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The switching of submicrometer ferromagnetic wire junctions is investigated by controlled injection of domain walls (DWs). A three-terminal continuous [Ni.sub.80][Fe.sub.20] structure is described, consisting of two input wires and one output wire. Separate structures were fabricated by focused ion beam (FIB) milling, to inject either zero, one, or two DWs to the junction inputs. Introduction of DWs to the junction was performed using one or two DW injection pads with low switching fields. Hysteresis loops measured by magnetooptical Kerr effect (MOKE) magnetometry on the device output wires showed the coercivity of the output is strongly dependent on the number of DWs incident at the junction. By injecting either one or two DWs into the junction, it is possible to switch the output wire at two distinct field values, each markedly lower than the nucleation field of the junction. Results presented are relevant to the future development of spintronics DW logic systems, and for fundamental studies into DW resistance and interaction between DWs and wire morphology. Index Terms--Domain walls (DWs), focused ion beam (FIB), magnetic wires, magnetization reversal.

Experimental results of domain wall propagation velocity as a function of applied field in a 200-nm-wide permalloy nanostructure are presented. The structure was fabricated by focused-ion beam milling and designed to separate the domain wall nucleation from propagation. The measured velocities are very high, up to 1500 m/s at 49 Oe and the field dependence of the velocity is interpreted in terms of thermally activated wall motion through a series of pinning sites and a wall geometry that changes as a function of field. Index Terms--Domain walls, magnetic nanostructure, permalloy, thermal activation.

A detailed analysis of the structural and compositional changes in NiFe/Au bilayers induced by a focused ion beam (FIB) is presented. NiFe/Au bilayers with different thickness were irradiated with a focused 30 keV Ga+ ion beam, and the evaluation of the individual layers and interfaces were investigated systematically as a function of a broad range of irradiation fluence using grazing incidence x ray reflectivity (GIXRR) and angular dependent x ray fluorescence (ADXRF) techniques carried out at synchrotron radiation sources. Experimental data were collected from 1.3 mm × 4.5 mm structures, and irradiation of such a broad areas with a 100-nm-wide focused ion beam is a challenging task. Two irradiation regimes were identified: For Ga+ fluences < 15.6 × 1014 ion/cm2 (low dose regime), the main influence of the focused ion beam is on the interface and, beyond this dose (high dose regime), sputtering effects and ion implantation becomes significant, eventually causing amorphization of the bilayer system. The broadening of the NiFe/Au interface occurs even at the lowest dose, and above a critical fluence ([uppercase_phi_synonym] = 1.56 × 1014 ion/cm2) can be represented by an interfacial-intermixed layer (NixFeyAu(1-x-y); x = 0.5-0.6, y = 0.1-0.15) formed between the NiFe and Au layers. The thickness of this layer increases with irradiation fluence in the low dose regime. A linear relationship is found between the squared intermixing length and irradiation fluence, indicating that FIB-induced mixing is diffusion controlled. The ballistic model fails to describe FIB-induced intermixing, indicating that thermodynamical factors, which might be originated from FIB specific features, should be taken into account. Despite the complexity of the chemical and structural formation, good agreement between the experiment and theory highlights the functionality of the combined GIXRR and ADXRF techniques for studying intermixing in high resolution. [ABSTRACT FROM AUTHOR]

The magnetization behavior of a Permalloy thin-film (nominally Ni81Fe19) was investigated as a function of combined quasistatic and pulsed magnetic fields measured using magneto-optic Kerr effect magnetometry. We observed complex field dependent switching behavior that depends on the relative contributions to the total field of the quasistatic and pulsed fields. As the pulsed field amplitude was increased, complex switching behavior occurs for total fields in excess of the coercive field. A simple phenomenological domain wall propagation model suggests a qualitative understanding of this complex behavior based on Walker breakdown of the domain wall motion occurring in the Permalloy thin-film. [ABSTRACT FROM AUTHOR]

We have investigated the propagation of transverse domain walls in magnetic nanowires under axial and transverse magnetic fields using three-dimensional micromagnetic modeling. Transverse magnetic fields change the domain wall width and, below the Walker field, either increase or decrease the domain wall velocity depending when the field and wall magnetization are parallel or antiparallel, respectively. Furthermore, differences in the Walker field also appear for opposite transverse fields, and a surprising result is that under relatively high axial and transverse fields, Walker breakdown can be completely suppressed and the domain wall velocity returns to several hundreds of m s-1. [ABSTRACT FROM AUTHOR]

The controlled pinning and depinning of head-to-head domain walls with individual artificial nanotraps in rounded L-shaped Ni81Fe19 wires is discussed. Domain walls can be effectively pinned by domain wall nanotraps with dimensions of depth Dt=35nm and width Wt=55nm.

The determination of the magnetoelastic properties in Fe-rich amorphous alloys by using resonance methods is strongly affected by the kind of measurement done. In this work, we compare results obtained when using the vibrating reed method and the magnetically excited resonance one. Measurements have been performed on [Fe.sub.66][Co.sub.18][Si.sub.1][B.sub.15] amorphous ribbons with the induced anisotropy easy axis at 60 degrees with respect to the ribbon axis. The observed differences are large in all the measured range, and especially striking in the E(H = 0)/[E.sub.s] initial to saturation Young's modulus ratio. After a detailed analysis of the expressions used to derive magnetoelastic quantities from the resonant frequencies values, these discrepancies are explained by the fact that the two methods measure different quantities: dependence of the Young's modulus on the applied field (or [Delta]E effect) and magnetoelastic coupling coefficient, respectively. Index Terms--Metallic glasses, anisotropy, magnetostriction, magnetoelastic properties, magnetoelastic coupling.

We report on the controlled pinning and depinning of head-to-head domain walls with individual artificial nanotraps in rounded L-shaped Ni81Fe19 wires. Domain walls were nucleated and injected into one arm of an L-shaped planar wire structure with a wire width of 200 nm and a thickness of 5 nm. The domain walls were propagated through a rounded corner into an orthogonal output wire by a 27 Hz anticlockwise rotating field. A highly sensitive magneto-optical Kerr magnetometer system was used to detect magnetization reversals around single wedge shaped nanotraps in the output wire of different samples. Domain wall propagation occurred at a mean measured x-field value of 6.8 Oe in the output wire arm when not interacting with a trap. Domain wall nanotraps with dimensions as small as depth Dt=35 nm and width Wt=55 nm were found to effectively pin domain walls. In general, the depinning field of a domain wall from a trap increased with trap size. Hysteresis loops and plots of domain walls depinning fields as a function of trap depth are presented. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Author(s): James D. R. Buchanan [1]; Russell P. Cowburn (corresponding author) [1]; Ana-Vanessa Jausovec [1]; Dorothée Petit [1]; Peter Seem [1]; Gang Xiong [1]; Del Atkinson [2]; Kate Fenton [2]; [...]

Abstract: Magnetic properties of in-plane magnetized bilayers are investigated as a function of 30keV Ga+ ion dose and Ni81Fe19 layer thickness. Coercivity, saturation magnetization, hard axis anisotropy field, and hysteresis loop remanence ratio are tuned at low-ion doses. The magnetic properties of irradiated bilayers are found to be very sensitive to Ni81Fe19 layer thickness. Specifically, the critical ion dose for room temperature quenching of measured ferromagnetism in capped Ni81Fe19 samples is found to be proportional to the square root of Ni81Fe19 layer thickness. This square root dependence is consistent with a structural change due to radiation-induced displacement of interfacial atoms. Focused ion beam (FIB) intermixing can rapidly modify the magnetic properties of ultrathin in-plane magnetized capped films at lower ion doses than surface sputtering or ion implantation effects. [Copyright &y& Elsevier]

In this work high-frequency magnetization dynamics and statics of artificial spin-ice lattices with different geometric nanostructure array configurations are studied where the individual nanostructures are composed of ferromagnetic/non-magnetic/ferromagnetic trilayers with different non-magnetic thicknesses. These thickness variations enable additional control over the magnetic interactions within the spin-ice lattice that directly impacts the resulting magnetization dynamics and the associated magnonic modes. Specifically the geometric arrangements studied are square, kagome and trigonal spin ice configurations, where the individual lithographically patterned nanomagnets (NMs) are trilayers, made up of two magnetic layers ofNi81Fe19of 30 nm and 70 nm thickness respectively, separated by a non-magnetic copper layer of either 2 nm or 40 nm. We show that coupling via the magnetostatic interactions between the ferromagnetic layers of the NMs within square, kagome and trigonal spin-ice lattices offers fine-control over magnetization states and magnetic resonant modes. In particular, the kagome and trigonal lattices allow tuning of an additional mode and the spacing between multiple resonance modes, increasing functionality beyond square lattices. These results demonstrate the ability to move beyond quasi-2D single magnetic layer nanomagnetics via control of the vertical interlayer interactions in spin ice arrays. This additional control enables multi-mode magnonic programmability of the resonance spectra, which has potential for magnetic metamaterials for microwave or information processing applications., (Creative Commons Attribution license.)

The controlled modification of the electronic properties of ZnO nanorods via transition metal doping is reported. A series of ZnO nanorods were synthesized by chemical bath growth with varying Co content from 0 to 20 atomic% in the growth solution. Optoelectronic behavior was probed using cathodoluminescence, time-resolved luminescence, transient absorbance spectroscopy, and the incident photon-to-current conversion efficiency (IPCE). Analysis indicates the crucial role of surface defects in determining the electronic behavior. Significantly, Co-doping extends the light absorption of the nanorods into the visible region, increases the surface defects, and shortens the non-radiative lifetimes, while leaving the radiative lifetime constant. Furthermore, for 1 atomic% Co-doping the IPCE of the ZnO nanorods is enhanced. These results demonstrate that doping can controllably tune the functional electronic properties of ZnO nanorods for applications., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)