Permalloy Microstripes Research Articles

Non-conventional resonant behavior of an unconfined magnetic domain wall in a permalloy strip

The resonant dynamic of a magnetic domain wall in a permalloy microstrip has been investigated using an innovative experimental setup that enables a simultaneous measurement of the ferromagnetic resonance and the magnetoresistance. The resonance frequency associated with the presence of the magnetic domain wall increases linearly with the external magnetic field in the range of fields where the domain wall is present in the microstrip. This linear behavior is unusual in a domain wall and not related to the standard resonant modes of a magnetic domain wall, such as breathing, twisting, or translational modes. The slope of this linear dependency is 1.38 GHz/mT, which is an incredibly large value and allows the detection of very small changes in the external magnetic field. This linear behavior opens a path for developing a highly tunable radio frequency oscillator or a magnetic sensing device where the presence of an external field is detected via small variations in the resonant frequency of the domain wall.

Tuning the Ferromagnetic Resonance Frequency of Microstructured Permalloy Film on Flexible Substrate

The importance of flexible ferromagnetic films in the application of flexible spintronic devices and microwave magnetic devices underscores the necessity for an in‐depth understanding of the dynamic magnetic properties of these films. In particular, it is crucial to comprehend the regulation of the ferromagnetic resonance (FMR) frequency of flexible ferromagnetic films. This work outlines the preparation of periodic permalloy microstrip arrays with stripe domain on flexible PET films and applies them to linearly tune the FMR. The high‐frequency optical branch (5.17 GHz) and low‐frequency acoustic branch (2.89 GHz) are observed in the direction perpendicular (x‐direction) and parallel (y‐direction) to the microstrip, respectively. The Young's modulus mismatch between the PET film and permalloy layer leads to the directional distribution of local tension. This results in the enhancement of the Ht (219.4 Oe) required for the in‐plane uniform precession on the PET film, compared to that on the Si substrate (181.6 Oe). By adjusting the width and thickness of the permalloy microstrip, Ht can be adjusted linearly on the PET film. This flexible ferromagnetic film with linear regulation of FMR frequency presents a new option for the future development of flexible microwave detectors and filters.

Nonstationary spin waves in a single rectangular permalloy microstrip under uniform magnetic excitation

Ferromagnetic resonance modes in a single rectangular ${\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}$ microstrip were directly imaged using time-resolved scanning transmission x-ray microscopy combined with a phase-locked ferromagnetic resonance excitation scheme, and the findings were corroborated by micromagnetic simulations. Although under uniform excitation in a single confined microstructure typically standing spin waves are expected, all imaged spin waves showed a nonstationary character both at and off resonance, the latter being additionally detected with microantenna-based ferromagnetic resonance. The effect of the edge quality on the spin waves was observed in micromagnetic simulations.

Microresonators and Microantennas—Tools to Explore Magnetization Dynamics in Single Nanostructures

The phenomenon of magnetic resonance and its detection via microwave spectroscopy provide insight into the magnetization dynamics of bulk or thin film materials. This allows for direct access to fundamental properties, such as the effective magnetization, g-factor, magnetic anisotropy, and the various damping (relaxation) channels that govern the decay of magnetic excitations. Cavity-based and broadband ferromagnetic resonance techniques that detect the microwave absorption of spin systems require a minimum magnetic volume to obtain a sufficient signal-to-noise ratio (S/N). Therefore, conventional techniques typically do not offer the sensitivity to detect individual micro- or nanostructures. A solution to this sensitivity problem is the so-called planar microresonator, which is able to detect even the small absorption signals of magnetic nanostructures, including spin-wave or edge resonance modes. As an example, we describe the microresonator-based detection of spin-wave modes within microscopic strips of ferromagnetic A2 Fe60Al40 that are imprinted into a paramagnetic B2 Fe60Al40-matrix via focused ion-beam irradiation. While microresonators operate at a fixed microwave frequency, a reliable quantification of the key magnetic parameters like the g-factor or spin relaxation times requires investigations within a broad range of frequencies. Furthermore, we introduce and describe the step from microresonators towards a broadband microantenna approach. Broadband magnetic resonance experiments on single nanostructured magnetic objects in a frequency range of 2–18 GHz are demonstrated. The broadband approach has been employed to explore the influence of lateral structuring on the magnetization dynamics of a Permalloy (Ni80Fe20) microstrip.

Study of magnetization reversal in Néel and Bloch regime of nickel and permalloy stripes using Kerr microscopy

We present a systematic study of the magnetization reversal of nickel and permalloy micro-stripes with Néel and Bloch domain walls using Kerr microscopy. Magnetic field driven domain propagation was observed from higher width to lower width stripes for magnetic fields applied along the length of micro-stripes. Stripe like domains were observed with nucleation starting in lower width region followed by their propagation to higher width regions for magnetic fields applied along the width of micro-stripes. The comparison of magnetization reversal in Bloch and Néel domain wall regime showed higher domain wall density in Bloch regime for both nickel and permalloy stripes.

Observation of the dispersion relations for quantized coherent spin waves excited by a microwave antenna

The propagation of coherent spin waves in permalloy microstrips was investigated using a heterodyne-magneto-optical Kerr effect technique. The two-dimensional imaging reveals the mode interference with a high-order spin-wave mode along the microstrip width. The spin-wave dispersion relations across the microstrip width were deduced from fast Fourier transformations on the complex spin-wave amplitude of the one-dimensional scan, and multiple spin-wave modes were observed at the edges of the microstrips. These experimental results provide direct evidence for the quantization of spin-wave dispersion due to the finite width of the microstrips and enables us to evaluate the attenuation length for each quantized spin-wave mode.

Direct Imaging of the ac Component of Pumped Spin Polarization with Element Specificity

Spin pumping in a ferromagnet/nonferromagnet heterostructure is directly imaged with spatial resolution as well as element selectivity. The time-resolved detection in scanning transmission x-ray microscopy allows to directly probe the spatial extent of the ac spin polarization in Co-doped ZnO which is generated by spin pumping from an adjacent permalloy microstrip. Comparing the relative phases of the dynamic magnetization component of the two constituents is possible and found to be antiphase. The correlation between the distribution of the magnetic excitation in the permalloy and the Co-doped ZnO reveals that laterally there is no one-to-one correlation. The observed distribution is rather complex, but integrating over larger areas clearly demonstrates that the spin polarization in the nonferromagnet extends laterally beyond the region of the ferromagnetic microstrip. Therefore the observations are better explained by a local spin pumping efficieny and a lateral propagation of the ac spin polarization in the nonferromagnet over the range of a few micrometers.

Simulation of the Interaction of a Magnetic Resonance Force Microscope Probe with a Ferromagnetic Sample

We propose an algorithm and present results of micromagnetic simulation of the resonant response of a probe pickup (cantilever) of a magnetic resonance force microscope. Simulation of induced oscillations of sample magnetization makes it possible to calculate the varying component of the force exerted on the probe by the sample and to construct spectra in the form of dependences of the amplitude of oscillations of the cantilever on the external magnetic field strength. Simulation of time dependences of all magnetization field components makes it possible to analyze the spatial distributions of spin-wave resonances of samples. For test objects in the form of rectangular permalloy microstrips, good agreement between model and experimental spectra is achieved.

Manifestation of ferromagnetic resonance of permalloy microstripes in magnetic force spectroscopy measurements

Abstract Ferromagnetic resonance (FMR) of individual permalloy microstripe is investigated by magnetic resonance force microscopy (MRFM) in the geometry when a probe magnetic moment is parallel to a sample. Three resonant dips in the MRFM spectrum are observed, the lateral shift of the probe relatively to the microstripe leads to consequent transformation of the dips into peaks. This change of the contribution of the same FMR mode in the MRFM spectrum is explained by the change of the phase between magnetic and nonmagnetic probe-sample interaction due to inhomogeneity of the probe magnetic field. Developed micromagnetic simulations of MRFM signal are in a good agreement with experimental data and allow one to analyze the spatial distributions of magnetization oscillations corresponding to the experimental resonant modes.

Моделирование взаимодействия зонда магнитно-резонансного силового микроскопа с ферромагнитным образцом

We report the calculating algorithm and micromagnetic simulation of the resonance response of a magnetic resonance force microscope (MRFM) probe sensor. The simulation of the sample magnetization forced oscillations enables calculating the alternating component of the probe-sample force interaction and to draw the MRFM spectrum in the form of the dependence of cantilever oscillation amplitude on an external magnetic field. In addition, the simulation of the time dependences for all components of the magnetization allows the analysis of spatial distributions for spin-wave resonances in the samples. For the test object in the form of rectangular permalloy microstrips a good agreement between model and experimental MRFM spectra was observed.

Influence of the Magnetic Moment of the Probe of a Magnetic Resonance Force Microscope on the Spin-Wave Resonance Spectra

Abstract—The ferromagnetic resonance in an array of permalloy microstrips 3000 × 500 × 30 nm3 in size, which are ordered on a rectangular 3.5 × 6 μm2 lattice, is studied using magnetic resonance force microscopy with strong probe–sample interaction. This interaction induces intricate modifications of the observed spectra, which are manifested both in line splitting and in changes in shape. The dependences of the observed spectra on the sample–probe distance and the orientation of the magnetic moment of the probe are analyzed.

Spectrum of the Ferromagnetic Resonance of a Lattice of Orthogonal Permalloy Microwaveguides

The ferromagnetic resonance spectrum at a frequency of ~9.85 GHz for an in-plane magnetized 2D square lattice with the unit cell parameter а ≈ 15 μm consisting of orthogonal microwaveguides with a width of w ≈ 5 μm on the basis of a permalloy film with thickness of d ≈ 90 nm has been experimentally and numerically investigated. It is shown that upon variation in the angle θ between the magnetic field direction and the unit cell axis, the total spectrum of spin-wave excitations of the lattice can be presented as a superposition of the spectra of separate permalloy microstrips magnetized at angles θ and π/2–θ and regions corresponding to the lattice nodes. It has been found that, in the case of magnetization along the lattice diagonal (θ ≈ 45о), excitations localized at the lattice nodes dominate in the spectrum, whereas, at θ ≈ 0 and 90°, the main contribution is made by excitations localized mainly on the microwaveguide segments between the lattice nodes; at θ ≈ 10°–13° and 18–20°, “repulsion” of absorption lines in the spectrum is observed.

Magnetic Resonance Force Microscopy of a Permalloy Microstrip Array

The ferromagnetic resonance in an array of permalloy microstrips 3000 × 500 × 30 nm in size ordered on a rectangular grid 3.5 × 6 μm in size has been investigated by magnetic resonance force microscopy. The dependences of magnetic resonance force microscopy spectra of a sample on the probe–sample distance are analyzed. The possibility of detection of a ferromagnetic resonance spectrum of a single microstrip is demonstrated.

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.

Магнитно-резонансная силовая спектроскопия массива микрополосок пермаллоя

AbstractThe ferromagnetic resonance in an array of permalloy microstrips 3000 × 500 × 30 nm in size ordered on a rectangular grid 3.5 × 6 μm in size has been investigated by magnetic resonance force microscopy. The dependences of magnetic resonance force microscopy spectra of a sample on the probe–sample distance are analyzed. The possibility of detection of a ferromagnetic resonance spectrum of a single microstrip is demonstrated.

Влияние ориентации магнитного момента зонда магнитно-резонансного силового микроскопа на спектры спин-волновых резонансов

Abstract —The ferromagnetic resonance in an array of permalloy microstrips 3000 × 500 × 30 nm^3 in size, which are ordered on a rectangular 3.5 × 6 μm^2 lattice, is studied using magnetic resonance force microscopy with strong probe–sample interaction. This interaction induces intricate modifications of the observed spectra, which are manifested both in line splitting and in changes in shape. The dependences of the observed spectra on the sample–probe distance and the orientation of the magnetic moment of the probe are analyzed.

Ferromagnetic resonance in submicron permalloy stripes

We present systematic experimental investigation and micromagnetic simulation of ferromagnetic resonance (FMR) in planar rectangular permalloy microstripes. The experimental microwave absorption was studied for different sample orientations in an external magnetic field. To analyze the FMR modes we developed the algorithm for the simulation of spectrum and spatial distribution of magnetization oscillations in dependence on swept external magnetic field based on numerical solution of Landau-Lifshitz-Gilbert equation. It was shown good agreement between experimental and model FMR spectra that enables the reliable visualization for spatial distributions of oscillating magnetization in modes of spin-wave resonances for different excitation conditions.

Direct observation of isolated Damon-Eshbach and backward volume spin-wave packets in ferromagnetic microstripes.

The analysis of isolated spin-wave packets is crucial for the understanding of magnetic transport phenomena and is particularly interesting for applications in spintronic and magnonic devices, where isolated spin-wave packets implement an information processing scheme with negligible residual heat loss. We have captured microscale magnetization dynamics of single spin-wave packets in metallic ferromagnets in space and time. Using an optically driven high-current picosecond pulse source in combination with time-resolved scanning Kerr microscopy probed by femtosecond laser pulses, we demonstrate phase-sensitive real-space observation of spin-wave packets in confined permalloy (Ni80Fe20) microstripes. Impulsive excitation permits extraction of the dynamical parameters, i.e. phase- and group velocities, frequencies and wave vectors. In addition to well-established Damon-Eshbach modes our study reveals waves with counterpropagating group- and phase-velocities. Such unusual spin-wave motion is expected for backward volume modes where the phase fronts approach the excitation volume rather than emerging out of it due to the negative slope of the dispersion relation. These modes are difficult to excite and observe directly but feature analogies to negative refractive index materials, thus enabling model studies of wave propagation inside metamaterials.

Geometrical optimization of microstripe arrays for microbead magnetophoresis.

Manipulation of magnetic beads plays an increasingly important role in molecular diagnostics. Magnetophoresis is a promising technique for selective transportation of magnetic beads in lab-on-a-chip systems. We investigate periodic arrays of exchange-biased permalloy microstripes fabricated using a single lithography step. Magnetic beads can be continuously moved across such arrays by combining the spatially periodic magnetic field from microstripes with a rotating external magnetic field. By measuring and modeling the magnetophoresis properties of thirteen different stripe designs, we study the effect of the stripe geometry on the magnetophoretic transport properties of the magnetic microbeads between the stripes. We show that a symmetric geometry with equal width of and spacing between the microstripes facilitates faster transportation and that the optimal period of the periodic stripe array is approximately three times the height of the bead center over the microstripes.

Directly Excited Backward Volume Spin Waves in Permalloy Microstrips

A patterned magnetic microstrip will remain saturated along its length at remanence so the backward volume (BV) configuration is a natural geometry for spin wave devices, yet there are few experimental studies of spin waves in this geometry. In this paper, BV spin waves that were directly excited by a micrometer-sized antenna in a Permalloy microstrip were studied using microfocus Brillouin light scattering. The measured BV spin wave excitation efficiencies are approximately an order of magnitude smaller compared to the more commonly studied Damon-Eshbach configuration where the static magnetization is in-plane, perpendicular to the microstrip. Nevertheless, measureable signals were detected for a range of fields including zero magnetic field, which is important for applications.