instability. For SCF heads, a method for electrically removing zig-zag walls is possible and secondary pulse removal has now been demonstrated on a spin test strand.
Generalized parton distributions from domain wall valence quarks and staggered sea quarks
Renner, Dru; Bratt, Jonathan; Edwards, Robert; Engelhardt, Michael; Fleming, George; Haegler, Philipp; Musch, Bernhard; Negele, John; Orginos, Konstantinos; Pochinsky, Andrew; Richards, David; Schroers, Wolfram
2007-11-01
Moments of the generalized parton distributions of the nucleon, calculated with a mixed action of domain wall valence quarks and asqtad staggered sea quarks, are presented for pion masses extending down to 359 MeV. Results for the moments of the unpolarized, helicity, and transversity distributions are given and compared to the available experimental measurements. Additionally, a selection of the generalized form factors are shown and the implications for the spin decomposition and transverse structure of the nucleon are discussed. Particular emphasis is placed on understanding systematic errors in the lattice calculation and exploring a variety of chiral extrapolations.
K(13) FORM FACTOR WITH TWO FLAVORS OF DYNAMICAL DOMAIN WALL QUARKS.
SONI, A.; DAWSON, T.; IZUBUCHI, T.; KANEKO, T.; SASAKI, S.
2005-07-25
We report on our calculation of K {yields} {pi} vector form factor by numerical simulations of two-flavor QCD on a 16{sup 3} x 32 x 12 lattice at a {approx_equal} 0.12 fm using domain-wall quarks and DBW2 glue. Our preliminary result at a single sea quark mass corresponding to m{sub PS}/m{sub V} {approx_equal} 0.53 shows a good agreement with previous estimate in quenched QCD and that from a phenomenological model.
Quark Contributions to Nucleon Momentum and Spin from Domain Wall fermion calculations
S. N. Syritsyn, J. R. Green, J. W. Negele, A. V. Pochinsky, M. Engelhardt, Ph. Hagler, B. Musch, W. Schroers
2011-12-01
We report contributions to the nucleon spin and momentum from light quarks calculated using dynamical domain wall fermions with pion masses down to 300 MeV and fine lattice spacing a=0.084 fm. Albeit without disconnected diagrams, we observe that spin and orbital angular momenta of both u and d quarks are opposite, almost canceling in the case of the d quark, which agrees with previous calculations using a mixed quark action. We also present the full momentum dependence of n=2 generalized form factors showing little variation with the pion mass.
Nonperturbative renormalization of quark bilinear operators and B{sub K} using domain wall fermions
Aoki, Y.; Dawson, C.; Boyle, P. A.; Tweedie, R. J.; Christ, N. H.; Li, S.; Mawhinney, R. D.; Donnellan, M. A.; Juettner, A.; Sachrajda, C. T.; Izubuchi, T.; Noaki, J.; Soni, A.; Yamaguchi, A.
2008-09-01
We present a calculation of the renormalization coefficients of the quark bilinear operators and the K-K mixing parameter B{sub K}. The coefficients relating the bare lattice operators to those in the RI/MOM scheme are computed nonperturbatively and then matched perturbatively to the MS scheme. The coefficients are calculated on the RBC/UKQCD 2+1 flavor dynamical lattice configurations. Specifically we use a 16{sup 3}x32 lattice volume, the Iwasaki gauge action at {beta}=2.13 and domain wall fermions with L{sub s}=16.
Improving chiral property of domain-wall fermions by reweighting method
Ishikawa, T.; Aoki, Y.; Izubuchi, T.
2009-07-25
The reweighting method is applied to improve the chiral property of domain-wall fermions. One way to achieve this is to enlarge L{sub s}, the size of fifth dimension, which controls the size of the induced chiral symmetry breaking. While this is a type of reweighting method for shifting the action parameter, it seems non-trivial since this reweighting means change of the five dimensional lattice volume. In this report, we address issues in this direction of reweighting and evaluate its effectiveness.
Domain-wall melting as a probe of many-body localization
NASA Astrophysics Data System (ADS)
Hauschild, Johannes; Heidrich-Meisner, Fabian; Pollmann, Frank
2016-10-01
Motivated by a recent optical-lattice experiment by Choi et al. [Science 352, 1547 (2016), 10.1126/science.aaf8834], we discuss how domain-wall melting can be used to investigate many-body localization. First, by considering noninteracting fermion models, we demonstrate that experimentally accessible measures are sensitive to localization and can thus be used to detect the delocalization-localization transition, including divergences of characteristic length scales. Second, using extensive time-dependent density matrix renormalization group simulations, we study fermions with repulsive interactions on a chain and a two-leg ladder. The extracted critical disorder strengths agree well with the ones found in existing literature.
Current-induced resonant depinning of a transverse magnetic domain wall in a spin valve nanostrip
NASA Astrophysics Data System (ADS)
Metaxas, P. J.; Anane, A.; Cros, V.; Grollier, J.; Deranlot, C.; Lemaître, Y.; Xavier, S.; Ulysse, C.; Faini, G.; Petroff, F.; Fert, A.
2010-11-01
We study the impact of rf and dc currents on domain wall depinning in the soft layer of a 120 nm wide Co/Cu/NiFe spin valve nanostrip. A strong resonant reduction in the depinning field (from ˜75 to 25 Oe) is observed for rf currents near 3.5 GHz. Notably, the features of the resonant depinning depend not only on the rf current but also on the simultaneously applied dc current. Consequently, we discuss both the role of the adiabatic spin torque at resonance and that of the current generated Oersted fields.
Nonadiabatic spin transfer torque in high anisotropy magnetic nanowires with narrow domain walls.
Boulle, O; Kimling, J; Warnicke, P; Kläui, M; Rüdiger, U; Malinowski, G; Swagten, H J M; Koopmans, B; Ulysse, C; Faini, G
2008-11-21
Current induced domain wall (DW) depinning of a narrow DW in out-of-plane magnetized (Pt/Co)_{3}/Pt multilayer elements is studied by magnetotransport. We find that for conventional measurements Joule heating effects conceal the real spin torque efficiency and so we use a measurement scheme at a constant sample temperature to unambiguously extract the spin torque contribution. From the variation of the depinning magnetic field with the current pulse amplitude we directly deduce the large nonadiabaticity factor in this material and we find that its amplitude is consistent with a momentum transfer mechanism. PMID:19113434
Axial couplings of heavy hadrons from domain-wall lattice QCD
W. Detmold, C.J.D. Lin, S. Meinel
2011-12-01
We calculate matrix elements of the axial current for static-light mesons and baryons in lattice QCD with dynamical domain wall fermions. We use partially quenched heavy hadron chiral perturbation theory in a finite volume to extract the axial couplings g{sub 1}, g{sub 2}, and g{sub 3} from the data. These axial couplings allow the prediction of strong decay rates and enter chiral extrapolations of most lattice results in the b sector. Our calculations are performed with two lattice spacings and with pion masses down to 227 MeV.
Dynamics of the magnetic moments for chain of dipoles in domain wall
NASA Astrophysics Data System (ADS)
Shutyıˇ, Anatoliy M.; Sementsov, Dmitriy I.
2016-03-01
We report on the dynamics of the magnetic moment numerically simulated for a chain of the magnetic nanodots coupled through the dipole-dipole interaction and in the presence of the magnetic anisotropy of various types. It is shown that a static field applied to the system causes specific fluctuations of the transverse components of the magnetic moment leading to a sequence of the oscillation trains observed in the domain wall. Various oscillation modes governed by the external alternating field are revealed. The influence of the unidirectional and uniaxial anisotropy ("easy-plane" and "easy axis" anisotropy) on the system behavior is described.
Micromagnetic structure of the domain wall with Bloch lines in an electric field
NASA Astrophysics Data System (ADS)
Borich, M. A.; Tankeev, A. P.; Smagin, V. V.
2016-07-01
The micromagnetic structure of the domain wall (DW) with periodically distributed horizontal Bloch lines in a ferromagnetic film in an external electric field has been studied. The effect of the electric field on the internal DW micromagnetic structure is caused by inhomogeneous magnetoelectric coupling. Possible scenarios of the DW internal structure transformations implemented with varying the electric fields strength have been analyzed in detail. For each scenario, static characteristics of the system, such as the energy, DW profile, DW effective thickness, and electric polarization have been calculated.
Anomalous switching in Nb/Ru/Sr2RuO4 topological junctions by chiral domain wall motion
NASA Astrophysics Data System (ADS)
Anwar, M. S.; Nakamura, Taketomo; Yonezawa, S.; Yakabe, M.; Ishiguro, R.; Takayanagi, H.; Maeno, Y.
2013-08-01
A spontaneous symmetry breaking in a system often results in domain wall formation. The motion of such domain walls is utilized to realize novel devices like racetrack-memories, in which moving ferromagnetic domain walls store and carry information. Superconductors breaking time reversal symmetry can also form domains with degenerate chirality of their superconducting order parameter. Sr2RuO4 is the leading candidate of a chiral p-wave superconductor, expected to be accompanied by chiral domain structure. Here, we present that Nb/Ru/Sr2RuO4 topological superconducting-junctions, with which the phase winding of order parameter can be effectively probed by making use of real-space topology, exhibit unusual switching between higher and lower critical current states. This switching is well explained by chiral-domain-wall dynamics. The switching can be partly controlled by external parameters such as temperature, magnetic field and current. These results open up a possibility to utilize the superconducting chiral domain wall motion for future novel superconducting devices.
Intrinsic Nature of Stochastic Domain Wall Pinning Phenomena in Magnetic Nanowire Devices
Hayward, T. J.
2015-01-01
Finite temperature micromagnetic simulations are used to probe stochastic domain wall pinning behaviours in magnetic nanowire devices. By exploring field-induced propagation both below and above the Walker breakdown field it is shown that all experimentally observed phenomena can be comprehensively explained by the influence of thermal perturbations on the domain walls’ magnetisation dynamics. Nanowires with finite edge roughness are also investigated, and these demonstrate how this additional form of disorder couples with thermal perturbations to significantly enhance stochasticity. Cumulatively, these results indicate that stochastic pinning is an intrinsic feature of DW behaviour at finite temperatures, and would not be suppressed even in hypothetical systems where initial DW states and experimental parameters were perfectly defined. PMID:26304797
Hysteretic magnetoresistance and unconventional anomalous Hall effect in the frustrated magnet TmB4
Sunku, Sai Swaroop; Kong, Tai; Ito, Toshimitsu; Canfield, Paul C.; Shastry, B. Sriram; Sengupta, Pinaki; Panagopoulos, Christos
2016-05-11
We study TmB4, a frustrated magnet on the Archimedean Shastry-Sutherland lattice, through magnetization and transport experiments. The lack of anisotropy in resistivity shows that TmB4 is an electronically three-dimensional system. The magnetoresistance (MR) is hysteretic at low temperature even though a corresponding hysteresis in magnetization is absent. The Hall resistivity shows unconventional anomalous Hall effect (AHE) and is linear above saturation despite a large MR. In conclusion, we propose that complex structures at magnetic domain walls may be responsible for the hysteretic MR and may also lead to the AHE.
Hysteretic magnetoresistance and unconventional anomalous Hall effect in the frustrated magnet TmB4
NASA Astrophysics Data System (ADS)
Sunku, Sai Swaroop; Kong, Tai; Ito, Toshimitsu; Canfield, Paul C.; Shastry, B. Sriram; Sengupta, Pinaki; Panagopoulos, Christos
2016-05-01
We study TmB4, a frustrated magnet on the Archimedean Shastry-Sutherland lattice, through magnetization and transport experiments. The lack of anisotropy in resistivity shows that TmB4 is an electronically three-dimensional system. The magnetoresistance (MR) is hysteretic at low temperature even though a corresponding hysteresis in magnetization is absent. The Hall resistivity shows unconventional anomalous Hall effect (AHE) and is linear above saturation despite a large MR. We propose that complex structures at magnetic domain walls may be responsible for the hysteretic MR and may also lead to the AHE.
Hysteretic magnetoresistance and unconventional anomalous Hall effect in the frustrated magnet TmB4
NASA Astrophysics Data System (ADS)
Sunku, Sai Swaroop; Kong, Tai; Ito, Toshimitsu; Canfield, Paul C.; Shastry, B. Sriram; Sengupta, Pinaki; Panagopoulos, Christos
We study TmB4, a frustrated magnet on the Archimedean Shastry-Sutherland lattice, through magnetization and transport experiments. The lack of anisotropy in resistivity shows that TmB4 is an electronically three-dimensional system. The magnetoresistance (MR) is hysteretic at low-temperature even though a corresponding hysteresis in magnetization is absent. The Hall resistivity shows unconventional anomalous Hall effect (AHE) and is linear above saturation despite a large MR. We suggest that both hysteretic MR and AHE arise from the formation of complex non-coplanar structures at magnetic domain walls. Current address: Department of Applied Physics and Applied Mathematics, Columbia University.
Graham, Joseph T.; Brennecka, Geoff L.; Ihlefeld, Jon F.; Ferreira, Paulo; Small, Leo; Duquette, David; Apblett, Christopher; Landsberger, Sheldon
2013-03-28
The effects of neutron-induced damage on the ferroelectric properties of thin film lead zirconate titanate (PZT) were investigated. Two sets of PbZr{sub 0.52}Ti{sub 0.48}O{sub 3} films of varying initial quality were irradiated in a research nuclear reactor up to a maximum 1 MeV equivalent neutron fluence of (5.16 {+-} 0.03) Multiplication-Sign 10{sup 15} cm{sup -2}. Changes in domain wall mobility and reversibility were characterized by polarization-electric field measurements, Rayleigh analysis, and analysis of first order reversal curves (FORC). With increasing fluence, extrinsic contributions to the small-signal permittivity diminished. Additionally, redistribution of irreversible hysterons towards higher coercive fields was observed accompanied by the formation of a secondary hysteron peak following exposure to high fluence levels. The changes are attributed to the radiation-induced formation of defect dipoles and other charged defects, which serve as effective domain wall pinning sites. Differences in damage accumulation rates with initial film quality were observed between the film sets suggesting a dominance of pre-irradiation microstructure on changes in macroscopic switching behavior.
Phase Competition, Solitons, and Domain Walls in Neutral–Ionic Transition Systems
NASA Astrophysics Data System (ADS)
Tsuchiizu, Masahisa; Yoshioka, Hideo; Seo, Hitoshi
2016-10-01
Phase competition and excitations in the one-dimensional neutral-ionic transition systems are theoretically studied comprehensively. From the semiclassical treatment of the bosonized Hamiltonian, we examine the competition among the neutral (N), ferroelectric-ionic (I$_\\mathrm{ferro}$) and paraelectric-ionic (I$_\\mathrm{para}$) states. The phase transitions between them can become first-order when the fluctuation-induced higher-order commensurability potential is considered. In particular, the description of the first-order phase boundary between N and I$_\\mathrm{ferro}$ enables us to analyze N-I$_\\mathrm{ferro}$ domain walls. Soliton excitations in the three phases are described explicitly and their formation energies are evaluated across the phase boundaries. The characters of the soliton and domain-wall excitations are classified in terms of the topological charge and spin. The relevance to the experimental observations in the molecular neutral-ionic transition systems is discussed. We ascribe the pressure-induced crossover in tetrathiafulvalene-$p$-chloranil (TTF-CA) at a high-temperature region to that from the N to the I$_\\mathrm{para}$ state, and discuss its consequence.
Artificial chemical and magnetic structure at the domain walls of an epitaxial oxide
NASA Astrophysics Data System (ADS)
Noheda, Beatriz
Progress in nanotechnology requires new paradigms for materials synthesis that allow controlling their functionality down to the smallest scales. Here we report a novel two-dimensional ferromagnetic phase that is synthesized at the domain walls (DWs) of the antiferromagnetic insulator TbMnO3 when grown in thin layers under epitaxial strain. This Mn oxide phase presents an atomic arrangement that does not exist in bulk and cannot be synthesized by standard chemical routes. The number of 2D ferromagnetic sheets can be controlled by tuning the thickness of the thin films, giving rise to volume fractions that go up to 25% of the total film volume. Such novel phases are driven by a unique environment induced by the symmetry breaking and large stresses present at domain walls, which function as nanoreactors. This new class of nanoscale materials may find innovative applications in nanoelectronics and spintronics. The work is published as S. Farokhipoor, C. Magén, S. Venkatesan, J. Íñiguez, C. J. M. Daumont, D. Rubi, E. Snoeck, M. Mostovoy, C. de Graaf, A. Müller, M. Döblinger, C. Scheu, B. Noheda, Nature 515, 379 (2014)
Magnetic fingerprint of interfacial coupling between CoFe and nanoscale ferroelectric domain walls
NASA Astrophysics Data System (ADS)
Zhang, Qintong; Murray, Peyton; You, Lu; Wan, Caihua; Zhang, Xuan; Li, Wenjing; Khan, Usman; Wang, Junling; Liu, Kai; Han, Xiufeng
2016-08-01
Magnetoelectric coupling in ferromagnetic/multiferroic systems is often manifested in the exchange bias effect, which may have combined contributions from multiple sources, such as domain walls, chemical defects, or strain. In this study we magnetically "fingerprint" the coupling behavior of CoFe grown on epitaxial BiFeO3 (BFO) thin films by magnetometry and the first-order-reversal-curves (FORC). The contribution to exchange bias from 71°, 109° and charged ferroelectric domain walls (DWs) was elucidated by the FORC distribution. CoFe samples grown on BFO with 71° DWs only exhibit an enhancement of the coercivity, but little exchange bias. Samples grown on BFO with 109° DWs and mosaic DWs exhibit a much larger exchange bias, with the main enhancement attributed to 109° and charged DWs. Based on the Malozemoff random field model, a varying-anisotropy model is proposed to account for the exchange bias enhancement. This work sheds light on the relationship between the exchange bias effect of the CoFe/BFO heterointerface and the ferroelectric DWs, and provides a path for multiferroic device analysis and design.
NASA Astrophysics Data System (ADS)
Zahnd, G.; Pham, V. T.; Marty, A.; Jamet, M.; Beigné, C.; Notin, L.; Vergnaud, C.; Rortais, F.; Vila, L.; Attané, J.-P.
2016-05-01
We study domain wall injection in 100 nm wide NiFe nanowires, followed by domain wall propagation and pinning on 50 nm wide constrictions. The injection is performed using local and external magnetic fields. Using several nucleation pad geometries, we show that at these small dimensions the use of an external field only does not allow obtaining a reproducible injection/pinning process. However, the use of an additional local field, created by an Oersted line, allows to nucleate a reversed domain at zero external applied field. Then, an external field of 5 mT enables the domain wall to propagate far from the Oersted line, and the pinning occurs reproducibly. We also show that notwithstanding the reproducibility of the pinning process, the depinning field is found to be stochastic, following a bimodal distribution. Using micromagnetic simulation we link two different DW configurations, vortex and transverse, to the two typical depinning fields.
Shield-related signal instability in magnetoresistive heads
NASA Astrophysics Data System (ADS)
Nakamoto, K.; Narumi, S.; Kawabe, T.; Kobayashi, T.; Fukui, H.
1999-04-01
Magnetoresistive (MR) heads with various upper shield materials were fabricated and their read-write performance was tested to clarify the shield-related effect on the signal instability in MR heads. Comparison of a head with an upper shield layer of higher magnetostriction and one with lower magnetostriction showed that the latter had better stability in the output signal of a repeated read-write test. The output amplitude of a head with an upper shield layer of Co52Ni27Fe21 film, which had a high magnetostriction of about +3×10-6, was varied by applying a low external longitudinal field, which affected just the shield layers. This change in the output corresponded well to the output variation in the repeated read-write test. The spin scanning electron micrograph image of this head revealed a distinct domain wall in the air bearing surface near the MR sensor. These results indicated that instability of the domain structure in a shield layer was one of the causes of the signal instability in MR heads; an unusual bias field from a domain wall of the shield layer, which could be moved easily by a repeated writing operation, caused a variation in the biased state of the MR layer which resulted in the signal variation, and that low magnetostriction was required for a shield material to achieve a stable head.
Zero-line modes at stacking faulted domain walls in multilayer graphene
NASA Astrophysics Data System (ADS)
Lee, Changhee; Kim, Gunn; Jung, Jeil; Min, Hongki
2016-09-01
Rhombohedral multilayer graphene is a physical realization of the chiral two-dimensional electron gas that can host zero-line modes (ZLMs), also known as kink states, when the local gap opened by inversion symmetry breaking potential changes sign in real space. Here we study how the variations in the local stacking coordination of multilayer graphene affects the formation of the ZLMs. Our analysis indicates that the valley Hall effect develops whenever an interlayer potential difference is able to open up a band gap in stacking faulted multilayer graphene, and that ZLMs can appear at the domain walls separating two distinct regions with imperfect rhombohedral stacking configurations. Based on a tight-binding formulation with distant hopping terms between carbon atoms, we first show that topologically distinct domains characterized by the valley Chern number are separated by a metallic region connecting AA and AA' stacking line in the layer translation vector space. We find that gapless states appear at the interface between the two stacking faulted domains with different layer translation or with opposite perpendicular electric field if their valley Chern numbers are different.
Visualizing anisotropic propagation of stripe domain walls in staircaselike transitions of IrTe2
NASA Astrophysics Data System (ADS)
Mauerer, Tobias; Vogt, Matthias; Hsu, Pin-Jui; Pascut, Gheorghe Lucian; Haule, Kristjan; Kiryukhin, Valery; Yang, Junjie; Cheong, Sang-Wook; Wu, Weida; Bode, Matthias
2016-07-01
We present a scanning tunneling microscopy (STM) study of the domain evolution across two first-order phase transitions of stripe modulations in IrTe2 that occur at TC≈275 K and TS≈180 K, respectively. Phase coexistence of the hexagonal (1 ×1 ) structure and the (5 ×1 ) stripe modulation is observed at TC, while various (p ×1 ) modulations (p =3 n +2 with 2 ≤n ∈N ) are observed below TS. Using STM atomic resolution, we observe anisotropic propagation of domain boundaries along different directions, indicating significantly different kinetic energy barriers. These results are consistently explained by a theoretical analysis of the energy barrier for domain wall propagation as obtained by density functional theory. Individual switching processes observed by STM indicate that the wide temperature range of the transition from the (5 ×1 ) stripes to the (6 ×1 ) -ordered ground state is probably caused by the numerically limited subset of switching processes that are allowed between a given initial and the final state. The observations on IrTe2 are discussed in terms of a "harmless staircase" with a finite number of first-order transitions between commensurate phases and within a "dynamical freezing" scenario.
SU(5) grand unification on a domain-wall brane from an E{sub 6}-invariant action
Davidson, Aharon; George, Damien P.; Kobakhidze, Archil; Volkas, Raymond R.; Wali, Kameshwar C.
2008-04-15
An SU(5) grand unification scheme for effective 3+1-dimensional fields dynamically localized on a domain-wall brane is constructed. This is achieved through the confluence of the clash-of-symmetries mechanism for symmetry breaking through domain-wall formation, and the Dvali-Shifman gauge-boson localization idea. It requires an E{sub 6} gauge-invariant action, yielding a domain-wall solution that has E{sub 6} broken to differently embedded SO(10) x U(1) subgroups in the two bulk regions on opposite sides of the wall. On the wall itself, the unbroken symmetry is the intersection of the two bulk subgroups, and contains SU(5). A 4+1-dimensional fermion family in the 27 of E{sub 6} gives rise to localized left-handed zero modes in the 5*+10+1+1 representation of SU(5). The remaining ten fermion components of the 27 are delocalized exotic states, not appearing in the effective 3+1-dimensional theory on the domain-wall brane. The scheme is compatible with the type-2 Randall-Sundrum mechanism for graviton localization; the single extra dimension is infinite.
NASA Astrophysics Data System (ADS)
Bang, Do; Yu, Jiawei; Qiu, Xuepeng; Wang, Yi; Awano, Hiroyuki; Manchon, Aurelien; Yang, Hyunsoo
2016-05-01
We investigate the current-induced domain wall motion in perpendicular magnetized Tb/Co wires with structure inversion asymmetry and different layered structures. We find that the critical current density to drive domain wall motion strongly depends on the layered structure. The lowest critical current density ˜15 MA /c m2 and the highest slope of domain wall velocity curve are obtained for the wire having thin Co sublayers and more inner Tb/Co interfaces, while the largest critical current density ˜26 MA /c m2 required to drive domain walls is observed in the Tb-Co alloy magnetic wire. It is found that the Co/Tb interface contributes negligibly to Dzyaloshinskii-Moriya interaction, while the effective spin-orbit torque strongly depends on the number of Tb/Co inner interfaces (n ). An enhancement of the antidamping torques by extrinsic spin Hall effect due to Tb rare-earth impurity-induced skew scattering is suggested to explain the high efficiency of current-induced domain wall motion.
Neutron and proton electric dipole moments from Nf=2 +1 domain-wall fermion lattice QCD
NASA Astrophysics Data System (ADS)
Shintani, Eigo; Blum, Thomas; Izubuchi, Taku; Soni, Amarjit; Rbc; Ukqcd Collaborations
2016-05-01
We present a lattice calculation of the neutron and proton electric dipole moments (EDMs) with Nf=2 +1 flavors of domain-wall fermions. The neutron and proton EDM form factors are extracted from three-point functions at the next-to-leading order in the θ vacuum of QCD. In this computation, we use pion masses of 0.33 and 0.42 GeV and 2.7 fm3 lattices with Iwasaki gauge action, and a 0.17 GeV pion and a 4.6 fm3 lattice with I-DSDR gauge action, all generated by the RBC and UKQCD collaborations. The all-mode averaging technique enables an efficient and high statistics calculation. Chiral behavior of lattice EDMs is discussed in the context of baryon chiral perturbation theory. In addition, we also show numerical evidence on the relationship of three- and two-point correlation functions with the local topological charge distribution.
Dynamics of three-dimensional helical domain wall in cylindrical NiFe nanowires
NASA Astrophysics Data System (ADS)
Wong, D. W.; Chandra Sekhar, M.; Gan, W. L.; Purnama, I.; Lew, W. S.
2015-05-01
We report on a micromagnetic study on the dynamics of current-driven helical domain wall (DW) in cylindrical NiFe nanowires. The helical DW is a three-dimensional transition region between magnetizations with clockwise and anticlockwise vortex orientations. A minimum current density is needed to overcome an intrinsic pinning to drive the helical DW, and the propagation along the nanowire is accompanied by a rotational motion. As the driving current strength is increased, the rotation ceases while the DW propagates at an increased velocity. However, a velocity barrier is experienced which results in the decrease of the DW mobility. Throughout its motion, the propagated helical DW maintains a stable profile without showing any sign of structural breakdown even at relatively high driving current.
Geometrically pinned magnetic domain wall for multi-bit per cell storage memory
NASA Astrophysics Data System (ADS)
Bahri, M. Al; Sbiaa, R.
2016-06-01
Spintronic devices currently rely on magnetic switching or controlled motion of domain walls (DWs) by an external magnetic field or a spin-polarized current. Controlling the position of DW is essential for defining the state/information in a magnetic memory. During the process of nanowire fabrication, creating an off-set of two parts of the device could help to pin DW at a precise position. Micromagnetic simulation conducted on in-plane magnetic anisotropy materials shows the effectiveness of the proposed design for pinning DW at the nanoconstriction region. The critical current for moving DW from one state to the other is strongly dependent on nanoconstricted region (width and length) and the magnetic properties of the material. The DW speed which is essential for fast writing of the data could reach values in the range of hundreds m/s. Furthermore, evidence of multi-bit per cell memory is demonstrated via a magnetic nanowire with more than one constriction.
Miniature Hall sensor integrated on a magnetic thin film for detecting domain wall motion
NASA Astrophysics Data System (ADS)
Kubota, M.; Tokunaga, Y.; Kanazawa, N.; Kagawa, F.; Tokura, Y.; Kawasaki, M.
2013-08-01
We have fabricated a cross-bar Hall sensor made of 50-nm-wide and 100-nm-thick bismuth wires patterned by an electron-beam lithography and lift-off. The Hall coefficient at 300 K is as large as -0.44 cm3/C, yielding in a high product sensitivity of about 5 V/(A T). The series resistance was reduced as low as 1.7 kΩ with a short bar configuration, resulting in a high signal-to-noise ratio of 38.5 dB. These characteristics are far better than those reported with similar dimensions. The Hall element was successfully demonstrated for detecting the domain wall motion in an iron garnet film employed as the substrate.
Domain wall depinning from notches using combined in- and out-of-plane magnetic fields
NASA Astrophysics Data System (ADS)
Goertz, Jelle J. W.; Ziemys, Grazvydas; Eichwald, Irina; Becherer, Markus; Swagten, Henk J. M.; Breitkreutz-v. Gamm, Stephan
2016-05-01
Controlled domain wall motion and pinning in nanowires with perpendicular magnetic anisotropy are of great importance in modern magnetic memory and logic devices. Here, we investigate by experiment the DW pinning and depinning from a notch in a magnetic nanowire, under the influence of combined in- and out-of-plane magnetic fields. In our experiment, the perpendicular magnetization of the Co/Pt nanowires is tilted with the help of sub-μs in-plane field pulses generated by an on-chip coil. Consequently, the energy density of the DW is decreased and the depinning field of the notch is reduced. A theoretical model is applied and compared to the measurement results. The DW depinning mechanism and the DW type are further investigated by micromagnetic simulations.
Current-driven domain wall motion enhanced by the microwave field
Wang, Xi-guang; Guo, Guang-hua Nie, Yao-zhuang; Wang, Dao-wei; Li, Zhi-xiong; Tang, Wei; Zeng, Zhong-ming
2014-07-14
The magnetic domain wall (DW) motion driven by a spin-polarized current opens a new concept for memory and logic devices. However, the critical current density required to overcome the intrinsic and/or extrinsic pinning of DW remains too large for practical applications. Here, we show, by using micromagnetic simulations and analytical approaches, that the application of a microwave field offers an effective solution to this problem. When a transverse microwave field is applied, the adiabatic spin-transfer torque (STT) alone can sustain a steady-state DW motion without the sign of Walker breakdown, meaning that the intrinsic pinning disappears. The extrinsic pinning can also be effectively reduced. Moreover, the DW velocity is increased greatly for the microwave-assisted DW motion. This provides a new way to manipulate the DW motion at low current densities.
Ring-shaped Racetrack memory based on spin orbit torque driven chiral domain wall motions
NASA Astrophysics Data System (ADS)
Zhang, Yue; Zhang, Xueying; Hu, Jingtong; Nan, Jiang; Zheng, Zhenyi; Zhang, Zhizhong; Zhang, Youguang; Vernier, Nicolas; Ravelosona, Dafine; Zhao, Weisheng
2016-10-01
Racetrack memory (RM) has sparked enormous interest thanks to its outstanding potential for low-power, high-density and high-speed data storage. However, since it requires bi-directional domain wall (DW) shifting process for outputting data, the mainstream stripe-shaped concept certainly suffers from the data overflow issue. This geometrical restriction leads to increasing complexity of peripheral circuits or programming as well as undesirable reliability issue. In this work, we propose and study ring-shaped RM, which is based on an alternative mechanism, spin orbit torque (SOT) driven chiral DW motions. Micromagnetic simulations have been carried out to validate its functionality and exhibit its performance advantages. The current flowing through the heavy metal instead of ferromagnetic layer realizes the “end to end” circulation of storage data, which remains all the data in the device even if they are shifted. It blazes a promising path for application of RM in practical memory and logic.
Coercivity of domain wall motion in thin films of amorphous rare earth-transition metal alloys
NASA Technical Reports Server (NTRS)
Mansuripur, M.; Giles, R. C.; Patterson, G.
1991-01-01
Computer simulations of a two dimensional lattice of magnetic dipoles are performed on the Connection Machine. The lattice is a discrete model for thin films of amorphous rare-earth transition metal alloys, which have application as the storage media in erasable optical data storage systems. In these simulations, the dipoles follow the dynamic Landau-Lifshitz-Gilbert equation under the influence of an effective field arising from local anisotropy, near-neighbor exchange, classical dipole-dipole interactions, and an externally applied field. Various sources of coercivity, such as defects and/or inhomogeneities in the lattice, are introduced and the subsequent motion of domain walls in response to external fields is investigated.
Strain-mediated deterministic control of 360° domain wall motion in magnetoelastic nanorings
NASA Astrophysics Data System (ADS)
Liang, Cheng-Yen; Sepulveda, Abdon E.; Hoff, Daniel; Keller, Scott M.; Carman, Gregory. P.
2015-11-01
This study provides numerical simulations for deterministic 360° magnetization rotation of the transverse domain walls in a nickel nano-ring (outer diameter: 500 nm, inner diameter: 300 nm, and thickness: 10 nm) on a lead zirconate titanate (Pb[ZrxTi1-x]O3 0 < x < 1) (PZT) thin film (500 nm) deposited onto a Si substrate with surface patterned electrodes. Two alternative electrode architectures are studied, namely, a 4-electrode and a 6-electrode configuration. The 4-electrode configuration relies on magnetization dynamics to produce an overshoot coupled with proper timing control of the voltage applied to achieve 360° magnetization rotation. In contrast, the 6-electrode configuration only requires sequential voltage application to successive pairs of electrodes and thus can be operated at quasi-static speeds and does not rely on magnetization dynamics to achieve 360° magnetization rotation. These analytical models provide support for developing new devices such as nanoscale multiferroic driven electromagnetic motors.
The kaon B-parameter from 2+1-flavor Domain-Wall-Fermion lattices
Cohen, Saul; Anthony, David
2007-11-01
We present the final results of the RBC/UKQCD calculation of the kaon B-parameter on 2+1- flavor domain-wall fermion lattices at a^?1 = 1.73(3) GeV. We simulate on two lattice volumes of about (1.8 fm)^3 and (2.7 fm)^3, with the lightest valence pion about on the large volume approximately 250 MeV. The light pion masses and our chiral fermion action allow us to compare lattice data to NLO chiral perturbation theory, facilitating a controlled extrapolation to the physical point. We present a final result including nonperturbative renormalization and detailed systematic errors. Our final result is BMS/K (2 GeV) = 0.524(10)(28).
NASA Astrophysics Data System (ADS)
Zhuo, Fengjun; Sun, Z. Z.
2016-04-01
Field-driven domain wall (DW) motion in ferromagnetic nanowires with easy- and hard-axis anisotropies was studied theoretically and numerically in the presence of the bulk Dzyaloshinskii-Moriya interaction (DMI) based on the Landau-Lifshitz-Gilbert equation. We propose a new trial function and offer an exact solution for DW motion along a uniaxial nanowire driven by an external magnetic field. A new strategy was suggested to speed up DW motion in a uniaxial magnetic nanowire with large DMI parameters. In the presence of hard-axis anisotropy, we find that the breakdown field and velocity of DW motion was strongly affected by the strength and sign of the DMI parameter under external fields. This work may be useful for future magnetic information storage devices based on DW motion.
Ring-shaped Racetrack memory based on spin orbit torque driven chiral domain wall motions
Zhang, Yue; Zhang, Xueying; Hu, Jingtong; Nan, Jiang; Zheng, Zhenyi; Zhang, Zhizhong; Zhang, Youguang; Vernier, Nicolas; Ravelosona, Dafine; Zhao, Weisheng
2016-01-01
Racetrack memory (RM) has sparked enormous interest thanks to its outstanding potential for low-power, high-density and high-speed data storage. However, since it requires bi-directional domain wall (DW) shifting process for outputting data, the mainstream stripe-shaped concept certainly suffers from the data overflow issue. This geometrical restriction leads to increasing complexity of peripheral circuits or programming as well as undesirable reliability issue. In this work, we propose and study ring-shaped RM, which is based on an alternative mechanism, spin orbit torque (SOT) driven chiral DW motions. Micromagnetic simulations have been carried out to validate its functionality and exhibit its performance advantages. The current flowing through the heavy metal instead of ferromagnetic layer realizes the “end to end” circulation of storage data, which remains all the data in the device even if they are shifted. It blazes a promising path for application of RM in practical memory and logic. PMID:27725741
Influence of nonlocal damping on the field-driven domain wall motion
NASA Astrophysics Data System (ADS)
Yuan, H. Y.; Yuan, Zhe; Xia, Ke; Wang, X. R.
2016-08-01
We derive a general expression of nonlocal damping in noncollinear magnetization due to the nonuniform spin current pumped by precessional magnetization and incorporate it into a generalized Thiele equation to study its effects on the dynamics of the transverse and vortex domain walls (DWs) in ferromagnetic nanowires. We demonstrate that the transverse component of nonlocal damping slows down the field-driven DW propagation and increases the Walker breakdown field, whereas it is neglected in many previous works in literature. The experimentally measured DW mobility variation with the damping tuned by doping with heavy rare-earth elements that had discrepancy from micromagnetic simulation is now well understood with the nonlocal damping. Our results suggest that the nonlocal damping should be properly included as a prerequisite for quantitative studies of current-induced torques in noncollinear magnetization.
A novel diversiform stochastic resonance of a domain wall and its performance at different states
NASA Astrophysics Data System (ADS)
Zhang, Haibin; Ouyang, Kesai; He, Qingbo; Kong, Fanrang
2016-03-01
The response of an underdamped stochastic resonance (SR) with a new pining potential model of domain wall (DW) in ferromagnetic strips driven by additive Gaussian white noise to an additive weak harmonic forcing is investigated. We address that the new nonlinear system can be converted between bi-stable and mono-stable freely by tuning the system parameters. Analytical expressions of signal-to-noise ratio (SNR) of the bi-stable stage is obtained based on the linear response theory. In addition, another type of SR, which occurs when the system is mono-stable, is also reported with the intrinsic frequency derived analytically. The SR in mono-stable stage confirms to the typical physical resonance better with frequency-selection characteristic. Numerical simulation of both stages is carried out with outputs conforming to the theoretical derivation. Owing to the diversity of potential model, the new system possesses considerable merits for engineering applications.
Domain walls, fusion rules, and conformal field theory in the quantum Hall regime.
Ardonne, Eddy
2009-05-01
We provide a simple way to obtain the fusion rules associated with elementary quasiholes over quantum Hall wave functions, in terms of domain walls. The knowledge of the fusion rules is helpful in the identification of the underlying conformal field theory describing the wave functions. We show that, for a certain two-parameter family (k,r) of wave functions, the fusion rules are those of su(r)k. In addition, we give an explicit conformal field theory construction of these states, based on the Mk(k+1,k+r) "minimal" theories. For r=2, these states reduce to the Read-Rezayi states. The "Gaffnian" wave function is the prototypical example for r>2, in which case the conformal field theory is nonunitary.
Emergence of electromotive force in precession-less rigid motion of deformed domain wall
NASA Astrophysics Data System (ADS)
Farajollahpour, Tohid; Darmiani, Narges; Phirouznia, Arash
2016-08-01
Recently it has been recognized that the electromotive force (emf) can be induced just by the spin precession where the generation of the electromotive force has been considered as a real-space topological pumping effect. It has been shown that the amount of the electromotive force is independent of the functionality of the localized moments. It was also demonstrated that the rigid domain wall (DW) motion cannot generate electromotive force in the system. Based on real-space topological pumping approach in the current study we show that the electromotive force can be induced by rigid motion of a deformed DW. We also demonstrate that the generated electromotive force strongly depends on the DW bulging. Meanwhile results show that the DW bulging leads to generation of the electromotive force both along the axis of the DW motion and normal to the direction of motion.
Self-tuning flat domain walls in 5D gravity and string theory
Kachru, Shamit; Schulz, Michael; Silverstein, Eva
2000-08-15
We present Poincare-invariant domain wall (''three-brane'') solutions to some five-dimensional effective theories which can arise naturally in string theory. In particular, we find theories where Poincare-invariant solutions exist for arbitrary values of the brane tension, for certain restricted forms of the bulk interactions. We describe examples in string theory where it would be natural for the quantum corrections to the tension of the brane (arising from quantum fluctuations of modes with support on the brane) to maintain the required form of the action. In such cases, the Poincare-invariant solutions persist in the presence of these quantum corrections to the brane tension, so that no 4D cosmological constant is generated by these modes. (c) 2000 The American Physical Society.
Zhuo, Fengjun; Sun, Z. Z.
2016-01-01
Field-driven domain wall (DW) motion in ferromagnetic nanowires with easy- and hard-axis anisotropies was studied theoretically and numerically in the presence of the bulk Dzyaloshinskii-Moriya interaction (DMI) based on the Landau-Lifshitz-Gilbert equation. We propose a new trial function and offer an exact solution for DW motion along a uniaxial nanowire driven by an external magnetic field. A new strategy was suggested to speed up DW motion in a uniaxial magnetic nanowire with large DMI parameters. In the presence of hard-axis anisotropy, we find that the breakdown field and velocity of DW motion was strongly affected by the strength and sign of the DMI parameter under external fields. This work may be useful for future magnetic information storage devices based on DW motion. PMID:27118064
Xu, Qingping; Mengin-Lecreulx, Dominique; Liu, Xueqian W.; Patin, Delphine; Farr, Carol L.; Grant, Joanna C.; Chiu, Hsiu -Ju; Jaroszewski, Lukasz; Knuth, Mark W.; Godzik, Adam; Lesley, Scott A.; Elsliger, Marc -André; Deacon, Ashley M.; Wilson, Ian A.
2015-09-15
Bacterial SH3 (SH3b) domains are commonly fused with papain-like Nlp/P60 cell wall hydrolase domains. To understand how the modular architecture of SH3b and NlpC/P60 affects the activity of the catalytic domain, three putative NlpC/P60 cell wall hydrolases were biochemically and structurally characterized. In addition, these enzymes all have γ-
Xu, Qingping; Mengin-Lecreulx, Dominique; Liu, Xueqian W.; Patin, Delphine; Farr, Carol L.; Grant, Joanna C.; Chiu, Hsiu-Ju; Jaroszewski, Lukasz; Knuth, Mark W.; Godzik, Adam; Lesley, Scott A.; Elsliger, Marc-André; Deacon, Ashley M.; Wilson, Ian A.
2015-09-15
Bacterial SH3 (SH3b) domains are commonly fused with papain-like Nlp/P60 cell wall hydrolase domains. To understand how the modular architecture of SH3b and NlpC/P60 affects the activity of the catalytic domain, three putative NlpC/P60 cell wall hydrolases were biochemically and structurally characterized. These enzymes all have γ-
Xu, Qingping; Mengin-Lecreulx, Dominique; Liu, Xueqian W.; Patin, Delphine; Farr, Carol L.; Grant, Joanna C.; Chiu, Hsiu -Ju; Jaroszewski, Lukasz; Knuth, Mark W.; Godzik, Adam; et al
2015-09-15
Bacterial SH3 (SH3b) domains are commonly fused with papain-like Nlp/P60 cell wall hydrolase domains. To understand how the modular architecture of SH3b and NlpC/P60 affects the activity of the catalytic domain, three putative NlpC/P60 cell wall hydrolases were biochemically and structurally characterized. In addition, these enzymes all have γ-d-Glu-A2pm (A2pm is diaminopimelic acid) cysteine amidase (ordl-endopeptidase) activities but with different substrate specificities. One enzyme is a cell wall lysin that cleaves peptidoglycan (PG), while the other two are cell wall recycling enzymes that only cleave stem peptides with an N-terminall-Ala. Their crystal structures revealed a highly conserved structure consisting ofmore » two SH3b domains and a C-terminal NlpC/P60 catalytic domain, despite very low sequence identity. Interestingly, loops from the first SH3b domain dock into the ends of the active site groove of the catalytic domain, remodel the substrate binding site, and modulate substrate specificity. Two amino acid differences at the domain interface alter the substrate binding specificity in favor of stem peptides in recycling enzymes, whereas the SH3b domain may extend the peptidoglycan binding surface in the cell wall lysins. Remarkably, the cell wall lysin can be converted into a recycling enzyme with a single mutation.Peptidoglycan is a meshlike polymer that envelops the bacterial plasma membrane and bestows structural integrity. Cell wall lysins and recycling enzymes are part of a set of lytic enzymes that target covalent bonds connecting the amino acid and amino sugar building blocks of the PG network. These hydrolases are involved in processes such as cell growth and division, autolysis, invasion, and PG turnover and recycling. To avoid cleavage of unintended substrates, these enzymes have very selective substrate specificities. Our biochemical and structural analysis of three modular NlpC/P60 hydrolases, one lysin, and two recycling enzymes, show
NASA Astrophysics Data System (ADS)
Ono, Teruo
Topological defects such as magnetic solitons, vortices, Bloch lines, and skyrmions start to play an important role in modern magnetism due to their extraordinary stability which can be hailed as future memory devices. Recently, novel type of antisymmetric exchange interaction, namely the Dzyaloshinskii-Moriya interaction (DMI), has been uncovered and found to influence on the formation of topological defects. Exploring how the DMI affects the dynamics of topological defects is therefore an important task. Here we investigate the dynamics of the magnetic domain wall (DW) under a DMI by developing a time-of-flight measurement scheme which allows us to measure the DW velocity for magnetic fields up to 0.3T. For a weak DMI, the trend of DW velocity follows the Walker's model which predicts that the velocity of DW increases with field up to a threshold (Walker field) and decreases abruptly. On the other hand, for a strong DMI, velocity breakdown is completely suppressed and the DW keeps its maximum velocity even far above the Walker field. Such a distinct trend of the DW velocity, which has never been predicted, can be explained in terms of magnetic soliton, of which topology can be protected by the DMI. Importantly, such a soliton-like DW motion is only observed in two dimensional systems, implying that the vertical Bloch lines (VBLs) creating inside of the magnetic domain-wall play a crucial role. This work was partly supported by JSPS KAKENHI Grant Numbers 15H05702, 26870300, 26870304, 26103002, 25.4251, Collaborative Research Program of the Institute for Chemical Research, Kyoto University, and R & D Project for ICT Key Technology of MEXT from the Japan Society for the Promotion of Science (JSPS).
Precision Lattice Calculation of Kaon Decays with Mobius Domain Wall Fermions
NASA Astrophysics Data System (ADS)
Yin, Hantao
We report our recent development in algorithms and progress in measurements in lattice QCD. The algorithmic development includes the forecasted force gradient integrator, and further theoretical development and implementation of the Mobius domain wall fermions. These new technologies make it practical to simulate large 483 x 96 and 643 x 128 lattice ensembles with (5.5fm)3 boxes and 140MeV pion. The calculation was performed using the Mobius domain wall fermions and the Iwasaki gauge action. Simulated directly at physical quark masses, these ensembles are of great value for our ongoing and future lattice measurement projects. With the help of measurement techniques such as the eigCG algorithm and the all mode averaging method, we perform a direct, precise lattice calculation of the semileptonic kaon decay K → pilnu using these newly generated high quality lattice ensembles. Our main result is the form factor f+/-Kp q2 evaluated directly at zero momentum transfer q2 = 0. Free of various systematic errors, this new result can be used to determine the CKM matrix element Vus to a very high precision when combined with experimental input. The calculation also provides results for various low energy strong interaction constants such as the pseudoscalar decay constants fK and fpi, and the neutral kaon mixing matrix element BK. These calculations are naturally performed by reusing the propagators calculated for the kaon semileptonic decay mentioned above. So they come with no or very low additional cost. The results allow us to also determine these important low energy constants on the lattice to unprecedented accuracy.
Wang, Xi-guang; Guo, Guang-hua Nie, Yao-zhuang; Xia, Qing-lin; Tang, Wei; Wang, D.; Zeng, Zhong-ming
2013-12-23
We have studied the current-induced displacement of a 180° Bloch wall by means of micromagnetic simulation and analytical approach. It is found that the adiabatic spin-transfer torque can sustain a steady-state domain wall (DW) motion in the direction opposite to that of the electron flow without Walker Breakdown when a transverse microwave field is applied. This kind of motion is very sensitive to the microwave frequency and can be resonantly enhanced by exciting the domain wall thickness oscillation mode. A one-dimensional analytical model was established to account for the microwave-assisted wall motion. These findings may be helpful for reducing the critical spin-polarized current density and designing DW-based spintronic devices.
Chapman, J N; Batson, P E; Waddell, E M; Ferrier, R P
1978-01-01
A new technique for the quantitative investigation of magnetic structures in ferromagnetic thin films is proposed. Unlike previous techniques the detected signal is simply related to the magnetic induction in the film, and as such the direct determination of domain wall profiles is possible. The technique utilizes a differential phase contrast mode of scanning transmission electron microscopy in which the normal bright field detector is replaced by a split-detector lying symmetrically about the optic axis of the system. The difference signal from the two halves of the detector provides the required magnetic information. Analysis of the image formation mechanism shows that, using a commercially available scanning transmission electron microscope equipped with a field emission gun, wall profiles should be obtainable directly from most structures of interest in Lorentz microscopy. Furthermore, signal-to-noise considerations indicate that these results can be obtained in acceptably short recording times. Finally, experimental results using both polycrystalline and single crystal specimens are presented, which confirm the theoretical predictions. PMID:358526
NASA Astrophysics Data System (ADS)
Metaxas, P. J.; Chanthbouala, A.; Matsumoto, R.; Cros, V.; Anane, A.; Grollier, J.; Fert, A.; Zvezdin, K. A.; Fukushima, A.; Yuasa, S.
2012-02-01
The ability to efficiently drive fast domain wall (DW) motion will pave the way for revolutionary new electronic devices ranging from DW-MRAMs to spintronic memristors. The majority of domain wall devices use a lateral, current-in-plane configuration in which critical current densities for domain wall motion remain quite high, typically being on the order of 100 MA/cm^2 with velocities generally limited to about 100 m/s. In this contribution we show that critical current densities can be decreased by up to two orders of magnitude using the current-perpendicular-to-plane geometry. Indeed, we demonstrate that a DW can be propagated back and forth along the free layer of a MgO-based magnetic tunnel junction (MTJ) in the absence of an external magnetic field using current densities that are on the order of 5 MA/cm^2. More notably however, we obtain high domain wall velocities for these low current densities: the MTJ's large resistance variations allow us to carry out time-resolved measurements of the wall motion from which we evidence DW velocities exceeding 500m/s.
Influence of defects and domain walls on dielectric and mechanical resonances in LiNbO3.
Nataf, Guillaume F; Aktas, Oktay; Granzow, Torsten; Salje, Ekhard K H
2016-01-13
Monodomain and periodically poled LiNbO3 crystals (congruent composition) show dielectric and piezoelectric resonances between 100 K and 900 K. Dielectric measurements show resonances in some samples between 10-100 kHz. These resonances vanish under thermal anneal in monodomain crystals while they remain stable in periodically poled samples with high domain wall densities. The low activation energy of 0.18 eV suggests their electronic (bi-polaronic) origin. Resonant piezoelectric spectroscopy, RPS, shows two features in virgin samples: a relaxation peak at 420 K and a rapid hardening when the sample was slowly heated to ~500 K. The dynamic relaxation and the hardening are related to excitations and reorientations of Li defects. The relaxations and hardening are irreversibly suppressed by high temperature anneal. We do not observe domain wall related RPS resonances in annealed samples, which excludes the existence of highly charged walls. We suggest that domain walls stabilize polaronic states with (bi-)polarons located inside or near to the ferroelectric domain walls. PMID:26642928
NASA Astrophysics Data System (ADS)
Benguria, R. D.; Depassier, M. C.
2016-04-01
We study the dynamics of the equation obtained by Schryer and Walker for the motion of domain walls. The reduced equation is a reaction diffusion equation for the angle between the applied field and the magnetization vector. If the hard-axis anisotropy Kd is much larger than the easy-axis anisotropy Ku, there is a range of applied fields where the dynamics does not select the Schryer-Walker solution. We give an analytic expression for the speed of the domain wall in this regime and the conditions for its existence.
NASA Astrophysics Data System (ADS)
Metaxas, P. J.; Jamet, J. P.; Mougin, A.; Cormier, M.; Ferré, J.; Baltz, V.; Rodmacq, B.; Dieny, B.; Stamps, R. L.
2007-11-01
We report on magnetic domain-wall velocity measurements in ultrathin Pt/Co(0.5 0.8nm)/Pt films with perpendicular anisotropy over a large range of applied magnetic fields. The complete velocity-field characteristics are obtained, enabling an examination of the transition between thermally activated creep and viscous flow: motion regimes predicted from general theories for driven elastic interfaces in weakly disordered media. The dissipation limited flow regime is found to be consistent with precessional domain-wall motion, analysis of which yields values for the damping parameter, α.
Giant photovoltaic effect of ferroelectric domain walls in perovskite single crystals
Inoue, Ryotaro; Ishikawa, Shotaro; Imura, Ryota; Kitanaka, Yuuki; Oguchi, Takeshi; Noguchi, Yuji; Miyayama, Masaru
2015-01-01
The photovoltaic (PV) effect in polar materials offers great potential for light-energy conversion that generates a voltage beyond the bandgap limit of present semiconductor-based solar cells. Ferroelectrics have received renewed attention because of the ability to deliver a high voltage in the presence of ferroelastic domain walls (DWs). In recent years, there has been considerable debate over the impact of the DWs on the PV effects, owing to lack of information on the bulk PV tensor of host ferroelectrics. In this article, we provide the first direct evidence of an unusually large PV response induced by ferroelastic DWs—termed ‘DW’-PV effect. The precise estimation of the bulk PV tensor in single crystals of barium titanate enables us to quantify the giant PV effect driven by 90° DWs. We show that the DW-PV effect arises from an effective electric field consisting of a potential step and a local PV component in the 90° DW region. This work offers a starting point for further investigation into the DW-PV effect of alternative systems and opens a reliable route for enhancing the PV properties in ferroelectrics based on the engineering of domain structures in either bulk or thin-film form. PMID:26443381
Giant photovoltaic effect of ferroelectric domain walls in perovskite single crystals.
Inoue, Ryotaro; Ishikawa, Shotaro; Imura, Ryota; Kitanaka, Yuuki; Oguchi, Takeshi; Noguchi, Yuji; Miyayama, Masaru
2015-10-07
The photovoltaic (PV) effect in polar materials offers great potential for light-energy conversion that generates a voltage beyond the bandgap limit of present semiconductor-based solar cells. Ferroelectrics have received renewed attention because of the ability to deliver a high voltage in the presence of ferroelastic domain walls (DWs). In recent years, there has been considerable debate over the impact of the DWs on the PV effects, owing to lack of information on the bulk PV tensor of host ferroelectrics. In this article, we provide the first direct evidence of an unusually large PV response induced by ferroelastic DWs-termed 'DW'-PV effect. The precise estimation of the bulk PV tensor in single crystals of barium titanate enables us to quantify the giant PV effect driven by 90° DWs. We show that the DW-PV effect arises from an effective electric field consisting of a potential step and a local PV component in the 90° DW region. This work offers a starting point for further investigation into the DW-PV effect of alternative systems and opens a reliable route for enhancing the PV properties in ferroelectrics based on the engineering of domain structures in either bulk or thin-film form.
Giant photovoltaic effect of ferroelectric domain walls in perovskite single crystals
NASA Astrophysics Data System (ADS)
Inoue, Ryotaro; Ishikawa, Shotaro; Imura, Ryota; Kitanaka, Yuuki; Oguchi, Takeshi; Noguchi, Yuji; Miyayama, Masaru
2015-10-01
The photovoltaic (PV) effect in polar materials offers great potential for light-energy conversion that generates a voltage beyond the bandgap limit of present semiconductor-based solar cells. Ferroelectrics have received renewed attention because of the ability to deliver a high voltage in the presence of ferroelastic domain walls (DWs). In recent years, there has been considerable debate over the impact of the DWs on the PV effects, owing to lack of information on the bulk PV tensor of host ferroelectrics. In this article, we provide the first direct evidence of an unusually large PV response induced by ferroelastic DWs—termed ‘DW’-PV effect. The precise estimation of the bulk PV tensor in single crystals of barium titanate enables us to quantify the giant PV effect driven by 90° DWs. We show that the DW-PV effect arises from an effective electric field consisting of a potential step and a local PV component in the 90° DW region. This work offers a starting point for further investigation into the DW-PV effect of alternative systems and opens a reliable route for enhancing the PV properties in ferroelectrics based on the engineering of domain structures in either bulk or thin-film form.
Benitez, M. J.; Hrabec, A.; Mihai, A. P.; Moore, T. A.; Burnell, G.; McGrouther, D.; Marrows, C. H.; McVitie, S.
2015-01-01
The microscopic magnetization variation in magnetic domain walls in thin films is a crucial property when considering the torques driving their dynamic behaviour. For films possessing out-of-plane anisotropy normally the presence of Néel walls is not favoured due to magnetostatic considerations. However, they have the right structure to respond to the torques exerted by the spin Hall effect. Their existence is an indicator of the interfacial Dzyaloshinskii–Moriya interaction (DMI). Here we present direct imaging of Néel domain walls with a fixed chirality in device-ready Pt/Co/AlOx films using Lorentz transmission electron and Kerr microscopies. It is shown that any independently nucleated pair of walls in our films form winding pairs when they meet that are difficult to annihilate with field, confirming that they all possess the same topological winding number. The latter is enforced by the DMI. The field required to annihilate these winding wall pairs is used to give a measure of the DMI strength. Such domain walls, which are robust against collisions with each other, are good candidates for dense data storage. PMID:26642936
Eugster, Marcel R.
2012-01-01
The C-terminal cell wall binding domains (CBDs) of phage endolysins direct the enzymes to their binding ligands on the bacterial cell wall with high affinity and specificity. The Listeria monocytogenes Ply118, Ply511, and PlyP40 endolysins feature related CBDs which recognize the directly cross-linked peptidoglycan backbone structure of Listeria. However, decoration with fluorescently labeled CBDs primarily occurs at the poles and septal regions of the rod-shaped cells. To elucidate the potential role of secondary cell wall-associated carbohydrates such as the abundant wall teichoic acid (WTA) on this phenomenon, we investigated CBD binding using L. monocytogenes serovar 1/2 and 4 cells deficient in WTA. Mutants were obtained by deletion of two redundant tagO homologues, whose products catalyze synthesis of the WTA linkage unit. While inactivation of either tagO1 (EGDe lmo0959) or tagO2 (EGDe lmo2519) alone did not affect WTA content, removal of both alleles following conditional complementation yielded WTA-deficient Listeria cells. Substitution of tagO from an isopropyl-β-d-thiogalactopyranoside-inducible single-copy integration vector restored the original phenotype. Although WTA-deficient cells are viable, they featured severe growth inhibition and an unusual coccoid morphology. In contrast to CBDs from other Listeria phage endolysins which directly utilize WTA as binding ligand, the data presented here show that WTAs are not required for attachment of CBD118, CBD511, and CBDP40. Instead, lack of the cell wall polymers enables unrestricted spatial access of CBDs to the cell wall surface, indicating that the abundant WTA can negatively regulate sidewall localization of the cell wall binding domains. PMID:23002226
Zuo, Yinan; Genenko, Yuri A.; Xu, Bai-Xiang
2014-07-28
The effect of the polarization charge compensation by ionic and electronic space charges on domain properties in ferroelectrics with semiconducting features is considered, in particular, the conductivity of head-to-head and tail-to-tail domain walls is studied. It is shown that the domain wall conductivity that is enhanced by electrons or holes depends on the configuration and the types of domains as well as on the energy levels and concentrations of the defects involved. Phase field simulation results are used to explain recent equivocal experimental results on conductivity of charged domain walls in different ferroelectrics.
Continuum limit physics from 2+1 flavor domain wall QCD
NASA Astrophysics Data System (ADS)
Aoki, Y.; Arthur, R.; Blum, T.; Boyle, P. A.; Brömmel, D.; Christ, N. H.; Dawson, C.; Flynn, J. M.; Izubuchi, T.; Jin, X.-Y.; Jung, C.; Kelly, C.; Li, M.; Lichtl, A.; Lightman, M.; Lin, M. F.; Mawhinney, R. D.; Maynard, C. M.; Ohta, S.; Pendleton, B. J.; Sachrajda, C. T.; Scholz, E. E.; Soni, A.; Wennekers, J.; Zanotti, J. M.; Zhou, R.
2011-04-01
We present physical results obtained from simulations using 2+1 flavors of domain wall quarks and the Iwasaki gauge action at two values of the lattice spacing a, [a-1=1.73(3)GeV and a-1=2.28(3)GeV]. On the coarser lattice, with 243×64×16 points (where the 16 corresponds to Ls, the extent of the 5th dimension inherent in the domain wall fermion formulation of QCD), the analysis of C. Allton (RBC-UKQCD Collaboration), Phys. Rev. DPRVDAQ1550-7998 78 is extended to approximately twice the number of configurations. The ensembles on the finer 323×64×16 lattice are new. We explain in detail how we use lattice data obtained at several values of the lattice spacing and for a range of quark masses in combined continuum-chiral fits in order to obtain results in the continuum limit and at physical quark masses. We implement this procedure for our data at two lattice spacings and with unitary pion masses in the approximate range 290-420 MeV (225-420 MeV for partially quenched pions). We use the masses of the π and K mesons and the Ω baryon to determine the physical quark masses and the values of the lattice spacing. While our data in the mass ranges above are consistent with the predictions of next-to-leading order SU(2) chiral perturbation theory, they are also consistent with a simple analytic ansatz leading to an inherent uncertainty in how best to perform the chiral extrapolation that we are reluctant to reduce with model-dependent assumptions about higher order corrections. In some cases, particularly for fπ, the pion leptonic decay constant, the uncertainty in the chiral extrapolation dominates the systematic error. Our main results include fπ=124(2)stat(5)systMeV, fK/fπ=1.204(7)(25) where fK is the kaon decay constant, msMS¯(2GeV)=(96.2±2.7)MeV and mudMS¯(2GeV)=(3.59±0.21)MeV (ms/mud=26.8±1.4) where ms and mud are the mass of the strange quark and the average of the up and down quark masses, respectively, [ΣMS¯(2GeV)]1/3=256(6)MeV, where Σ is the chiral
NASA Astrophysics Data System (ADS)
Yang, See-Hun; Ryu, Kwang-Su; Parkin, Stuart
2015-03-01
The operation of racetrack memories is based on the motion of domain walls in atomically thin, perpendicularly magnetized nanowires, which are interfaced with adjacent metal layers with high spin-orbit coupling. Such domain walls have a chiral Néel structure and can be moved efficiently by electrical currents. High-capacity racetrack memory requires closely packed domain walls, but their density is limited by dipolar coupling from their fringing magnetic fields. These fields can be eliminated using a synthetic antiferromagnetic structure composed of two magnetic sub-layers, exchange-coupled via an ultrathin antiferromagnetic-coupling spacer layer. Here, we show that nanosecond-long current pulses can move domain walls in synthetic antiferromagnetic racetracks that have almost zero net magnetization. The domain walls can be moved even more efficiently and at much higher speeds (up to ˜750 m s-1) compared with similar racetracks in which the sub-layers are coupled ferromagnetically. This is due to a stabilization of the Néel domain wall structure, and an exchange coupling torque that is directly proportional to the strength of the antiferromagnetic exchange coupling between the two sub-layers. Moreover, the dependence of the wall velocity on the magnetic field applied along the nanowire is distinct from that of the single-layer racetrack due to the exchange coupling torque. The high domain wall velocities in racetracks that have no net magnetization allow for densely packed yet highly efficient domain-wall-based spintronics.
Molecular anisotropic magnetoresistance
NASA Astrophysics Data System (ADS)
Otte, Fabian; Heinze, Stefan; Mokrousov, Yuriy
2015-12-01
Using density functional theory calculations, we demonstrate that the effect of anisotropic magnetoresistance (AMR) can be enhanced by orders of magnitude with respect to conventional bulk ferromagnets in junctions containing molecules sandwiched between ferromagnetic leads. We study ballistic transport in metal-benzene complexes contacted by 3 d transition-metal wires. We show that a gigantic AMR can arise from spin-orbit coupling effects in the leads, drastically enhanced by orbital-symmetry filtering properties of the molecules. We further discuss how this molecular anisotropic magnetoresistance (MAMR) can be tuned by the proper choice of materials and their electronic properties.
Magnetic configuration of submicron-sized magnetic patterns in domain wall motion memory
NASA Astrophysics Data System (ADS)
Ohshima, Norikazu; Numata, Hideaki; Fukami, Shunsuke; Nagahara, Kiyokazu; Suzuki, Tetsuhiro; Ishiwata, Nobuyuki; Fukumoto, Keiki; Kinoshita, Toyohiko; Ono, Teruo
2010-05-01
We observed magnetic configuration and its change by external magnetic fields in submicron-sized U- and H-shaped NiFe patterns with an x-ray magnetic circular dichroism photoemission electron microscope. The microscope images showed the formation of a single domain wall (DW) with transverse structure at one corner of the U- and H-shaped patterns by applying the magnetic field from the oblique direction. By applying the magnetic field from the direction parallel to a horizontal bar in the patterns, the magnetic configuration in the U-shaped pattern was changed and four patterns were formed: (1) the DW moved from one trap site to another, (2) the DW moved beyond the trap site and formed a single domain, (3) the DW moved and stopped between the trap sites, and (4) the DW remained at the initial position. Only pattern (1) showed reversible DW motion, although pattern (2) was predominantly formed. In contrast, the magnetization configurations showed pattern (1), and reversible DW motion was observed for more than 80% of the H-shaped patterns. Micromagnetic simulation revealed that the DW in the U-shaped pattern was not sufficiently fixed at the corner and easily moved and vanished at the edge of the patterns because the magnetization in the two parallel bars rotated with a magnetic field. The DW was trapped with sufficient strength at the corner, and DW motion occurred only between the trap sites for the H-shaped patterns. The DW motion process was observed with an in situ magnetic field using the x-ray magnetic circular dichroism photoemission electron microscope and the process could be optimized by controlling the pattern shape.
Lattice dynamics and domain wall oscillations of morphotropic Pb (Zr ,Ti ) O3 ceramics
NASA Astrophysics Data System (ADS)
Buixaderas, E.; Bovtun, V.; Kempa, M.; Nuzhnyy, D.; Savinov, M.; Vanek, P.; Gregora, I.; Malic, B.
2016-08-01
The temperature dependence of the optical phonons and high-frequency microwave excitations of morphotropic Pb (Z r1 -xT ix ) O3 (PZT) ceramics with compositions PZT 52/48 and 53/47 were studied by a broadband spectroscopy approach, using Raman, far-infrared, time-domain terahertz (THz), and microwave spectroscopies. A careful evaluation of the evolution of phonon parameters with temperature clearly revealed only two macroscopic phase transitions of intrinsic origin, driven by phonons: the ferroelectric one at high temperatures near 650 K (driven by an anharmonic soft mode at THz frequencies coupled to a weak component at higher frequencies, ω ˜70 c m-1 ) and a transition to an antiferrodistortive phase around 400 K, signaled by a new peak (ω ˜60 c m-1 ) that appeared in the infrared and Raman spectra. This peak confirmed the onset of the antiphase tilt of the oxygen octahedra and the doubling of the unit cell, as well as the splitting of the B1-E doublet in the Raman spectra. No indications of an additional phase transition were found by these techniques down to 20 K. On the other hand, dielectric measurements below the phonon frequencies showed anomalies at lower temperatures; however, they had extrinsic character and were not related to the atomic vibrations. An excitation in the gigahertz range displayed a softening towards 270 K, in agreement with a maximum in the low-frequency dielectric loss spectra. The quantitative analysis of this excitation revealed the presence of two contributions assigned to piezoelectric resonances in grains and domain wall oscillations, which, together, satisfactorily explain the dielectric anomaly below room temperature, without taking into account another transition to a lower-symmetry phase.
Defect ordering and defect-domain-wall interactions in PbTiO3: A first-principles study
NASA Astrophysics Data System (ADS)
Chandrasekaran, Anand; Damjanovic, Dragan; Setter, Nava; Marzari, Nicola
2013-12-01
The properties of ferroelectric materials, such as lead zirconate titanate (PZT), are heavily influenced by the interaction of defects with domain walls. These defects are either intrinsic or are induced by the addition of dopants. We study here PbTiO3 (the end member of a key family of solid solutions) in the presence of acceptor (Fe) and donor (Nb) dopants, and the interactions of the different defects and defect associates with the domain walls. For the case of iron acceptors, the calculations point to the formation of defect associates involving an iron substitutional defect and a charged oxygen vacancy (FeTi'-VO..). This associate exhibits a strong tendency to align in the direction of the bulk polarization; in fact, ordering of defects is also observed in pure PbTiO3 in the form of lead-oxygen divacancies. Conversely, calculations on donor-doped PbTiO3 do not indicate the formation of polar defect complexes involving donor substitutions. Last, it is observed that both isolated defects in donor-doped materials and defect associates in acceptor-doped materials are more stable at 180∘ domain walls. However, polar defect complexes lead to asymmetric potentials at domain walls due to the interaction of the defect polarization with the bulk polarization. The relative pinning characteristics of different defects are then compared, to develop an understanding of defect-domain-wall interactions in both doped and pure PbTiO3. These results may also help in understanding hardening and softening mechanisms in PZT.
Chu, P.; Chen, D. P.; Wang, Y. L.; Xie, Y. L.; Yan, Z. B.; Wan, J. G.; Liu, J.-M.; Li, J. Y.
2014-01-01
The dielectric and ferroelectric behaviors of a ferroelectric are substantially determined by its domain structure and domain wall dynamics at mesoscopic level. A relationship between the domain walls and high frequency mesoscopic dielectric response is highly appreciated for high frequency applications of ferroelectrics. In this work we investigate the low electric field driven motion of 90°-domain walls and the frequency-domain spectrum of dielectric permittivity in normally strained ferroelectric lattice using the phase-field simulations. It is revealed that, the high-frequency dielectric permittivity is spatially inhomogeneous and reaches the highest value on the 90°-domain walls. A tensile strain favors the parallel domains but suppresses the kinetics of the 90° domain wall motion driven by electric field, while the compressive strain results in the opposite behaviors. The physics underlying the wall motions and thus the dielectric response is associated with the long-range elastic energy. The major contribution to the dielectric response is from the polarization fluctuations on the 90°-domain walls, which are more mobile than those inside the domains. The relevance of the simulated results wth recent experiments is discussed. PMID:24845806
Interlocked chiral/polar domain walls and large optical rotation in Ni{sub 3}TeO{sub 6}
Wang, Xueyun; Huang, Fei-Ting; Yang, Junjie; Oh, Yoon Seok; Cheong, Sang-Wook
2015-07-01
Chirality, i.e., handedness, pervades much of modern science from elementary particles, DNA-based biology to molecular chemistry; however, most of the chirality-relevant materials have been based on complex molecules. Here, we report inorganic single-crystalline Ni{sub 3}TeO{sub 6}, forming in a corundum-related R3 structure with both chirality and polarity. These chiral Ni{sub 3}TeO{sub 6} single crystals exhibit a large optical specific rotation (α)—1355° dm{sup −1} cm{sup 3} g{sup −1}. We demonstrate, for the first time, that in Ni{sub 3}TeO{sub 6}, chiral and polar domains form an intriguing domain pattern, resembling a radiation warning sign, which stems from interlocked chiral and polar domain walls through lowering of the wall energy.
NASA Astrophysics Data System (ADS)
Baghel, A. P. S.; Sai Ram, B.; Chwastek, K.; Daniel, L.; Kulkarni, S. V.
2016-11-01
The anisotropy of magnetic properties in grain-oriented steels is related to their microstructure. It results from the anisotropy of the single crystal properties combined to crystallographic texture. The magnetization process along arbitrary directions can be explained using phase equilibrium for domain patterns, which can be described using Neel's phase theory. According to the theory the fractions of 180° and 90° domain walls depend on the direction of magnetization. This paper presents an approach to model hysteresis loops of grain-oriented steels along arbitrary in-plane directions. The considered description is based on a modification of the Jiles-Atherton model. It includes a modified expression for the anhysteretic magnetization which takes into account contributions of two types of domain walls. The computed hysteresis curves for different directions are in good agreement with experimental results.
NASA Astrophysics Data System (ADS)
Yoshimura, Yoko; Kim, Kab-Jin; Taniguchi, Takuya; Tono, Takayuki; Ueda, Kohei; Hiramatsu, Ryo; Moriyama, Takahiro; Yamada, Keisuke; Nakatani, Yoshinobu; Ono, Teruo
2016-02-01
Topological defects such as magnetic solitons, vortices and skyrmions have started to play an important role in modern magnetism because of their extraordinary stability, which can be exploited in the production of memory devices. Recently, a type of antisymmetric exchange interaction, namely the Dzyaloshinskii-Moriya interaction (DMI; refs ,), has been uncovered and found to influence the formation of topological defects. Exploring how the DMI affects the dynamics of topological defects is therefore an important task. Here we investigate the dynamics of the magnetic domain wall (DW) under a DMI by developing a real time DW detection scheme. For a weak DMI, the DW velocity increases with the external field and reaches a peak velocity at a threshold field, beyond which it abruptly decreases. For a strong DMI, on the other hand, the velocity reduction is completely suppressed and the peak velocity is maintained constant even far above the threshold field. Such a distinct trend of the velocity can be explained in terms of a magnetic soliton, the topology of which is protected during its motion. Our results therefore shed light on the physics of dynamic topological defects, which paves the way for future work in topology-based memory applications.
Polarization domain wall pulses in a microfiber-based topological insulator fiber laser.
Liu, Jingmin; Li, Xingliang; Zhang, Shumin; Zhang, Han; Yan, Peiguang; Han, Mengmeng; Pang, Zhaoguang; Yang, Zhenjun
2016-01-01
Topological insulators (TIs), are novel two-dimension materials, which can act as effective saturable absorbers (SAs) in a fiber laser. Moreover, based on the evanescent wave interaction, deposition of the TI on microfiber would create an effective SA, which has combined advantages from the strong nonlinear optical response in TI material together with the sufficiently-long-range interaction length in fiber taper. By using this type of TI SA, various scalar solitons have been obtained in fiber lasers. However, a single mode fiber always exhibits birefringence, and hence can support two orthogonal degenerate modes. Here we investigate experimentally the vector characters of a TI SA fiber laser. Using the saturated absorption and the high nonlinearity of the TI SA, a rich variety of dynamic states, including polarization-locked dark pulses and their harmonic mode locked counterparts, polarization-locked noise-like pulses and their harmonic mode locked counterparts, incoherently coupled polarization domain wall pulses, including bright square pulses, bright-dark pulse pairs, dark pulses and bright square pulse-dark pulse pairs are all observed with different pump powers and polarization states. PMID:27381942
Nucleon Structure from 2+1 Flavor Domain Wall QCD at Nearly Physical Pion Mass
Ohta, Shigemi
2011-05-24
The RBC and UKQCD collaborations have been investigating hadron physics in numerical lattice quantum chromodynamics (QCD) with (2+1) flavors of dynamical domain wall fermions (DWF) quarks that preserves continuum-like chiral and flavor symmetries. The strange quark mass is adjusted to physical value via reweighting and degenerate up and down quark masses are set as light as possible. In a recent study of nucleon structure we found a strong dependence on pion mass and lattice spatial extent in isovector axialvector-current form factors. This is likely the first credible evidence for the pion cloud surrounding nucleon. Here we report the status of nucleon structure calculations with a new (2+1)-flavor dynamical DWF ensembles with much lighter pion mass of 180 and 250 MeV and a much larger lattice spatial exent of 4.6 fm. A combination of the Iwasaki and dislocation-suppressing-determinant-ratio (I+DSDR) gauge action and DWF fermion action allows us to generate these ensembles at cutoff of about 1.4 GeV while keeping the residual breaking of chiral symmetry sufficiently small. Nucleon source Gaussian smearing has been optimized. Preliminary nucleon mass estimates are 0.98 and 1.05 GeV.
Bottomonium spectrum from lattice QCD with 2+1 flavors of domain wall fermions
Meinel, Stefan
2009-05-01
Recently, realistic lattice QCD calculations with 2+1 flavors of domain wall fermions and the Iwasaki gauge action have been performed by the RBC and UKQCD Collaborations. Here, results for the bottomonium spectrum computed on their gauge configurations of size 24{sup 3}x64 with a lattice spacing of approximately 0.11 fm and four different values for the light quark mass are presented. Improved lattice nonrelativistic QCD is used to treat the b quarks inside the bottomonium. The results for the radial and orbital energy splittings are found to be in good agreement with experimental measurements, indicating that systematic errors are small. The calculation of the {upsilon}(2S)-{upsilon}(1S) energy splitting provides an independent determination of the lattice spacing. For the most physical ensemble it is found to be a{sup -1}=1.740(25)(19) GeV, where the first error is statistical/fitting and the second error is an estimate of the systematic errors due to the lattice nonrelativistic QCD action.
Exploring 360 domain walls in ferromagnetic nanostructures using circular magnetic fields
NASA Astrophysics Data System (ADS)
Sarella, Anandakumar; Kaya, F. I.; Aidala, K. E.
Ferromagnetic nanostructures can exhibit intriguing magnetic states, such as the metastable 360 domain wall (DW), in which two 180 DWs combine to form a nearly flux closed state in sufficiently thin structures. These composite structures have potential to maximize storage densities due to their minimal stray fields. We study a straightforward method to nucleate 360 DWs in nanorings, nanowires, using in-plane circular fields, as if from a current carrying wire passing through the substrate in close proximity to the nanostructures. Our simulations, using OOMMF, predict that the vortex state of a ring with appropriate geometry will reverse from CW to CCW through an intermediate state consisting of pairs of 360 DWs. We examine the dependence of the switching field and intermediate states on geometric properties such as the diameter, thickness, and width of the ring. Using the local circular field, we can also nucleate 360 DWs in nanowires, pinning the location of the DWs at notches spaced as close as 100 nm apart, suggesting high density storage. We are currently studying these structures experimentally using AFM/MFM. We generate the circular field by passing current through AFM tip and image the resulting magnetic states with MFM. NSF Grants No. DMR 1208042 and 1207924. Simulations were run on the Odyssey cluster, Research Computing Group at Harvard.
Spin-orbit torques for current parallel and perpendicular to a domain wall
Schulz, Tomek; Lee, Kyujoon; Karnad, Gurucharan V.; Alejos, Oscar; Martinez, Eduardo; Moretti, Simone; Garcia, Karin; Ravelosona, Dafiné; Vila, Laurent; Lo Conte, Roberto; Kläui, Mathias; Ocker, Berthold; Brataas, Arne
2015-09-21
We report field- and current-induced domain wall (DW) depinning experiments in Ta\\Co{sub 20}Fe{sub 60}B{sub 20}\\MgO nanowires through a Hall cross geometry. While purely field-induced depinning shows no angular dependence on in-plane fields, the effect of the current depends crucially on the internal DW structure, which we manipulate by an external magnetic in-plane field. We show depinning measurements for a current sent parallel to the DW and compare its depinning efficiency with the conventional case of current flowing perpendicularly to the DW. We find that the maximum efficiency is similar for both current directions within the error bars, which is in line with a dominating damping-like spin-orbit torque (SOT) and indicates that no large additional torques arise for currents perpendicular to the DW. Finally, we find a varying dependence of the maximum depinning efficiency angle for different DWs and pinning levels. This emphasizes the importance of our full angular scans compared with previously used measurements for just two field directions (parallel and perpendicular to the DW) to determine the real torque strength and shows the sensitivity of the SOT to the precise DW structure and pinning sites.
Polarization domain wall pulses in a microfiber-based topological insulator fiber laser
Liu, Jingmin; Li, Xingliang; Zhang, Shumin; Zhang, Han; Yan, Peiguang; Han, Mengmeng; Pang, Zhaoguang; Yang, Zhenjun
2016-01-01
Topological insulators (TIs), are novel two-dimension materials, which can act as effective saturable absorbers (SAs) in a fiber laser. Moreover, based on the evanescent wave interaction, deposition of the TI on microfiber would create an effective SA, which has combined advantages from the strong nonlinear optical response in TI material together with the sufficiently-long-range interaction length in fiber taper. By using this type of TI SA, various scalar solitons have been obtained in fiber lasers. However, a single mode fiber always exhibits birefringence, and hence can support two orthogonal degenerate modes. Here we investigate experimentally the vector characters of a TI SA fiber laser. Using the saturated absorption and the high nonlinearity of the TI SA, a rich variety of dynamic states, including polarization-locked dark pulses and their harmonic mode locked counterparts, polarization-locked noise-like pulses and their harmonic mode locked counterparts, incoherently coupled polarization domain wall pulses, including bright square pulses, bright-dark pulse pairs, dark pulses and bright square pulse-dark pulse pairs are all observed with different pump powers and polarization states. PMID:27381942
Improvement of domain wall conduit properties in cobalt nanowires by global gallium irradiation.
Serrano-Ramón, L; Fernández-Pacheco, A; Córdoba, R; Magén, C; Rodríguez, L A; Petit, D; Cowburn, R P; Ibarra, M R; De Teresa, J M
2013-08-30
Applications based on the movement of domain walls (DWs) in magnetic nanowires (NWs) require a good DW conduit behavior, i.e. a significant difference between DW nucleation and propagation fields. In this work, we have systematically studied how this property evolves in cobalt NWs grown by focused electron beam induced deposition (FEBID) as a function of global gallium irradiation, for irradiation doses up to 1.24 × 10(17) ions cm(-2). Whereas for high doses the DW conduit is lost, below 6.42 × 10(15) ions cm(-2) the difference between the two fields increases with irradiation, becoming up to ∼9 times larger than for non-irradiated wires, due to a strong increase in the nucleation field, while the propagation field remains approximately constant. This behavior stems from two effects. The first effect is a decrease in the magnetic volume of the parasitic halo around the NW, typically present in FEBID nanostructures, leading to the disappearance of weak nucleation centers. The second effect is the formation of a 20 nm outer shell with Co crystals about twice the size of those forming the NW core, causing a net increase of the local magnetocrystalline anisotropy. The results presented here are important for the potential use of magnetic NWs grown by FEBID in DW-based devices, and might also be of interest for magnetic NWs fabricated by other techniques.
CHIRAL LIMIT AND LIGHT QUARK MASSES IN 2+1 FLAVOR DOMAIN WALL QCD.
SCHOLZ,E.; LIN, M.
2007-07-30
We present results for meson masses and decay constants measured on 24{sup 3} x 64 lattices using the domain wall fermion formulation with an extension of the fifth dimension of L{sub s} = 16 for N{sub f} 2 + 1 dynamical quark flavors. The lightest dynamical meson mass in our set-up is around 331MeV. while partially quenched mesons reach masses as low as 250MeV. The applicability of SU(3) x SU(3) and SU(2) x SU(2) (partially quenched) chiral perturbation theory will be compared and we quote values for the low-energy constants from both approaches. We will extract the average light quark and strange quark masses and use a non-perturbative renormalization technique (RI/MOM) to quote their physical values. The pion and kaon decay constants are determined at those values from our chiral fits and their ratio is used to obtain the CKM-matrix element |V{sub us}|. The results presented here include statistical errors only.
Tuning interfacial domain walls in GdCo/Gd/GdCo' spring magnets
NASA Astrophysics Data System (ADS)
Blanco-Roldán, C.; Choi, Y.; Quirós, C.; Valvidares, S. M.; Zarate, R.; Vélez, M.; Alameda, J. M.; Haskel, D.; Martín, J. I.
2015-12-01
Spring magnets based on GdCo multilayers have been prepared to study the nucleation and evolution of interfacial domain walls (iDWs) depending on layer composition and interlayer coupling. GdCo alloy compositions in each layer were chosen so that their net magnetization aligns either with the Gd (G d35C o65 ) or Co (G d11C o89 ) sublattices. This condition forces an antiparallel arrangement of the layers' net magnetization and leads to nucleation of iDWs above critical magnetic fields whose values are dictated by the interplay between Zeeman and exchange energies. By combining x-ray resonant magnetic scattering with Kerr magnetometry, we provide detailed insight into the nucleation and spatial profile of the iDWs. For strong coupling (GdCo/GdCo' bilayer), iDWs are centered at the interface but with asymmetric width depending on each layer magnetization. When interlayer coupling is weakened by introducing a thin Gd interlayer, the exchange spring effect becomes restricted to a lower temperature and field range than observed in the bilayer structure. Due to the ferromagnetic alignment between the high magnetization G d35C o65 layer and the Gd interlayer, the iDW shrinks and moves into the lower exchange Gd interlayer, causing a reduction of iDW energy.
Mixed Meson Mass for Domain-Wall Valence and Staggered Sea Fermions
Konstantinos Orginos; Andre Walker-Loud
2007-05-01
Mixed action lattice calculations allow for an additive lattice spacing dependent mass renormalization of mesons composed of one sea and one valence quark, regardless of the type of fermion discretization methods used in the valence and sea sectors. The value of the mass renormalization depends upon the lattice actions used. This mixed meson mass shift is the most important lattice artifact to determine for mixed action calculations: because it modifies the pion mass, it plays a central role in the low energy dynamics of all hadronic correlation functions. We determine the leading order and next to leading order additive mass renormalization of valence-sea mesons for a mixed lattice action with domain-wall valence fermions and staggered sea fermions. We find that on the asqtad improved coarse MILC lattices, the leading order additive mass renormalization for the mixed mesons is Δ(am)^2 LO = 0.0409(11) which corresponds to a^2 Δ_Mix = (319 MeV)^2± (53 MeV)^2 for a = 0.125 fm. We also find significant next to leading order contributions which reduce the mass renormalization by a significant amount, such that for 0 < am_π ≤ 0.22 the mixed meson mass renormalization is well approximated by Δ(am)^2 = 0.0340 (23) or a^2δ_Mix = (290 MeV)^2 ± (76 MeV)^2. The full next-to-leading order analysis is presented in the text.
Kong, Minsuk; Sim, Jieun; Kang, Taejoon; Nguyen, Hoang Hiep; Park, Hyun Kyu; Chung, Bong Hyun; Ryu, Sangryeol
2015-09-01
Rapid, specific and sensitive detection of pathogenic bacteria is crucial for public health and safety. Bacillus cereus is harmful as it causes foodborne illness and a number of systemic and local infections. We report a novel phage endolysin cell wall-binding domain (CBD) for B. cereus and the development of a highly specific and sensitive surface plasmon resonance (SPR)-based B. cereus detection method using the CBD. The newly discovered CBD from endolysin of PBC1, a B. cereus-specific bacteriophage, provides high specificity and binding capacity to B. cereus. By using the CBD-modified SPR chips, B. cereus can be detected at the range of 10(5)-10(8) CFU/ml. More importantly, the detection limit can be improved to 10(2) CFU/ml by using a subtractive inhibition assay based on the pre-incubation of B. cereus and CBDs, removal of CBD-bound B. cereus, and SPR detection of the unbound CBDs. The present study suggests that the small and genetically engineered CBDs can be promising biological probes for B. cereus. We anticipate that the CBD-based SPR-sensing methods will be useful for the sensitive, selective, and rapid detection of B. cereus.
Direct observation of deterministic domain wall trajectory in magnetic network structures.
Sethi, P; Murapaka, C; Goolaup, S; Chen, Y J; Leong, S H; Lew, W S
2016-01-12
Controlling the domain wall (DW) trajectory in magnetic network structures is crucial for spin-based device related applications. The understanding of DW dynamics in network structures is also important for study of fundamental properties like observation of magnetic monopoles at room temperature in artificial spin ice lattice. The trajectory of DW in magnetic network structures has been shown to be chirality dependent. However, the DW chirality periodically oscillates as it propagates a distance longer than its fidelity length due to Walker breakdown phenomenon. This leads to a stochastic behavior in the DW propagation through the network structure. In this study, we show that the DW trajectory can be deterministically controlled in the magnetic network structures irrespective of its chirality by introducing a potential barrier. The DW propagation in the network structure is governed by the geometrically induced potential barrier and pinning strength against the propagation. This technique can be extended for controlling the trajectory of magnetic charge carriers in an artificial spin ice lattice.
Spin wave based parallel logic operations for binary data coded with domain walls
Urazuka, Y.; Oyabu, S.; Chen, H.; Peng, B.; Otsuki, H.; Tanaka, T. Matsuyama, K.
2014-05-07
We numerically investigate the feasibility of spin wave (SW) based parallel logic operations, where the phase of SW packet (SWP) is exploited as a state variable and the phase shift caused by the interaction with domain wall (DW) is utilized as a logic inversion functionality. A designed functional element consists of parallel ferromagnetic nanowires (6 nm-thick, 36 nm-width, 5120 nm-length, and 200 nm separation) with the perpendicular magnetization and sub-μm scale overlaid conductors. The logic outputs for binary data, coded with the existence (“1”) or absence (“0”) of the DW, are inductively read out from interferometric aspect of the superposed SWPs, one of them propagating through the stored data area. A practical exclusive-or operation, based on 2π periodicity in the phase logic, is demonstrated for the individual nanowire with an order of different output voltage V{sub out}, depending on the logic output for the stored data. The inductive output from the two nanowires exhibits well defined three different signal levels, corresponding to the information distance (Hamming distance) between 2-bit data stored in the multiple nanowires.
Differential Domain Wall Propagation in Y-Shaped Permalloy Nanowire Devices
NASA Astrophysics Data System (ADS)
Das, Bipul; Chen, Ting-Chieh; Shiu, Deng-Shiang; Horng, Lance; Wu, Jong-Ching
2016-05-01
Here, we report an investigation of magnetic domain wall (DW) evolution and propagation in Y-shaped permalloy (Py) nanowire (NW) devices. The devices are fabricated using standard electron-beam lithography technique. Each device consists of three connected NWs that form a Y-junction structure with one branch connecting either symmetrically or asymmetrically to a circular disk for DW nucleation. The DW dynamics in the devices are studied by in situ magnetic force microscopy (MFM) by pinning the DWs to triangular notches at each branch of the two devices. We observe that the DW injection field values differ depending on whether they are connected to the circular disks symmetrically or asymmetrically. However, after they pass the Y-junctions, a selection is made by the DWs to propagate easily either through both or through only one particular outgoing branch of the devices. The experimental observations are analyzed by micromagnetic simulation. It can be inferred from the results that the influence of detailed geometrical shape of the devices leads to significantly different interactions among the innate topological defects and the notches with the injected DWs.
Precise determination of BK and light quark masses in quenched domain-wall QCD
NASA Astrophysics Data System (ADS)
Nakamura, Yousuke; Aoki, Sinya; Taniguchi, Yusuke; Yoshié, Tomoteru
2008-08-01
We calculate nonperturbative renormalization factors at hadronic scale for ΔS=2 four-quark operators in quenched domain-wall QCD using the Schrödinger functional method. Combining them with the nonperturbative renormalization group running by the Alpha Collaboration, our result yields the fully nonperturbative renormalization factor, which converts the lattice bare BK to the renormalization group invariant (RGI) B^K. Applying this to the bare BK previously obtained by the CP-PACS Collaboration at a-1≃2,3,4GeV, we obtain B^K=0.782(5)(7) [equivalent to BKM Smacr (NDR,2GeV)=0.565(4)(5) by two-loop running] in the continuum limit, where the first error is statistical and the second is systematic due to the continuum extrapolation. Except the quenching error, the total error we have achieved is less than 2%, which is much smaller than the previous ones. Taking the same procedure, we obtain mu,dRGI=5.613(66)MeV and msRGI=147.1(17)MeV [equivalent to mu,dM Smacr (2GeV)=4.026(48)MeV and msM Smacr (2GeV)=105.6(12)MeV by four-loop running] in the continuum limit.
Kong, Minsuk; Sim, Jieun; Kang, Taejoon; Nguyen, Hoang Hiep; Park, Hyun Kyu; Chung, Bong Hyun; Ryu, Sangryeol
2015-09-01
Rapid, specific and sensitive detection of pathogenic bacteria is crucial for public health and safety. Bacillus cereus is harmful as it causes foodborne illness and a number of systemic and local infections. We report a novel phage endolysin cell wall-binding domain (CBD) for B. cereus and the development of a highly specific and sensitive surface plasmon resonance (SPR)-based B. cereus detection method using the CBD. The newly discovered CBD from endolysin of PBC1, a B. cereus-specific bacteriophage, provides high specificity and binding capacity to B. cereus. By using the CBD-modified SPR chips, B. cereus can be detected at the range of 10(5)-10(8) CFU/ml. More importantly, the detection limit can be improved to 10(2) CFU/ml by using a subtractive inhibition assay based on the pre-incubation of B. cereus and CBDs, removal of CBD-bound B. cereus, and SPR detection of the unbound CBDs. The present study suggests that the small and genetically engineered CBDs can be promising biological probes for B. cereus. We anticipate that the CBD-based SPR-sensing methods will be useful for the sensitive, selective, and rapid detection of B. cereus. PMID:26043681
Extending the velocity-dependent one-scale model for domain walls
NASA Astrophysics Data System (ADS)
Martins, C. J. A. P.; Rybak, I. Yu.; Avgoustidis, A.; Shellard, E. P. S.
2016-02-01
We report on an extensive study of the evolution of domain wall networks in Friedmann-Lemaître-Robertson-Walker universes by means of the largest currently available field-theory simulations. These simulations were done in 40963 boxes and for a range of different fixed expansion rates, as well as for the transition between the radiation and matter eras. A detailed comparison with the velocity-dependent one-scale model shows that this cannot accurately reproduce the results of the entire range of simulated regimes if one assumes that the phenomenological energy loss and momentum parameters are constants. We therefore discuss how a more accurate modeling of these parameters can be done, specifically by introducing an additional mechanism of energy loss (scalar radiation, which is particularly relevant for regimes with relatively little damping) and a modified momentum parameter which is a function of velocity (in analogy to what was previously done for cosmic strings). We finally show that this extended model, appropriately calibrated, provides an accurate fit to our simulations.
Polarization domain wall pulses in a microfiber-based topological insulator fiber laser
NASA Astrophysics Data System (ADS)
Liu, Jingmin; Li, Xingliang; Zhang, Shumin; Zhang, Han; Yan, Peiguang; Han, Mengmeng; Pang, Zhaoguang; Yang, Zhenjun
2016-07-01
Topological insulators (TIs), are novel two-dimension materials, which can act as effective saturable absorbers (SAs) in a fiber laser. Moreover, based on the evanescent wave interaction, deposition of the TI on microfiber would create an effective SA, which has combined advantages from the strong nonlinear optical response in TI material together with the sufficiently-long-range interaction length in fiber taper. By using this type of TI SA, various scalar solitons have been obtained in fiber lasers. However, a single mode fiber always exhibits birefringence, and hence can support two orthogonal degenerate modes. Here we investigate experimentally the vector characters of a TI SA fiber laser. Using the saturated absorption and the high nonlinearity of the TI SA, a rich variety of dynamic states, including polarization-locked dark pulses and their harmonic mode locked counterparts, polarization-locked noise-like pulses and their harmonic mode locked counterparts, incoherently coupled polarization domain wall pulses, including bright square pulses, bright-dark pulse pairs, dark pulses and bright square pulse-dark pulse pairs are all observed with different pump powers and polarization states.
Geometrically pinned magnetic domain wall for multi-bit per cell storage memory
Bahri, M. Al; Sbiaa, R.
2016-01-01
Spintronic devices currently rely on magnetic switching or controlled motion of domain walls (DWs) by an external magnetic field or a spin-polarized current. Controlling the position of DW is essential for defining the state/information in a magnetic memory. During the process of nanowire fabrication, creating an off-set of two parts of the device could help to pin DW at a precise position. Micromagnetic simulation conducted on in-plane magnetic anisotropy materials shows the effectiveness of the proposed design for pinning DW at the nanoconstriction region. The critical current for moving DW from one state to the other is strongly dependent on nanoconstricted region (width and length) and the magnetic properties of the material. The DW speed which is essential for fast writing of the data could reach values in the range of hundreds m/s. Furthermore, evidence of multi-bit per cell memory is demonstrated via a magnetic nanowire with more than one constriction. PMID:27334038
pion Kaon Scattering in full QCD with domain wall valence quarks
Silas Beane; Paulo Bedaque; Thomas Luu; Konstantinos Orginos; Elisabetta Pallante; Assumpta Parreno; Martin Savage
2006-07-24
We calculate the {pi}{sup +}K{sup +} scattering length at pion masses of m{sub {pi}} {approx} 290, 350, 490 and 600 MeV in fully-dynamical lattice QCD with domain-wall valence quarks and rooted staggered sea quarks. The lattice data, analyzed at next-to-leading order in chiral perturbation theory, allows an extraction of the full piK scattering amplitude at threshold. Extrapolating to the physical point gives m{sub {pi}} {alpha}{sub 3/2} = -0.0574 {+-} 0.0016{sub -0.0058}{sup +0.0024} and m{sub {pi}} {alpha}{sub 1/2} = 0.1725 {+-} 0.0017{sub -0.0156}{sup +0.0023} for the I = 3/2 and I = 1/2 scattering lengths, respectively, where the first error is statistical and the second error is an estimate of the systematic error due to truncation of the chiral expansion.
Atomic-scale mapping of dipole frustration at 90° charged domain walls in ferroelectric PbTiO3 films
Tang, Y. L.; Zhu, Y. L.; Wang, Y. J.; Wang, W. Y.; Xu, Y. B.; Ren, W. J.; Zhang, Z. D.; Ma, X. L.
2014-01-01
The atomic-scale structural and electric parameters of the 90° domain-walls in tetragonal ferroelectrics are of technological importance for exploring the ferroelectric switching behaviors and various domain-wall-related novel functions. We have grown epitaxial PbTiO3/SrTiO3 multilayer films in which the electric dipoles at 90° domain-walls of ferroelectric PbTiO3 are characterized by means of aberration-corrected scanning transmission electron microscopy. Besides the well-accepted head-to-tail 90° uncharged domain-walls, we have identified not only head-to-head positively charged but also tail-to-tail negatively charged domain-walls. The widths, polarization distributions, and strains across these charged domain-walls are mapped quantitatively at atomic scale, where remarkable difference between these domain-walls is presented. This study is expected to provide fundamental information for understanding numerous novel domain-wall phenomena in ferroelectrics. PMID:24534846
Kim, Young-Ki; Cukrov, Greta; Xiang, Jie; Shin, Sung-Tae; Lavrentovich, Oleg D
2015-05-28
We investigate the origin of "secondary disclinations" that were recently described as new evidence of a biaxial nematic phase in an oxadiazole bent-core thermotropic liquid crystal C7. Using an assortment of optical techniques such as polarizing optical microscopy, LC PolScope, and fluorescence confocal polarizing microscopy, we demonstrate that the secondary disclinations represent non-singular domain walls formed in a uniaxial nematic phase during the surface anchoring transition, in which surface orientation of the director changes from tangential (parallel to the bounding plates) to tilted. Each domain wall separates two regions with the director tilted in opposite azimuthal directions. At the centre of the wall, the director remains parallel to the bounding plates. The domain walls can be easily removed by applying a moderate electric field. The anchoring transition is explained by the balance of (a) the intrinsic perpendicular surface anchoring produced by the polyimide aligning layer and (b) tangential alignment caused by ionic impurities forming electric double layers. The model is supported by the fact that the temperature of the tangentially tilted anchoring transition decreases as the cell thickness increases and as the concentration of ionic species (added salt) increases. We also demonstrate that the surface alignment is strongly affected by thermal degradation of the samples. This study shows that C7 exhibits only a uniaxial nematic phase and demonstrates yet another mechanism (formation of "secondary disclinations") by which a uniaxial nematic phase can mimic a biaxial nematic behaviour. PMID:25820380
NASA Astrophysics Data System (ADS)
Metaxas, P. J.; Anane, A.; Cros, V.; Grollier, J.; Deranlot, C.; Petroff, F.; Fert, A.; Ulysse, C.; Faini, G.
2010-03-01
A new generation of proposed spintronic devices are based on domain wall (DW) motion (DW-MRAM, DW logic, racetrack memory...). However, reliable depinning of domain walls remains elusive, especially in zero field. Here, we have studied the combined effect of rf and dc currents on the depinning of transverse walls in the soft NiFe layer of a 100 nm wide Co/Cu/NiFe spin valve wire. Using the GMR effect, we ensure that the domain wall is always prepared at the same intrinsic defect and then measure the depinning field for different applied dc and rf currents. Notably, for a narrow range of rf frequencies at around 3GHz, we evidence a strong reduction in the depinning field (from ˜80 Oe to ˜30 Oe). Our results are suggestive of a very efficient resonant depinning effect in our spin valve wire which depends not only on the rf power but also on the polarity and amplitude of the accompanying dc current.
Kim, Young-Ki; Cukrov, Greta; Xiang, Jie; Shin, Sung-Tae; Lavrentovich, Oleg D
2015-05-28
We investigate the origin of "secondary disclinations" that were recently described as new evidence of a biaxial nematic phase in an oxadiazole bent-core thermotropic liquid crystal C7. Using an assortment of optical techniques such as polarizing optical microscopy, LC PolScope, and fluorescence confocal polarizing microscopy, we demonstrate that the secondary disclinations represent non-singular domain walls formed in a uniaxial nematic phase during the surface anchoring transition, in which surface orientation of the director changes from tangential (parallel to the bounding plates) to tilted. Each domain wall separates two regions with the director tilted in opposite azimuthal directions. At the centre of the wall, the director remains parallel to the bounding plates. The domain walls can be easily removed by applying a moderate electric field. The anchoring transition is explained by the balance of (a) the intrinsic perpendicular surface anchoring produced by the polyimide aligning layer and (b) tangential alignment caused by ionic impurities forming electric double layers. The model is supported by the fact that the temperature of the tangentially tilted anchoring transition decreases as the cell thickness increases and as the concentration of ionic species (added salt) increases. We also demonstrate that the surface alignment is strongly affected by thermal degradation of the samples. This study shows that C7 exhibits only a uniaxial nematic phase and demonstrates yet another mechanism (formation of "secondary disclinations") by which a uniaxial nematic phase can mimic a biaxial nematic behaviour.
Wang, Y. J.; Chen, D.; Tang, Y. L.; Zhu, Y. L.; Ma, X. L.
2014-12-14
Determination of atomic and electronic structures of ferroelectric domain walls is crucial to understand and explore their unusual properties. Using first-principles calculations based on the density functional theory, we explored the atomic and electronic structures of 180° domain walls in PbTiO{sub 3}, in order to understand the origin of Bloch-type polarization components. It is found that Bloch-type polarization components originate from the large displacements of Pb atoms and the Pb-O hybridization at the domain walls. The development of Bloch-type polarization components significantly reduce the domain wall energies and change the Peierls barriers of domain wall motion in different orientations.
Theory of domain wall motion mediated magnetoelectric effects in a multiferroic composite
NASA Astrophysics Data System (ADS)
Petrov, V. M.; Srinivasan, G.
2014-10-01
A model is discussed for magnetoelectric (ME) interactions originating from the motion of magnetic domain walls (DWs) in a multiferroic composite of orthoferrites RFeO3 (RFO) with magnetic stripe domains and a piezoelectric such as lead magnesium niobate-lead titanate (PMN-PT). The DWs in RFO can be set in motion with an ac magnetic field up to a critical speed of 20 km/s, the highest for any magnetic system, leading to the excitation of bulk and shear magnetoacoustic waves. Thus, the ME coupling will arise from flexural deformation associated with DW motion (rather than the Joule magnetostriction mediated coupling under a static or quasistatic condition). A c plane orthoferrite with a single Néel-type DW in the bc plane and an ac magnetic field H along the c axis is assumed. The deflection in the bilayer due to DW motion is obtained when the DW velocity is a linear function H and the resulting induced voltage across PMN-PT is estimated. It is shown that a combination of spatial and time harmonics of the bending deformation leads to (i) a linear ME coefficient defined by αE=E/H and (ii) a quadratic ME coefficient αEQ=E/H2. The model is applied to yttrium orthoferrites (YFO) and a PMN-PT bilayer since YFO has one of the highest DW mobility amongst the orthoferrites. The coefficient αE is dependent on the DW position, and it is maximum when the DW equilibrium position is at the center of the sample. In YFO/PMN-PT the estimated low-frequency αE ˜ 30 mV/cm Oe and resonance value is 1.5 V/(cm Oe). Since orthoferrites (and PMN-PT) are transparent in the visible region and have a large Faraday rotation, the DW dynamics and the ME coupling could be studied simultaneously. The theory discussed here is of interest for studies on ME coupling and for applications such as magnetically controlled electro-optic devices.
NASA Astrophysics Data System (ADS)
García-Fernández, Pablo; Íñiguez, Jorge; Junquera, Javier
Symmetry breaking at ferroelectric domain walls gives rise to new physical properties, offering the opportunity to use the domain walls themselves as a functional separate object in a device. One example is the appearance of an enhanced conductivity at the boundaries between ferroelectric domains in oxides. A realistic first-principles simulation of the domains walls is limited to highly-symmetric cleanly-cut walls in order to keep the number of atoms in the simulation box small. Here we use a recently developed second-principles method that treats all the lattice degrees of freedom and the relevant electronic ones on the same foot with high accuracy at a modest computational cost. We apply it to the demading physical problem of head-to-head (HH) and tail-to-tail (TT) domain walls in ferroelectric PbTiO3 thin films. These interfaces present a large and unfavourable electrostatic energy due to the polarization-induced bound charge at the domain wall. An accurate simulation should capture eventual charge transfers between the walls, and the concomitant electron-lattice coupling. We show how the polarization discontinuity in HH and TT domain walls in PbTiO3 thin films can be effectively screened by the formation of two-dimensional electron gases of electrons and holes. Finantial support from MINECO Grant No. FIS2012-37549-C05-04.
Nucleon structure in lattice QCD with dynamical domain-wall fermions quarks
Huey-Wen Lin; Shigemi Ohta
2006-07-23
We report RBC and RBC/UKQCD lattice QCD numerical calculations of nucleon electroweak matrix elements with dynamical domain-wall fermions (DWF) quarks. The first, RBC, set of dynamical DWF ensembles employs two degenerate flavors of DWF quarks and the DBW2 gauge action. Three sea quark mass values of 0.04, 0.03 and 0.02 in lattice units are used with about 200 gauge configurations each. The lattice cutoff is about 1.7 GeV and the spatial volume is about (1.9 fm){sup 3}. Despite the small volume, the ratio of the isovector vector and axial charges g{sub A}/g{sub V} and that of structure function moments
Nucleon isovector structure functions in (2+1)-flavor QCD with domain wall fermions
Aoki, Y.; Blum, Tom; Lin, Huey-Wen; Ohta, Shigemi; et al.
2010-07-02
We report on numerical lattice QCD calculations of some of the low moments of the nucleon structure functions. The calculations are carried out with gauge configurations generated by the RBC and UKQCD Collaborations with (2+1)-flavors of dynamical domain-wall fermions and the Iwasaki gauge action ({beta} = 2.13). The inverse lattice spacing is a{sup -1} = 1.73 GeV, and two spatial volumes of (2.7 fm){sup 3} and (1.8 fm){sup 3} are used. The up and down quark masses are varied so the pion mass lies between 0.33 and 0.67 GeV, while the strange mass is about 12% heavier than the physical one. The structure function moments we present include the fully nonperturbatively renormalized isovector quark momentum fraction x{sub u-d}, the helicity fraction x{sub {Delta}u-{Delta}d}, and transversity 1{sub {delta}u-{delta}d}, as well as an unrenormalized twist-3 coefficient d{sub 1}. The ratio of the momentum to helicity fractions, x{sub u-d}/x{sub {Delta}u-{Delta}d}, does not show dependence on the light quark mass and agrees well with the value obtained from experiment. Their respective absolute values, fully renormalized, show interesting trends toward their respective experimental values at the lightest quark mass. A prediction for the transversity, 0.7 < 1{sub {delta}u-{delta}d} < 1.1, in the MS{sup -} scheme at 2 GeV is obtained. The twist-3 coefficient, d{sub 1}, though yet to be renormalized, supports the perturbative Wandzura-Wilczek relation.
NUCLEON STRUCTURE IN LATTICE QCD WITH DYNAMICAL DOMAIN--WALL FERMIONS QUARKS.
LIN H.-W.; OHTA, S.
2006-10-02
We report RBC and RBC/UKQCD lattice QCD numerical calculations of nucleon electroweak matrix elements with dynamical domain-wall fermions (DWF) quarks. The first, RBC, set of dynamical DWF ensembles employs two degenerate flavors of DWF quarks and the DBW2 gauge action. Three sea quark mass values of 0.04, 0.03 and 0.02 in lattice units are used with 220 gauge configurations each. The lattice cutoff is a{sup -1} {approx} 1.7GeV and the spatial volume is about (1.9fm){sup 3}. Despite the small volume, the ratio of the isovector vector and axial charges g{sub A}/g{sub V} and that of structure function moments