FMR Spectra Research Articles

Manganite Heterostructures: SrIrO<sub>3</sub>/La<sub>0.7</sub>Sr<sub>0.3</sub>MnO<sub>3</sub> and Pt/La<sub>0.7</sub>Sr<sub>0.3</sub>MnO<sub>3</sub> for Generation and Registration of Spin Current

This paper presents the results of experimental studies of the cross section of the boundaries of the SrIrO3/La0.7Sr0.3MnO3 и Pt/La0.7Sr0.3MnO3, heterostructures, in which, upon excitation of ferromagnetic resonance in a La0.7Sr0.3MnO3 film, a spin current arises that flows through the boundary in structure. Epitaxial growth of thin films of strontium iridate SrIrO3 and manganite La0.7Sr0.3MnO3 on a (110) NdGaO3 single-crystal substrate was carried out using magnetron sputtering at high temperature in a mixture of argon and oxygen gases. The spin mixing conductance, which determines the amplitude of the spin current and generally has real Re g↑↓ and imaginary Im g↑↓ parts, was determined from the frequency dependence of the FMR spectrum of the LSMO film and heterostructures. It is shown that the Im g↑↓ quantity, can play an important role in determining the spin Hall angle (θSH) from the angular dependence of the spin magnetoresistance. For the SrIrO3/La0.7Sr0.3MnO3 heterostructures, θSH turned out to be significantly higher (almost an order of magnitude) than for the Pt/La0.7Sr0.3MnO3 heterostructure.

Low temperature garnet phase formation in Mn-substituted Y3Fe5-xMnxO12 nanoparticles via citrate combustion synthesis

In this article, we report on the formation of a low-temperature garnet phase in Mn-substituted Y3Fe5-xMnxO12 (x = 0, 0.05, 0.15, and 0.25) nanopowders. We studied the structural, microstructural, static, and dynamic magnetic properties of Mn-substituted Y3Fe5-xMnxO12 (YIG) nanopowders calcined at two different temperatures. The Mn-substituted garnet powders were synthesized using the citrate combustion method followed by calcination at 800 and 1200 °C for 3 h. An increase in Mn substitution (x = 0.15, 0.25) favored the growth of a single garnet phase at low temperatures, even at 800 °C. The lattice constant of these samples ranged from 12.3815 to 12.3679 Å. Microstructural and morphological studies revealed the growth of homogeneous and dense particles, with an average particle size in the range of ∼35–58 nm, close to the single-domain particle size in YIG. Microwave resonance spectra and magnetic hysteresis curves revealed the formation of a ferromagnetic phase in undoped and Mn-doped garnet ferrites at room temperature. The maximum saturation magnetization (26 emu/g) was observed for the sample with Mn content x = 0.05 at 1200 °C, while the largest coercivity (33 Oe) was found for the sample with Mn content x = 0.15 at 1200 °C, among all the samples. The increase in Mn content led to a decrease in peak-to-peak linewidth of FMR spectra from 698.8 to 569.4 G at 800 °C and from 916 to 614.7 G at 1200 °C. This study suggests that Mn substitution in YIG garnet improves structural properties and enhances magnetic anisotropy.

Structural, Magnetic, and Magneto-Optical Properties of Thin Films of BaM Hexaferrite Grown by Laser Molecular Beam Epitaxy.

Thin films of BaM hexaferrite (BaFe12O19) were grown on α-Al2O3(0001) substrates by laser molecular beam epitaxy. Structural, magnetic, and magneto-optical properties were studied using medium-energy ion scattering, energy dispersive X-ray spectroscopy, atomic force microscopy, X-ray diffraction, magneto-optical spectroscopy, and magnetometric techniques, and the dynamics of magnetization by ferromagnetic resonance method. It was shown that even a short time annealing drastically changes the structural and magnetic properties of films. Only annealed films demonstrate magnetic hysteresis loops in PMOKE and VSM experiments. The shape of hysteresis loops depends on thickness of films showing practically rectangular loops and high value of remnant magnetization (Mr/Ms~99%) for thin films (50 nm) and much broader and sloped loops in thick (350-500 nm) films. The magnitude of magnetization 4πMs ≈ 4.3 kG in thin films corresponds to that in bulk BaM hexaferrite. Photon energy and sign of bands in magneto-optical spectra of thin films correspond to ones observed earlier in bulk samples and films of BaM hexaferrite. FMR spectra of 50 nm films at 50 GHz consist of a number of narrow lines. The width of main line ΔH~20 Oe is lower than has been reported up to now.

Determining spin-orbit torque in a single ferrimagnetic film without heavy metal via spin-torque ferromagnetic resonance

We report spin-orbit torque (SOT) in a single ferrimagnetic (FIM) GdFeCo alloy based on spin-torque ferromagnetic resonance (ST FMR). Thickness-dependent anomalous Hall resistance shows a bulk perpendicular magnetic anisotropy, which lead double peaks of ST FMR spectra at a larger thickness of 50 nm. Oblique-angle-dependent ST FMR is performed to study SOT, and the spin torque efficiency in the y axis is evaluated. This phenomenon is explained by the relationship between SOT and saturation magnetization. This finding provides an alternative method to modulate SOT in a single ferrimagnetic spintronic device.

Light-Induced Modification of the FMR Spectra of a Bismuth-Substituted Yttrium Ferrite Garnet Film

Light-Induced Modification of the FMR Spectra of a Bismuth-Substituted Yttrium Ferrite Garnet Film

Enhanced static and dynamic magnetic properties of PEG-400 coated CoFe2−xErxO4 (0.7 [formula omitted] x [formula omitted]) nanoferrites

The present work is focused on probing the spin dynamics of PEG (polyethylene glycol)−400 coated Erbium substituted nanocrystalline CoFe2−xErxO4 (0.7≤ x≤0) by a novel method using FMR spectroscopy. The highest magnetization is achieved for the x = 0.3 which suggests that the optimized concentration of the doping improves the dc magnetic characteristics of the nanoferrites (NFs). The static magnetic measurement exhibits that all the sample compositions display ferromagnetic behavior with saturation magnetization and coercivity varying from 37 to 58 emu/g and 1147.80–2148.71 Oe, respectively. The enhancement of magnetic properties was observed due to the super-exchange interaction (SEI) of Er3+ to Fe3+ ion from their lattice sites. Further, the room temperature FMR spectra confirms the ferromagnetic behavior of NFs with resonance field from 2746.8 G for pure CoFe2O4 which reduces to for 1760.5 G for x = 0.5 samples which suggests that the samples magnetization fields can align more easily, and their dynamic response has improved. The broad linewidth indicates that the dipolar-dipolar interactions are more dominant as compared to the SEI. The super-exchange interaction dominants when the distance between the oxygen and magnetic ions decreases and their bond angle increases. A comprehensive structural modeling has been carried out by the Rietveld refinement to various structural parameters were calculated which has been corroborated with the static and dynamic magnetic properties. The resonance field of the Er3+doping causes a decrease in the resonance field in all the doped samples. This decrease in the resonance field can be attributed to the weak SEI between the magnetic ions (Fe3+-O- Fe3+) and (Fe3+-O-Er3+) at A and B sites. Further, the morphology, chemical bonding, and optical characteristics have been studied in detail using TEM, FTIR, and UV spectroscopy. The detailed experimental investigation of PEG-coated CoFe2−xErxO4 provides tunable spin dynamics and improves the saturation magnetization, which is a key parameter for spintronics, magneto-opto-electronics, EMI shielding, and supercapacitor applications.

Ferromagnetic resonance in iron tubes deposited on a copper grid

In the work, a composite material, which is an iron coating on a copper microgrid with a mesh size of 50 μm, is investigated. Iron coatings were synthesized by electroless deposition using arabinogalactan as a reducing agent. Samples were investigated using transmission electron microscopy, Mossbauer spectroscopy and ferromagnetic resonance methods. Magnetic anisotropy in the grid plane was studied by measuring the FMR spectra. The results of the study are discussed by modeling the composite as a wireframe system of magnetic tubes.

Characterization of Spin-Orbit Torque Efficiency in Magnetic Heterostructures with Perpendicular Magnetic Anisotropy via Spin-Torque Ferromagnetic Resonance

Characterization of spin-orbit torques (SOTs) in the perpendicular magnetic anisotropy (PMA) system is of great importance for fundamental studies and technological applications in spintronic devices. Here, we report a spin Hall magnetoresistance (SMR) based spin-torque ferromagnetic resonance (ST FMR) study of SOT efficiency in perpendicularly magnetized $\mathrm{W}$/${\mathrm{Co}}_{40}{\mathrm{Fe}}_{40}{\mathrm{B}}_{20}$/$\mathrm{Mg}\mathrm{O}$ structures. A full analysis of the ST FMR spectrum is developed for the PMA sample. A typical ST FMR spectrum of the PMA system shows two resonance modes, i.e., in-plane and out-of-plane magnetization precession modes. By performing modulation of the damping measurement for the in-plane mode, the dampinglike torque efficiency is determined to be \ensuremath{-}0.38, which is consistent with the reference value obtained in samples with in-plane magnetic anisotropy. The dampinglike torque efficiency of \ensuremath{-}0.31 is also obtained from the out-of-plane resonance mode, in which the significant contribution of the spin-pumping-induced inverse spin Hall effect is carefully considered. The obtained values of dampinglike torque efficiency by different means are consistent with each other. The present work provides useful insights to determine the dampinglike torque efficiency of the PMA sample via ST FMR measurements.

Tunable ferromagnetic resonance in coupled trilayers with crossed in-plane and perpendicular magnetic anisotropies

An original approach to tune the ferromagnetic resonance frequency of a soft magnetic Ni80Fe20 (Permalloy = Py) film with in-plane magnetic anisotropy (IMA) based on the controlled coupling to a hard magnetic NdCox film with perpendicular magnetic anisotropy (PMA) through a nonmagnetic Al spacer is studied. Using the transverse magneto-optical Kerr effect (T-MOKE), alternating gradient magnetometry (AGM), and vector network analyzer ferromagnetic resonance (VNA-FMR) spectroscopy, the influence of both the Co concentration and the Al spacer thickness on the static and dynamic magnetic properties of the coupled IMA/PMA system is investigated. Compared to a single Py film, two striking effects of the coupling between IMA and PMA layers can be observed in their FMR spectra. First, there is a significant increase in the zero-field resonance frequency from 2.0 GHz up to 6.4 GHz, and second, an additional frequency hysteresis occurs at low magnetic fields applied along the hard axis. The maximum frequency difference between the frequency branches for increasing and decreasing magnetic fields is as high as 1 GHz, corresponding to a tunability of about 20% at external fields of typically less than ±70 mT. The origin of the observed features in the FMR spectra is discussed by means of magnetization reversal curves.

FMR and Magnetic Studies of RF-Sputtered Mn-Zn Ferrite Thin Films

The Manganese–Zinc ferrite (MZF) thin films were deposited on quartz substrates by radio frequency (RF) magnetron sputtering at 10 mTorr of argon gas pressure. The FMR and magnetization measurement were carried out to understand magnetic properties of the as-deposited and annealed MZF films. The resonance field (Hr) of the FMR spectra shifts towards higher magnetic field when angle between applied field and thin film plane is changed from 0 to 90° indicating the existence of uniaxial anisotropy in the film. Whereas, Hr shifts towards lower magnetic field with decrease in temperature of the film. This is due to ferrimagnetic ordering in the films at low temperatures. The magnetization versus field (M-H) plots reveal the soft ferrimagnetic behavior of the films. The post-deposition annealing of the film leads to increase in crystallite size with more uniform film surface and dense columnar growth compared to the as-deposited film. The increase in magnetization and decreases in Hr-values compared to that of as-deposited film are observed for annealed film. The optical band gap of the film is also found to increase with annealing.

High microwave absorption characteristic nanomaterial preparation and mechanism analysis

Due to the excellent microwave absorption characteristics, YIG has a broad prospect in microwave application. This paper successfully synthesized YIG nanoparticles with the average size of 68.2 nm. The size uniformity of nanoparticles was verified and calculated by TEM and XRD. Microwave absorption value reached up to -34.5 dB, which was far more than microwave absorption threshold value (−10 dB). The mechanism of high microwave absorption characteristics discovered in the study is derived from four aspects: (a) Multiple scattering and interfacial polarization of YIG nanoparticles on surfaces. (b) High coercivity and high magnetic loss parameters of YIG nanoparticles in the high frequency region. (c) Magnetic loss mechanism and ferromagnetic resonance of YIG. (d) The influence of lesser pinning site caused by smaller grain size. The study found that the fundamental reasons of FMR spectrum asymmetric behavior come from three factors: (І) Nanoparticles random orientation. (П) Different easy axis. (Ш) Non-uniform resonance modes in the process of YIG synthesis. It was observed that microwave absorption markedly reduced due to the influence of skin effect and temperature. The effects of temperature on skin depth and microwave absorption are because of different amounts of excited electrons from the valence band and different magnetic spin configurations. The mechanism of the effect of temperature on the resistance of YIG was discovered, which is derived from electron hoping mechanism, remnant phases influence, the effect of the lattice atoms thermal vibration and skin effect.

Tens of micron-thick, crack-free yttrium iron garnet films on a Gd3Ga5O12 substrate based on the layer by layer growth method

In this paper, the maximum thickness of crack-free yttrium-iron-garnet ferrite film was increased from 7 to 13 µm by layer by layer growth method. Also, the effect of a layer by layer growth method on films morphology, crystal structure and magnetic properties were investigated. X-ray diffraction θ–2θ revealed the orientation of crystal structure could be increased by the layer-by-layer growth method. Scanning electron microscopy and stylus profiler measurement showed the roughness and morphology of film surface were improved efficiently after using the layer-by-layer growth method. Magnetic hysteresis loops and FMR spectrum representing this layer-by-layer growth method could efficiently increase film magnetism and decrease FMR linewidth. Consequently, this innovative method of layer-by-layer growth efficiently provides a pathway to prepare excellent properties, tens of micron-thick, crack-free yttrium iron garnet films and creates unique significance in the electronics industry.

Vector network analyzer ferromagnetic resonance spectrometer with field differential detection.

This work presents a vector network analyzer ferromagnetic resonance (VNA-FMR) spectrometer with field differential detection. This technique differentiates the S-parameter by applying a small binary modulation field in addition to the DC bias field to the sample. By setting the modulation frequency sufficiently high, slow sensitivity fluctuations of the VNA, i.e., low-frequency components of the trace noise, which limit the signal-to-noise ratio of the conventional VNA-FMR spectrometer, can be effectively removed, resulting in a very clean FMR signal. This paper presents the details of the hardware implementation and measurement sequence as well as the data processing and analysis algorithms tailored for the FMR spectrum obtained with this technique. Because the VNA measures a complex S-parameter, it is possible to estimate the Gilbert damping parameter from the slope of the phase variation of the S-parameter with respect to the bias field. We show that this algorithm is more robust against noise than the conventional algorithm based on the linewidth.

Oriented of micron-thick Y3Fe5O12 film on Gd3Ga5O12 substrate based on layer by layer growth method

In this paper, oriented of micron-thick yttrium-iron-garnet ferrite films were deposited on Gd3Ga5O12 substrate by magnetron sputtering based on layer-by-layer growth method. The effect of layer by layer growth method on films morphology, crystal structure and magnetic properties were investigated. X-ray diffraction θ-2θ reveals the maximum thickness of oriented film was increased by layer-by-layer growth method. In addition, scanning electron microscopy displays excellent morphology with uniform size of grain for the film prepared under 2.4 μm@800 nm condition. Magnetic hysteresis loops and FMR spectrum represent this layer-by-layer growth method can effective increase film saturation magnetization and decrease FMR linewidth. Specifically, oriented micron-thick (2.4 μm) YIG film with only 12 Oe of FMR linewidth has been obtained by this layer-by-layer growth method.

Rotational remagnetization and orientational transitions in submicron YIG films

It is shown that for the quasinormal remagnetization of the submicron YIG films with the normal along the [111] axis, which are in the single-domain state, two types of orientation transitions (OT) due to the influence of easy axes can be distinguished. The nonreciprocity of the FMR spectrum for forward and reverse magnetization due to the influence of easy axes is shown.

Electric-field tuning of ferromagnetic resonance in CoFeB/MgO magnetic tunnel junction on a piezoelectric PMN-PT substrate

We investigated the strain-induced modulation of in-plane magnetic anisotropy in single crystal Pb(Mg1/3Nb2/3)0.7Ti0.3O3 (PMN-PT) with a (011) orientation/seed layer/IrMn/CoFeB/MgO/CoFeB/capping layer structure using spin-torque ferromagnetic resonance (ST-FMR) at room temperature. An in-plane biaxial strain is produced by an electric field applied across the substrate, which results in the tuning of the magnetic anisotropy of the CoFeB layer. As the change in the electric field value progresses, the MR loop becomes slanted, indicating the change in the easy axis direction. A strain-induced FMR frequency shift dependence of 145 MHz⋅cm⋅kV−1 is obtained by analyzing the experimental FMR spectra. An analytical model of the potential dynamic mechanism based on the strain induced reorientation of magnetization was discussed. Our results suggest that PMN-PT based magnetic tunnel junctions can have applications in electric-field driven spintronic devices.

Dynamic magnetic permeability of the heterogeneous nanosystems based on (Co41Fe39B20) x (SiO2)100 – x composites

Thin films of (Co41Fe39B20) x (SiO2)100 – x nanocomposites and hybrid nanocomposite–semiconductor [(Co41Fe39B20) x (SiO2)100 – x /C]50 multilayers are synthesized by ion-beam deposition at various contents x of ferromagnetic metallic Co41Fe39B2O nanogranules in an SiO2 matrix and at various carbon layer thicknesses h < 2 nm. Their magnetic and electrical properties, high-frequency magnetic permeability, magnetooptical spectra, and FMR spectra are studied. It is found that both the single-layer nanocomposites and the multilayers with carbon interlayers are superparamagnetic at x < x per, where x per is the electric conduction percolation threshold: a hysteresis at room temperature is absent, and the blocking temperature determined in quasi-static measurements does not exceed 20–30 K and weakly depends on the carbon layer thickness. At a carbon layer thickness h = 1.2–1.8 nm, the real and imaginary parts of complex magnetic permeability at 50 MHz and room temperature are substantially higher than those of the nanocomposites without carbon layers: their values are typical of ferromagnets. This dependence points to an exchange interaction between nanogranules in layers through a carbon interlayer. The influence of a conducting layer on the static and dynamic magnetic properties of a system of interacting superparamagnetic particles is discussed.

Structure and Magnetic Properties of Hydrothermal-Treated Cu–Zn Ferrite/CuO Multilayers

The Cu0.8Zn0.4Fe2O4 ferrite/CuO multilayers (CZF ML) were obtained by RF sputtering. These ML were given hydrothermal heat treatment for phase stabilization. The X-ray diffraction pattern show the CZF spinel ferrite phase in all the multilayered films. The CuO-monoclinic phase appeared as the number of CuO layers (n) increased. The field emission electron micrographs show clear nonmagnetic (NM) CuO separations with columnar growth structure for the multilayers. The micrographs in surface view show uniform cluster distribution. The magnetization (M(H)) plots at 80 and 300 K show anisotropy as a function of angle between applied field (H) and ML surface. The oscillatory magnetization behavior is observed for H perpendicular to ML surface. It is more pronounced when H is perpendicular to ML surface than when it is parallel to it. At low temperature, the increased saturation magnetization is observed due to ferromagnetic cluster formation. The structural-induced magnetic anisotropy is verified using FMR spectra of the ML films with a number of NM separations.

Thickness dependent structural, magnetic and magneto-dynamic properties of Mn rich Ni-Mn-Sn films

Off-stoichiometric Mn-rich Ni-Mn-Sn films of different thicknesses were deposited on Si (100) substrate by dc magnetron sputtering at ambient temperature and then annealed ex situ at 550 °C for 1 h under high vacuum. X-ray diffraction patterns revealed that as deposited films were amorphous, whereas the annealed films exhibited room temperature cubic structure with space group Fm3¯m (space group 225) with high degree of L21 ordering. Magnetic study of the annealed film disclosed room temperature ferromagnetic order with easy axis of magnetization along the plane of the film. Magneto-dynamic study of the annealed films was carried out using a micro strip-ferromagnetic resonance (FMR) spectrometer. The deduced values of saturation magnetization from frequency dependence of the resonance field of the FMR spectra were in close agreement with those obtained from dc magnetization measurement. The analysis of frequency variation of linewidth shows the presence of low Gilbert damping constant of 0.007 for the 500 nm thick film. Gilbert damping constant was found to increase slightly with film thickness. The polar angle variation FMR study for 1500 nm film revealed the presence of high effective perpendicular anisotropy (K1 ≈ −9.0 ± 0.5 × 105 erg/cm3) and easy magnetization along its plane.

Theoretical formalism for collective spin-wave edge excitations in arrays of dipolarly interacting magnetic nanodots

A general theory of edge spin wave excitations in semi-infinite and finite periodic arrays of magnetic nanodots existing in a spatially uniform magnetization ground state is developed. The theory is formulated using a formalism of multi-vectors of magnetization dynamics, which allows one to study edge excitations in arrays having arbitrary complex primitive cells and lattice geometry. The developed formalism can describe edge excitations localized both at the physical edges of the array and at the internal "domain walls" separating array regions existing in different static magnetization states. Using a perturbation theory in the framework of the developed formalism it is possible to calculate damping of edge modes and their excitation by external variable magnetic fields. The theory is illustrated on the following practically important examples: (i) calculation of the FMR absorption in a finite nanodot array having the shape of a right triangle, (ii) calculation of nonreciprocal spin wave spectra of edge modes, including modes at the physical edges of an array and modes at the domain walls inside an array, (iii) study of the influence of the domain wall modes on the FMR spectrum of an array existing in a non-ideal chessboard antiferromagnetic ground state.