Ferromagnetic Resonance Signal Research Articles

Bi2O2.33/Bi4O5I2-heterojunction photocatalysts for adsorption and visible light-driven degradation of pharmaceutical pollutants

This study introduces the innovative Bi4O5I2/Bi2O2.33 heterojunction for diclofenac (DF) degradation. Pharmaceutical pollutants, especially DF, pose significant threats to water sources, necessitating efficient treatment methods. Bi2O2.33, renowned for its unique ferromagnetic properties, emerges as a promising photocatalyst for pollutant degradation. Bi4O5I2, known for strong visible light absorption and stability, holds potential for environmental applications. Interestingly, the inclusion of titanium dioxide (TiO2) in the composite catalysts significantly influences their observed ferromagnetic properties, as revealed by Electron Paramagnetic Resonance (EPR) spectroscopy, by influencing the interactions within the Bi4O5I2/Bi2O2.33 heterojunction and influencing its structure, morphology, and spin behavior. This interaction results in enhanced EPR and Ferromagnetic Resonance (FMR) signals, indicating intriguing spin interactions, polarization effects, charge transfers, surface dynamics, and stabilized magnetic domains. While the enhanced ferromagnetism holds promise for efficient charge separation and potential applications in environmental remediation, the expected boost in visible light-driven activity was not fully realized. This limitation is attributed to TiO2 inherent inability to directly absorb visible light, hindering its utilization for enhanced photocatalysis within the heterojunction. Nevertheless, these findings elucidate the multifaceted role of TiO2 in modulating the magnetic properties of these catalysts, offering valuable insights for future advancements in the design of advanced photocatalysts for effective environmental remediation.

Large-angle analytical solution of magnetization precession in ferromagnetic resonance

Abstract Dynamics of magnetization M driven by microwave are derived analytically from the nonlinear Landau-Lifshitz-Gilbert equation. Analytical M and susceptibility are obtained self-consistently under a positive circularly polarized microwave field, h=(hcosωt,hsinωt,0), with frequency ω, which is perpendicular to a static field, H=(0,0,H). It is found that the orbital of M is always a cone along H. However, with increasing h the polar angle θ of M initially increases, then keeps 90° when h≥h 0=αω/γ in ferromagnetic resonance (FMR) mode, where α is Gilbert damping constant and γ is gyromagnetic ratio. These effects result in a nonlinear variation of FMR signal as h increases to h≥h 0, where the maximum of resonance peak decreases from a steady value, linewidth increases from a decreasing trend. These analytical solutions provide a complete picture of the dynamics of M with different h and H.

Magnetic properties of polycrystalline bulk crystals of MnGeP2

Room temperature ferromagnetism observed in polycrystalline MnGeP2 bulk samples was investigated by different experimental techniques. The magnetization measurements show a high temperature ferromagnetic phase with a critical temperature TC = 294.0 K and a low temperature magnetic phase transition at TN = 40.5 K. As these parameters (TC,TN) correspond to those of MnP, a ferromagnetic half-metal, whose composition of the samples was further characterized by x-ray diffraction and Rutherford backscattering measurements. They confirmed the presence of orthorhombic MnP precipitates. Electron paramagnetic resonance (EPR) and ferromagnetic resonance (FMR) measurements in the temperature range of T = 4 K to T = 380 K confirm the attribution of the magnetic phase to MnP and show no additional EPR or FMR signal associated with MnGeP2. We conclude that the magnetic properties of the polycrystalline MnGeP2 bulk samples grown by the horizontal gradient freeze technique are dominated by MnP inclusions and that phase pure chalcopyrite MnGeP2 is not ferromagnetic in contrary to previous reports.

Spin dynamics investigation and structural analysis of ambient scalable Sr2+ doped zirconium ferrite nanoparticles synthesized by low temperature auto combustion route

Microwave spin resonance behaviour of Sr2+ doped Zirconium ferrite Zr1-xSrxFe2O4; (0 ≤ x ≥ 0.20) nanoparticles synthesized by auto combustion route has been investigated by electron paramagnetic resonance (EPR) which show a broad ferromagnetic resonance signal with a superimposed hump signal which is attributed to ferrite Fe3+ ions and oxygen vacancies which is in agreement with XRD and XPS. EPR shows low spin concentration and smaller relaxation time for Zr0.80Sr0.20Fe2O4 which can be used for hyperthermia and for use as a MRI contrast agent. EDS and XPS confirms the presence of Zr, Sr, Fe, O, and C and HRTEM images confirm growth along (220) and (311) with an interatomic distance of 0.3327 nm and 0.2622 nm respectively, thus, authenticating the formation of spinel structure in agreement with FTIR studies. The magnetic behaviour (M − H loop) shows high saturation magnetization and higher value of effective magnetocrystalline anisotropy (Keff) for Zr0.80Sr0.20Fe2O4.

Osobennosti povedeniya linii epr (<i>g </i>≈ 4<i>.</i>3) v magnitnykh nanogranulyarnykh kompozitakh

Films of metal-insulator nanogranular composites MxD100 – x with different composition and percentage of metal and dielectric phases (M = Fe, Co, CoFeB; D = Al2O3, SiO2, LiNbO3; x ≈ 15–70 at %) are investigated by magnetic resonance in a wide range of frequencies (f = 7–37 GHz) and temperatures (T = 4.2–360 K). In addition to the usual ferromagnetic resonance signal from an array of nanogranules, the experimental spectra contain an additional absorption peak, which we associate with the electron paramagnetic resonance (EPR) of Fe and Co ions dispersed in the insulating space between the granules. In contrast to the traditional EPR of Fe and Co ions in weakly doped non-magnetic matrices, the observed peak demonstrates a number of unusual properties, which we explain by the presence of magnetic interactions between ions and granules.

Dzyaloshinsky–Moriya Interaction Induced Anomalous g Behavior of Sr2IrO4 Probed by Electron Spin Resonance

Among the 5d transition metal iridates, Sr2IrO4, which has a layered chalcogenide structure, has received much attention due to its strong spin–orbit coupling (SOC), which produces Mott insulating states and anomalous physical behaviors. In this paper, the microscopic magnetism of Sr2IrO4 is studied with electron spin resonance (ESR) measurements. The Lande factor g of the ferromagnetic resonance signal of Sr2IrO4 shows anomalous behavior compared to typical ferromagnets. It gradually decreases, and the corresponding resonance field Hr increases, with decreasing temperature. The various physical parameters. including the saturated magnetic field Hs derived from M-H, Hr, ΔHpp, the g factor and the intensity I extracted from ESR spectra, are analyzed in detail. Eventually, it is revealed that the anomalous behavior of the g-factor is induced by in-plane Dzyaloshinsky–Moriya interaction (DMI) rather than the SOC effect.

Mechanical and Magnetic Investigations of Balls Made of AISI 1010 and AISI 1085 Steels after Nitriding and Annealing

This paper discusses the changes in the phase composition and magnetic properties of the AISI 1010 and AISI 1085 steels that were nitrided at 570 °C in an ammonia atmosphere for 5 h and that were then annealed at 520 °C in a N2/Ar atmosphere for 4 h. The test samples were made in the form of balls with diameters of less than 5 mm. The thickness of the obtained iron nitride layers was assessed through metallographic tests, while the phase composition was verified through X-ray tests. The magnetic properties were determined using ferromagnetic resonance (FMR) and superconducting quantum interference device (SQUID) techniques. Our research shows that, during the annealing of iron nitrides with a structure of ε + γ′, the ε phase decomposes first. As a result of this process, an increase in the content of the γ′ phase of the iron nitride is observed. When the ε phase is completely decomposed, the γ′ phase begins to decompose. The observed FMR signals did not come from isolated ions but from more magnetically complex systems, e.g., Fe–Fe pairs or iron clusters. Studies have shown that nitriding and annealing can be used to modify the magnetic properties of the tested steels.

Ferromagnetic resonance excited by interfacial microwave electric field: the role of current-induced torques

Excitation of magnetization dynamics in magnetic materials, especially in ultrathin ferromagnetic films, is of utmost importance for developing various ultrafast spintronics devices. Recently, the excitation of magnetization dynamics, i.e. ferromagnetic resonance (FMR) via electric field-induced modulation of interfacial magnetic anisotropies, has received particular attention due to several advantages, including lower power consumption. However, several additional torques generated by unavoidable microwave current induced because of the capacitive nature of the junctions may also contribute to the excitation of FMR apart from electric field-induced torques. Here, we study the FMR signals excited by applying microwave signal across the metal-oxide junction in CoFeB/MgO heterostructures with Pt and Ta buffer layers. Analysis of the resonance line shape and angular dependent behavior of resonance amplitude revealed that apart from voltage-controlled in-plane magnetic anisotropy (VC-IMA) torque a significant contribution can also arises from spin-torques and Oersted field torques originating from the flow of microwave current through metal-oxide junction. Surprisingly, the overall contribution from spin-torques and Oersted field torques are comparable to the VC-IMA torque contribution, even for a device with negligible defects. This study will be beneficial for designing future electric field-controlled spintronics devices.

산화철 나노입자의 결합 모양에 따른 강자성 공명 신호 분석

산화철 나노입자는 고온 열분해법을 이용하여 제조하였으며, 2차원 나노입자 박막 재료의 FMR 신호를 측정하여 산화철 나노입자의 유효 포화자화 MSUBeff/SUB = 202 emu/cc와 g-factor = 2.12를 얻었다. 나노입자를 포함하고 있는 최종 반응 원액의 강자성 공명 신호를 분석하기 위하여 자성 재료의 모양에 따른 Kittel의 강자성 공명 조건을 활용하였다. 반응 원액의 강자성 공명신호는 두 개의 신호로 분리되어 나타났다. 하나는 초상자성에 의한 신호였고, 다른 하나는 1차원 체인(chain) 구조를 갖는 나노입자들에 의한 신호임을 알 수 있었다.

Transport and electron spin resonance studies in Mo-doped LaMnO3

We report the magnetic, electrical, thermoelectric, and magnetic resonance properties of the Mn-site doped manganite LaMn0.94Mo0.06O3. This sample undergoes an insulator-metal transition around 235 K, near the ferromagnetic Curie temperature (TC = 237 K) in zero external magnetic field. On the other hand, thermopower exhibits a maximum at TS = 258 K, which is 23 K higher than TC. This discrepancy is attributed to nucleation of ferromagnetic clusters (Griffiths phase) above TC, which is supported by the deviation of inverse susceptibility from Curie-Weiss from linear behavior below 270 K and non-linear field dependence of magnetization. The magnetic resonance spectra shows both paramagnetic and ferromagnetic resonance signals between 240 and 260 K. It is suggested that the ferromagnetic clusters enlarge in size with lowering temperature and percolate leading to long-range ferromagnetism and metallicity.

Local Ferromagnetic Resonance Measurements of Mesoscopically Patterned Ferromagnets Using Deterministically Placed Nanodiamonds

Nitrogen-vacancy centers in diamond have recently been established as effective sensors of the magnetization dynamics in vicinal ferromagnetic materials. We demonstrate sub-100 nm placement accuracy of nitrogen-vacancy-containing nanodiamonds and use these as local sensors that probe optically detected ferromagnetic resonance in mesoscopically patterned Permalloy islands. These measurements reveal variations in the ferromagnetic resonance signal at different sites on these structures with distinct behavior in the edge and the bulk of patterned features. These test measurements establish an easily implemented approach for spatially targeted measurements of spin dynamics in mesoscale ferromagnets. In principle, the methodology can also be extended to local studies of nanoscale ferromagnets such as single magnetic nanowires and nanoparticles.

Magnetic Properties of La0.81Sr0.19Mn0.9Fe0.1−xZnxO3 (x = 0, x = 0.05)

Magnetic properties of polycrystalline La0.81Sr0.19Mn0.9Fe0.1−xZnxO3 (x = 0, 0.05) have been investigated by means of electron spin resonance, magnetic susceptibility, and Mössbauer measurements. Both samples show a clear ferromagnetic transition. The Curie temperature TC decreases on increasing Fe content (x = 0.05—TC = 222 K; x = 0—TC = 148 K). Mössbauer studies indicate that Fe in these compounds is in the trivalent high-spin state. The temperature evolution of the Mössbauer spectra at low temperatures (T < TC) is typical for ferromagnetic clusters with a wide distribution in size and magnetic correlation length. The inverse susceptibility of all the samples deviates from the Curie–Weiss law above TC, indicating the presence of fluctuations on approaching magnetic order. An anomalous downturn of the inverse susceptibility for x = 0.05 significantly above TC and the concomitant observation of ferromagnetic resonance signals coexisting with the paramagnetic resonance up to approximately room temperature, is caused by a Griffiths-like behavior. This regime is characterized by the coexistence of ferromagnetic entities within the globally paramagnetic phase.

Origin of high-frequency magnetic loss of Y3Fe5O12 single crystal thin films prepared with high-throughput screening by magnetron sputtering

In this study, yttrium iron garnet (Y3Fe5O12, YIG) single crystal nanofilms were deposited at room temperature on a Gd3Ga5O12 (GGG) (111) substrate via magnetron sputtering and ex situ annealing. A high-throughput method was used to systematically study the effects of sputtering gas pressure, sputtering power, and annealing temperature on the microstructure, ferromagnetic resonance signal, and high-frequency magnetic loss. The YIG films fabricated at an Argon pressure of 3 Pa, a sputtering power of 95 W, and an annealing temperature of 800 °C possessed the highest saturation magnetization and lowest linewidth (13.6 Oe). Furthermore, the maximum value of permeability (μ′) was 25.54 under an applied field Hex = 30 Oe of the YIG/GGG (111) film for the first time. In addition, the sources of the high-frequency magnetic loss in the YIG film were investigated. In detail, the roughness, thickness, and polycrystalline structure, along with the existence of oxygen vacancies and anisotropic fields, influenced the linewidth of the film. This study provides a method to prepare single-crystalline YIG films via room-temperature deposition and ex situ annealing for potential applications in high-frequency microwave devices.

Current-induced perpendicular effective magnetic field in magnetic heterostructures

The generation of perpendicular effective magnetic field or perpendicular spins (σz) is central for the development of energy-efficient, scalable, and external-magnetic-field-free spintronic memory and computing technologies. Here, we report the first identification and the profound impacts of a significant effective perpendicular magnetic field that can arise from asymmetric current spreading within magnetic microstrips and Hall bars. This effective perpendicular magnetic field can exhibit all the three characteristics that have been widely assumed in the literature to “signify” the presence of a flow of σz, i.e., external-magnetic-field-free current switching of uniform perpendicular magnetization, a sin 2φ-dependent contribution in spin-torque ferromagnetic resonance signal of in-plane magnetization (φ is the angle of the external magnetic field with respect to the current), and a φ-independent but field-dependent contribution in the second harmonic Hall voltage of in-plane magnetization. This finding suggests that it is critical to include current spreading effects in the analyses of various spin polarizations and spin–orbit torques in the magnetic heterostructure. Technologically, our results provide a perpendicular effective magnetic field induced by asymmetric current spreading as a novel, universally accessible mechanism for efficient, scalable, and external-magnetic-field-free magnetization switching in memory and computing technologies.

Voltage Signals Caused by Surface Acoustic Wave Driven Ferromagnetic Resonance Under Out‐of‐Plane External Fields

AbstractUnder an external magnetic field, surface acoustic waves (SAWs) propagating onto a ferromagnetic thin film can excite ferromagnetic resonance (FMR). The magnetization precessional motion in resonance pumps spin current into the Rashba interface across an adjacent non‐magnetic layer, which can be converted to charge current via the inverse Edelstein effect (IEE). Here, the SAW‐driven FMR and the IEE voltage signals under in‐ and out‐of‐plane external magnetic fields are reported. When the external magnetic field has only an in‐plane component, the SAW‐driven FMR for positive and negative resonant fields have the same sign (even), while the spin‐conversion due to IEE results in voltage signals with opposite signs for positive and negative fields (odd). However, when the out‐of‐plane component of the external magnetic field increases, the acoustic ferromagnetic resonance signal remains even. In contrast, the IEE voltage signal exhibits a sum of even and odd signal contributions. It is discussed that the appearance of the even contribution to the voltage signal does not correspond to well‐known spin rectification mechanisms. The result may constitute a novel resonant spin rectification mechanism under SAW excitations.

Charge-to-spin conversion in Bi/Ag bilayer investigated by spin-torque ferromagnetic resonance

The charge-to-spin conversion in Bi/Ag bilayer is studied by spin-torque ferromagnetic resonance experimentally. Fe and permalloy layers sandwich the Bi/Ag bilayer in a multilayer structure, which allows the injection of spin current generated in the Bi/Ag bilayer into the two ferromagnetic layers from opposite directions. The spin Hall effect and the Rashba–Edelstein effect in Bi/Ag are expected to show qualitatively different spin-torque ferromagnetic resonance signals in such a setup. The results show the dominant contribution from the spin Hall effect rather than the Rashba–Edelstein effect, consistent with our recent finding of the spin-to-charge conversion in Bi/Ag bilayer (Shen et al., 2021).

Application of a Microfabricated Microwave Resonator in a Co - Pd –Based Magnetic Hydrogen-Gas Sensor

We investigate the ferromagnetic resonance (FMR) response of microfabricated microwave resonators loaded with small ${\mathrm{Co}}_{16}{\mathrm{Pd}}_{84}$ alloy rectangles. A major increase in the FMR signal-to-noise ratio is achieved by employing the microwave-resonator structure. A FMR peak shift similar to that of ${\mathrm{Co}}_{16}{\mathrm{Pd}}_{84}$ continuous films is measured in the presence of hydrogen gas in the sample environment. We show that the very high sensitivity of the FMR signal of the ${\mathrm{Co}}_{16}{\mathrm{Pd}}_{84}$ alloy rectangle to hydrogen exposure can be used to measure relatively small hydrogen-concentration steps near 100% ${\mathrm{H}}_{2}$. Additionally, we also demonstrate that this structure can measure hydrogen over a concentration range from 3% to 100% ${\mathrm{H}}_{2}$ in ${\mathrm{N}}_{2}$. In time-dependent FMR measurements, we discover a temperature dependence of the FMR signal, which we relate to intrinsic temperature-dependent changes in saturation magnetization and the magnetic anisotropy of the $\mathrm{Co}$-$\mathrm{Pd}$ alloy.

Spin rectification by planar Hall effect in synthetic antiferromagnets

We study spin rectification effects in NiFe/Ru/NiFe synthetic antiferromagnets at the saturated, non-collinear and antiparallel magnetic states. The change in magnetization orientation at these states allows us to study the angle dependence of spin rectification phenomena by only changing the applied field. This approach avoids the need of changing the sample orientation within the experiment for this kind of studies. Our results show large planar Hall effect contributions to the measured spin rectified voltage with interesting features in the non-collinear and antiparallel states, which bring new possibilities for device design and applications. The results improve the understanding of electrically detected ferromagnetic resonance signals, not only for synthetic antiferromagnets, but also for other samples where the signals coming from the anisotropic magneto resistance effect and the inverse spin hall effect are superimposed.

Applying the FMR Technique to Analyzing the Influence of Nitriding on the Magnetic Properties of Steel.

This paper presents the relationship between the chemical composition and size of steel balls, the parameters of the nitriding process, and their magnetic properties, defined in this study by ferromagnetic resonance (FMR) and SQUID. Balls made from AISI 1010 and AISI 52100 steels, with diameters of 2.5 and 3 mm, respectively, were investigated. On samples made of AISI 1010 and AISI 52100 steel, single-phase layers of iron nitrides γ’ with a thickness of gmp = 50 and 37 μm, respectively, were produced. Then, the samples were annealed at a temperature of 520 °C for 4 h in an inert atmosphere (N2/Ar) at a pressure of 200 Pa. After the nitriding processes, steel balls were subjected to standard physical metallurgy and X-ray examinations. During annealing of nitrided layers with a two-phase layer of iron nitrides, at first, the transformation of the ε phase into the γ’ phase with the release of nitrogen into the atmosphere takes place. The FMR signals did not originate from isolated ions, but from more magnetically complex systems, e.g., Fe–Fe pairs or iron clusters, while the observed FMR line position is normally even lower and occurs for a magnetic induction below 200 mT. The fact that the magnetic centers did not contain mainly isolated Fe ions, additionally confirmed the abnormal increase in resonance signal intensity as a function of temperature, which is a behavior inconsistent with the Curie–Weiss law. The results obtained from measurements by the SQUID method, recording variations in magnetization as a function of temperature, confirm the untypical reinforcement of the magnetic conditions of the samples with the increase in temperature. For the samples tested, the magnetization was relatively weaker when the tests were conducted in a stronger magnetic field.

Annealing enhanced ferromagnetic resonance of thickness-dependent FeGa films

We report the influence of different annealing temperatures on the magnetic property of FeGa thin films. The measurement was done for the film thickness from 42 to 420 nm. Our results show that the annealing temperature affects not only the microstructure but also the ferromagnetic resonance signal of the film. Annealing of a FeGa film improves the in-plane remanence ratio and reduces the in-plane ferromagnetic resonance linewidth by a factor of five. This annealing treatment promotes film texture and releases compressive stresses in the film. Our results demonstrate that the structural control via annealing is viable. The necessary magnetic softness of the FeGa film for microwave applications can be achieved.