640 research outputs found
Dynamics of ferromagnetic nanomagnets with vortex or single-domain configuration
We study the dynamics of flat circular permalloy nanomagnets for 1.) magnetic
vortex and 2.) single-domain configurations, using micromagnetic simulation.
Dynamical studies for isolated vortex structures show that both the vorticity
and the central polarity of the out-of-plane component can be switched fast
(50-100 ps) and independently. Micromagnetic simulations of the switching
process in thin cylindrical Permalloy (Py) nanoparticles with an initial stable
single-domain state show nearly homogeneous single-domain behaviour followed by
excitation of spin waves.Comment: 2 pages with 3 eps-figures, --> ICM2003 Rome 28.7.-1.8.03, --> JMM
Simulation Studies of Nanomagnet-Based Architecture
We report a simulation study on interacting ensembles of Co nanomagnets that
can perform basic logic operations and propagate logic signals, where the state
variable is the magnetization direction. Dipole field coupling between
individual nanomagnets drives the logic functionality of the ensemble and
coordinated arrangements of the nanomagnets allow for the logic signal to
propagate in a predictable way. Problems with the integrity of the logic signal
arising from instabilities in the constituent magnetizations are solved by
introducing a biaxial anisotropy term to the Gibbs magnetic free energy of each
nanomagnet. The enhanced stability allows for more complex components of a
logic architecture capable of random combinatorial logic, including horizontal
wires, vertical wires, junctions, fanout nodes, and a novel universal logic
gate. Our simulations define the focus of scaling trends in nanomagnet-based
logic and provide estimates of the energy dissipation and time per nanomagnet
reversal
Evolution and stability of a magnetic vortex in small cylindrical ferromagnetic particle under applied field
The energy of a displaced magnetic vortex in a cylindrical particle made of
isotropic ferromagnetic material (magnetic dot) is calculated taking into
account the magnetic dipolar and the exchange interactions. Under the
simplifying assumption of small dot thickness the closed-form expressions for
the dot energy is written in a non-perturbative way as a function of the
coordinate of the vortex center. Then, the process of losing the stability of
the vortex under the influence of the externally applied magnetic field is
considered. The field destabilizing the vortex as well as the field when the
vortex energy is equal to the energy of a uniformly magnetized state are
calculated and presented as a function of dot geometry. The results (containing
no adjustable parameters) are compared to the recent experiment and are in good
agreement.Comment: 4 pages, 2 figures, RevTe
Interacting circular nanomagnets
Regular 2D rectangular lattices of permalloy nanoparticles (40 nm in
diameter) were prepared by the method of the electron lithography. The
magnetization curves were studied by Hall magnetometry with the compensation
technique for different external field orientations at 4.2K and 77K. The shape
of hysteresis curves indicates that there is magnetostatic interaction between
the particles. The main peculiarity is the existence of remanent magnetization
perpendicular to easy plain. By numerical simulation it is shown, that the
character of the magnetization reversal is a result of the interplay of the
interparticle interaction and the magnetization distribution within the
particles (vortex or uniform).Comment: 16 pages, 8 figure
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Magnetic Properties and Interfacial Anisotropies of Pt/Co/AlO<inf>x</inf> Perpendicularly Magnetized Thin Films
The thin films of Pt/Co/AlOx, showing perpendicular magnetic anisotropy, were grown by magnetron sputtering with AlOx formed by the oxidation of thin Al layers using an oxygen atom source. Films were studied as a function of Pt thickness and Al oxidation, and films that showed full remanence and sharp switching coercivity were achieved. In order to prevent further oxidation of the interface in ambient conditions, we use a double Al growth and oxidation process. The magnetooptical Kerr effect and vibrating sample magnetometry were used to analyze these films. We find an effective perpendicular anisotropy of 2 × 106 erg/cm3, with the majority of the perpendicular anisotropy coming from the Pt/Co interface. From the sweep rate dependence on the coercivity, we are able to extract an activation volume of 4.3-0.5 × 10-18cm3, similar to other Co-based perpendicular systems.This research is funded by the European Community under the Seventh Framework Program ERC Contract No. 247368: 3SPIN. AB acknowledges DTA funding from the EPSRC
Effect of photodynamic therapy in combination with ionizing radiation on human squamous cell carcinoma cell lines of the head and neck
Photodynamic therapy (PDT) is a promising treatment modality for head and neck, and other tumours, using drugs activated by light. A second generation drug, 5-aminolaevulinic acid (5-ALA), is a precursor of the active photosensitizer protoporphyrin IX (PpIX) and has fewer side-effects and much more transient phototoxicity than previous photosensitizers. We have investigated the effect of 5-ALA mediated PDT in combination with γ-irradiation on the colony forming ability of several human head and neck tumour cell lines. The effect of treatments on the DNA cell cycle kinetics was also investigated. Our results indicate that the combination of 5-ALA mediated PDT and γ-irradiation results in a level of cytotoxicity which is additive and not synergistic. 5-ALA mediated PDT had no discernible effect on DNA cell cycle distributions. γ-irradiation-induced cell cycle arrest in G2 did not enhance the phototoxicity of 5-ALA. © 2000 Cancer Research Campaig
Micromagnetics Simulation of Deep-Submicron Supermalloy Disks
The results of recent micromagnetic simulations of deep submicron supermalloy disks are presented. A recent experimental measurement of the hysteresis and magnetic domain structure in supermalloy disks with diameters ranging from 55 to 500 nm and thickness ranging from 6 to 15 nm has been reported. Our micromagnetic simulations show remarkable agreement with the experimental hysteresis loops. The simulation results show that for thin or small diameter disks a single magnetic domain exists with all spins aligned. The hysteresis loop represents free rotation of these spins. For larger diameter disks or as the thickness increases the hysteresis loops change shape due to the appearance of a single vortex state appearing at low applied fields
Near-field interaction between domain walls in adjacent Permalloy nanowires
The magnetostatic interaction between two oppositely charged transverse
domain walls (DWs)in adjacent Permalloy nanowires is experimentally
demonstrated. The dependence of the pinning strength on wire separation is
investigated for distances between 13 and 125 nm, and depinning fields up to 93
Oe are measured. The results can be described fully by considering the
interaction between the full complex distribution of magnetic charge within
rigid, isolated DWs. This suggests the DW internal structure is not appreciably
disturbed by the pinning potential, and that they remain rigid although the
pinning strength is significant. This work demonstrates the possibility of
non-contact DW trapping without DW perturbation and full continuous flexibility
of the pinning potential type and strength. The consequence of the interaction
on DW based data storage schemes is evaluated.Comment: 4 pages, 4 figures, 1 page supplimentary material (supporting.ps
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Two-dimensional control of field-driven magnetic bubble movement using Dzyaloshinskii-Moriya interactions
The field-induced asymmetric growth of magnetic bubble domains in Pt/Co/Pt out-of-plane magnetized films with Dzyaloshinskii–Moriya interactions (DMI) is used to control the lateral displacement of bubbles. We demonstrate experimentally that we can laterally translate bubbles away from their nucleation site by applying a series of alternating 3-dimensional field pulses with a controlled relative sign between the out-of-plane and in-plane components. Using magneto optical Kerr effect imaging, the domain wall velocity as a function of applied field strength was measured from which the magnitude of the DMI field was estimated.This work was supported by the European Community
under the Seventh Framework Programme '3SPIN' (ERC
contract 247368) and by EMRP JRP EXL04 SpinCal.
The EMRP is jointly funded by the EMRP participating
countries within EURAMET and the EU.This is the accepted manuscript. The final version is available from AIP at http://scitation.aip.org/content/aip/journal/apl/106/2/10.1063/1.4905600
Coupling and induced depinning of magnetic domain walls in adjacent spin valve nanotracks
The magnetostatic interaction between magnetic domain walls (DWs) in adjacent
nanotracks has been shown to produce strong inter-DW coupling and mutual
pinning. In this paper, we have used electrical measurements of adjacent
spin-valve nanotracks to follow the positions of interacting DWs. We show that
the magnetostatic interaction between DWs causes not only mutual pinning, as
observed till now, but that a travelling DW can also induce the depinning of
DWs in near-by tracks. These effects may have great implications for some
proposed high density magnetic devices (e.g. racetrack memory, DW logic
circuits, or DW-based MRAM).Comment: The following article has been accepted by the Journal of Applied
Physic
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