Permalloy Thin Films Research Articles

Canted standing spin-wave modes of permalloy thin films observed by ferromagnetic resonance

Non-collinear spin structures in materials that combine perpendicular and in-plane magnetic anisotropies are of great technological interest for microwave and spin wave-assisted magnetization switching. [Co/Pt] multilayers are well-known perpendicular anisotropy materials that have the potential to pin the magnetization of a soft magnetic layer, such as permalloy (Py), that has in-plane anisotropy, thereby forming a magnetic exchange spring. Here we report on multilayered [Co/Pt]/Pt/Py films, where an additional ultrathin Pt spacer has been included to control the coupling between the sub-units with in-plane and perpendicular magnetic anisotropy. Vector network analyser (VNA)-ferromagnetic resonance (FMR) measurements were made to obtain a complete picture of the resonant conditions, while the dynamical response of the sub-units was probed by synchrotron-based element- and phase selective x-ray detected FMR (XFMR). For all samples, only slight pinning of the dynamic magnetization of the Py by the [Co/Pt] was noted, and the FMR results were dominated by the 50 nm thick Py layer. Out-of-plane VNA-FMR maps reveal the presence of additional modes, e.g. a perpendicular standing spin-wave (PSSW) state. However, as the magnetic field is reduced below the saturation field, the PSSW state morphs continuously through a series of canted standing spin-wave (CSSW) states into a horizontal standing spin-wave (HSSW) state. The PSSW, CSSW and HSSW states are well described using a multilayer model of the Py film. The observation of CSSW modes is of particular relevance to microwave assisted magnetic recording, where microwave excitation stimulates precession of a soft layer canted out of plane by a pulsed magnetic field.

Effects of Co-60 gamma irradiation on the surface morphology and magnetic properties in thin film permalloy Ni80Fe20 for magnetic sensor

The thin film of permalloy Ni80Fe20 were synthesized by electro-deposition method on PCB substrate. Then the sample irradiated by using Co-60 gamma for 20 Gy and 30 Gy. The sample were investigated by scanning electron microscopy and vibrating sample magnetometer, before and after gamma irradiation process by Co-60 gamma irradiation. The decrease in grain size with the increase of radiation dose is observed. The hysteresis curve also showed an increase in saturation magnetization with the increase of radiation dose from 708 emu/cc to 920 emu/cc. The investigation results indicate that the modification of the surface-microstructure samples by gamma irradiation change a magnetic properties in thin film permalloy Ni80Fe20.

Magnetic, optical and electrical properties of permalloy films by DC magnetron sputtering

Permalloy (NiFe) thin films were prepared by direct current (DC) magnetron sputtering (MS). XRD, EDS, AFM, PPMS, Hall effect Test Station, UV–Vis spectrometer , and spectroscopic ellipsometer (SE) were used to characterize the microstructure, electrical, magnetic and optical properties of the films. Magnetic anisotropy was observed in NiFe films grown on , and -STO substrates, and among them , NiFe/STO showed higher saturation magnetization $${M_{\rm{s}}}$$ = 8.4 emu/g , residual magnetization $${M_{\rm{r}}}$$ = 6.625 emu/g and smaller coercivity $${H_{\rm{c}}}$$ = 28 Oe. Films grown at 300° C exhibit stronger magnetization, smaller sheet resistance ( $${R_{\rm{s}}}$$ ), resistivity ( $${\rho }$$ ), and optical reflectivity ( $${R\%}$$ ) growth relative to room temperature (RT). Greater absorption (A) and smaller reflection at 230 nm . showed better transmittance ( $${T\%}$$ ) at 336 nm. Finally, the characterization results using the a spectroscopic ellipsometer are also given.

Micromagnetic simulation of domain structure in thin permalloy films with in-plane and perpendicular anisotropy

We investigate the domain structure formation and magnetization processes in thin permalloy films with in-plane and perpendicular magnetic anisotropy by using micromagnetic simulation. We show that the films of thicknesses less than a critical value Lcr are in the monodomain state, and their magnetization processes are specified by the in-plane anisotropy. Above the critical thickness Lcr, the perpendicular anisotropy dominates, leading to the formation of the stripe domain structure that significantly complicates the magnetization reversal. The values of the critical thickness, parameters of the domain structure, and the saturation field obtained from the micromagnetic simulations are compared with the corresponding values calculated using analytical expressions derived by Murayama in the framework of the domain structures theory.

Ultrafast coherent control of higher-order spin waves in a NiFe thin film by double-pulse excitation

By using a double-pulse excitation scheme, we demonstrate the optical control of higher-order spin waves in a ferromagnetic permalloy thin film. Three spin precession modes are observed in the film under single pulse excitation. Based on a theoretical calculation, these spin precession modes are assigned to the fundamental Kittel mode and the first- and second-order perpendicular standing spin-wave (PSSW) modes. In order to excite the first-order PSSW mode selectively, we use double-pulse excitation at 400 nm. We show that, by choosing an appropriate time interval between the two pump pulses, it is possible to obtain a relatively large amplitude of the first-order PSSW mode while the amplitudes of the other two modes are almost completely suppressed. By analyzing the spin dynamics, it is found that the spin precession motion under the double-pulse excitation condition can be explained by the interference between the spin waves that have been induced by the first and second pulses. Our finding indicates that the selective excitation of a spin precession mode with a high precession frequency in a ferromagnetic metal may be realized by a multiple-pump pulse excitation scheme with more than two pulses.

The use of a piezoelectric force sensor in the magnetic force microscopy of thin permalloy films

A piezoelectric force sensor is suggested for magnetic force microscopy (MFM) purposes. Added between the piezoelectric resonator and the magnetic probe is a mechanical force amplifier in the form of a thin, long resonant arm with an integral micro-rod whereby the amplitude of the force acting on the probe is amplified by a factor of 20 to 40 at a low noise level. When the sensor was operated in air, its noise floor was found to be 1.4 pN (RMS) at a bandwidth of 100 Hz. The piezoelectric sensor requires no repeated calibration; and it is capable of operating in a vacuum, and at cryogenic temperatures. By using this sensor we carried out the MFM of ultrathin (1.5- and 3-nm-thick) Ni79Fe21 permalloy films. The 1.5-nm-thick permalloy films studied have a nanoisland structure, whereas 3-nm-thick ones are contiouous. Domain structures were found in both. The MFM image was found to suffer substantial changes when the external magnetic field was altered by 1 Oe. The structures under study featured both “elastic” and “viscous” magnetic force components.

Anisotropy engineering of soft thin films in the undulated magnetic state

Advanced materials often involve multi-dependent approaches, merging electrical, optical and magnetic responses in nanostructured systems. To this purpose we have explored a semi-transparent, soft magnetic thin film (Permalloy) of nano-undulated morphology with which uniaxial anisotropy can be induced and tuned. This media is grown on the ripple surface of flexible, polymeric foil of polyethylene terephthalate (PET) that was previously patterned by a versatile pulsed-laser irradiation technique achieving a linear array with periodicity 220–250 nm and large amplitudes around 45 nm. Vectorial Kerr (reflection) as well as Voight (transmission) magneto-optical effects confirm a complete uniaxial anisotropy induced with easy axis along the ripple pattern for Py films of thickness ranging from 10 to 30 nm. Analysis of curved magnetic systems is a major challenge, so we need to combine measurements of surface magnetization with thorough micromagnetic modelling of a quasi-infinite ripple film (same dimensions as the media). Remarkably, our modelling indicates unique features confirmed by experiments; namely, two disparate demagnetizing fields in hard axis magnetization and a distinctive thickness evolution. These findings are characteristic of an undulated magnetic state with the uniaxial anisotropy driven by volume-like poles. The choice of large pattern dimensions has made possible to realize the undulated state where the anisotropy strength can simply be tuned with film thickness without any role of surface contributions. This approach to anisotropy engineering provides ground for applications design without the limitations of surface preparation.

Spinwave detection by nitrogen-vacancy centers in diamond as a function of probe–sample separation

Magnetic field noise from magnons can reduce the lifetimes of proximate spins and degrade the performance of spin based technologies. However, spatial and temporal averaging over the area of typical field sensors makes measuring magnetic field noise challenging. Here, we use an ensemble of nitrogen-vacancy (NV) point-defects in diamond to measure the spectral profile of thermally excited spinwave noise at room temperature as a function of the distance away from a 20 nm thick Permalloy (Py) thin film. We systematically vary the separation between the NV and Py layers using a silicon-dioxide wedge and measure the longitudinal relaxation rate of the NV center ms = 0 state as a function of the separation. The measured spinwave-induced relaxation of an ensemble of NV centers is well described by a magnetostatic model of dipole fields from the spinwaves. We furthermore find that our all-optical, nonperturbative measurements of the spinwave noise can be used to extract information about the ferromagnetic source, such as magnetization, damping, and fluctuating amplitude. This technique is amenable to application with stand-off from ferromagnetic elements and from buried structures.

Magnetic Structure of Thin Permalloy Films with Interacting Domain Walls

The regularities of the formation of the magnetic structure near the systems of Bloch–Neel domain walls realized in the presence of an external magnetic field have been studied using the example of thin Fe0.25Ni0.75 films. It has been established that when the film is magnetized along the easy axis (EA), a stable quasi-closed distribution of magnetization (a blocked domain structure) is formed near the approaching domain walls. Under the action of a field oriented perpendicular to the EA, the blocked domain structure is transformed into a system of localized domains. A model that substantiates the observed transition is proposed.

Tailoring of uniaxial magnetic anisotropy in Permalloy thin films using nanorippled Si substrates

In this work the investigation of in-plane uniaxial magnetic anisotropy induced by the morphology due to ion beam erosion of Si(1 0 0) has been done. Ion beam erosion at an oblique angle of incidence generates a well-ordered nanoripple structure on the Si surface and ripple propagates in a direction normal to ion beam erosion. Permalloy thin films grown on such periodic nanopatterns show a strong uniaxial magnetic anisotropy with easy axis of magnetization in a direction normal to the ripple wave vector. The strength of uniaxial magnetic anisotropy is found to be high for the low value of ripple wavelength; it is decreasing with increasing value of ripple wavelength. Similarly, the strength of uniaxial magnetic anisotropy decreases with increasing Permalloy film thickness. Grazing incidence small angle x-ray scattering data reveals an anisotropic growth of Permalloy thin films with preferential orientation of grains in the direction normal to the ripple wave vector. Permalloy thin film growth is highly conformal with the film surface replicating the substrate ripple morphology up to a film thickness of 50 nm has been observed. Correlation between observed uniaxial magnetic anisotropy to surface modification has been addressed.

A low-cost vibrating sample magnetometry based on audio components

In this paper, we developed a low-cost, highly sensitive magnetization characterization instrument using a sound card and compared its sensitivity with commercially available measurement techniques. Firstly, we use an RLC circuit to measure the frequency-dependent response of the sound card and compare it with a lock-in amplifier. Then, we construct a simple but versatile measuring instrument, vibrating sample magnetometer (VSM) based on audio components, where data acquisition is performed by the sound card and the commercial lock-in amplifier. We test our magnetometry by measuring the magnetic hysteresis of three distinct samples: Nickel bulk piece, perm-alloy thin film with an easy-plane anisotropy, and Co/Pt multilayer with perpendicular magnetic anisotropy. We also analyze the magnetizations of three samples for different vibration frequencies and compare the sensitivities of two data acquisition methods. Although the sound card performs slightly worse than the lock-in amplifier at the vibration frequencies lower than 20 Hz due to the frequency cut-off, the sound card provides approximately seven times better sensitivity than the lock-in amplifier does at higher frequencies up to 60 Hz. We found that the sound card based VSM can have a sensitivity as high as 2 micro-emu at 34.7 Hz vibration frequency, which can be suitable for various laboratory and industrial applications.

Spin Hall angle and spin diffusion length of permalloy

The inverse spin Hall effect (ISHE) in a ferromagnetic material (FM) has been attracting much attention due to its importance in spintronic applications. ISHE, which converts a spin current into a charge current, is an effective method for detecting spin currents. In this work, we report the observation of ISHE on permalloy (Py) thin films under the ferromagnetic resonance condition. The values of the spin Hall angle (θSHE) and the spin diffusion length (λPy) for Py are determined to be 0.034% and 7.0 nm, respectively. The values of θSHE and λPy are investigated for the first time with spin pumping techniques for a FM.

Особенности поведения магнитных характеристик вблизи краев тонких пермаллоевых пленок

Особенности поведения магнитных характеристик вблизи краев тонких пермаллоевых пленок

Electrically tunable miniaturized band-stop frequency selective surface on engineered substrate with embedded permalloy patterns

This paper presents a miniaturized and electrically tunable band-stop frequency selective surface (FSS) with magneto-dielectric engineered substrate which has high and electrically tunable effective permeability. The perspective magneto-dielectric substrate is implemented with multiple layers of 100 nm thick patterned Permalloy (Py) thin film embedded in Roger RT/Duriod 5880 substrate, and each Py thin film layer consists of an array of 15μm×20μm Py patterns with 10 μm gaps among them to suppress the magnetic loss. The tunability of effective permeability for the proposed substrate is achieved by the static magnetic field produced from the applied DC current through the patterned gold bias lines beneath Py patterns. The engineered substrate has been implemented and studied, results show that the substrate embedded with a single layer of patterned Py has an equivalent permeability of 1.14 with tunability of 3.3%, and the substrate embedded with ten layers of patterned Py has an increased equivalent permeability of 2.398 and tunability of 15.8%. A magnetic FSS is designed on the implemented engineered substrate to demonstrate the efficacy of miniaturization and tunability. Compared to non-magnetic FSS on normal dielectric substrate, the size of the designed FSS has been reduced by 16.02%, and the operating frequency of the proposed FSS is continuously tunable from 2.450GHz to 2.672GHz with DC current.

Oblique angle deposition of nickel thin films by high-power impulse magnetron sputtering.

Background: Oblique angle deposition is known for yielding the growth of columnar grains that are tilted in the direction of the deposition flux. Using this technique combined with high-power impulse magnetron sputtering (HiPIMS) can induce unique properties in ferromagnetic thin films. Earlier we have explored the properties of polycrystalline and epitaxially deposited permalloy thin films deposited under 35° tilt using HiPIMS and compared it with films deposited by dc magnetron sputtering (dcMS). The films prepared by HiPIMS present lower anisotropy and coercivity fields than films deposited with dcMS. For the epitaxial films dcMS deposition gives biaxial anisotropy while HiPIMS deposition gives a well-defined uniaxial anisotropy.Results: We report on the deposition of 50 nm polycrystalline nickel thin films by dcMS and HiPIMS while the tilt angle with respect to the substrate normal is varied from 0° to 70°. The HiPIMS-deposited films are always denser, with a smoother surface and are magnetically softer than the dcMS-deposited films under the same deposition conditions. The obliquely deposited HiPIMS films are significantly more uniform in terms of thickness. Cross-sectional SEM images reveal that the dcMS-deposited film under 70° tilt angle consists of well-defined inclined nanocolumnar grains while grains of HiPIMS-deposited films are smaller and less tilted. Both deposition methods result in in-plane isotropic magnetic behavior at small tilt angles while larger tilt angles result in uniaxial magnetic anisotropy. The transition tilt angle varies with deposition method and is measured around 35° for dcMS and 60° for HiPIMS.Conclusion: Due to the high discharge current and high ionized flux fraction, the HiPIMS process can suppress the inclined columnar growth induced by oblique angle deposition. Thus, the ferromagnetic thin films obliquely deposited by HiPIMS deposition exhibit different magnetic properties than dcMS-deposited films. The results demonstrate the potential of the HiPIMS process to tailor the material properties for some important technological applications in addition to the ability to fill high aspect ratio trenches and coating on cutting tools with complex geometries.

Strong Coupling between Magnons and Microwave Photons in On-Chip Ferromagnet-Superconductor Thin-Film Devices.

We demonstrate strong magnon-photon coupling of a thin-film Permalloy device fabricated on a coplanar superconducting resonator. A coupling strength of 0.152GHz and a cooperativity of 68 are found for a 30-nm-thick Permalloy stripe. The coupling strength is tunable by rotating the biasing magnetic field or changing the volume of Permalloy. We also observe an enhancement of magnon-photon coupling in the nonlinear regime of the superconducting resonator, which is attributed to the nucleation of dynamic flux vortices. Our results demonstrate a critical step towards future integrated hybrid systems for quantum magnonics and on-chip coherent information transfer.

A study of Barkhausen avalanche statistics through the critical disorder in a ferromagnetic thin film: Experimental investigation and theoretical modeling

It is well known from theoretical models that a ferromagnetic system should undergo a disorder induced phase transition in its magnetization reversal mode at a critical disorder level RC, below which, the reversal is characterized by the appearance of the so-called spanning avalanche. The critical regime above RC is characterized by power-law distributed avalanche sizes and durations, whose exponents determine the universality class to which the magnetic system belongs. The most commonly studied among these is the size-exponent τ, which most theoretical models estimate to be in the range 1.3–1.5. However, experimental determinations of this exponent fall in a much wider interval, between 0.98 and 1.8, well outside the domain of the models. This discrepancy, which is far more common for 2D systems, has not been effectively addressed for more than a decade. In this article, we have determined experimentally the size-exponent ‘τ’ in 2D Permalloy(Ni80Fe20) thin films by measuring Barkhausen noise through the disorder-induced transition using planar Hall effect. This was compared with our simulations of the random field Ising model, an established nucleation model, with a modification that better represented the experimental condition. Our findings indicated that large ‘τ’-values would arise in samples with very low disorder levels well outside the critical regime, where the statistics were non-universal. In such samples, our measured ‘τ’ increased monotonically with temperature, which indicated a decrease in the effective disorder with temperature according to the nucleation models. This temperature dependence could be understood in the light of an extended Néel-Brown model which we had studied earlier, that had predicted a decrease in the width of switching field distribution with increasing temperature. In this context, we also used micromagnetic simulations, which helped to understand the dependence of coercivity on disorder, a property not predicted correctly by the Ising model.

Form and magnetic birefringence in undulated Permalloy/PET films.

We report the measurement of form and magnetic birefringence in Permalloy (Ni80Fe20) films grown on rippled Poly(Ethylene Terephthalate), PET, substrates. Prior to Permalloy deposition, Laser Induced Periodic Surface Structures (LIPSS) were generated on the polymeric substrate by a nanosecond laser beam, developing an ordered rippled nanostructure. Due to their high transparency factor, we could investigate the behavior of linear polarized light transmitting at normal incidence on Permalloy/PET sample. The results show the existence of an optical axis parallel to the ripples direction, which yields an strong form birefringence effect arising from the laser patterning. Concerning the Permalloy thin film, the study of its in-plane magnetization was carried out measuring the Voigt magnetooptical effect. The obtained data in our samples reveal the appearance of two different mechanisms to reverse the magnetization, as the external magnetic field is parallel or perpendicular to the ripples direction. Accordingly, the transmitted light shows a magnetic birefringence depending on the relative orientation between the ripple direction, i.e. the optical axis of the LIPSS, and the in-plane magnetization of the Permalloy film.

Quantitative magnetic force microscopy using calibration on superconducting flux quanta

We present a new procedure that takes advantage of the magnetic flux quantization of superconducting vortices to calibrate the magnetic properties of tips for magnetic force microscopy (MFM). Indeed, a superconducting vortex, whose quantized flux is dependent upon Plank constant, speed of light and electron charge, behaves as a very well defined magnetic reference object. The proposed calibration procedure has been tested on new and worn tips and shows that the monopole point-like approximation of the probe is a reliable model. This procedure has been then applied to perform quantitative MFM experiments on a soft ferromagnetic thin film of permalloy, leading to the determination of the local out-of-plane component of the canted magnetization, together with its spatial variations across a few μm2 scan area.

Nonuniform Spin-Wave Softening in Two-Dimensional Magnonic Crystals as a Tool for Opening Omnidirectional Magnonic Band Gaps

By means of the plane wave method we study spin wave dynamics in two-dimensional bi-component magnonic crystals based on a squeezed hexagonal lattice and consist of a permalloy thin film with cobalt inclusions. We explore the dependence of a spin wave frequency on the external magnetic field, especially in weak fields where the mode softening takes place. For considered structures, the mode softening proves to be highly non-uniform on both the mode number and the wave vector. We found this effect to be responsible for the omnidirectional band gap opening. Moreover, we show that the enhancement of the demagnetizing field caused by the squeezing of the structure is of crucial importance for the non-uniform mode softening. This allows us to employ this mechanism to design magnonic gaps with different sensitivity for the tiny change of the external field. The effects we have found should be useful in designing and optimization of spin wave filters highly tunable by a small external magnetic field.