Ferromagnetic Resonance Spectra Research Articles

Interfacial reaction behavior between ferromagnetic CoFeB and the topological insulator Sb2Te3

The successful prevention of interfacial reactions between ferromagnetic materials and topological insulators (TIs) is crucial for the realization of reliable spintronic devices using TIs. To this end, we investigated the magnetic properties and interfacial reaction behavior of a bilayer structure composed of ferromagnetic CoFeB and TI Sb2Te3. The effects of including a MgO interlayer was also investigated. Ferromagnetic resonance (FMR) studies showed a remarkably weak resonance peak for the sample annealed at 400 °C for the 2-nm-thick interlayer, and finally, no resonance peak for a film below 1 nm in thickness was observed. X-ray diffraction (XRD) results demonstrated that the Sb2Te3 peak intensities started to decrease upon annealing at 200 °C and completely disappeared for annealing temperatures >400 °C. Hard X-ray photoelectron spectroscopy (HAXPES) results also support that the core-level peaks of Sb and Te split upon annealing at temperatures >200 °C, suggesting the dissociation of Sb2Te3. These results indicate that Sb2Te3 and CoFeB react at the interface during annealing, resulting in a loss of the ferromagnetic properties of the CoFeB layer. Meanwhile, a sample containing a 3-nm-thick MgO layer retained its original Sb2Te3/MgO/CoFeB structure even after annealing at 400 °C, as evidenced by its unchanged XRD peak intensity and FMR spectrum. We expect that our findings will be highly valuable in developing TI-based spintronic devices.

Magnetic properties of the mixed ferrites MnZnFe2O4 and MnAl-Fe2O4: A comparative study

Nanosized particles of Mn1-xZnxFe2O4, where 0 ≤ x ≤ 1, and MnAlxFe2-xO4, where 0 ≤ x ≤ 2, were synthesized by the sol–gel combustion method and the magnetic properties of these compounds were investigated and compared. The saturation magnetization of the samples of Mn1-xZnxFe2O4 was taken from the literature and the saturation magnetization of the samples of MnAlxFe2-xO4 was estimated from the cation distribution; ferromagnetic resonance spectra were used to determine the magnetocrystalline anisotropy. The results show that the saturation magnetization and the magnetocrystalline anisotropy of Zn- and Al- doped MnFe2O4 vary over a wide range, a result that could be useful for practical applications of these materials.

Reciprocity relations in a biologically inspired nanomagnonic system with dipolar coupling

Magnetosome chains in magnetotactic bacteria present ideal nanomagnonic model systems for studying collective resonance modes of dipolar-coupled single domain particles in relation to their spatial arrangement. Using microresonator-based ferromagnetic resonance (FMR) spectroscopy, electron microscopy, and micromagnetic modeling, we here provide insights into the complex magnonic activity within a single magnetosome chain. While the angular dependence of its FMR spectrum is dominated by twofold symmetry features due to the uniaxial anisotropy of linear chain segments, we also observed an unexpected behavior such as interrupted lines and flat bands due to the intricate geometrical details of this particular chain, such as a cross-like structural anomaly where a pair of particles is oriented perpendicular to the main axis of the chain and thus breaks the prevailing axial dipolar coupling symmetry. Such a cross junction formed by four particles exhibits interesting magnonic network properties. Notably, we observe reciprocity in the sense that the spectral response of one particle to an excitation of another one is identical to the response of the latter given an excitation of the former. Furthermore, we have identified that magnonic coupling between A and B can be facilitated via a dark state, as in magnonic stimulated Raman adiabatic passage, and that this dark-state coupling can be made non-reciprocal between A and B by breaking the symmetry of the spatial arrangement of the four particles.

Investigation of magnetization dynamics in trilayer width-modulated nanowires

We have investigated the magnetization reversal processes and dynamic behavior of trilayered Py(50 nm)/Pd(tPd)/Py(20 nm) nanowires with periodic width modulation as a function of spacer layer thickness tPd in the range from 0 to 10 nm and compared them with single-layer nanowires. The ferromagnetic resonance spectra show more than three modes that result from a non-uniform demagnetizing field in width-modulated nanowires. We observe that the spacer layer thickness influenced the ferromagnetic resonance spectra, which showed different numbers and values of modes and frequencies due to the different magnetization configurations for different spacer layer thicknesses. We also found that the two ferromagnetic layers are exchange-coupled for tPd = 2 nm nanowire arrays, showing the sharp switching of magnetization from the static measurements and sharp frequency jump from 13.6 to 14.7 GHz around −18 mT from the dynamic measurements. However, for tPd = 10 nm, the two layers switch at different fields, indicating a gradual decrease in magnetization as the reversal is mediated through dipolar coupling. The origin of modes is well explained from the spatial mode profiles of top and bottom magnetic layers. The dynamic responses in this spin-valve-type structure are useful for designing microwave-based spintronic devices.

Excitation and Tuning of Spin Waves in Magnonic Crystals by Magnetic Coupling

Magnonic crystals with artificial micro/nanomagnetic pattern act as low‐loss information carriers in many microwave devices. The excitation and control of spin waves inside is essential and fundamental in magnonic crystal applications. Herein, permalloy micro‐disk patterns are constructed on a continuous permalloy film, and they succeed in exciting spin waves in this bilayer‐structured magnonic crystal. The spin‐wave modes can be effectively tuned by varying the periodic parameter (P) of upper‐layer disk pattern, which is confirmed by the transition from single‐peak to multi‐peak in ferromagnetic resonance (FMR) spectra with P decreased from 4 to 0.5 μm. The split in FMR spectra is reconstructed by micromagnetic simulation, revealing that three spin‐wave modes are respectively excited by the domain walls of below‐layer continuous film, geometrical restriction of permalloy micro‐disk, and magnetic coupling between neighboring permalloy micro‐disks. The tunable spin‐wave behavior in this bilayer‐structured magnonic crystal presents broad application prospect in programmable spintronic devices at micro/nanoscale.

Ferromagnetic resonance spectra of linear magnetosome chains.

The ferromagnetic resonance (FMR) spectra of oriented and non-oriented assemblies of linear magnetosome chains are calculated by solving the stochastic Landau-Lifshitz equation. The dependence of the shape of the FMR spectrum of a dilute assembly of chains on the particle diameter, the number of particles in a chain, the distance between the centers of neighboring particles, the mutual orientation of the cubic axes of particle anisotropy, and the value of the magnetic damping constant is studied. It is shown that FMR spectra of non-oriented chain assemblies depend on the average particle diameter at a fixed thickness of the lipid magnetosome membrane, as well as on the value of the magnetic damping constant. At the same time, they are practically independent of the number Np of particles in the chain under the condition Np ≥ 10. The FMR spectra of non-oriented assemblies of magnetosome chains are compared with that of random clusters of interacting spherical magnetite nanoparticles. The shape of FMR spectra of both assemblies is shown to differ appreciably even at sufficiently large values of filling density of random clusters.

Splitting phenomenon of ferromagnetic resonance spectra in NiFe films deposited on periodically rippled sapphire substrates

The splitting phenomenon of ferromagnetic resonance (FMR) spectra of Ni80Fe20 (NiFe) films deposited on periodically rippled sapphire substrates is studied experimentally with the help of micromagnetic simulation. The analyses show that the splitting of FMR spectra is related to the periodic ripple topography of films. When the applied magnetic field is perpendicular to the ripple direction, the effective field of periodically rippled films becomes inhomogeneous. The splitting of FMR spectra originates from localized FMR peaks corresponding to different regions with different effective field intensities in the rippled structure. Furthermore, the relative intensity and position between the split mode and the main FMR mode can be changed by designing ripple topography. This work would help understand the splitting phenomenon of FMR spectra for magnetic thin films deposited on the periodically rippled sapphire substrates.

Ferromagnetic Resonance Heating of Magnetic Nanoparticles Resovist for Biomedical Applications

Ferromagnetic resonance (FMR)-based magnetic energy dissipation potentially generates effective heating for cancer therapy in magnetic hyperthermia. We demonstrated the FMR characteristics of normal/customized Resovist® (particle sizes of 60 and 16 nm) for biomedical applications and revealed the bias magnetic field-dependent FMR spectrum in the range of 1–10 GHz under 0–2000 Oe. Moreover, an improvement in heating power was observed under the FMR condition. The maximum temperature increment rate was 2.5 °C/s, which is 10-fold greater than that of conventional magnetic hyperthermia with a frequency range of several hundred kHz. Our results indicate that magnetic hyperthermia by utilizing FMR enables the progressive study of cancer treatment.

Chemical Approach Towards Broadband Spintronics on Nanoscale Pyrene Films

AbstractThe injection of pure spin current into the non‐magnetic layer plays a crucial role in transmitting, processing, and storing data information in the realm of spintronics. To understand broadband molecular spintronics, pyrene oligomer film (≈20 nm thickness) was prepared using an electrochemical method forming indium tin oxide (ITO) electrode/pyrene covalent interfaces. Permalloy (Ni80Fe20) films with different nanoscale thicknesses were used as top contact over ITO/pyrene layers to estimate the spin pumping efficiency across the interfaces using broadband ferromagnetic resonance spectra. The spintronic devices are composed of permalloy/pyrene/ITO orthogonal configuration, showing remarkable spin pumping from permalloy to pyrene film. The large spin pumping is evident from the linewidth broadening of 5.4 mT at 9 GHz, which is direct proof of spin angular momentum transfer across the interface. A striking observation is made with the high spin‐mixing conductance of ≈1.02×1018 m−2, a value comparable to the conventional heavy metals. Large spin angular moment transfer was observed at the permalloy‐pyrene interfaces, especially at the lower thickness of permalloy, indicating a strong spinterface effect. Pure spin current injection from ferromagnetic into electrochemically grown pyrene films ensures efficient broadband spin transport, which opens a new area in molecular broadband spintronics.

Chemical Approach Towards Broadband Spintronics on Nanoscale Pyrene Films.

The injection of pure spin current into the non-magnetic layer plays a crucial role in transmitting, processing, and storing data information in the realm of spintronics. To understand broadband molecular spintronics, pyrene oligomer film (~20 nm thickness) was prepared using an electrochemical method forming indium tin oxide (ITO) electrode/pyrene covalent interfaces. Permalloy (Ni80Fe20) films with different nanoscale thicknesses were used as top contact over ITO/pyrene layers to estimate the spin pumping efficiency across the interfaces using broadband ferromagnetic resonance spectra. The spintronic devices are composed of permalloy/pyrene/ITO orthogonal configuration, showing remarkable spin pumping from permalloy to pyrene film. The large spin pumping is evident from the linewidth broadening of 5.4 mT at 9 GHz, which is direct proof of spin angular momentum transfer across the interface. A striking observation is made with the high spin-mixing conductance of ~1.02 1018 m-2, a value comparable to the conventional heavy metals. Large spin angular moment transfer was observed at the permalloy-pyrene interfaces, especially at the lower thickness of permalloy, indicating a strong spinterface effect. Pure spin current injection from ferromagnetic into electrochemically grown pyrene films ensures efficient broadband spin transport, which opens a new area in molecular broadband spintronics.

Spin pumping in NbRe/Co superconductor-ferromagnet heterostructures

Ferromagnetic resonance (FMR) spectroscopy measurements were performed on NbRe/Co/NbRe trilayers in order to probe spin pumping across the superconductor/ferromagnet interface and to detect the possible presence of spin-triplet pairing in the superconducting NbRe layer. FMR spectra were acquired as a function of frequency, magnetic field, and temperature, and reveal that the Gilbert damping parameter associated with spin pumping remains almost constant as temperature goes down through the superconducting transition. Additionally, the dependence of the Gilbert damping parameter on the thickness of the NbRe layer in trilayers is used to determine the values of the spin mixing conductance at the interface ( nm−2) and the spin diffusion length ( nm) in the NbRe layer. These findings may suggest that spin pumping would still be effective even though NbRe becomes superconducting, which would indicate that the spin-triplet would be the dominant pairing mechanism. Future experiments are proposed in light of these results.

Effect of pH and precursor solution on the microstructural properties and ferromagnetic resonance of nickel nanowires

This study presents the influence of pH and precursors present in the electrolyte on the microstructure and magnetic properties of nickel nanowires. Polycarbonate membranes were used as a template for electrodeposition of nanowires. The SEM results showed that the wires have lengths ranging from 2.68 ± 0.28 µm to 18.77 ± 1.18 µm. X-ray diffraction confirmed the fcc structure of Ni0 and demonstrated how different solutions can modify the reflection intensity of the peaks. Finally, ferromagnetic resonance spectra demonstrated how pH and precursors present in the electrolyte can modify the ferromagnetic response of NiNWs grown on polycarbonate membranes, emphasizing the influence of both factors on the magnetic behavior of nanowires. This study provides an understanding of the role that solution chemistry plays in the manufacture of magnetic nanomaterials.

Giant efficiency of long-range orbital torque in Co/Nb bilayers

We report unambiguously experimental evidence of a strong orbital current in Nb films with weak spin-orbit coupling via the spin-torque ferromagnetic resonance (ST-FMR) spectrum for Fe/Nb and Co/Nb bilayers. The sign change of the damping-like torque in Co/Nb demonstrates a large spin-orbit correlation and thus great efficiency of orbital torque in Co/Nb. By studying the efficiency as a function of the thickness of Nb sublayer, we reveal a long orbital diffusion length (~3.1 nm) of Nb. Further planar Hall resistance (PHE) measurements at positive and negative applying current confirm the nonlocal orbital transport in ferromagnetic-metal/Nb heterostructures.

Magnetic nanoparticles in the body parts of Polistes versicolor and Polybia paulista wasps are biomineralized: evidence from magnetization measurements and ferromagnetic resonance spectroscopy.

The detection of the geomagnetic field by animals to use as a cue in homing and migration is known as magnetoreception. The ferromagnetic hypothesis explains magnetoreception assuming that magnetic nanoparticles in cellular structures are used as magnetic field transducers. Considering magnetoreception in social insects, the most studied has been the honeybee Apis mellifera and only in two wasp species (Vespa orientalis and Polybia paulista) have been shown a magnetosensitive behavior. In the present report the body parts (abdomen, head and antennae) of Polistes versicolor and Polybia paulista wasps were studied aiming to find biomineralized magnetic nanoparticles, using magnetometry measurements and ferromagnetic resonance spectroscopy. The magnetometry measurements show the presence of magnetic nanoparticles in all body parts, being characterized as mixtures of superparamagnetic, single domain and pseudo-single domain nanoparticles. From the ferromagnetic resonance spectra were obtained the asymmetry ratio A and the effective g factor geff, and those parameters are consistent with the presence of biomineralized magnetic nanoparticles in both wasps. In the case of Polybia paulista, the magnetic nanoparticles can be associated with some sort of magnetosensor once this wasp is magnetosensitive. For Polistes versicolor, the results indicate that this wasp can be magnetosensitive as Polybia paulista once their magnetic nanoparticles are biomineralized in the body. Behavioral studies with Polistes versicolor wasps deserve to be performed.

Integrated magnetic resonance technique for the complete analysis of magnetic properties and interlayer interactions in two-layer film heterostructures ferromagnet/nonmagnetic metal

The paper proposes a technique based on the set of angular dependences of the ferromagnetic resonance (FMR) spectra, which makes it possible to quantitatively determine the parameters of all in-plane and out-of-plane magnetic anisotropies, as well as the magnitude of the interlayer interaction in film two-layer ferromagnet/non-magnetic metal (FM/NM) heterostructures. The obtained value of the interlayer interaction, in turn, makes it possible to unambiguously determine the value of the spin-mixing conductance. The effectiveness of the technique was demonstrated using the example of the analysis of a two-layer film heterostructure La0.7Sr0.3MnO3/SrIrO3 (LSMO/SIO). In particular, the temperature dependences of the value of the perpendicular magnetic anisotropy and the magnitude of the FMR resonant field shift, which is determined by the imaginary part of the spin-mixing conductance at the LSMO/SIO interface, are determined.

Self-assembly epitaxial lithium ferrite nanostructures with tunable magnetic properties

High-performance ordered arrays of nanostructure has attracted significant attention due to the needs for miniaturization in electronic and spintronic devices. However, the traditional templete-assisted method often entails expensive equipment and complicated processing. Herein, a series of high quality LiFe5O8 (LFO) arrays are obtained by chemically etching the MgO phase in the self-assembly (LFO)1:(MgO)x nanocomposite films. The LFO arrays show excellent epitaxial quality and nano-island or nano-pillar morphology, which can be easily fabricated by controlling the thickness and chemical component of the grown nanocomposite films. In comparison with the LFO planar film, the LFO nanopillar arrays exhibit higher saturation magnetization, lower non-zero coercivity and remanence. Moreover, the morphology of the nanostructures can effectively modulate the ferromagnetic resonance spectra of the LFO nanopillar arrays, which can be explained by the calculated demagnetization field. This work shows that nanostructure engineering is very useful to modulate the magnetic properties and to design compact microwave magnetism devices.

Element-specific visualization of dynamic magnetic coupling in a Co/Py bilayer microstructure

We present the element-specific and time resolved visualization of uniform ferromagnetic resonance excitations of a Permalloy (Py) disk–Cobalt (Co) stripe bilayer microstructure. The transverse high frequency component of the resonantly excited magnetization is sampled in the ps regime by a combination of ferromagnetic resonance (FMR) and scanning transmission X-ray microscopy (STXM-FMR) recording snapshots of the local magnetization precession of Py and Co with nanometer spatial resolution. The approach allows us to individually image the resonant dynamic response of each element, and we find that angular momentum is transferred from the Py disk to the Co stripe and vice versa at their respective resonances. The integral (cavity) FMR spectrum of our sample shows an unexpected additional third resonance. This resonance is observed in the STXM-FMR experiments as well. Our microscopic findings suggest that it is governed by magnetic exchange between Py and Co, showing for the Co stripe a difference in relative phase of the magnetization due to stray field influence.

Magnetization dynamics affected by phonon pumping

"Pumping" of phonons by a dynamic magnetization promises to extend the range and functionality of magnonic devices. We explore the impact of phonon pumping on room-temperature ferromagnetic resonance (FMR) spectra of bilayers of thin yttrium iron garnet (YIG) films on thick gadolinium gallium garnet substrates over a wide frequency range. At low frequencies the Kittel mode hybridizes coherently with standing ultrasound waves of a bulk acoustic resonator to form magnon polarons that induce rapid oscillations of the magnetic susceptibility, as reported before. At higher frequencies, the phonon resonances overlap, merging into a conventional FMR line, but with an increased line width. The frequency dependence of the increased line broadening follows the predictions from phonon pumping theory in the thick substrate limit. In addition, we find substantial magnon-phonon coupling of a perpendicular standing spin wave (PSSW) mode. This evidences the importance of the mode overlap between the acoustic and magnetic modes, and provides a route towards engineering the magnetoelastic mode coupling.

Synthesis and Characterization of Hyper‐Branched Nanoparticles with Magnetic and Plasmonic Properties

AbstractHybrid nanoparticles, composed of an iron oxide magnetic core embedded with gold fractal‐grown hyper branches, have been synthesized by a seed‐mediated growth approach. Magnetic and plasmonic properties have been described respectively through ferromagnetic resonance (FMR) and extinction spectra. According to the hydroxylamine amount, used as a surface catalysed reducing agent, the number of branches and the intensity of the fractal growth have been finely tuned and were observed through TEM microscopy. The magnetic core allowed their motion control via an external magnetic field. The plasmonic properties of these hyper‐branched hybrid nanoparticles were recorded similar to those shown by the branched gold nanoparticles, but it is interesting to note that they showed an encouraging photothermal response.

HYDROTHERMAL TEMPERATURE INFLUENCE ON MAGNETIC AND FMR PROPERTIES OF HEMATITE NANOPARTICLES

Investigation of the role of hydrothermal temperature on hematite nanoparticles structural, magnetic, and ferromagnetic resonance (FMR) properties was done. Ferric chloride and sodium hydroxide were used as the starting precursors. The hydrothermal temperature was varied in the range of 140–200∘C by a step of 20∘C. XRD, SEM, VSM, and FMR analyses were used to check the particles’ properties. The prevailing strongly phase was hematite with some small peaks related to other phases. A reduction in lattice constant and increase in the crystallite size to more than 27[Formula: see text]nm is observed. The particles’ morphology exhibited polygon particles down to spherical particles as the average particle size gets larger up to 45[Formula: see text]nm. The hysteresis loops showed unsaturated curves with rising coercivity up to 150Oe. The antiferromagnetism permeability, magnetization saturation, and dipole moment were found by Langevin fitting to the experimental hysteresis loops, where all of them have the same behavior represented by an initial drop followed by increase in their values. The FMR spectra are characterized by low intensities and low linewidths accompanied by very low blue shift in the resonance field. All samples showed Lorentzian distribution as checked by the Lorentz function. Landé [Formula: see text]-factor has values very close but less than 2 due to the effect of crystal field and particle magnetic moment variations.