Sputtered Permalloy Films Research Articles

Radiative damping in waveguide-based ferromagnetic resonance measured via analysis of perpendicular standing spin waves in sputtered permalloy films

The damping $\alpha$ of the spinwave resonances in 75 nm, 120 nm, and 200nm -thick Permalloy films is measured via vector-network-analyzer ferromagnetic-resonance (VNA-FMR) in the out-of-plane geometry. Inductive coupling between the sample and the waveguide leads to an additional radiative damping term. The radiative contribution to the over-all damping is determined by measuring perpendicular standing spin waves (PSSWs) in the Permalloy films, and the results are compared to a simple analytical model. The damping of the PSSWs can be fully explained by three contributions to the damping: The intrinsic damping, the eddy-current damping, and the radiative damping. No other contributions were observed. Furthermore, a method to determine the radiative damping in FMR measurements with a single resonance is suggested.

Effect of Ti seed and spacer layers on structure and magnetic properties of FeNi thin films and FeNi-based multilayers

Abstract The microstructure and magnetic properties of sputtered permalloy films and FeNi-based multilayers prepared by magnetron sputtering have been studied. X-ray diffraction measurements indicate that Ti/FeNi films exhibit good (1 1 1) texture and crystallinity. Ti/FeNi bilayers with high crystallographic quality have relatively low resistivity. The Ti seed layer does not influence the magnetic properties of FeNi film in Ti/FeNi bilayers, but the thick Cu seed layer leads to an increase of the coercive force of the magnetic layer. For the FeNi films deposited on thick Cu seed layer, the (0 1 0) and (0 0 2) diffraction peaks of hcp nickel were clearly observed. The thin Ti spacer between Cu and FeNi layers prevents the formation of the nickel phase and restores the magnetic softness of the FeNi layer in the Cu/Ti/FeNi sample. Obtained results can be important for the development of multilayer sensitive elements for giant magnetoimpedance or magnetoresistance detectors.

Effect of etching on the electrical and magnetic properties of writer shield material

Magnetron sputtered permalloy films are treated by wet chemical etchings with acid etchant as well as fluorine based reactive ion etch (RIE). Upon these treatments, the resistivity and coercivity of the permalloy film increase is within 10 %. No significant increase observed with prolonged etching time. The effective magnetization change of the permalloy films are within 5 % post the treatments. Atomic force microscope (AFM) and transmission electron microscope (TEM) are used to study the surface and interface evolution of permalloy film upon etching. The small impact on the electrical and magnetic properties of permalloy films can be correlated with the surface oxide protecting layer formation during the etch. Consequently, sputtered NiFe is a safe material to expose to these etching processes for write pole shield application.

Observation of rotatable stripe domain in permalloy films with oblique sputtering

Stripe domain (SD) in obliquely sputtered permalloy films were investigated by comparing with normally sputtered ones. The critical thickness for SD formation of obliquely sputtered films was about 100 nm thinner than that of normally sputtered films. The hysteresis loops of obliquely sputtered films showed a peculiar shape. A rotation of SD towards easy axis was observed in the obliquely sputtered films, which was confirmed by permeability spectra under a bias field. The origin of the rotation could result from in-plane uniaxial anisotropy, which is induced by the shape effect of the oblique columnar growth of permalloy grains.

FeNi-based magnetoimpedance multilayers: Tailoring of the softness by magnetic spacers

The microstructure and magnetic properties of sputtered permalloy films and FeNi(170 nm)/X/FeNi(170 nm) (X = Co, Fe, Gd, Gd-Co) sandwiches were studied. Laminating of the thick FeNi film with various spacers was done in order to control the magnetic softness of FeNi-based multilayers. In contrast to the Co and Fe spacers, Gd and Gd-Co magnetic spacers improved the softness of the FeNi/X/FeNi sandwiches. The magnetoimpedance responses were measured for [FeNi/Ti(6 nm)]2/FeNi and [FeNi/Gd(2 nm)]2/FeNi multilayers in a frequency range of 1–500 MHz: for all frequencies under consideration the highest magnetoimpedance variation was observed for [FeNi/Gd(2 nm)]2/FeNi multilayers.

Magnetic vortex dynamics in the presence of pinning

We have measured the frequency ${f}_{G}$ of the gyrotropic mode of a magnetic vortex formed in individual soft ferromagnetic disks with diameters from 600 nm to $2\text{ }\ensuremath{\mu}\text{m}$. For low excitation amplitudes, we observe fluctuations in ${f}_{G}$ as a function of applied magnetic field. The relationship between the applied field and the spatial displacement of the vortex core from the center of the disk indicates that the fluctuations are due to a distribution of nanoscale defects that pin the vortex core, which has a diameter of $\ensuremath{\sim}10\text{ }\text{nm}$. In the limit of high excitation amplitude, the gyrotropic frequency is independent of field, indicating that the core is depinned. In this limit ${f}_{G}={f}_{ideal}$ where ${f}_{ideal}$ is the frequency predicted by analytical models and micromagnetic simulations of ideal vortex behavior. We also find both experimentally and in simulations that the average frequency shift $⟨\ensuremath{\Delta}f⟩=⟨{f}_{\text{max}}\ensuremath{-}{f}_{ideal}⟩$ is independent of disk diameter. From this observation we argue that $\ensuremath{\Delta}f$ for a particular fluctuation is proportional to the interaction energy ${W}_{P}$ of the vortex core with a single nanoscale defect and estimate the average energy to be ${W}_{P}/e\ensuremath{\approx}2\text{ }\text{eV}$ for the defects in these sputtered permalloy films.

Hysteresis Modeling of Thin Permalloy Films and Parameter Interpretation

An energetic model is used to calculate macroscopic magnetization behavior of thin Permalloy films. Therefore it is extended by magnetocrystalline anisotropy energy and domain classes that particularly represent magnetization rotation. Some model parameters can be related to coherent rotation of domain magnetizations. A qualitative agreement is achieved with measurements on sputtered Permalloy films used for anisotropic magnetoresistance (AMR) sensors.

Effects of spacer layer on growth, stress and magnetic properties of sputtered permalloy film

A microelectromechanical (MEMS) flux concentrator (J. Appl. phys. 91 (2002) 7795), is a device that will minimize 1/f noise in magnetic sensors by modulating the magnetic field at the position of the sensor. This requires high permeability and low stress permalloy (Py) films to be deposited on the MEMS flaps (J. Appl. phys. 91 (2002) 7795). Py (Ni80Fe20) films from 100 to 560nm thick were deposited on Si substrates using DC magnetron sputtering. The effects of deposition conditions on the grain morphology, texture, stress and magnetic properties were studied. Lower sputtering pressure changes film stress from tension to compression and increases the 〈111〉 out of film plane texture, while higher power increases tension and texture. Neutral film stress was obtained with 100W of sputtering power and 1.25mTorr of Ar gas pressure. With increasing thickness, the Py film was found to develop a stripe-like domain configuration at low fields because of strong out-of-plane magnetic anisotropy. The critical thickness is around 180nm.This may be explained by a competition between planar demagnetization fields and columnar magnetic anisotropy. Adding 5nm of Ta or Cr layer as spacer successfully broke up the continuity of the magnetic structure and allowed us to produce high-permeability films by fabricating (Ta/Py) or (Cr/Py) multilayer films with each Py layer thinner than the critical thickness.

Incorporation of ferromagnetic metallic films in planar transmission lines for microwave device applications

We constructed a series of microstrip and coplanar microwave waveguides. These structures use metallic ferromagnets and therefore exhibit strongly frequency-dependent attenuation and phase-shift effects. The lines have maximum attenuation peaks occurring at the ferromagnetic resonance frequency, which increases with applied magnetic field. Such properties are used in band-stop filters. The devices used monocrystalline Fe films grown by molecular beam epitaxy and polycrystalline sputtered permalloy films. For our devices that incorporated Fe the band-stop frequencies ranged from 10-20 GHz for applied fields up to only 80 kA/m (1000 Oersted). For devices using permalloy, the band-stop frequency was in the 5-10 GHz range for applied fields less than 80 kA/m. The maximum power attenuation was about 100 dB/cm, much larger than the previously reported values of 4 dB/cm. The resonance condition also affects the phase of the transmitted wave, strongly changing phase above and below the resonance frequency. The result is a phase-shifter that is tunable with applied magnetic field. We observed phase changes of over 360/spl deg//cm with an applied field of less than 40 kA/m.

Comment on `Exchange penetration and anisotropy magnetoresistance in Co-Ni multilayers'

In this comment we show how the claim of Hernando et al (1998 J. Phys. D: Appl. Phys. 31 637) of an enhanced magnetoresistance of 130% with a field sensitivity of 6%/Oe in Co/Ni sputtered multilayers is based on a misinterpretation of the magnetoresistance effect. To illustrate this we use their square four-point probe arrangement to obtain a magnetoresistance effect of 176% with a field sensitivity of 11.7%/Oe in a sputtered permalloy film. We present critical analysis of this `extraordinary' effect showing that the high magnetoresistance values obtained are not intrinsic to the material but are an artefact of the measurement method.

Cathode sputtered permalloy films of high anisotropic magnetoresistive effect

The anisotropic magnetoresistive effect of dc-sputtered Ni 81% - Fe 19% films has been increased up to Δρ/ρ = 3.93% at 50nm thickness. Investigations have been concentrated on the influence of the target current, the target-substrate-distance, and of the temperature of both target and substrate material. As a function of the applied magnetic bias field, the easy-axis coercivity of the permalloy film is between 100A/m and 200A/m due to induced anisotropy. The dc-magnetization curves represent an almost ideal Stoner-Wohlfarth behaviour.

Magnetic and magnetoresistive properties of sputtered permalloy thin films

The dependence of the magnetic properties, especially magnetoresistivity, of sputtered permalloy thin films on the sputtering Ar pressure is studied. The Ar pressure is varied between 0.106 and 1.06 pa. The coercivity and the electrical resistivity of permalloy films both remain stable in this pressure range. These two properties are dependent on the grain size of a permalloy film, which is independent of the Ar pressure in this pressure range. The average grain size is 10–12 nm in diameter. The magnetoresistivity δϱ decreases and the anisotropy field increases as the Ar pressure decreases. Magnetoresistivity is related to the preferred orientation of the sputtered permalloy film. The permalloy films deposited at high Ar pressures have no preferred orientation; therefore, they show high magnetoresistivity.

Frequency dependence of the transverse biased permeability in thin permalloy films

The frequency dependence of the transverse biased permeability μ′t(f ) has been measured up to 250 MHz in thin (0.044 μm) and thick (2.1 μm) unpatterned sputtered permalloy films with uniaxial anisotropy. In these films, the initial permeability along the hard axis can be described by the classical eddy current damping model assuming uniform rotation. For both films, μ′t at low frequency agrees reasonably well with Hoffman’s ripple model assuming appropriate values for the structure factor. In the thin film, μ′t(f ) is independent of frequency within experimental error up to at least 250 MHz. However, in the thick film μ′t(f ) decreases more rapidly with frequency than can be explained by classical eddy currents, when the transverse bias field HB is not very large compared to the net anisotropy field. The value of HB at which μ′t(f ) reaches a maximum amplitude is also found to increase monotonically with increasing frequency, also inconsistent with simple eddy current predictions. It is suggested that the formation of ripple walls leads to anomalous eddy current losses similar to that observed in bulk materials.

Surface Morphology of the Grain of Permalloy Films

Surface morphologies of sputtered permalloy films were investigated by SEM. Grain sizes decreased with slanting of the substrate surface or the presence of N <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> in the sputtering gas. The preferred orientations of permalloy films were changed from ≪111≫ to ≪100≫ by the N <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> presence. SEM observations of crystal orientations suggested that the changes in the preferred orientations of permalloy films were caused by reduction of the surface energy, which was, in turn, thought to be caused by nitrogen adsorption.

Rf-diode sputtered Permalloy film

Permalloy films were deposited by rf-diode sputtering on silicon and glass substrates. The in-plane film stress was measured as a function of film thickness. The cause of stress changes with film thickness is discussed. The deposition rate and the in-plane stress have been correlated with various process parameters, such as rf power, argon pressure, and substrate bias. A regression analysis yields an excellent fit to the experimental data. The in-plane stress in the film was measured using the wafer-bending method and the x-ray method. The stress of Permalloy films on silicon wafer can be either compressive or tensile, depending on the deposition parameters. The stress increases with increased deposition rate. Stress-free films on silicon can be obtained for a deposition rate of about 7.5 nm/min. The films have good magnetic properties when deposited in these conditions.

Glow-discharge optical spectroscopy as a diagnostic of sputtered permalloy film composition and saturation magnetostriction

We show that the composition and saturation magnetostriction of sputtered permalloy films can be correlated with the relative intensities of iron and nickel atomic emissions from a 13.56-MHz rf glow discharge. Wavelength-resolved emission spectra as a function of discharge pressure were recorded while sputtering iron and permalloy targets. Intensities of some emission lines were highly correlated, so that their ratios were nearly independent of argon pressure. This occurred in spite of a ∼50-fold change in the brightness of the glow over the pressure range studied, and suggested that the stoichiometry of the sputtering target and the sputtered permalloy film can each be assessed during the sputtering process. The selection of appropriate emission lines is discussed, along with considerations of the type of equilibrium distribution prevalent in a sputtering discharge. We used five sputtering targets with different Ni/Fe ratios to grow films. The films were analyzed in terms of composition, stress, and saturation magnetostriction. Film stress was not observed to vary significantly with sputtering target composition. A high degree of correlation was observed between Fe/Ni emission intensity ratio, target composition, film composition, and saturation magnetostriction.

Composition distribution and magnetic characteristics of sputtered Permalloy films with substrate angle

Permalloy sputtered films for a thin magnetic head are deposited under precisely controlled conditions. The head pattern on a substrate shows not only a flat portion but also an inclined portion. The film characteristics on the inclined portions are important for a good thin-film head. Using a rf magnetron sputtering device with an 8-in. target, the angular distributions of sputtered Permalloy atoms (Ni and Fe), composition profile, and the magnetic characteristics were investigated. The results showed that the angular distributions of the Ni–Fe atoms depended on the rf power and were different from those of the cosine rule. A comparison of the film characteristics between the flat and inclined portions was carried out using a special substrate holder, in which nine glass substrates were fixed. The film thickness of the inclined portion differed, depending on the positions where the substrates were fixed. The coercive forces decreased with decreasing sputtering gas pressures, and those of thin films deposited on the inclined substrates were 20–50 A/m.

パーマロイ膜結晶粒の表面形態

Surface morphologies of sputtered permalloy films were investigated by SEM. Grain sizes became small with the inclination of the substrate or the presence of N2 in sputtering gas. Preferred orientations of permalloy films were changed from to by the N2 presence. SEM observation of crystal orientations suggested that the changes of the preferred orientations of permalloy films were caused by reduction of the surface energy, which was, in turn, thought to be caused by nitrogen adsorption.

Thickness dependence of the magnetoresistance effect in RF sputtered thin permalloy films

Because of their importance to the development of magnetoresistive recording heads, the thickness dependence of the magnetoresistive properties of thin R.F. sputtered Permalloy films has been measured in the thickness range from 220A to 5490A. It was found that the \Delta\rho = \rho_{\parellel} - \rho_{\perp} exhibits an oscillatory dependence on film thickness when saturated in a magnetic field. The resistivity ρ and Δρ/ρ also exhibit tendencies in this regard to a lesser degree. The primary source of this oscillatory thickness dependence is the exsistence of a quantum size effect [7] modified by the magnetic quantization producing a Landau level spectrum.[1]

Magnetic, structural and magnetoresistive properties of magnetron-sputtered thin NiFe films

The resistivity, magnetoresistance ratio, magnetic hysteresis loop and structure of magnetron-sputtered permalloy (Ni 81Fe 19) films of thickness 200–1600 Å were studied and compared with the corresponding properties of permalloy films prepared by electron beam evaporation. The r.f.-sputtered films were prepared in an argon plasma from a sputter gun with an aligning magnetic field of 400 Oe applied in the plane of the substrates. No external heating or substrate bias voltage was used during the deposition. The resistivities of sputtered permalloy films show a similar thickness dependence to that for evaporated films, although with higher values. The residual resistances of the sputtered films are also higher; this is attributed to the greater amount of incorporated gases and possibly less atomic ordering. From the thickness dependence of the resistivity as measured in the range 200–1600 Å, the value of the boundary reflection coefficient was estimated and was found to be almost the same as that reported earlier for permalloy films deposited in an ultrahigh vacuum. X-ray diffraction techniques were employed to measure the intrinsic isotropic stress σ which was found to be about 6×10 9 dyn cm −2. The magnetoresistance ratio of the sputtered films is less than 2%, which might be explained by their higher resistivity values. The coercivity of the films is in the range 1.5–3 Oe, which is higher than that of evaporated permalloy films. The same was true of the anisotropy field, which is between 5 and 6.5 Oe.