Permalloy Structures Research Articles

Measurement and Analysis on Magnetic Field Influence of Substation for Magnetic Shielding Device

The residual magnetic field in a magnetic shielding device with a multilayer high permeability material (permalloy) structure can be obtained at the nanotesla (nT) level or even lower. At present, in the process of designing a magnetic shielding device, most of the external environmental magnetic field settings are set at the size of the Earth’s environmental magnetic field, but the instruments inside the magnetic shielding device need to be powered, the active compensation coil needs to be powered, and the degaussing coil of passive shielding layer needs to be powered, so substations need to be used around magnetic shielding devices. The magnetic field generated by the substation will affect the magnetic shielding device, so this paper analyzes and measures the magnetic field generated by the substation. Firstly, the finite element model of a substation is established, and the influence of different substations on the environmental magnetic field is analyzed by changing the power. Secondly, the test method of a substation environment magnetic field is determined. Finally, the site test was carried out to measure the influence of different power substations and different distances on the magnetic field, and its influence on the magnetic shielding device was analyzed, which provided an important basis for the construction of the magnetic shielding device.

Control of band gap's in a permalloy Structure by changing the meander profile

Control modes of band gap in meander-shaped permalloy (NiFe) thin films have been investigated by the method of micromagnetic modeling. The electrodynamic problem is considered by the finite element method and the dispersion characteristics of spin waves are obtained when the geometrical parameters of the meander are changed. The character of changes in the frequency ranges of the Bragg band gaps depending on the meander profile has been investigated. The results can be used to create devices for microwave signal processing, microwave filters and systems with spatio-temporal division of the signal. Keywords: spin waves, magnonics, meander structures, magnon crystal.

Spin wave wavevector up-conversion in Y-shaped Permalloy structures

Spin waves in micrometer-sized, patterned Y-shaped Permalloy structures were studied using micro-focus Brillouin light scattering (BLS) with a magnetic field applied in-plane. For in-plane magnetized thin films and microstrips, the dispersion relations depend on the angle of the magnetization with respect to the microstrip axis. BLS measurements show that spin waves generated in the two arms that form the top of the Y structure can be channeled into a longer magnetic microstrip that forms the base when the applied field is oriented perpendicular to the long axis of the base. In this configuration, the base supports surface spin waves. A comparison of the BLS data with micromagnetic simulations reveals that low-k spin waves generated by a microstrip antenna in the arms are converted to higher-k spin waves in the base, which may be useful for nanomagnonic applications.

Magnetically dependent plasmon drag in permalloy structures

Significant photovoltages are observed in permalloy grating-like structures in response to pulsed laser light illumination. Electrical signals are enhanced at plasmon resonance conditions and show a clear dependence on the magnetic field with a characteristic hysteresis. Estimations show that the effect could not be explained solely by laser-induced heating. Alternative mechanisms are discussed.

Ferromagnetic spin waves in nanostriped magnonic crystals with quasiperiodic vertical development

A theoretical analysis is reported for the spin waves in ferromagnetically-ordered magnonic crystals consisting of lateral periodic arrays of composite nanowires. The structure of each nanowire is a vertically-developed multilayer built up according to a quasiperiodic Fibonacci sequence. Each nanowire is separated by a non-magnetic spacer in either direction. The quasiperiodicity in these composite nanowires is addressed in two ways: the geometric variation in a single-component (permalloy) structure and the compositional variation (using cobalt and permalloy). These composite nanowire structures are compared and contrasted with one another. A microscopic approach is used to calculate the spectra of spin-wave bands and band gaps for several generation numbers of the Fibonacci sequence. Comparison of the density of states for these structures is made with that for the periodic cases, which highlights distinct characteristics of the quasiperiodicity. The fractal-like scaling properties of the modes show characteristics analogous to some complex biological systems.

Non-standing spin-waves in confined micrometer-sized ferromagnetic structures under uniform excitation

A non-standing characteristic of directly imaged spin-waves in confined micrometer-sized ultrathin Permalloy (Ni80Fe20) structures is reported along with evidence of the possibility to alter the observed state by modifications to the sample geometry. Using micromagnetic simulations, the presence of the spin-wave modes excited in the Permalloy stripes along with the quasi-uniform modes was observed. The predicted spin-waves were imaged in direct space using time resolved scanning transmission x-ray microscopy, combined with a ferromagnetic resonance excitation scheme (STXM-FMR). STXM-FMR measurements revealed a non-standing characteristic of the spin-waves. Also, it was shown by micromagnetic simulations and confirmed using STXM-FMR results that the observed characteristic of the spin-waves can be influenced by the local magnetic fields in different sample geometries.

Amplitude and Phase Tuning of Microwave Signals in Magnetically Biased Permalloy Structures

In this paper, a permalloy layer has been employed in the fabrication of a coupled line electromagnetic bandgap (EMBG) device to tune both amplitude and phase. A magnetically biased microwave coplanar configuration manufactured with evaporated permalloy has been measured, and a circuit modelling has been studied to evaluate the measured effects in terms of variable attenuation and phase shift. Starting from a permalloy made by the mixture 80% nickel and 20% iron content, we fabricated an electromagnetic bandgap (EMBG) structure based on a periodic arrangement of single sections of a transmission line with variable impedance, also including a central region with coupled lines. The bandpass characteristics of the EMBG device can be tuned by changing permalloy’s permeability through the application of a DC magnetic field $H_{0}$ (parallel to the plane of the structure). In particular, using a magnetic field up to 3000 Oe, it was possible to change the phase by ca. 45° and the amplitude by ca. 7 dB in the X band.

(Invited) On-Wafer Microwave Devices Based on Magnetic Materials

We present a review of theoretical and experimental results for on-wafer microwave devices. Specifically, we discuss construction of on-wafer inductors designed to operate in frequencies below 1-2 GHz. We also present recent progress in tunable microwave band-stop filters, band-pass filters, phase shifters, and a signal to noise enhancer, all based on a microstrip geometry and using a variety of magnetic thin films and layered structures. These devices are compatible in size and growth process with on-chip high-frequency electronics. For tunable devices based on metallic ferromagnetic films of Fe and Permalloy, the operational frequency ranges from 5 to 35 GHz for external fields below 5 kOe. For the band-stop filters, we observed power attenuation up to ∼100 dB/cm, and an insertion loss on the order of ∼2–3 dB, for both Permalloy and Fe-based structures. We also will discuss the use of thin films of hexagonal ferrites, and liquid crystals/magnetic nano-rods colloids, and show these materials can be used to make on-wafer microwave devices. The devices based on hexagonal ferrite operate in the frequency range 35-70 GHz while devices based on liquid crystal/magnetic nano-rods colloids operate in the frequency range 5 - 110 GHz.

Pseudo exchange bias due to rotational anisotropy

Ferromagnetic nanostructure arrays with particle dimensions between 160nm and 400nm were created by electron-beam lithography. The permalloy structures consist of rectangular-shaped walls around a square open space. While measuring their magnetic properties using the Magneto-Optical Kerr Effect (MOKE), in some angular regions an exchange bias (EB) seemed to appear. This paper gives an overview of possible reasons for this “pseudo exchange bias” and shows experimentally and by means of micromagnetic simulations that this effect can be attributed to unintentionally measuring minor loops.

On-Wafer Microwave Devices based on Magnetic Materials

We present a review of theoretical and experimental results for tunable microwave band-stop filters, band-pass filters, phase shifters, and a signal to noise enhancer, all based on a microstrip geometry and using a variety of magnetic thin films and layered structures. These devices are compatible in size and growth process with on-chip high-frequency electronics. For devices based on metallic ferromagnetic films of Fe and Permalloy, the operational frequency ranges from 5 to 35 GHz for external fields below 5 kOe. For the band-stop filters, we observed power attenuation up to ∼100 dB/cm, and an insertion loss on the order of ∼2–3 dB, for both Permalloy and Fe-based structures. We also will discuss the use of thin films of hexagonal ferrites, and liquid crystals/magnetic nano-rods colloids, and show these materials can be used to make on-wafer microwave devices. The devices based on hexagonal ferrite operate in the frequency range 35-70 GHz while devices based on liquid crystal/magnetic nano-rods colloids operate in the frequency range 5 - 110 GHz. We will also review the properties of hexagonal ferrites doped Al and grown on Si substrates in details.

Surface Roughness Effects on Magnetization Reversal of Magnetic Ring Elements

The effect of surface roughness on magnetoresistance of permalloy ring structure is investigated. Microstructured permalloy rings with surface roughness varying from 4.2 to 21 nm were fabricated using electron beam lithography and a chemical etching process. It is found experimentally that the first and second nucleation fields decrease obviously with the surface roughness increasing, and the field range for the flux-closure state is not associated with surface roughness. The results indicate that surface roughness in permalloy ring structure is an important factor that influences the magnetic behaviors of the ring. This result can provide important information for future designs of ring-shaped magnetic devices.

Magnetic Properties of NiFe Needles on Nanoporous Anodized Aluminum Oxides

In this study, a simple approach combining nanoporous templates with sputter deposition to obtain nano-sized permalloy structures is presented. The grain evolution and the corresponding magnetic anisotropy of permalloy films grown on the nanoporous anodized aluminum oxide (AAO) substrates with different deposition time were investigated. A grain evolution from a needle-like structure to a 2-D network was observed. As a consequence, the magnetization reversal of the permalloy films varied with the grain evolution. The magnetic domains of the permalloy films were pinned dominantly by the needle-like grain structure at the beginning; then, as the deposition time got longer, the domain sizes were constrained mainly by the underlying AAO network.

Microscopic dipole-exchange theory for magnonic crystals: Application to ferromagnetic films with patterned surfaces

Calculations are reported for the spin-wave bands and gaps in magnonic crystals formed by patterning one (or both) of the surfaces of ferromagnetic thin films. Specifically, a patterning in terms of a periodic array of rectangular grooves is considered, and the theory employs a microscopic (or Hamiltonian-based) method that incorporates exchange and magnetic dipole–dipole interactions, as well as an external magnetic field. The coupling between different periodic elements of the magnonic crystal involves both exchange and dipolar terms, allowing for control of the spin-wave bands and gaps as the depth and width of the grooves are varied. Numerical examples are given for Permalloy structures, considering the stripe patterning to be on one or two surfaces, and the applicability to Brillouin light scattering is discussed.

Comparison of electrical techniques for magnetization dynamics measurements in micro/nanoscale structures

Three all-electrical detection techniques—differential resistance (dV/dI), rf/microwave transmission, and spin rectification measurements—were used to measure the magnetic response of individual patterned Permalloy structures. The investigated techniques enable the identification of distinctive magnetization states, such as vortex nucleation and excitation, domain wall motion, ferromagnetic resonance, and spin wave excitations both in the quasistatic and dynamic regimes. The techniques differ in signal-to-noise ratio and sensitivity to the different types of magnetization responses studied here, suggesting that the use of multiple techniques can significantly improve the understanding of magnetically complex structures.

Imposing Local Magnetic Fields to Control Magnetotactic Bacteria Through Combining Microfabrication and Magnetism

The ability to impose localized magnetic fields on magnetic bacteria has a variety of applications including in biophysics, nature inspired materials, and non-destructive sensors. Herein we demonstrate our ability to locally direct swimming magnetotactic bacteria, Magnetospirillum magneticum strain AMB-1, through microfabricated magnetic field concentrators. To accomplish this, a pair of Helmholtz coils was built to magnetize microfabricated permalloy structures of shapes including circles, squares, and triangles, which may affect the local magnetic fields near the structures. The permalloy structures were fabricated through photolithography and depositing a thin film of NiFe on a master mold. The substrate was a #1 glass coverslip that permitted us to observe the interactions of the magnetotactic bacteria with the permalloy structures. These microfabricated structures were positioned at the center and along the axes of the Helmholtz coils. The response of the bacteria around the structure was quantified through analyzing the images of the bacteria in terms of orientation and velocity. The results indicate that the AMB-1 appeared to cross or stop at the regions on the structures possessing higher magnetic field intensity relative to the surroundings. Furthermore, the bacteria appeared to alter their orientation as they approached sharp corners of the structures. We also developed a model using Finite Element Method Magnetics (FEMM) to investigate the regions of local magnetic field gradients, which indicated higher magnetic fields at the protrusions and the sharp points of the magnetic structures. This work supports the idea of using these magnetotactic bacteria as an aqueous non-destructive sensor and also has implications in fields including physics, biology, material science, and engineering.

Domain-Wall Depinning Assisted by Pure Spin Currents

We study the depinning of domain walls by pure diffusive spin currents in a nonlocal spin valve structure based on two ferromagnetic Permalloy elements with copper as the nonmagnetic spin conduit. The injected spin current is absorbed by the second Permalloy structure with a domain wall, and from the dependence of the wall depinning field on the spin current density we find an efficiency of 6×10{-14} T/(A/m{2}), which is more than an order of magnitude larger than for conventional current induced domain-wall motion. Theoretically we find that this high efficiency arises from the surface torques exerted by the absorbed spin current that lead to efficient depinning.

Three-Dimensional Study of the Vector Potential of Magnetic Structures

The vector potential is central to a number of areas of condensed matter physics, such as superconductivity and magnetism. We have used a combination of electron wave phase reconstruction and electron tomographic reconstruction to experimentally measure and visualize the three-dimensional vector potential in and around a magnetic Permalloy structure. The method can probe the vector potential of the patterned structures with a resolution of about 13nm. A transmission electron microscope operated in the Lorentz mode is used to record four tomographic tilt series. Measurements for a square Permalloy structure with an internal closure domain configuration are presented.

Determination of Domain Wall Depinning and Driving Currents in Doped Permalloy Structures

In this paper we investigate the domain wall pinning positions at parabolic pinning potentials in Gd doped wires. Increasing the Gd doping percentage favors the formation of vortex domain walls, shown to be due to an increase in the out of plane anisotropy, allowing the pinning of a vortex and a transverse domain wall in two similar parabolic pinning potentials. Using pulsed currents to investigate the difference in the depinning characteristics of these two domain wall types, we show that the current density required for steady domain wall motion is smaller than the current density required to set it in motion and estimate this difference to be of the order .

Magnetic logic element based on an S-shaped Permalloy structure

Magnetic devices have shown the potential to be used not only as storage elements but also as nonvolatile and programmable logic devices. We present a magnetic logic device element—the S state element—that consists of a single magnetic layer. Its output can be controlled by orthogonal magnetic inputs. The reconfigurable logic element can be easily integrated with common magnetoresistive device concepts, such as spin valves or magnetic tunnel junctions. Using Permalloy as an example, we demonstrate the feasibility of magnetologic operation through micromagnetic simulations.

Fabrication of oxidation-free contacts to nanopatterned Permalloy structures

Fabrication of oxidation-free contacts to nanopatterned Permalloy structures