Permalloy Films Research Articles

Tuning the ferromagnetic resonance frequency of soft magnetic film by patterned permalloy micro-stripes with stripe-domain

Periodic micro-stripes arrays with stripe domains structures upon continuous permalloy (Py) film were fabricated by sputtering, photolithography and ion beam etching technology. These samples display in-plane magnetic anisotropy, and stripe domains structure is observed by the magnetic force microscopy (MFM) in the area of the micro-stripes. The periodic micro-stripes show an effective impact on static and dynamic magnetic properties of Py continuous film. In the case of dynamic magnetic properties, the resonance frequency fr of these samples can be tuned by periodic micro-stripes arrays. Compared to continuous film with resonance frequency fr of 0.64 GHz, the fr of composite structures can be tuned by the separation gap of periodic micro-stripes arrays from 0.8 GHz to 2.3 GHz at zero-field. At the same time, the fr could be also tuned by rotating the samples within the plane. This attributes to the competition of shape anisotropy induced by micro-stripes and the dynamic anisotropy originating by stripe domains structure.

Исследование химических процессов приготовления хлоридного электролита для электроосаждения пленок пермаллоя

Исследование химических процессов приготовления хлоридного электролита для электроосаждения пленок пермаллоя

Laser direct writing (LDW) of magnetic structures

Laser direct writing (LDW) has been used to pattern 90nm thick permalloy (Ni81Fe19) into 1-D and 2-D microstructures with strong shape anisotropy. Sub-nanosecond laser pulses were focused with a 0.75 NA lens to a 1.85μm diameter spot, to achieve a fluence of approximately 350 mJ.cm-2 and ablate the permalloy film. Computer-controlled sample scanning then allowed structures to be defined. Scan speeds were controlled to give 30% overlap between successive laser pulses and reduce the extent of width modulation in the final structures. Continuous magnetic wires that adjoined the rest of the film were fabricated with widths from 650 nm - 6.75μm and magneto-optical measurements showed coercivity reducing across this width range from 47 Oe to 11 Oe. Attempts to fabricate wires narrower than 650nm resulted in discontinuities in the wires and a marked decrease in coercivity. This approach is extremely rapid and was carried out in air, at room temperature and with no chemical processing. The 6-kHz laser pulse repetition rate allowed wire arrays across an area of 4 mm x 0.18 mm to be patterned in 85 s.

Large Uniaxial Anisotropy Induced in Soft Ferromagnetic Thin Films by Oblique Deposition of Underlayer

We produced a large uniaxial anisotropy $(H_{k})$ in ultrathin (1.2–2.4 nm) soft ferromagnetic layers through the oblique deposition of a nanometer-thick metallic underlayer. Fe, Ni, and Ni80Fe20 (Permalloy) films deposited on a 5 nm thick Nb layer grown at an oblique angle (up to 60 ${}^{\circ}$ ) exhibit an $H_{k}\approx 40-500$ Oe and have properties that are nearly ideal for use as a fixed layer in magnetic devices, such as for magnetic memory. A much higher induced $H_{k}$ is observed in Ni (500 Oe) and Fe (300 Oe) compared to Ni-Fe (40 Oe). We used this technique to increase the switching field ( $H_{{\rm{sw}}}$ ) by 3–5 times in an array of pattered Fe or Ni-Fe bits, and achieved an excellent relative switching distribution of about 0.05–0.06. We also controllably enhanced the $H_{k}$ in the fixed layer of patterned spin-valve devices for superconducting Josephson-junction magnetic random-access memory and produced a large difference in $H_{{\rm{sw}}}$ between the fixed and free layers. Different spacer layers between the Nb and the magnetic layers either propagate (for Ru) or reduce (for Cu, Ru/Al, ion-milled Ru) the effect of the oblique Nb. This technique was also effectively used in synthetic antiferromagnet structures and, therefore, has the potential to eliminate the need for an antiferromagnetic pinning layer when it degrades magnetic device performance.

Effects of average grain size on the magnetic properties of permalloy films

In this paper the results of substrate temperature effects on average grain size in FeNi 20:80 are shown. It was found that with an increase of the substrate temperature from 270 to 390 °C, the anisotropic magnetoresistive (AMR) effect increases from 1.2 to 2.3% and the coercive force from 1.6 to 5.3 Oe. The presence of two conflicting processes: the task of increasing AMR effect to achieve high sensitivity of AMR-sensor and to decrease the coercive force to increase the precision of conversion, leads to the necessity to find the optimum deposition temperature of the permalloy film. The dependence of the AMR effect and the coercive force on the substrate temperature during deposition was obtained. This dependence shows that the substrate temperature increasing above 320 °C leads to coercive force increasing and does not lead to a substantial AMR increasing. In this regard, the substrate temperature 320 °C was determined as optimal.

Unifying ultrafast demagnetization and intrinsic Gilbert damping in Co/Ni bilayers with electronic relaxation near the Fermi surface

The ability to controllably manipulate the laser-induced ultrafast magnetic dynamics is a prerequisite for future high-speed spintronic devices. The optimization of devices requires the controllability of the ultrafast demagnetization time ${\ensuremath{\tau}}_{M}$ and intrinsic Gilbert damping ${\ensuremath{\alpha}}_{\mathrm{intr}}$. In previous attempts to establish a relationship between ${\ensuremath{\tau}}_{M}$ and ${\ensuremath{\alpha}}_{\mathrm{intr}}$, the rare-earth doping of a permalloy film with two different demagnetization mechanisms was not a suitable candidate. Here, we choose Co/Ni bilayers to investigate the relations between ${\ensuremath{\tau}}_{M}$ and ${\ensuremath{\alpha}}_{\mathrm{intr}}$ by means of the time-resolved magneto-optical Kerr effect (TR-MOKE) via adjusting the thickness of the Ni layers, and obtain an approximately proportional relation between these two parameters. The remarkable agreement between the TR-MOKE experiment and the prediction of a breathing Fermi-surface model confirms that a large Elliott-Yafet spin-mixing parameter ${b}^{2}$ is relevant to the strong spin-orbital coupling at the Co/Ni interface. More importantly, a proportional relation between ${\ensuremath{\tau}}_{M}$ and ${\ensuremath{\alpha}}_{\mathrm{intr}}$ in such metallic films or heterostructures with electronic relaxation near the Fermi surface suggests the local spin-flip scattering dominates the mechanism of ultrafast demagnetization, otherwise the spin-current mechanism dominates. It is an effective method to distinguish the dominant contributions to ultrafast magnetic quenching in metallic heterostructures by simultaneously investigating both the ultrafast demagnetization time and Gilbert damping. Our work can open an avenue to manipulate the magnitude and efficiency of terahertz emission in metallic heterostructures such as perpendicular magnetic anisotropic Ta/Pt/Co/Ni/Pt/Ta multilayers, and then it has an immediate implication for the design of high-frequency spintronic devices.

Electrochemical Deposition of Permalloy Films for Magneto-Semiconductor Microsystems

The results of investigating local electrochemical deposition from a chloride electrolyte are presented. Ni81Fe19 permalloy films with magnetic properties similar to those of 3D samples with a uniform thickness and low mechanical stresses without high-temperature annealing are obtained. The dependences of the rate of congruent deposition of the permalloy on the current density are presented.

Tuning magnetic properties for domain wall pinning via localized metal diffusion

Precise control of domain wall displacement in nanowires is essential for application in domain wall based memory and logic devices. Currently, domain walls are pinned by creating topographical notches fabricated by lithography. In this paper, we propose localized diffusion of non-magnetic metal into ferromagnetic nanowires by annealing induced mixing as a non-topographical approach to form pinning sites. As a first step to prove this new approach, magnetodynamic properties of permalloy (Ni80Fe20) films coated with different capping layers such as Ta, Cr, Cu and Ru were investigated. Ferromagnetic resonance (FMR), and anisotropy magnetoresistance (AMR) measurements were carried out after annealing the samples at different temperatures (Tan). The saturation magnetization of Ni80Fe20 film decreased, and damping constant increased with Tan. X-Ray photoelectron spectroscopy results confirmed increased diffusion of Cr into the middle of Ni80Fe20 layers with Tan. The resistance vs magnetic field measurements on nanowires showed intriguing results.

Micro-Focused Pulse Laser-Induced Propagating Spin Waves in Permalloy Films With Different Thicknesses

Propagating spin waves excited by a micro-focused ultra-short pulse laser were investigated in Permalloy films with the thicknesses of 20, 50, and 100 nm by means of an all-optical space-and-time-resolved magneto-optical Kerr effect. Although various perpendicular standing spin-wave modes were excited, the propagating magneto-static surface spin wave was clearly detected in each film, where the group velocities of approximately 4, 8, and 12 km/s and the propagation lengths of 3.8, 6.6, and 13 ${\mu }\text{m}$ for the 20, 50, and 100 nm-thick films, respectively, were evaluated. The evaluated group velocities were consistent with the theoretical values, whereas the propagation lengths were smaller than the theoretical values with the Gilbert damping constant ${\alpha }$ of 0.008.

Nonlocal electrical detection of spin accumulation generated by anomalous Hall effect in mesoscopic Ni81Fe19 films

Spin accumulation generated by the anomalous Hall effects (AHE) in mesoscopic ferromagnetic Ni81Fe19 (permalloy or Py) films is detected electrically by a nonlocal method. The reciprocal phenomenon, inverse spin Hall effects (ISHE), can also be generated and detected all-electrically in the same structure. For accurate quantitative analysis, a series of nonlocal AHE/ISHE structures and supplementary structures are fabricated on each sample substrate to account for statistical variations and to accurately determine all essential physical parameters in-situ. By exploring Py thicknesses of 4 nm, 8 nm, and 12 nm, the Py spin diffusion length {\lambda}_Py is found to be much shorter than the film thicknesses. The product of {\lambda}_Py and the Py spin Hall angle {\alpha}_SH is determined to be independent of thickness and resistivity: {\alpha}_SH*{\lambda}_Py= (0.066 +/- 0.009) nm at 5 K and (0.041 +/- 0.010) nm at 295 K. These values are comparable to those obtained from mesoscopic Pt films.

Theory study of domain visibility optimization in single rotating compensator Kerr microscopy

In this work, an optical elements azimuth optimization method in single rotating compensator domain imaging system was provided to improve the domain image visibility. After that, simulations were performed on 200nm permalloy films and results displayed that the Kerr rotations exhibited a periodic increase-maximum-decrease tendency with the compensator rotating in one period. The Kerr effect enhancement can be achieved by collecting the light intensity at four compensator azimuths in a rotating period of the compensator. Furthermore, simulation results indicated that this method could effectively enhance the domain image contrast and signal-to-noise ratio of the permalloy film by setting the polarizer and analyzer at the optimal azimuth. What's more, to confirm the validity of this method, simulations were performed on 200 nm optically anisotropic cobalt film. The 2D image contrast figure indicated that unlike the isotropic permalloy film, there existed two large image contrast regions which are corresponding well to the extraordinary and ordinary light vector of the reflected light.

Ferromagnetic resonance of 2D array of magnetic nanocaps

Nanostructured Co and permalloy films are fabricated on top of a polymethyl methacrylate (PMMA) colloidal crystals by magnetron sputtering. The influence of the geometry of the samples on the ferromagnetic resonance spectra is studied. A number of spin-wave resonances are found in the nanostructured system, while only a single resonance is observed in the spatially uniform flat film. The number of the observed resonance peaks increases with both the period of the colloidal crystal (120÷340nm) and the film thickness (20÷90nm). The micromagnetic simulations of the system show that the excited spin-wave modes are nonreciprocal because of nonzero toroidal momentum of the magnetization of the system.

Spin-wave nonreciprocity and magnonic band structure in a thin permalloy film induced by dynamical coupling with an array of Ni stripes

An efficient way for the control of spin wave propagation in a magnetic medium is the use of periodic patterns known as magnonic crystals (MCs). However, the fabrication of MCs especially bi-components, with periodicity on nanoscale, is a challenging task due to the requirement for sharp interfaces. An alternative method to circumvent this problem is to use homogeneous ferromagnetic film with modified periodically surrounding. The structure is also suitable for exploiting nonreciprocal properties of the surface spin waves. In this work, we demonstrate that the magnonic band structure forms in thin permalloy film due to dynamical magnetostatic coupling with Ni stripes near its surface. We show, that the band gap width can be systematically tuned by the changing interlayer thickness between film and stripes. We show also the effect of nonreciprocity, which is seen at the band gap edge shifted from the Brillouin zone boundary and also in nonreciprocal interaction of propagating spin waves in Py film with the standing spin waves in Ni stripes. Our findings open possibility for further investigation and exploitation of the nonreciprocity and band structure in magnonic devices.

Universality and difference of electronic and spin transport properties at the irradiated oxide surface

The ion irradiation technique is utilized to modify the surface structure of transition metal oxides (TMOs), including SrTiO3 and TiO2. After low-energy Ar+ ion bombardment, oxygen vacancies are introduced into the TMO surface layer, and their resistance decreases with increasing irradiation time. For the two oxides, the temperature-dependent resistivity exhibits different conducting behaviors. Due to the generation of an electron-doped quasi-2D surface layer, the voltage signals of the inverse Rashba–Edelstein effect are extracted in the ion-irradiated TMO with ferromagnetic permalloy films, and the spin transport parameters are respectively calculated from the ferromagnetic resonance measurement data.

19pPSB-43 パーマロイ薄膜におけるレーザー励起スピン波伝播と膜厚依存性

19pPSB-43 パーマロイ薄膜におけるレーザー励起スピン波伝播と膜厚依存性

Achieving high magneto-impedance effect: Controlling the evolution of textures in FeNi thin films by thermal annealing

The controlled growth and tailorable magnetic properties of FeNi thin films are of critical importance for controlling the magneto-impedance (MI) effect. In this study, a Ti layer was introduced to eliminate thickness-driven perpendicular anisotropy in thick FeNi films and thereby preserve their magnetic softness. Furthermore, the temperature-driven anisotropy determined the in- and out-of-plane magnetization behavior in FeNi/Ti-based multilayers, and so dominated the MI properties of these films. The oriented (111) texture of the out-of-plane crystal structure was enhanced with increasing annealing temperature. This supported the formation of perpendicular anisotropy in FeNi films, and reduced their magnetic softness. The in-plane texture changed from a dominant (111) orientation to a (220) orientation with increasing annealing temperature. This appear to be related to magnetic properties of FeNi thin films, because a minimum in coercivity occurred at the critical temperature of the texture transition. Thus, the largest MI effect was obtained in the FeNi-based multilayer at this critical temperature. Moreover, the interdiffusion at higher temperature between the Ti layer and the FeNi layer should be considered, because the coercivities and saturation magnetization of permalloy films increase and decrease sharply at 520°C.

Reduction and control of permalloy thin film damping factor under microwave irradiation

Understand and control of the Gilbert damping, a fundamentally important magnetodynamic characteristic of magnetic materials is crucial for magnonics and high frequency applications. In this paper, we demonstrate the microwave irradiation as an easy and effective technique to control and reduce the damping factor of permalloy (Ni80Fe20) thin films deposited on SiO2 substrate. Based on different irradiation times, damping decreases by ∼16% in a short interval time of few minutes and increases within longer irradiation times. We found that within such short irradiation time, before significant changes occur in its structure, determined by XRD and probed by SEM, AFM, and conductivity measurements, the major influence on the damping factor is the “aspect” of the surface of the film. We found that there is a consistent experimental and theoretical behavior of surface roughness and correlation length that explains the trend of the damping factor. Finally, with irradiation for very long times, cracks at the surface appear due to the different absorption and heat coefficients of permalloy layer and SiO2 substrate, which leads to increment of the resistivity and oxidation of the permalloy and large enhancement of the damping factor. Our achievements are useful not only for control of the damping factor, but for evaluation of microwave irradiation threshold where material properties change which are highly valuable for magnonics devices.

Formation of Nanosized Coatings in Hybrid Plasma Reactor Combining Magnetron or Arc Deposition with RF Plasma Assistance

The hybrid plasma reactor is based on the combined magnetron or arc discharge and radio-frequency inductive discharge located in the external magnetic field. Magnetron or arc discharge provides the generation of atoms and ions of the target materials while the flow of accelerated ions used for the ion assistance is provided by the RF inductive discharge. An external magnetic field is used to optimize the power input to the discharge, to increase the ion current density in the realm of substrate and to enhance the area of uniform plasma. The high value of the ion flow bombarding the substrate gives the possibility to organize the effective ion assistance to the films growth in case of high rate deposition by the arc sources.The deposition of Ti, Al, Si and permalloy films showed that the presence of ion assistance leads to the substantial change of the films structure and properties.

Selective sensitivity in Kerr microscopy.

A new technique for contrast separation in wide-field magneto-optical Kerr microscopy is introduced. Utilizing the light from eight light emitting diodes, guided to the microscope by glass fibers and being switched synchronously with the camera exposure, domain images with orthogonal in-plane sensitivity can be displayed simultaneously at real-time, and images with pure in-plane or polar contrast can be obtained. The benefit of this new method of contrast separation is demonstrated for Permalloy films, a NdFeB sinter magnet, and a cobalt crystal. Moreover, the new technique is shown to strongly enhance the sensitivity of Kerr microscopy by eliminating parasitic contrast contributions occurring in conventional setups. A doubling of the in-plane domain contrast and a sensitivity to Kerr rotations as low as 0.6 mdeg is demonstrated.

Investigation of the Special Features of Low-Temperature Carbon Coating Deposition on the Permalloy Film Surface Under Normal Conditions During Interaction with Aromatic Solvents

Permalloy Fe19Ni81 films are prepared by the method of ion plasma deposition on a single crystal silicon substrate in the presence of a technological magnetic field (100 Oe). The surface of the samples so obtained is modified under various conditions either with preliminary exposure in the presence of atmospheric oxygen or without it. Processes of low-temperature carbon condensation and defective graphene-like coating formation are observed for the sputtered and toluene exposed films, correspondingly. The method of energy dispersive analysis demonstrates that after fortnight modification in toluene the carbon content on the surface exceeds 30%, which is much higher than the natural ambient carbon background. An increase in the surface modification time in the aromatic toluene solvent to 11 weeks leads to a linear growth of the carbon content on the surface up to 97%. Time of preliminary holding in air before immersion into the aromatic solvent does not influence significantly the kinetics of the carbon coating formation. As a whole, this coating does not influence significantly on the static magnetic properties of the film samples.