Microwave Ferromagnetic Resonance Research Articles

Novel synthesis of CuFe2O4/g-C3N4 based on microwave ferromagnetic resonance effect for the thorough removal of TC in mariculture wastewater under natural sunlight

Superior separation of photogenerated carriers holds the key to intensive degradation of tetracycline (TC) in mariculture wastewater under natural sunlight. CuFe2O4/g-C3N4 (CFO/g) was synthesized by secondary microwave co-precipitation (SMCP) based on the ferromagnetic resonance absorption effect. Under the reaction conditions of pH = 6.5, CFO/g = 0.2 g/L, [H2O2] = 1 mM, 99.0 % TC removal was realized in 40 min. Enhanced performance for TC removal in high-salinity environments heavily relied on elevated ionic strength and rapid electron transfer of CFO/g in conjunction with high-salinity interactions. To ecologically remediate mariculture wastewater under natural sunlight, we immobilized powdered CFO/g to a ferrite magnet and devised a continuous flow reaction apparatus, incorporating the controlled injection of hydrogen peroxide (H2O2), to achieve the 100 % TC removal and simultaneously undertake the pretreatment of other contaminants (∼70 %). Ultimately, a safety assessment demonstrated that the degradation of mariculture wastewater by the CFO/g photo-Fenton system is a reliable and efficient technology, and the growth of clownfish remained unimpaired. SMCP successfully accelerated the conversion of high-valent metal ions to low-valent ones and eased the activation barriers of H2O2, enabling various active species to execute their respective roles productively. Innovative application of microwave resonance to enhance the magnetic properties of CFO/g and to support the equilibrium conversion of elemental valence states in high-salinity environments from real wastewater.

Special features of low-temperature microwave ferromagnetic resonance in nanometer ferrite layer patterned by macroporous silicon substrate

Experimental magnetic resonance spectra for nanometer ferrite brand 1SCh4 layer deposited on macroporous silicon substrate, obtained at T = 300 and 4.2 K in the frequency ranges of 5–15 and 60–75 GHz, respectively, were analyzed. In addition to the ferromagnetic resonance mode, additional peaks were found in the magnetoresonance spectra. An analysis using the known theoretical concepts of the modern spin dynamic theory, together with the results of micromagnetic simulation, showed the formation of spin-wave oscillation modes that arise due to the structurization of the ferrite layer by a substrate of macroporous silicon.

Bending Switch of Gigahertz La0.67Sr0.33MnO3 Thin Film Under Spin Wave Excitation

Spin waves, used for information processing and transmission, promise huge potential in the applications of the spintronic devices with low loss, minimal sizes, and high frequency. More attentions have been focused on all-magnon data processing utilizing traveling spin waves and moving domain walls. Bending control of spin wave is an effective modulation method for magnetic properties, and easily attuned to the trends of flexible magnon spintronics in future. In this work, we demonstrate the excitation of spin waves in the flexible La0.67Sr0.33MnO3 thin film by mechanical bending, which can be taken as the states for On and Off in microwave single-pole single-throw switches. Besides, the microwave magnetisms of the unbent and bending La0.67Sr0.33MnO3 thin films have been studied. The bending of La0.67Sr0.33MnO3 thin films does not change the microwave ferromagnetic resonance field. Our results demonstrate that the controllable spin wave state by mechanical bending has enormous potential for future flexible magnon spintronics.

Enhanced Detection of Magnetic Nanoparticles Using a Novel Microwave Ferromagnetic Resonance Imaging System

For this proof of concept, the chamber has been equipped with four wire monopole antennas, and low-contrast oil-based targets have been tested with varying concentrations of iron oxide magnetic nanoparticles (MNP) to serve as ferromagnetic contrast agents. The electromagnet is capable of sustaining a static polarizing magnetic field (PMF) greater than 0.2Tesla (2000Gauss) across the imaging chamber to modulate the MNPs' ferromagnetic response, effectively changing the targets' magnetic permeability. Differential scattered field data are then collected through the application and withdrawal of this PMF. This study has successfully characterized a particular narrow band of frequencies within the asymmetric faceted chamber that demonstrate significant differential responses corresponding to the weak magnetic signal physically isolated from the MNPs, tested on different sizes and positions of targets containing various concentrations of MNPs. Similar to ferromagnetic resonance (FMR) spectroscopy, in which detection of FMR phenomena is best achieved at probing frequencies coinciding with the structural resonant frequency of a metallic cavity, these resonant frequencies of interest yield a high level of sensitivity to MNP permeability changes and are suitable for imaging within the chamber. These represent the first experimental results of a full-scale FRI system capable of detecting and eventually imaging MNPs at biologically relevant concentrations.

Spin orientation driven static and dynamic magnetic process in amorphous FeCoBSi thin films

The spin orientation dependence of magnetic hysteresis and microwave ferromagnetic resonance data are investigated in FeCoBSi amorphous thin films. Demagnetization effect allows the weak interface-rooted out-of-plane anisotropy to build up local spin orientation domains under the dominant in-plane anisotropy. As a result, two phase magnetization reversal and double-peak ferromagnetic resonance traces with varying damping behavior are observed. Due to the distribution of in-plane and out-of-plane spin orientations, the ferromagnetic resonance bandwidth has been extensively expanded with the full width at half maximum increased from 1.2 GHz to 3.5 GHz.

Evolution of microwave ferromagnetic resonance with magnetic domain structure in FeCoBSi antidot arrays

Magnetic domain structure of FeCoBSi antidot array thin films of varying thickness were characterized using surface magneto-optic Kerr effect. Vibrating sample magnetometry and microstrip transmission line measurements helped to associate the microwave magnetic analysis of the antidot arrays with hysteresis studies. The domain structure evolution from quasi-continuous domains to strip domains induced by the competing exchange and dipolar interaction resulted in the change of ferromagnetic resonance from multi-band to single-band. Hence, the mechanisms of multi-resonance are proposed to be related to domain wall motion, natural resonance and spin wave modes. This phenomenon can be used to control the magnetization dynamics in spin wave devices.

Enhanced microwave ferromagnetic resonance absorption and bandwidth using a microstrip meander line with step-impedance low-pass filter in a yttrium iron garnet–gallium arsenide layer structure

Simulations of the step-impedance low-pass filter (LPF) in gallium arsenide (GaAs) substrate show that, in contrast to a 50Ω microstrip, the magnetic fields of the propagating microwaves are heavily concentrated in its inductive elements. The concentrated local magnetic fields facilitate enhanced coupling into an yttrium iron garnet/gadolinium gallium garnet layer over the GaAs substrate and, thus, significantly increase the microwave power absorptions at the ferromagnetic resonance (FMR) frequencies. The large tunable range of FMR frequency and the corresponding S21 and S11 parameters measured have verified the simulation results. Simultaneous enhancement of FMR absorption level and widening of absorption bandwidth has been accomplished in a band-stop filter that utilizes a microstrip meander line with four identical step-impedance LPFs, each of 5.70mm long, inserted in a nonuniform bias magnetic field. A tunable FMR absorption frequency range of 5–21GHz, an absorption level of −35.5dB, and a corresponding 3dB absorption bandwidth as large as 1.70GHz, centered at 20.3GHz, have been demonstrated.

Microwave ferromagnetic resonance of cobalt and nickel substituted U-type hexaferrites

This paper presents accurate broad-band data on the complex relative permittivity (/spl epsiv/=/spl epsiv/'-j/spl epsiv/) and complex relative permeability (/spl mu/=/spl mu/'-j/spl mu/'') of two U-type hexaferrites. These hexaferrites have a general molecular formula of Ba/sub 4/Me/sub 2/Fe/sub 36/O/sub 60/ where Me is a bivalent transition-metal. In this work, Me=Co, Ni. In this paper, the dielectric and magnetic properties of these two U-type hexaferrites, Co/sub 2/U and Ni/sub 2/U, are investigated because of the potential applications of such ferrite materials in microwave devices. The dielectric and magnetic properties are obtained via the transmission-reflection technique. For Co/sub 2/U, the complex relative /spl epsiv/ and /spl mu/ are obtained from 12.4 GHz-18.0 GHz and for Ni/sub 2/U, the complex relative /spl epsiv/ and /spl mu/ are obtained from 18.0 GHz-40.0 GHz.

Nonlinear dynamics in microwave driven coupled magnetic multilayer systems

Conventional microwave ferromagnetic resonance (FMR) techniques have proven very useful in the investigation of coupled magnetic multilayer systems. Here we show theoretically that with sufficiently high powers, a microwave magnetic field applied either parallel or perpendicular to the dc field, can drive nonlinear effects. The Landau–Lifschitz equation is used to obtain the nonlinear equations of motion for the two normal modes of a coupled two-layer system. In the usual FMR configuration, only the acoustic mode is coupled to the driving field. However, for driving fields above a critical value, energy can be transferred to the optic mode, in a process similar to the subsidiary resonance observed in spin-wave systems. At higher driving the system may display well-known transitions to chaos.

A comparative study of FMR and Brillouin light scattering on FeNiB alloys

The magnetization and the g-factor of amorphous Fe 40Ni 40B 20 alloys have been determined by both microwave ferromagnetic resonance, operating at different frequencies, and Brillouin light scattering. All measurements have been performed at the same spot of the same sample in order to compare both techniques. We have found systematic differencies in the magnetization M from the results of FMR and Brillouin scattering experiments. The magnetization determined by Brillouin scattering tends to be 5% lower than that determined by FMR.

Direction dependence of microwave ferromagnetic resonance transmission along the surface of Fe-Si-B foils

Microwave transmission along the surface of metal-metalloid foils was examined with a ferromagnetic resonance transmission spectrometer, and a dependence on the static and microwave magnetic field directions was observed. The resonant transmission of microwave radiation depended strongly on the angle between the direction of the static magnetic field and that of the fine grooves running along the surface of the sample. The transmission intensity was a maximum when the static magnetic field was parallel to the grooves. It also depended on the relation between the directions of the static and the microwave magnetic fields.

Spin-wave turbulence

A high resolution study is made of spin-wave dynamics above the Suhl threshold in a sphere of yttrium iron garnet driven by microwave ferromagnetic resonance. In different regions of parameter space observed behavior includes: excitation of a single spatial spin-wave mode at threshold; when two modes are excited, low frequency collective oscillations with a period doubling route to chaos; nonperiodic relaxation oscillations when three modes are excited, quasiperiodic route to chaos; abrupt hysteretic onset of wide-band chaos. These results are accounted for in a unified way by numerical iteration of a model: coupled quantum oscillators representing the photons of the cavity and the magnons, including four-magnon scattering processes.

Microwave resonance and propagation in nonsaturated ferromagnetic media. I. Magnetic resonance in single crystal ferrite platelets

We present calculations of the magnetic resonance frequencies of multidomain single crystal ferrite platelets. The theoretical results are compared to our microwave ferromagnetic resonance (FMR) experiments performed at frequencies between 8 and 40 GHz and magnetic fields between 0 and 20 kOe. Good agreement is found between theory and experiment with no adjustable parameters. In the calculation we have included the effect of a change in the periodicity of regularly patterned domain structures on the FMR frequencies. The variation in periodicity is seen to influence the measured FMR frequencies f for magnetic fields H applied normal to the platelet plane in agreement with our calculations. The predicted variation in periodicity agrees with our visual observation of domain structures in the sample. The in-plane FMR data is also in reasonable agreement with calculations. Although the measured frequency and field FMR linewidths agree well with our calculations in magnetically saturating fields, the agreement is less satisfactory in the nonsaturated region.

Brillouin scattering from bulk and surface magnons in amorphous magnetic metals

In this paper we briefly review our recent work on Brillouin scattering from amorphous ferromagnetic metals, particularly our observation of discrete standing spin waves in amorphous Fe80B20. We also present new data on these spin-wave modes, consider the effects of anisotropy on our theoretical fits and compare the results with microwave ferromagnetic resonance measurements.

Ferromagnetic resonance and magnetic anisotropy in Pd Ni (∼ 5 at %)

Microwave ferromagnetic resonance has been observed in a Pd Ni (∼ 5 at % Ni) alloy. Magnetization, “ g” values and anisotropy constants have been derived from these measurements. The sign of K 1 is opposite to that for nickel but the magnetization dependence is closely similar.

Ferromagnetic resonance in dilute binary alloys of Pd and Pt with Fe and Co

Microwave ferromagnetic resonance has been observed in dilute binary alloys of Pd with Fe and Co and Pt with Co. Spectroscopic splitting factors (‘ g’ values), magnetization data, and anisotropy constants have been derived from these measurements.

Magnetic Resonance inK2CuCl4·2H2O

We have observed the microwave electron spin resonance of ${\mathrm{Cu}}^{2+}$ and the proton nuclear magnetic resonance in the temperature range $0.17\ensuremath{\leqq}T\ensuremath{\leqq}4.2\ifmmode^\circ\else\textdegree\fi{}$K and in fields in the range 3 to 6 kOe for single crystals of ${\mathrm{K}}_{2}$Cu${\mathrm{Cl}}_{4}$\ifmmode\cdot\else\textperiodcentered\fi{}2${\mathrm{H}}_{2}$O, an ideal Heisenberg insulating ferromagnet with a Curie temperature ${T}_{c}=1.1\ifmmode^\circ\else\textdegree\fi{}$K. The temperature dependence of the magnetization, as measured by the proton-magnetic-resonance field, is in close agreement with the molecular-field model. The dependence of the microwave ferromagnetic resonance on temperature and sample geometry is in agreement with Kittel's equation. Numerous sharp magnetostatic modes are observed and compared with the theory of Walker. The ferromagnetic resonance line width has a temperature-independent component of a few Oe, and a temperature-dependent component which narrows from 65 to 1 Oe as the temperature varies from 4.2 to 0.7\ifmmode^\circ\else\textdegree\fi{}K. From the observed shift in the ferromagnetic resonance below 0.6\ifmmode^\circ\else\textdegree\fi{}K due to the hyperfine (hfs) field of the copper nuclei, we find that the hfs constant $A=1.5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}2}$ ${\mathrm{cm}}^{\ensuremath{-}1}$. We observe a new type of ferromagnetic resonance induced by a microwave field parallel to the dc field, which we interpret as a "forbidden" hyperfine resonance corresponding to the simultaneous flip of an electron spin and a nuclear spin.

Properties of Single-Crystal Lithium Ferrite Grown in the Ordered State

Lithium ferrite, an inverse spinel with an order-disorder transition at about 800°C, has been grown in the ordered state. The narrowest ferromagnetic resonance linewidth yet observed in a spinel has resulted from the growth of single crystals of lithium ferrite in the ordered state. Details of the growth conditions, magnetization, and microwave ferromagnetic resonance linewidth are presented.

Precise Ferromagnetic Resonance Magnetometers for Differential Measurements in Fields Characterized by Large Gradients

Design considerations, construction details, and measured performance of two magnetometer systems utilizing microwave ferromagnetic resonance in small single-crystal spheres of stoichiometric yttrium iron garnet (YIG) are presented. One system is for general use at ambient temperatures, while the second is designed for high precision measurements at liquid helium temperatures. These instruments are capable of measuring magnetic field strength to a precision of approximately one part in 104 even when the field is characterized by gradients as large as 1000 G/in. Since the YIG spheres employed are only 0.015 in. in diameter, these magnetometers come close to being ideal point probes.