Permalloy Thin Films Research Articles

Influence of interface morphology on the magnetic damping of Al-sandwiched Permalloy thin films

Influence of interface morphology on the magnetic damping of Al-sandwiched Permalloy thin films

Spin-wave emission using a V-shaped antenna

We investigated the dynamics of spin waves in micro-patterned Permalloy thin films using time-resolved magneto-optic Kerr effect microscopy (TR-MOKE). By applying an external magnetic field, we observe the field dependence of spin wave signals with picosecond resolution. Fourier transform analysis of the signals confirms their agreement with the dispersion relation, demonstrating the successful detection of propagating spin waves using the MOKE technique. Furthermore, we perform dynamic measurements of interfering spin waves generated by a V-shaped antenna. The experimental results reveal differences in spin wave amplitude at each detection point. In combination with simulation analysis based on wave propagation from the V-shaped antenna, we reproduced the experimental results and revealed the existence of a protective zone.

Magnetization dynamics and domain reversal in electrodeposited permalloy thin films: impact of thickness and annealing treatment

The domain reversal and magnetization dynamics of electrodeposited permalloy (Fe20Ni80) thin films on conducting ITO/glass substrate was investigated using Magneto-optic Kerr effect microscopy and ferromagnetic resonance. Permalloy thin films were electrodeposited with thickness ranging from 66 nm to 330 nm. Synchrotron XRD confirmed the deposited permalloy in FCC phase without any impurity. The squared hysteresis with very low coercivity (Hc ∼ 5 Oe) established soft magnetic nature of the films. Further, angular MOKE hysteresis measurements with simultaneous domain imaging revealed four-fold surface anisotropy in as-deposited film ensuing magnetization reversal via branched and ripple domains. The annealing treatment in Ar+H2 atmosphere removed surface anisotropy and renovated the magnetization reversal through 180° branched domains with rapid magnetization switching. Ferromagnetic resonance spectroscopy discloses reduction in the gyromagnetic ratio (γ) as well as in Gilbert damping parameter (α) as the film thickness increases. The lowest Gilbert damping for 330 nm film measured at 0.022, which further reduced to 0.018 after annealing. The combination of rapid magnetization switching and low Gilbert damping in the electrodeposited permalloy thin films render them promising for implementation in high-frequency microwave devices devices and magnetic sensors.

Magnetization reversal phenomena in thin films presenting stripe domains

We present a study of the properties related to the magnetization reversal process in two thin-film samples with magnetic stripe domains: Fe0.82Ga0.18 (Fe–Ga) and Ni0.81Fe0.19 (permalloy). In Fe–Ga thin films, we focus on magnetization reversal driven by thermal activation by considering the magnetic viscosity behavior. The results suggest that the reversal process occurs gradually, where the magnetization switches direction via ∼10 nm-long jumps of the magnetic domain walls. On the other hand, vectorial hysteresis loops were performed in permalloy thin films with the aim to study the behavior of the transverse magnetization component (perpendicular to the applied field) during the magnetization reversal process. We show that the measurement of the transversal magnetization component shows a much higher sensitivity for the determination of the in-plane magnetic anisotropy than the usual hysteresis loops where the magnetization is parallel to the applied field. Moreover, this allows to highlight the competition between the intrinsic and rotatable anisotropies in thin films that present stripe domains.

Strain-enhanced spin-orbit coupling in permalloy thin films

Strain-enhanced spin-orbit coupling in permalloy thin films

Magnetization precession after non-collinear dual optical excitation

We investigate the impact of non-collinear dual optical excitation on magnetization precession in a permalloy thin film using two ultrashort laser pulses. By analyzing the magnetization dynamics using time-resolved magneto-optical methods, we find that excitation with two ultrashort optical pulses introduces a long-lasting modification of the electron system, as indicated by a sizable decrease in the precession frequency and a significant increase (approximately 25%) in the decay time. Our results reveal that the observed effect strongly depends on the respective polarizations of the two excitation pulses and the time delay between the two optical pulses. Our findings indicate the occurrence of a nonlinear opto-spin effect during photoexcitation with two interfering optical pulses, which can potentially be observed in various materials and at different photon wavelengths.

Coercivity enhancement in hematite/permalloy heterostructures across the Morin transition

Interfacial effects between antiferromagnetic (AFM) and ferromagnetic (FM) materials have long been a center of magnetism studies. Aside from the exchange bias occurring at the AFM/FM interface, controlling the coercivity is another significant topic in magnetic recordings. The coercivity of FM materials is often determined through varying grain size, alloy composition, density of defects, etc., which is set during material growth and offers limited room for modification after growth. Hematite (α-Fe2O3) is an AFM material that undergoes a temperature-controlled spin-flip transition, the so-called Morin transition. This transition gives an extra degree of freedom making hematite an intriguing component to study the exchange coupling when interfaced with an FM material. In this work, changes in the magnetic properties of soft magnetic permalloy (Ni81Fe19, or Py) thin films grown on hematite were studied across the Morin transition. Surprisingly, these samples showed a remarkable change in coercivity during the Morin transition. We attribute this effect to the magnetic domain mixture of hematite during the Morin transition. Our findings present a novel method of controlling the coercivity of plain ferromagnetic thin films.

Coherent and incoherent magnons induced by strong ultrafast demagnetization in thin permalloy films

Coherent and incoherent magnons induced by strong ultrafast demagnetization in thin permalloy films

High‐Quality NiFe Thin Films on Oxide/Non‐Oxide Platforms via Pulsed Laser Deposition at Room Temperature

AbstractSoft ferromagnetic permalloy (NiFe) thin films are promising for applications in spintronic devices because of their constituent electrical and magnetic properties. Electron beam evaporation and sputtering techniques have been used to deposit NiFe thin films. For in situ stacking of NiFe with functional complex oxides, the pulsed laser deposition (PLD) method is highly desirable. However, the growth of high‐quality NiFe (and non‐oxide thin films in general) by PLD remains a formidable task. Here, high‐quality NiFe thin films of various thicknesses on oxide/non‐oxide substrates with desirable magnetic properties by PLD at room temperature are reported. The magnetic properties are found to be strongly dependent on the laser fluence of the deposition process. The laser fluence of 4 J cm−2 produces the highest magnetization of ≈547 emu cc−1. The small coercivity (few Oersted) and sharp ferromagnetic switching behavior indicate uniaxial anisotropy with an easy axis along the in‐plane direction. In addition, thickness‐dependent magnetodynamics characterizations are studied via ferromagnetic resonance. These results offer significant insight into the PLD‐based development of thin metal magnetic films.

Emergent magneto-inductance effect in permalloy thin films on flexible polycarbonate substrates at room temperature

Emergent inductance has attracted significant interest for its relevance in both interesting fundamental physics and practical applications in magnetic devices that demand miniaturization without compromising inductance. In this Letter, we report the discovery of a stepwise magnetic field-induced emergent magneto-inductance (EML) effect in Permalloy (Py) thin films deposited on polycarbonate (PC) substrates. Remarkably, Py/PC devices exhibit an exceptionally large inductance variation exceeding 1 μH at room temperature, and intriguingly, a sign reversal of inductance occurs around the zero magnetic field. The dependencies of the EML effect on frequency, step magnetic field changes, and film width can be explained from the theory based on the spin motive force driven by transient domain wall motion. This study opens up exciting avenues for advancing our understanding of emergent inductance in fundamental physics and paves the way for practical applications in flexible magnetic devices.

Influence of oxidic and metallic interfaces on the magnetic damping of Permalloy thin films

Influence of oxidic and metallic interfaces on the magnetic damping of Permalloy thin films

Magnetic field sensing elements made of quasi-trapezoidal magnetoplasmonic crystals based on thin permalloy films

This work is devoted to the study of magnetic, optical, and magneto-optical properties of quasi-trapezoidal magnetoplasmonic crystals based on Ni80Fe20 permalloy films ranging in thickness from 5 to 20 nm. Magnetoplasmonic crystals’ dependencies of measuring range, required modulation magnetic field, sensitivity, and limit-of-detection on the thickness of the permalloy layer are comprehensively studied. It is shown, that an increase in magnetoplasmonic crystals’ differential susceptibility leads to the sensitivity increase of the proposed magnetic field sensing method, but also results in a decrease in the sensing elements’ measuring range. Obtained results can be used for sensing elements fabrication from magnetoplasmonic crystals with sensitivity and measuring range, suitable for particular applications.

Influence of sputter pressure on magnetic and structural properties of Permalloy thin films

Well-defined and technically relevant domain configurations are sought in patterned magnetic thin films. We used Magnetic Force Microscopy to investigate these in square-patterned Permalloy films. The films were prepared using dc sputter deposition by varying the Argon pressure from 1.5×10−3 to 30.0×10−3 mbar. The Landau domain configuration was found in films prepared at 1.5×10−3 mbar pressure. With an increase in pressure, tulip and irregular domains were consecutively formed. Based on magnetic and structural characterizations, an increase in coercivity and a decrease in Permalloy film density were observed at the same time.

A two-color dual-comb system for time-resolved measurements of ultrafast magnetization dynamics using triggerless asynchronous optical sampling.

We report on an Er-doped fiber (EDF)-laser-based dual-comb system that allows us to perform triggerless asynchronous optical sampling pump-probe measurements of ultrafast demagnetization and spin precession in magnetic materials. Because the oscillation frequencies of the two frequency-comb light sources are highly stabilized, the pulse-to-pulse timing jitter is sufficiently suppressed, and data accumulation without any trigger signals is possible. To effectively induce spin precession in ferromagnetic thin films, the spectral bandwidth of the output of one of the EDF frequency comb sources is broadened by a highly nonlinear fiber and then amplified at a wavelength of about 1030nm by a Yb-doped fiber amplifier. The output of the other frequency comb source is converted to about 775nm by second harmonic generation. We used this system to observe ultrafast demagnetization and spin precession dynamics on the picosecond and nanosecond time scales in a permalloy thin film. This time-domain spectroscopy system is promising for the rapid characterization of spin-wave generation and propagation dynamics in magnetic materials.

Role of intersublattice exchange interaction in ultrafast longitudinal and transverse magnetization dynamics in permalloy

We report on element-specific measurements of ultrafast demagnetization and magnetization precession damping in permalloy thin films. Magnetization dynamics induced by an optical pump at 1.5 eV is probed simultaneously at the ${M}_{2,3}$ edges of Ni and Fe with high-order harmonics for moderate demagnetization rates (less than 50%). The role of the intersublattice exchange interaction in both longitudinal and transverse dynamics is analyzed with a Landau-Lifshitz-Bloch description of ferromagnetically coupled Fe and Ni sublattices. It is shown that the intersublattice exchange interaction governs the dissipation during demagnetization as well as precession damping of the magnetization vector.

Barkhausen noise from formation of360∘domain walls in disordered permalloy thin films

Micromagnetic simulations reveal formation of 360${}^{\ensuremath{\circ}}$ domain walls in disordered, thin permalloy films during the field-driven magnetic reversal process. With stronger disorder, the reversal process is increasingly governed by discontinuous jumps, resulting in Barkhausen noise without explicit domain wall movement.

Investigation of ultrafast demagnetization and Gilbert damping and their correlation in different ferromagnetic thin films grown under identical conditions

Following the demonstration of laser-induced ultrafast demagnetization in ferromagnetic nickel, several theoretical and phenomenological propositions have sought to uncover its underlying physics. In this work we revisit the three temperature model (3TM) and the microscopic three temperature model (M3TM) to perform a comparative analysis of ultrafast demagnetization in 20 nm thick cobalt, nickel and permalloy thin films measured using an all-optical pump-probe technique. In addition to the ultrafast dynamics at the femtosecond timescales, the nanosecond magnetization precession and damping are recorded at various pump excitation fluences revealing a fluence-dependent enhancement in both the demagnetization times and the damping factors. We confirm that the Curie temperature to magnetic moment ratio of a given system acts as a figure of merit for the demagnetization time, while the demagnetization times and damping factors show an apparent sensitivity to the density of states at the Fermi level for a given system. Further, from numerical simulations of the ultrafast demagnetization based on both the 3TM and the M3TM, we extract the reservoir coupling parameters that best reproduce the experimental data and estimate the value of the spin flip scattering probability for each system. We discuss how the fluence-dependence of inter-reservoir coupling parameters so extracted may reflect a role played by nonthermal electrons in the magnetization dynamics at low laser fluences.

Magneto-mechanical Effect of NiFe Thin Films Depending on the Intrinsic Magnetic Anisotropy

Verifying magnetic anisotropy is essential for developing flexible magnetic devices. The magneto-mechanical effect is a unique phenomenon in magnetic materials for bending geometries and produces the stress magnetic anisotropy depending on the stress direction and its magneto-striction coefficient. In addition, the fabrication process for the flexible magnetic devices, such as deposition, annealing, and patterning, significantly causes the intrinsic magnetic anisotropy to change the reversal behaviors in the devices. This study investigated the variation of the stress magnetic anisotropy in the flexible NiFe (permalloy) thin films as a function of the bending repetition and its direction when the thin films had a different easy axis caused by the sputtering process. The variation of the stress magnetic anisotropy was observed by the magnetization reversal behaviors and the typical ferromagnetic resonance field detection before and after the application of the tensile stress. The stress effect was exponentially accumulated with increasing bending repetition on the thin film in both samples. However, when the repeated stress was applied in alternating x- and y-directions, minor resonance field fluctuation was observed in the film, which had the tilted intrinsic magnetic anisotropy. This result indicated that intrinsic magnetic anisotropy during the fabrication process played an essential role in determining the amount of effective field for designing flexible magnetic devices.

Low coercivity magnetoplasmonic crystal based on a thin permalloy film for magnetic field sensing applications

This research is devoted to the fabrication of 5-nm thick permalloy film-based magnetoplasmonic crystal for magnetic field sensing applications. Optical and magneto-optical activity of the magnetoplasmonic crystal is studied with the means of numerical modeling and spectroscopy techniques. The studied sample achieves sensitivity to an external DC magnetic field of 7.5 mOe in the 5.1 Oe required modulation AC magnetic field. Obtained experimental and modeling results can be used for the fabrication of cheaper and more energy-efficient sensing elements for magnetoplasmonic crystal-based magnetic field sensors due to the reduction of required ferromagnetic material and modulation magnetic field.

Magnetic and Structural Characterization of Permalloy (Ni79Fe21) Thin Films with Uniaxial Magnetic Anisotropy

Bu çalışmada, Si(100)/SiO2(~200 nm) alttaş üzerine 4 - 20 nm arasında değişen kalınlıklarda büyütülen permalloy ince filmlerin yapısal ve manyetik özellikleri araştırılmıştır. Permalloy ince filmler eğik açılı magnetron saçtırma tekniği kullanılarak yüksek vakumlu odada hazırlandı. X-ışını foto-elektron spektroskopisi ölçüm sonuçlarından, permalloyun alaşım komposizyonu oranı %21 Fe ve %79 Ni olarak bulundu. X-ışını kırınım ve yansıma ölçümleri, permalloy filmlerinin (111) yönünde, düşük yüzey pürüzlülüğüne sahip ve nominal kalınlıklarda büyüdüğünü gösterdi. Elde edilen ince filmlerin manyetik özellikleri ferromanyetik rezonans (FMR) ve titreşimli örnek manyetometresi (VSM) teknikleri kullanılarak araştırıldı. Film hazırlamada kullanılan eğik biriktirme nedeniyle, filmlerde düzlem içi tek-eksenli manyetik anizotropi gözlemlendi. Mıknatıslanma yönüne göre serbest enerji minimizasyonu yöntemini kullanan bir bilgisayar kodu yazılarak deneysel FMR verileri simule edildi ve bu sayede filmlerin tek eksenli anizotropi sabitleri belirlendi. Ayrıca, zorlayıcı alan ve anizotropi alanı gibi manyetik özelliklerin kalınlığa bağlı olarak değişimleri tartışıldı.