Dependence of Domain Wall Structure for Low Field Injection into Magnetic Nanowires

Micromagnetic simulation is used to model the injection of a domain wall into a magnetic nanowire with field strengths less than the so-called Walker field. This ensures fast, reliable motion of the wall. When the wire is located at the edge of a small injecting disk, a bias field used to control the orientation of the domain wall can reduce the pinning potential of the structure. The low field injection is explained by a simple model, which relies on the topological nature of a domain wall. The technique can quickly inject multiple domain walls with a known magnetic structure

Fast domain wall motion in nanostripes with out-of-plane fields

Controlling domain wall motion is important due to the impact on the viability of proposed nanowire devices. One hurdle is slow domain wall speed when driven by fields greater than the Walker field, due to nucleation of vortices in the wall. We present simulation results detailing the dynamics of these vortices; including the nucleation and subsequent fast ejection of the vortex core leading to fast domain wall speeds. The ejection is due to the reversal of the core moments by an out-of-plane field. The technique can be used to produce domain walls of known orientation independent of the initial state.Comment: 12 pages (3 figures

Enhancing Domain Wall Speed in Nanowires with Transverse Magnetic Fields

Dynamic micromagnetic simulation studies have been completed to observe the motion of a domain wall in a magnetic nanowire in an effort to increase the field-driven domain wall speed. Previous studies have shown that the wire dimensions place a cap on the maximum speed attainable by a domain wall when driven by a magnetic field placed along the direction of the nanowire. Here we present data showing a significant increase in the maximum speed of a domain wall due to the addition of a magnetic field placed perpendicular to the longitudinal driving field. The results are expressed in terms of the relative alignment of the transverse field direction with respect to the direction of the magnetic moments within the domain wall. In particular, when the transverse field is parallel to the magnetic moments within the domain wall, the velocity of the wall varies linearly with the strength of the transverse field increasing by up to 20%. Further examination of the domain wall structure shows that the length of the domain wall also depends linearly on the strength of the transverse field. We present a simple model to correlate the effects

Enhancing Domain Wall Speed in Nanowires with Transverse Magnetic Fields

Dynamic micromagnetic simulation studies have been completed to observe the motion of a domain wall in a magnetic nanowire in an effort to increase the field-driven domain wall speed. Previous studies have shown that the wire dimensions place a cap on the maximum speed attainable by a domain wall when driven by a magnetic field placed along the direction of the nanowire. Here we present data showing a significant increase in the maximum speed of a domain wall due to the addition of a magnetic field placed perpendicular to the longitudinal driving field. The results are expressed in terms of the relative alignment of the transverse field direction with respect to the direction of the magnetic moments within the domain wall. In particular, when the transverse field is parallel to the magnetic moments within the domain wall, the velocity of the wall varies linearly with the strength of the transverse field increasing by up to 20%. Further examination of the domain wall structure shows that the length of the domain wall also depends linearly on the strength of the transverse field. We present a simple model to correlate the effects.Comment: 11 pages, accepted by J. Appl. Phy

Injecting, Controlling, and Storing Magnetic Domain Walls in Ferromagnetic Nanowires

Domain walls in ferromagnetic nanowires are important for proposed devices in recording, logic, and sensing. The realization of such devices depends in part on the ability to quickly and accurately control the domain wall from creation until placement. Using micromagnetic computer simulation we demonstrate how a combination of externally applied magnetic fields is used to quickly inject, move, and accurately place multiple domain walls within a single wire for potential recording and logical operations. The use of a magnetic field component applied perpendicular to the principle domain wall driving field is found to be critical for increased speed and reliability. The effects of the transverse field on the injection and trapping of the domain wall will be shown to be of particular importance

Controlling Individual Domain Walls in Ferromagnetic Nanowires for Memory and Sensor Applications

Controlled motion of 180o and 360o domain walls along planar nanowires is presented. Standard Landau – Lifshitz micromagnetic modeling has been used to simulate the response of the domain walls to the application of an external magnetic field. A 180o wall is quickly and easily moved with the application of an applied. field along the axis of the wire but a 360odomain wall is stationary in the same case. An oscillatory applied field can be used to continually move the wall along the wires axis. The speed at which the 360o domain wall is found to be several times slower than a similar 180o domain wall and is limited by interaction between the magnetization of the domain wall and the external field

The Macronuclear Genome of \u3cem\u3eStentor coeruleus\u3c/em\u3e Reveals Tiny Introns in a Giant Cell

The giant, single-celled organism Stentor coeruleus has a long history as a model system for studying pattern formation and regeneration in single cells. Stentor [1, 2] is a heterotrichous ciliate distantly related to familiar ciliate models, such as Tetrahymena or Paramecium. The primary distinguishing feature of Stentor is its incredible size: a single cell is 1 mm long. Early developmental biologists, including T.H. Morgan [3], were attracted to the system because of its regenerative abilities—if large portions of a cell are surgically removed, the remnant reorganizes into a normal-looking but smaller cell with correct proportionality [2, 3]. These biologists were also drawn to Stentor because it exhibits a rich repertoire of behaviors, including light avoidance, mechanosensitive contraction, food selection, and even the ability to habituate to touch, a simple form of learning usually seen in higher organisms [4]. While early microsurgical approaches demonstrated a startling array of regenerative and morphogenetic processes in this single-celled organism, Stentor was never developed as a molecular model system. We report the sequencing of the Stentor coeruleus macronuclear genome and reveal key features of the genome. First, we find that Stentor uses the standard genetic code, suggesting that ciliate-specific genetic codes arose after Stentor branched from other ciliates. We also discover that ploidy correlates with Stentor’s cell size. Finally, in the Stentor genome, we discover the smallest spliceosomal introns reported for any species. The sequenced genome opens the door to molecular analysis of single-cell regeneration in Stentor

Radiation-Induced Chemical Changes to Iron Oxides

The radiolysis of a variety of iron oxide powders with different amounts of associated water has been performed using γ rays and 5 MeV ⁴He ions. Adsorbed water was characterized by both temperature-programmed desorption and diffuse reflection infrared Fourier transform spectroscopy to reveal a variety of active sites on the surface. Molecular hydrogen production was found only from water adsorbed on Fe₂O₃, and the yield was several orders of magnitude greater than that of bulk water. Aqueous slurries of FeO, Fe₃O₄, and Fe₂O₃ examined as a function of water fraction gave different yields of H₂ depending on the oxide type and the amount of water. Examination of the iron oxide powders following irradiation by X-ray diffraction showed no change in crystal structure. Raman spectroscopy of the oxides revealed the formation of islands of Fe₂O₃ on the surfaces of FeO and Fe₃O₄. X-ray photoelectron spectroscopy of the oxides revealed the general formation of oxygen species following radiolysis