Permalloy Thin Films Research Articles

Real-time FMR lorentzian visualization through a novel synchronous VNA-FMR measurement apparatus.

It is shown in this work that a synchronous measurement setup is able to conveniently and accurately retrieve ferromagnetic resonance's (FMR) main physical properties from a permalloy sample. The apparatus used comprises a vector network analyzer (VNA), coupled with external DC coils, driven by a controllable power supply. A permalloy thin film sample was subjected to a microwave signal through a grounded coplanar waveguide. A square wave signal generated by an Arduino microcontroller drives the coils to a triangular, 65.4ms period magnetic field. This field's half-cycle is synchronized to match a zero-span sampling time at the VNA. The system has the advantage of fast results, as the typical FMR lorentzian curve is completed in a few seconds and shown immediately on the VNA's scattering parameter S21 trace graph. The system showed an improved signal-to-noise ratio of 51.7 at 10GHz over 24.3 for the 100nm thick permalloy- sample used in this work. A magnetic field resonance point, collected at 10GHz, showed a five-fold improvement in the standard-error.

Self-assembly as a tool to study microscale curvature and strain-dependent magnetic properties

The extension of 2D ferromagnetic structures into 3D curved geometry enables to tune its magnetic properties such as uniaxial magnetic anisotropy. Tuning the anisotropy with strain and curvature has become a promising ingredient in modern electronics, such as flexible and stretchable magnetoelectronic devices, impedance-based field sensors, and strain gauges, however, has been limited to extended thin films and to only moderate bending. By applying a self-assembly rolling technique using a polymeric platform, we provide a template that allows homogeneous and controlled bending of a functional layer adhered to it, irrespective of its shape and size. This is an intriguing possibility to tailor the sign and magnitude of the surface strain of integrated, micron-sized devices. In this article, the impact of strain and curvature on the magnetic ground state and anisotropy is quantified for thin-film Permalloy micro-scale structures, fabricated on the surface of the tubular architectures, using solely electrical measurements.

Second harmonic generation as a probe of parametric spin wave instability processes in thin magnetic films

We have explored the dynamic response of in-plane magnetized thin permalloy films excited by microwave fields of high amplitudes (up to 3 Oe) at 1 GHz. The response was detected using a microstrip line by measuring the second harmonic signal generated by the dynamic components of the uniform magnetization. The data measured at ferromagnetic resonance showed the threshold effect of the Suhl parametric instability process. With the increase of the microwave power above the threshold value, the dynamic response revealed an intricate nonlinear behavior, including the emergence of an additional threshold. This second threshold can be explained in terms of the ``stage by stage'' process of parametric spin wave excitation following the $S$ theory of Zakharov, L'vov, and Starobinets.

Programmable Gilbert Damping in Py /Cu/Fe - Co - Tb Structures with Dynamic Interlayer Coupling

Magnetodynamics of magnetic nanolayers is central to the emerging research field of magnonics. Here, we demonstrate an effective tuning of the dynamic properties of permalloy (Py, response layer) thin films, by capping with $\mathrm{Cu}/\mathrm{Fe}$-$\mathrm{Co}$-$\mathrm{Tb}$ (spin-sink layer) layers with adjustable interlayer coupling and magnetic configurations. The strategy enables a remarkably enhanced Gilbert damping of the response layer, by about 10 times; this enhancement is higher than most of the results reported so far. More importantly, dynamic damping is programmable between the two opposite configurations (parallel vs antiparallel) in Py and $\mathrm{Fe}$-$\mathrm{Co}$-$\mathrm{Tb}$ and remains intact even in the form of nano- and microdevices. The interlayer coupling between Py and $\mathrm{Fe}$-$\mathrm{Co}$-$\mathrm{Tb}$ is systematically studied by changing the thickness of the $\mathrm{Cu}$ spacer. It is demonstrated that the dynamic interlayer coupling between ferromagnetic layers plays the key role in increased damping. Our work provides a feasible route towards reconfigurable magnonic devices, especially for logic and high-speed computing.

Investigating Coherent Magnetization Control with Ultrashort THz Pulses

Coherent terahertz control of magnetization dynamics is an area of current interest due to its great potential for the realization of magnetization control on ultrafast timescales in commercial devices. Here we report on an experiment realized at the THz beamline of the free electron laser FLASH at DESY which offers a tunable terahertz radiation source and spontaneously synchronized free-electron laser X-ray pulses to resonantly probe the magnetization state of a ferromagnetic film. In this proof-of-principle experiment, we have excited a thin Permalloy film at different THz wavelengths and recorded the induced magnetization dynamics with photons resonantly tuned to the Ni M2,3 absorption edge. For THz pump pulses including higher orders of the undulator source we observed demagnetization dynamics, which precise shape depended on the employed fundamental wavelength of the undulator source. Analyzing the shape in detail, we can reconstruct the temporal profile of the electric field of the THz pump pulse. This offers a new method for the realization of an in-situ terahertz beamline diagnostic which will help researchers to adjust the pulse characteristics as needed, for example, for future studies of THz induced coherent control of magnetization dynamics.

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.

Управление запрещенными зонами в пермаллоевой структуре при изменении профиля меандра

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.

Ferromagnetic resonance line broadening and shift effect in nanocrystalline thin magnetic films: Relation with crystalline and magnetic structure

With the rapid development of telecommunication technologies and highly integrated electronic devices, researchers show great interest in nanocrystalline soft magnetic thin films with unique characteristics for microwave applications. An important direction of the current research in this field is the study of high-frequency magnetization dynamics that directly depends on the damping processes in a magnetic medium. This paper reports on the effect of sharp broadening and shift of the ferromagnetic resonance (FMR) line revealed experimentally in a 40-nm-thick nanocrystalline permalloy (Fe20Ni80) thin film at a frequency of about 5 GHz. The effect arises only in films with crystallite size exceeding some critical value Dcr. The micromagnetic simulation demonstrates that exchange and dipolar interactions between randomly oriented crystallites form in the film a quasiperiodic magnetic structure with a characteristic wavelength in the range from 36 nm to 3.3 µm. An analysis of the two-magnon scattering model and simulation results shows that the formed magnetic structure provides the energy transfer from uniform magnetization oscillations (uniform FMR) to spin waves, which results in an additional energy dissipation channel and, consequently, sharp FMR line broadening. A theoretical estimate of the critical crystallite size Dcr based on this model yields a value of ~14.3 nm for 40-nm-thick Fe20Ni80 films.

57Fe Mössbauer and magneto-optical Kerr effect (MOKE) study of transcritical state in permalloy (FexNi100-x) thin films

57Fe Mössbauer and magneto-optical Kerr effect (MOKE) study of transcritical state in permalloy (FexNi100-x) thin films

Peculiarity of the low temperature magnetoresistive effect in the Corbino disk with magnetic ordering

The transverse magnetoresistance (MR) hysteresis loops of a magnetically ordered Corbino disk have been studied in the temperature range 300–2 K in an external magnetic field with induction up to 1 T oriented in the plane of the disk (ϕ = 0°) and perpendicularly to its plane (ϕ = 90°). The Corbino disk is made of a thin permalloy film obtained on an insulating sitall substrate by ion-beam sputtering. Independently of the temperature and measurement geometry, the field dependences of MR in the range of weak magnetic fields up to the magnetisation saturation exhibit sharp peaks of the negative MR caused by the domain walls motion during the magnetisation reversal of the sample. The position of the peak in the magnetic field (Bp) is determined by the temperature as well as the angle between magnetic field direction and the disk plane. It was found that a temperature change in the range of T = 300–2 K leads to a change in its position in the range of 0.2–6.0 mT and 8–22 mT at ϕ = 0° and ϕ = 90°, respectively. The magnetic field direction reorientation from in-plane to out-of-pane at T = 2 K leads to the Bp change from 6 to 22 mT. In the range of strong magnetic fields above the magnetization saturation field at ϕ = 0° the positive MR component decreases with induction and has a linear non-saturable dependence down to T ≈ 40–50 K due to the magnon MR component dominance. The complete freezing of magnons at T = 2 K leads to the absence of high-field magnetoresistive effect. At ϕ = 90° in weak fields, the MR changes its sign from positive to negative due to the anisotropic MR component dominance because of the disk magnetisation reorientation perpendicular to the current lines. In a strong field it changes the slope due to the saturation of negative anisotropic MR component, as well as possible additional contribution of the positive geometric Lorentzian MR.

Domain Structure and Magnetization Reversal in Multilayer Structures Consisting of Thin Permalloy Films Separated with Nonmagnetic Interlayers

Domain Structure and Magnetization Reversal in Multilayer Structures Consisting of Thin Permalloy Films Separated with Nonmagnetic Interlayers

Ferromagnetic Resonance Studies in Magnetic Nanosystems

Ferromagnetic resonance is a powerful method for the study of all classes of magnetic materials. The experimental technique has been used for many decades and is based on the excitation of a magnetic spin system via a microwave (or rf) field. While earlier methods were based on the use of a microwave spectrometer, more recent developments have seen the widespread use of the vector network analyzer (VNA), which provides a more versatile measurement system at almost comparable sensitivity. While the former is based on a fixed frequency of excitation, the VNA enables frequency-dependent measurements, allowing more in-depth analysis. We have applied this technique to the study of nanostructured thin films or nanodots and coupled magnetic layer systems comprised of exchange-coupled ferromagnetic layers with in-plane and perpendicular magnetic anisotropies. In the first system, we have investigated the magnetization dynamics in Co/Ag bilayers and nanodots. In the second system, we have studied Permalloy (Ni80Fe20, hereafter Py) thin films coupled via an intervening Al layer of varying thickness to a NdCo film which has perpendicular magnetic anisotropy.

Anisotropic properties of oblique angle deposited permalloy thin films

The structural, transport, and magnetic properties of permalloy (Ni81Fe19) thin films prepared by oblique angle deposition have been investigated. With the increasing oblique angle, column-like microstructures developed on the films while their porosity augmented. Due to the unique columnar microstructures, a deposition-angle-dependent uniaxial anisotropy was induced in the films. While the normally deposited film was electrically isotropic, the films grown at non-zero angles showed enhanced anisotropic conduction. The magnetization data showed that for the films deposited at angles < 70° the easy magnetization axis was along the films in-plane direction and perpendicular to the incident flux direction. As the oblique angle exceeded 70° the magnetization easy-axis reoriented along the long-columnar axis. The systematic increase of oblique angle triggered a noticeable enhancement in the coercivity , especially for the extreme oblique angles (α > 70°). The experimental results demonstrated that oblique angle deposition, particularly at angles > 70°, can substantially transform the electro-magnetic properties of thin films.

Second harmonic generation in thin permalloy film

Second harmonic generation versus strength and direction of the applied static magnetic field was measured for a thin permalloy (Ni80Fe20) film in a microstrip line at a driving frequency of 1 GHz and maximum input power of ∼110 mW. The measurements revealed two peaks in the double frequency signal—in the low static field (∼10 Oe) and the high one (∼45 Oe). To explain these findings, a macrospin model of a thin magnetic film with in-plane uniaxial magnetic anisotropy was considered. A perturbation expansion of the Landau–Lifshitz–Gilbert equation provided an explanation of the experimental data. The analysis of the model revealed that the low-field peak was caused by the longitudinal second-order magnetization component and the high-field peak by the transversal one. It was also shown that the uniaxial magnetic anisotropy of the film and the dependence of the magnetic damping parameter on the applied field play an important role in the process of the second harmonic generation. The results obtained give insights into some peculiarities of the nonlinear magnetization dynamics that are important in the development of magnetic film-based devices in the field of microwave signal processing and manipulation.

Polymer Micelle Directed Magnetic Cargo Assemblies Towards Spin‐wave Manipulation

AbstractSpin‐wave based technologies that use collective oscillation of electrons termed magnons have been proposed for future computing landscapes due to their low energy consumption and high data transfer speeds. Magnonic crystals, materials with magnetic properties periodically varied in space, are central to such technologies. However, they are currently limited by the lithography techniques used for the magnetic patterning. To address this issue, bottom‐up self‐assembly using polymer templates to order magnetic cargo is presented. In this work, block copolymer micelles are used as templates to direct the organization of polyoxometalate (POM) molecules into organized assemblies. The structural organization of these assemblies is evaluated using microscopy and scattering techniques. The organized POM assemblies are demonstrated to modulate spin‐waves excited in permalloy thin films. This work demonstrates the first use of a bottom‐up approach to realize the fabrication of a magnonic assembly at the nanoscale. It further paves the way to achieve magnon‐mediated self‐assembled computing architectures.

Damping of dipole-exchange spin waves in ferromagnetic thin films at elevated temperatures

A non-bosonic technique, based on the drone-fermion perturbation method and a high-density expansion, is employed to study the spin-wave (SW) scattering processes in a ferromagnetic thin film with exchange and dipole–dipole interactions. Specifically, the diagrammatic contributions to the spin–spin Green’s functions are evaluated within a 1/z perturbation expansion, where z is the number of spins interacting with any given spin. The results are used to calculate the SW damping at temperatures below the Curie temperature T C. It is found that, apart from the usual contributions due to three-magnon and four-magnon processes in the film, which are dominant at relatively low temperatures (consistent with boson expansion methods), there is an additional mechanism that becomes important for temperatures above about This is spin disorder damping, previously studied in bulk magnetic materials; it occurs when a spin wave is scattered by the instantaneous disorder produced when a longitudinal spin component undergoes a large thermal fluctuation. Numerical estimates are presented for thin films of Permalloy and EuO.

A GPU accelerated micromagnetic simulator for modelling complex magnetic systems

This paper demonstrates an object orientated GPU accelerated micromagnetic simulator designed to model the material characteristics of complex magnetic alloy systems. The GPU simulator is written in C++ and uses object orientated programming to create a class that stores the magnetic information required to solve the Landau-Lifshitz-Gilbert (LLG) equation for a distribution of magnetic objects. Each magnetic object can be assigned individual properties based on the alloy distribution of interest. The simulator is verified against standard problem 4 of the “Micromagnetic Modelling Activity Group” (μmag). Standard problem 4 is chosen as it provides a benchmark for the modelling tools ability to accurately predict the magnetisation dynamics of a 500 nm × 125 nm × 3 nm Permalloy thin film.

Exstraordinary and planar Hall effects in thin permalloy films

The Hall resistance hysteresis loops in thin (d = 80 –280 nm) magnetically ordered permalloy films (Ni0.8 Fe0.2) were studied at room temperature at different angles between the film plane and the magnetic field direction (φ = 0 –360°) (extraordinary and ordinary Hall effects), at different angles (θ = 0 – 90°) between the magnetic field direction and the flowing current (planar Hall effect at φ = 0°) in a magnetic field up to B = 1.25 T. The thin films were obtained on sitall dielectric substrate by ion beam sputtering. Sharp peaks of the Hall resistance were observed in the extraordinary and planar Hall effects during the magnetisation reversal of the films due to a change of the magnetisation direction with respect to the sampling current direction. In the extraordinary Hall effect the position and full width at half maximum of a peak is determined by the angle between the magnetic field direction and the film plane. It has been shown that as the direction of the external magnetic field approaches the spontaneous magnetisation direction, both the peak magnetic field position Bp and the full width at half maximum of the peak Δ Bp increase. In the angles range of φ = 0 – 90° Bp and Δ Bp varies in the magnetic field range from Δ В ≈ 0.2 to 5.0 mT. A non-monotonic dependence of the planar Hall resistance and its peak position on the angle between the flowing current and the magnetic field direction was detected. It is related to the change of the longitudinal and transverse components the resistance of the magnetically ordered solids by an external magnetic field. The values of the ordinary and extraordinary Hall effects coefficients have been determined: RH0 = 6 ⋅ 10–9 m3/C and RH1 = 3.2 ⋅ 10–8 m3/C, respectively.

Increase of Gilbert damping in Permalloy thin films due to heat-induced structural changes

Spin-wave based computing requires materials with low Gilbert damping, such as Ni80Fe20 (Permalloy) or yttrium iron garnet, in order to allow for spin-wave propagation on a length scale comparable to the device size. Many devices, especially those that rely on spin–orbit effects for operation, are subject to intense Joule heating, which can exacerbate electromigration and induce local phase changes. Here, the effect of annealing on the Gilbert damping coefficient α of 36 nm Py thin films grown on a Si substrate is examined. Ferromagnetic resonance measurements, high resolution transmission electron microscopy, as well as energy dispersive x-ray spectroscopy have been employed to determine α while also studying structural changes in the thin films. The Gilbert damping parameter was found to increase sixfold when annealed at 350 °C, which was linked to the diffusion of Ni atoms into the Si substrate on a length scale of up to 50 nm. The results demonstrate that magnonic devices have to be treated with caution when Joule heating occurs due to its detrimental effects on the magnonic properties, but the effect can potentially be exploited in the fabrication of magnonic devices by selectively modifying the magnonic damping locally.

Investigation of Laser Direct Writing as a Novel Method of Permalloy Patterning

The abilities of laser direct writing have been explored on thin films of permalloy (Ni81Fe19) for range of film thicknesses with two types of substrates for creating micro-scale magnetic structures. The thin films of Permalloy were deposited on both silicon and glass substrates using thermal evaporator with ranging from 5 to 100 nm. The permalloy films were successively patterned using a laser system containing of a pico-second pulsed laser with an 800 ps pulse width and wavelength of 532 nm. A series of magnetic wires were patterned then characterised by Magneto-Optic Kerr Effect system and Scanning Electron Microscopy. The patterned magnetic wires showed good responses to an applied magnetic field. The corresponding coercivities of the patterned magnetic wires were affected by their observed quality. These results can improve the understanding of laser direct writing technique to fabricate the micromagnetic structures for future application as easy, low cost and high throughput technique.