Py Nanowires Research Articles

Temperature and medium structurization effect on spontaneous evolution of domains and bubbles in magnetic nanostructures

Spontaneous evolutions of domains in magnetic nanowires and of magnetic bubbles in open ferromagnetic nanolayers are investigated using micromagnetic simulations. We compare temperature dependent dynamics of domain wall (DW) systems in Permalloy (Py) nanowires and systems of chiral DWs in ultra-thin nanowires with perpendicular magnetic anisotropy (PMA) and Dzyaloshinskii-Moriya interaction (DMI). In Py nanowires DWs collide and, in majority of cases, the collision leads to the DW annihilation in disagreement with the expectation of topological protection of sums of all the magnetic charges attached to the nanowire edges which are carried by DWs. For our purpose of discussing the DW collision in the presence of thermal excitations, we revisit the problem of field-driven collisions of DWs in Py nanowires at zero temperature. We claim that thermal fluctuations can counteract the collision-induced annihilation of DWs, thought further improvement of stabilization of domain structures is achievable via structurization of the magnetic nanowires (dividing them into grains). In PMA-DMI nanowires, thermally-excited chiral DWs can be randomly approaching or moving away while not being annihilated. A problem related to the motion of chiral DWs is the spontaneous motion of magnetic bubbles in open PMA-DMI planes. The magnetic bubbles expand or shrink to vanishing dependent on strength of the DMI interaction. Such a motion appears to be be strongly influenced by temperature and by structural discontinuities of the magnetic layer.

Magnetodynamic Properties of Rare-Earth-Doped Permalloy Nanowires

We investigated the effect of rare-earth (RE) element doping on magnetodynamic properties of 1D Ni80Fe20 (Py) nanowires. 5% of doping of RE element (La, Nd, and Sm) in Py nanowires was successfully done by electrodeposition technique in porous anodic alumina template. It is observed by the X-ray diffraction (XRD) measurements that the crystal structure of Py nanowires decreases from polycrystalline to amorphous phase with doping of RE element. The magnetic properties demonstrated that the saturation magnetization decreases upto 98% with the higher atomic number RE dopant. The ferromagnetic resonance measurements in field-sweep mode were done to analyze the magnetization dynamics of RE-doped nanowires. The fitting of resonance field and field linewidth was done by using the Landau–Lifshitz–Gilbert equation. It is observed that the resonance field increases with Sm doping as compared to La doping. The damping constants have been achieved by decocting the extrinsic linewidth and found to increase by ~12 times with RE doping. The increase of Gilbert damping emanates from the enhancement of L–S coupling in Py nanowires.

Controlled magnetic behaviour of Ni80Fe20 nanowire by a selection of nucleation pads

Magnetic nanowires are of technological importance as their magnetic properties can be controlled by their dimensions and shape. In soft magnetic nanowires (e.g. Ni 80 Fe 20 alloy or Permalloy), shape anisotropy has a very strong effect on their magnetic properties and thus the wire width and thickness control the domain patterns, nature of magnetization reversal, and the switching field. The switching field of a permalloy (Py) nanowire (NW) can be reduced substantially by attaching a microsized nucleation pad (NPD) to it. In this work, the OOMMF software package was used to perform micromagnetic simulations for selected NPD-NW structures. In this present study, we proved that the shape of the attached NPD is an important factor to consider. For instance, the switching field of structure comprises a triangular NPD (area = 0.25 μm2) with its head connected to a Py NW (20 nm wide) is about one fourth of the switching field of a square-like NPD-NW structure of the same size. Also the NPD size has an effect on the quality of the obtained hysteresis loop and thus it has to be comparable to the size of the NW for the sake of having a step-free hysteresis loop. These findings suggest that the rectangular NPD with its head connected to the NW may serve better than other shapes as it provides a directed motion for the domain walls to reach the NPD/NW interface easily. Thus it gives the highest reduction in the switching field of the Py nanowire in addition to a step-free hysteresis loop when the NPD size is 0.01 μm2.

Current-Direction-Dependent Depinning of Vortex Domain Walls in Permalloy Zigzag Nanowires

We investigate the current induced depinning of magnetic domain walls (DWs) trapped at the kinks in a patterned Py nanowire with two-kink zigzag shape on Si/SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> substrate. By injecting pulse current with varying amplitude, two threshold current densities with a slight difference of around 6 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sup> A m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> have been determined according to the different depinning process. The smaller threshold current density corresponds to the depinning of a single DW which is always the first DW facing to the electron flow. This fact indicates that the different pinning potential caused by the structural asymmetry is not the key to determine which DW is to depin. Micromagnetic simulations provide evidence that the specific current-driven behavior of the vortex DW might account for the single depinning process. The larger threshold corresponds to the simultaneous depinning of two DWs which has been commonly observed in a variety of shaped nanowires.

Direct-current effects on magnetization reversal properties of submicron-size Permalloy patterns for radio-frequency devices

Ferromagnetic resonance (FMR) spectroscopy is used to measure direct-current (dc) effects on the magnetization reversal properties of submicron-sized lateral patterned magnetic material. The observed FMR frequency-field relationship shows that for both 240 and 550 nm wide Permalloy (Py) nanowires the coercivity is reduced by ∼33% when a 50 mA dc passes through the transmission line where the nanowires are incorporated. The temperature dependence of the coercivity has a T relationship which suggests the coherent rotation mode tendency in such 100 nm thick Py nanowires.

Hall magnetometry on Co, Fe, and Py nanowires

Abstract We have studied the magnetization reversal behavior of Co, Fe, and Py nanowires by Hall magnetometry at 4.2 K. The wires with a width w ranging from 100 nm to 1 μm were fabricated with one end on a Hall cross prepared from a GaAs/AlxGa1−xAs heterostructure, containing a two-dimensional electron system. The magnetization reversal behavior differs significantly for the smallest wires (w∼100 nm) and for wider wires (w>250 nm). We found that the coercitivity is inversely proportional to the width of the wire, as expected from theoretical considerations.

Study of Spin-Valve Operation in Permalloy–SiO2–Silicon Nanostructures

Magnetotransport studies are performed on nanoscale Permalloy(Py)–(Mg)–SiO2-degenerate Si(100) tunneling devices in spin-valve geometry with and without Mg interlayer. Highly remanent, single domain Py electrodes (15–100-μm length, 100–1000-nm width) are realized by electron-beam lithography, electron-beam evaporation, and subsequent lift-off. Different widths ensure subsequent switching of the Py nanoelectrodes in increasing magnetic fields. A suppression of spin-polarized current is expected for antiparallel magnetization configuration of source and drain contacts (i.e. positive magnetoresistance) if spin injection and detection have been successfully implemented. Magnetic hysteresis curves of Py nanowire arrays measured at temperatures from 5 K up to 300 K reveal increasing coercive fields (up to 40 mT) for decreased nanowire widths as required for device operation. Small positive magnetoresistance is observed for the spin-valve geometry with Mg interlayer at 4.2 K, contrary to the negative anisotropic magnetoresistance measured of single wires.