Ferromagnetic Resonance Behavior Research Articles

Revealing the effect of gamma irradiation on structural, ferromagnetic resonance, optical, and dispersion properties of PVC/Mn0.5Zn0.5Fe2O4 nanocomposite films

Herein, this work aims to reveal the impact of gamma irradiation with different doses on structural, ferromagnetic resonance, optical, and dispersion properties of PVC/Mn 0.5 Zn 0.5 Fe 2 O 4 nanocomposite films. The Mn 0.5 Zn 0.5 Fe 2 O 4 nanoparticles (NPs) were synthesized via the sol-gel method. XRD pattern of Mn 0.5 Zn 0.5 Fe 2 O 4 powder confirmed of presence of the hematite (α-Fe 2 O 3 ) as a second phase. The PVC/Mn 0.5 Zn 0.5 Fe 2 O 4 nanocomposite films were assembled via the solution casting technique. The EDX spectra confirmed the elemental composition of Mn 0.5 Zn 0.5 Fe 2 O 4 NPs. Also, the XRD, and FTIR patterns proved the successful preparation of PVC/Mn 0.5 Zn 0.5 Fe 2 O 4 nanocomposite films. The effect of radiation on the produced defects has a significant role in tuning the properties. Likewise, the ferromagnetic resonance behavior was examined via EPR spectrometer. The number of spins was reduced sharply as the γ -rays doses increasing up to 50 kGy and then increased at 75 kGy. The energy gap was decreased by increasing the irradiation doses up to 50 kGy and then increased at 75 kGy. Besides, a remarkable impact of γ -irradiation on the oscillator energy and the dispersion energy of pristine and γ - rays irradiated PVC/Mn 0.5 Zn 0.5 Fe 2 O 4 nanocomposite films was detected. Further, the static dielectric constant was decreased with the increase in the gamma irradiation doses. Moreover, the nonlinear optical susceptibility was reduced with the increase in the gamma irradiation doses. Furthermore, the VELF, SELF functions and the optical conductivity were enhanced as the γ - rays doses increased. Overall, the linear/nonlinear optical and dispersion properties of irradiated PVC/Mn 0.5 Zn 0.5 Fe 2 O 4 nanocomposite films make of them proper materials for flexible optoelectronic devices. • The PVC/Mn 0.5 Zn 0.5 Fe 2 O 4 nanocomposite films were prepared via the solution casting technique. • The role of the hematite phase on structural and optical properties of the films was illustrated. • Remarkable impact of γ -irradiation on the oscillator and the dispersion energies of the nanocomposite films was detected. • The optical properties of PVC/Mn 0.5 Zn 0.5 Fe 2 O 4 nanocomposite films are suitable for flexible optoelectronic devices.

Design and Implementation of a Magnetic Press System for Creating Magnetically Oriented Barium Hexaferrite Pucks

We present initial magnetic and structural characterization results of pressing barium hexaferrite pucks under the influence of a magnetic field using a custom-built uniaxial press. The press can be operated up to 500 pounds of load inside a 30 kG axially uniform magnetic field. We present details on the system specifications and operation procedures as well as results of pressing pucks in the system in a 0, 25, or 30 kG field. We find that the pucks pressed under a 25 or 30 kG field show similar properties but are significantly magnetically and crystallographically textured along the magnetic field direction used during pressing compared to the no-field pucks. For the 30 kG pressed pucks, we find a squareness value of 0.6, a saturation magnetization of 2.7 kG, a coercivity of 3.4 kOe, and a magnetic texture of 0.74. We also characterize the ferromagnetic resonance (FMR) behavior up to 66 GHz and find an anisotropy field of 21 kOe and zero-field FMR of 42 GHz.

Post-Deposition Annealing Effects on Ferromagnetic CoFeB Thin Films

We investigate the role of annealing Co40Fe40B20 at different temperatures and how it affects the crystallinity and the ferromagnetic resonance (FMR) behavior. The onset of crystallization was shown to occur after annealing in nitrogen at 370 °C for 1 h. The crystallization peak of the post-annealed Co40Fe40B20 was matched to the analysis of (110) Co7Fe3, due to secondary phase segregation. Magnetic force microscopy images show a pattern of magnetization ripples in the magnetic phase images for samples upto 250 °C. The grain size of the Co7Fe3 (110) was shown to increase from 20 to 56 nm when annealed above 370 °C to 600 °C. The segregated Co7Fe3 causes scattering of the FMR linewidth, which shifts the resonance peak location, broadens peak-to-peak linewidth, and causes an additional resonance peak to appear close to the uniform resonance of the amorphous phase. Annealing above 500 °C leads to a complete phase change to Co7Fe3, which changes the FMR spectra back to a single resonance peak, shifted to lower fields with broader peak-to-peak linewidth of ~71.2 (kA/m).

Size-dependent magnetic properties of FeGaB/Al2O3 multilayer micro-islands

Recently, micrometer-size patterned magnetic materials have been widely used in MEMS devices. However, the self-demagnetizing action is significantly influencing the performance of the magnetic materials in many MEMS devices. Here, we report an experimental study on the magnetic properties of the patterned micro-scale FeGaB/Al2O3 multilayers. Ferromagnetic hysteresis loop, ferromagnetic resonance (FMR), permeability and domain behavior have been demonstrated by complementary techniques. Magnetic annealing was used to enhance the performance of magnetic multilayers. The comparisons among micro-islands with different sizes in the range of 200 μm∼500 μm as well as full film show a marked influence of size-effect, the exchange coupling effect, and the different domain structures inside the islands.

Tunable ferromagnetic resonance behavior in Co2FeSi film by post-annealing

Co2FeSi film is potential in the spintronics applications, due to its low damping factor, which is reflected in the ferromagnetic resonance behavior. In this work, we demonstrate that the ferromagnetic resonance behavior in Co2FeSi film can be well engineered by post-annealing. After 450 °C post-annealing for 1 hour, the Gilbert damping factor decreases drastically from 0.039 at as-deposited state to 0.006, and the inhomogeneity contribution of ferromagnetic resonance linewidth decreases to 60.5 Oe. These decreases are ascribed to the crystallization of film from amorphous state to an ordered B2 phase. Higher annealing temperature, however, leads to the formation of the A2 phase with higher atomic disorder, instead of B2 phase, and brings about the increase of Gilbert damping.

The FMR Behaviour of Li–Ni Ferrite Prepared by Hydrothermal Method

Magnetic hysteresis loop and ferromagnetic resonance (FMR) behaviour had been studied by considering the variation of the molar ratio of Li0.5−0.5x Ni x Fe2.5−0.5x O 4 ferrite nanostructure prepared by the hydrothermal method. The parameters of the ferrite nanostructure include coercivity (H c), saturation magnetisation (M s) and magnetic susceptibility. There was low coercivity at x = 0.3, high saturation magnetisation and high susceptibility (χ i) at (x = 0.5). These parameters showed an improvement in their values compared with the samples prepared by conventional methods. The FMR analysis indicated that these samples were lossy materials due to having a broad line width ranging from 800 to 925 G. The FMR lines had asymmetric shapes due to anisotropic broadening and conduction mechanism.

Investigation of ferromagnetic heterogeneities in La0.7Sr0.3MnO3 thin films

La0.7Sr0.3MnO3 manganite thin films are interesting since they have a fully spin-polarized conduction band at room temperature and this opens the way for applications in electronics. An important issue is their magnetic heterogeneity, which is very difficult to detect. We address here the heterogeneity detection issue in two epitaxial LSMO thin films (57 nm and 90 nm thick) on Si substrate fabricated by reactive molecular beam epitaxy (MBE) deposition. Combining three complementary analytic techniques, we measured structural and magnetic behavior of these films. The high frequency ferromagnetic resonance behavior observed in these two LSMO samples put in evidence a standard dynamic behaviour in the case of the homogeneous material and an uncommon multi-mode behavior in the heterogeneous bi-layered film. The multi-mode behavior can be attributed to the presence of two magnetic sub-layers inside the LSMO film. Indeed, transmission electron microscopy observations and neutron reflectivity measurements are essential to give a microscopic description of the structure and intrinsic magnetic homo/heterogeneity of the composite film.

Influence of lattice defects on the ferromagnetic resonance behaviour of 2D magnonic crystals.

This paper studies, from a modelling point of view, the influence of randomly distributed lattice defects (non-patterned areas and variable hole size) on the ferromagnetic resonance behaviour and spin wave mode profiles of 2D magnonic crystals based on Ni80Fe20 antidot arrays with hexagonal lattice. A reference sample is first defined via the comparison of experimental and simulated hysteresis loops and magnetoresistive curves of patterned films, prepared by self-assembly of polystyrene nanospheres. Second, a parametric analysis of the dynamic response is performed, investigating how edge, quasi-uniform and localized modes are affected by alterations of the lattice geometry and bias field amplitude. Finally, some results about the possible use of magnetic antidot arrays in frequency-based sensors for magnetic bead detection are presented, highlighting the need for an accurate control of microstructural features.

Tuning of the microwave magnetization dynamics in CoZr-based thin films by Nd-doping

To enhance the damping of microwave magnetization dynamics, we investigate the effect of Nd-doping (0–3.0 at. %) into CoZr thin films. The saturation magnetization decreases with Nd-doping. The coercivities generally decrease in the case of 1.5 at. % Nd-doping, while increase in the case of 3.0 at. % Nd-doping. The magnetization dynamics is characterized with the permeability spectra, which are determined by the ferromagnetic resonance behavior at the microwave range. The permeability spectra are analyzed through the fittings with Landau-Lifshitz-Gilbert equation. From the fittings, both the dynamic magnetic anisotropy field and the damping factor increase, due to the enhanced spin-orbital coupling by Nd-doping.

Abnormal spin-pumping effect at Pt/NiFe interface by an oxidation of ferromagnet

The Inverse Spin Hall Effect (ISHE) voltage induced by spin-pumping was measured in Pt/[nonoxidized or oxidized NiFe] samples. The spectrum shape of the DC voltage signal was well-reproduced by simple Lorentzian functions, which were consistent with the prediction of ISHE in Pt/nonoxidized NiFe sample. On the other hand, the voltage signal from the Pt/oxidized NiFe was significantly decreased in accordance with abnormal ferromagnetic resonance (FMR) behavior. The origin of the ISHE voltage degradation was investigated by the FMR spectrum and X-ray photoelectron spectroscopy (XPS) analyses. The spin-pumping was suppressed by the oxidation of NiFe layer and deficient Pt/NiFe interface. The well-defined ferromagnet and clear interface with a normal spin mixing conductance were experimentally demonstrated to be reasonable spin-pumping.

Investigation of the temperature-dependence of ferromagnetic resonance and spin waves in Co2FeAl0.5Si0.5

Co2FeAl0.5Si0.5 (CFAS) is a Heusler compound that is of interest for spintronics applications, due to its high spin polarization and relatively low Gilbert damping constant. In this study, the behavior of ferromagnetic resonance as a function of temperature was investigated in CFAS, yielding a decreasing trend of damping constant as the temperature was increased from 13 to 300 K. Furthermore, we studied spin waves in CFAS using both frequency domain and time domain techniques, obtaining group velocities and attenuation lengths as high as 26 km/s and 23.3 μm, respectively, at room temperature.

Transmission electron microscopy and ferromagnetic resonance investigations of tunnel magnetic junctions using Co2MnGe Heusler alloys as magnetic electrodes

High resolution transmission electron microscopy, nano-beam electronic diffraction, energy dispersive X-rays scanning spectroscopy, vibrating sample magnetometry (VSM) and ferromagnetic resonance (FMR) techniques are used in view of comparing (static and dynamic) magnetic and structural properties of Co2MnGe(13nm)/Al2O3(3nm)/Co(13nm) tunnel magnetic junctions (TMJs), deposited on various single crystalline substrates (a-plane sapphire, MgO(100) and Si(111)). They allow for providing a correlation between these magnetic properties and the fine structure investigated at atomic scale. The Al2O3 tunnel barrier is always amorphous and contains a large concentration of Co atoms, which, however, is significantly reduced when using a sapphire substrate. The Co layer is polycrystalline and shows larger grains for films grown on a sapphire substrate. The VSM investigation reveals in-plane anisotropy only for samples grown on a sapphire substrate. The FMR spectra of the TMJs are compared to the obtained ones with a single Co and Co2MnGe films of identical thickness deposited on a sapphire substrate. As expected, two distinct modes are detected in the TMJs while only one mode is observed in each single film. For the TMJ grown on a sapphire substrate, the FMR behavior does not significantly differ from the superposition of the individual spectra of the single films, allowing for a conclusion that the exchange coupling between the two magnetic layers is too small to give rise to observable shifts. For TMJs grown on a Si or on a MgO substrate, the resonance spectra reveal one mode which is nearly identical to the obtained one in the single Co film, while the other observed resonance shows a considerably smaller intensity and cannot be described using the magnetic parameters appropriate to the single Co2MnGe film. The large Co concentration in the Al2O3 interlayer prevents for a simple interpretation of the observed spectra when using Si or MgO substrates.

Broadband ferromagnetic resonance characterization of GaMnAs thin films

The precessional magnetization dynamics of GaMnAs thin films are characterized by broadband network analyzer ferromagnetic resonance (FMR) in a coplanar geometry at cryogenic temperatures. The FMR frequencies are characterized as function of in-plane field angle and field amplitude. Using an extended Kittel model of the FMR dispersion, the magnetic film parameters such as saturation magnetization and anisotropies are derived. The modification of the FMR behavior and of the magnetic parameters of the thin film upon annealing is analyzed.

NiFe/CoFe/Cu/CoFe/MnIr spin valves studied by ferromagnetic resonance

Ion-beam deposited (Glass/Ta/NiFe/CoFe/Cu/CoFe/MnIr/Ta) spin valves (SVs) with a Cu-spacer thickness (tCu) varying from 14 to 28 Å have been studied by ferromagnetic resonance (FMR) and magnetoresistance (MR) measurements. With respect to the interlayer coupling strength between the free and fixed ferromagnetic layers, the samples have been divided in those with a weak coupling (for tCu > 16 Å) and a strong coupling regimes (for tCu ≤ 16 Å). The FMR behavior in these two regimes is quite different. For the weakly coupled series, there are two well-defined FMR peaks stemming from the free and fixed layers. Their in-plane angular dependences exhibit 180° and 360° symmetries, respectively. For the strongly coupled SVs, the resonance modes are hybridized and possess features of both layers simultaneously. The main coupling mechanism between the two layers, as concluded from the FMR and MR measurements, is the Néel “orange-peel” magnetostatic interaction, accompanied by a direct exchange due to pinholes in the Cu spacer for tCu < 17 Å.

Ferromagnetic resonance behavior of spark plasma sintered Ni–Zn ferrite nanoparticles produced by a chemical route

Ferrite nanoparticles of composition Zn0.5Ni0.5Fe2O4 were prepared by forced hydrolysis in a polyol (polyol process) from the corresponding iron, nickel, and zinc acetates. Synthesis conditions allowed for obtaining polycrystalline epitaxial clusters of about 22 nm in size with an average crystal size of about 5 nm. These powders were subsequently consolidated by spark plasma sintering (SPS) technique under a pressure of 80 MPa and temperatures in the 350 to 500 °C range for short periods (5 to 10 min). Densities reached 92% to 94% of the theoretical density. Particle size remained smaller than 61 nm, even for the highest temperature. Ferromagnetic resonance experiments at 77 K showed broadened resonance lines. In contrast with powdered nanoparticles, these high-density bodies can be used in many high-frequency applications.

Multipeak ferromagnetic resonance behaviour tailored by magnetoelastic coupling in FeSiB/CoNi layered microwires

The aim of this work is to report on the influence of the presence of a magnetically hard layer with large thickness on the ferromagnetic resonance (FMR) behaviour of soft/hard biphase microwires. Such microwires consist of a FeSiB soft nucleus, an intermediate glass layer and a CoNi hard outer shell, and are prepared by the combined quenching and drawing technique with electrochemical deposition. The unusual FMR response observed for this biphase system is characterized by the presence of a multipeak absorption spectrum that depends on the static field and on the thickness of the hard phase by means of magnetoelastic coupling. For a thick enough CoNi layer, the internal stresses induced in the nucleus during the electroplating process are very strong, giving rise to three electromagnetic absorptions: one at a low frequency related to the CoNi shell and two at higher frequencies corresponding to the FeSiB nucleus which are ascribed to two well-defined magnetization regions with different magnetic anisotropies.

High frequency magneto impedance in amorphous microwires

We report the novel results on studies of the magneto impedance (MI) effect at GHz-range in 20 μm amorphous glass-coated microwire and 40 μm melt-extracted wire with nearly-zero magnetostriction constant. Both types of wires demonstrated similar behavior although the MI effect is higher in glass-coated microwire. In high field region, when the sample is magnetically saturated, the MI dependence demonstrates typical ferromagnetic resonance behavior. In the low field region the magnetization rotation process is dominant resulting in the highest sensitivity of the impedance to magnetic field. The drawback found in the studied samples is the low field magnetic hysteresis which is undesieble for potential application. The cause of this hysteresis is found to be the helical surface anisotropy in the wires which is characterized by a nonzero angle between the anisotropy easy axis and the wire's transversal plane.

Ferromagnetic Resonance Study of Ga1−x Mn x As Fabricated on (311) GaAs Wafers by Mn Ion Implantation and Pulsed-Laser Melting

We present a ferromagnetic resonance (FMR) study of Ga1−xMnxAs fabricated by Mn ion implantation (II) into (311) GaAs wafers followed by pulsed-laser melting (PLM). We measured the angular dependence of FMR at 4 K, and the data were then fitted by Stoner–Wohlfarth model to obtain the cubic and uniaxial anisotropy parameters. The observed angular behavior of FMR can be understood in terms of two contributions: a cubic anisotropy field parallel to the 〈001〉 axes, and a uniaxial anisotropy field parallel to the [311] direction. Our results show that the magnetic anisotropy fields in II-PLM (Ga,Mn)As are fundamentally similar to those in Ga1−xMnxAs samples grown by molecular beam epitaxy (MBE), indicating that the two different growth methods lead to materials with very similar magnetic properties.

Ru-Co가 치환된 M-형 육방정 페라이트(BaFe12-2xRuxCoxO19)의 자기적 성질 및 전파흡수 특성

Ru-Co가 복합 치환된 M-type Ba-ferrite(<TEX>$BaFe_{12-2x}Ru_xCo_xO_{19}$</TEX>)의 치환량 x의 변화에 따른 자기적 특성과 전파흡수 특성에 관해 조사하였다. 기존의 Ti-Co를 치환시킨 경우보다 적은 양의 치환(x=0.3)으로 면내 자기이방성을 보이는 낮은 보자력(<TEX>$H_c$</TEX>)과 높은 포화자화(<TEX>$M_s$</TEX>) 값을 얻을 수 있었다. 따라서 Ru-Co 치환량 조절에 의해 GHz 대역에서 자연공명주파수의 조절이 가능하였다. 소결체 및 복합체에서 흡수 주파수 대역은 보자력이 증가할수록 고주파 대역으로 이동한다. 복합체에서 페라이트 혼합량이 증가함에 따라 복소투자율과 복소유전율의 값이 증가하기 때문에 정합주파수는 저주파 대역으로 이동한다. 이러한 특성들을 이용하여 순수한 M-형 육방정 페라이트에 Ru-Co의 치환량, 복합체에서 페라이트 분말의 혼합량, 그리고 흡수체의 두께의 제어를 통하여 GHz 주파수 대역에서 양호한 전자파 흡수체, 노이즈 감쇠재의 제조가 가능함을 제시할 수 있다. In this study, the magnetic(static and high-frequency) and microwave absorbing properties have been investigated in Ru-Co substituted M-hexaferrites(<TEX>$BaFe_{12-2x}Ru_xCo_xO_{19}$</TEX>). The powders and sintered specimens were prepared by conventional ceramic processing technique. With the calcined powders, the composite specimens were prepared using the silicone rubber as a matrix material. The substitution ratio of Ru-Co to obtain in-plane magnetic anisotropy, thus having the minimum coercivity, is much smaller (about x=0.3) than the previously reported Ti-Co substituted specimen. Owing to this low substitution, the specimen has a large value of saturation magnetization(<TEX>$M_s$</TEX>=65 emu/g). Ferromagnetic resonance behavior and microwave absorbing frequency band is strongly influnced by the coercvity which can be controlled by Ru-Co substitution ratio. It is found that the M-hexaferrites with planar magnetic anisotropy by doping Ru-Co in both sintered and composite form have superior microwave absorbing properties in GHz frequency range.

Magnetic resonance in iron oxide nanoparticles: Quantum features and effect of size

In order to better understand the transition from quantum to classical behavior in spin system, electron magnetic resonance (EMR) is studied in suspensions of superparamagnetic magnetite nanoparticles with an average diameter of ∼9 nm and analyzed in comparison with the results obtained in the maghemite particles of smaller size (∼5 nm). It is shown that both types of particles demonstrate common EMR behavior, including special features such as the temperature-dependent narrow spectral component and multiple-quantum transitions. These features are common for small quantum systems and not expected in classical case. The relative intensity of these signals rapidly decreases with cooling or increase of particle size, marking gradual transition to the classical ferromagnetic resonance (FMR) behavior.