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1.
Antiferromagnetic/ferromagnetic (AF/F) NiMn/Fe37Co48Hf15 films were investigated with respect to their exchange bias, in-plane unidirectional anisotropy, polarisation and high frequency behaviour. After deposition, carried out by r.f. magnetron sputtering, the films were post-annealed for 4 h at 300 °C in a static magnetic field, in order to induce exchange-bias, which results in a unidirectional anisotropy. Dependent on the presence of a bi-layer or multi-layer sandwich structure the films show a different exchange-bias field-ferromagnetic inter-layer thickness behaviour with exchange-bias fields μ0?Heb between 2 and 10 mT. The in-plane uniaxial (single film) or unidirectional anisotropy fields μ0*HUF were between 4 and 18 mT. This results in a significant increase of the cut-off frequency in the GHz range in comparison to a single Fe37Co48Hf15 film, which is shown by frequency-dependent permeability plots. High damping in the imaginary part of the permeability, i.e., high resonance line broadening could be observed for films with high coercivity μ0*Hc of around 7 mT in the easy axis of magnetisation. 相似文献
2.
In order to describe high-frequency damping mechanisms of ferromagnetic films by means of the imaginary part of the frequency-dependant permeability, CMOS compatible ferromagnetic Fe36Co44Hf9N11 films were deposited by reactive r.f. magnetron sputtering on oxidised 5×5 mm2×380 μm (1 0 0)-silicon substrates with a 6-in. Fe38Co47Hf15 target, as well as magnetic field annealing between 300 and 600 °C. An in-plane uniaxial anisotropy of around 4.5 mT as well as an excellent soft magnetic behaviour with a saturation polarisation of approximately 1.4 T could be observed after heat treatment at the above-mentioned temperatures, which drives these films to a high-frequency suitability. Ferromagnetic resonance frequencies of approximately up to 2.4 GHz could be obtained. The frequency-dependant permeability was measured with a broadband permeameter. Depending on the heat treatment, an increase of the full-width at half-maximum (FWHM) of the imaginary part of the frequency-dependant permeability is discussed in terms of two-magnon scattering, anisotropy-type competition and local resonance generation through predominant grain growth causing magnetisation and anisotropy inhomogeneities in the magnetic films. The grain size of the films was determined by (HRTEM) imaging and amounts from a few nanometres for films heat treated at 300 °C to more than 10 nm at 600 °C where the FWHM Δfeff and the Landau–Lifschitz–Gilbert equation damping parameter αeff increases with dnm2 and dnm (e.g. dnm is the grain diameter of the nonmagnetic Hf–N phase), respectively. 相似文献
3.
Ferromagnetic nanocomposite (Fe44Co56)77Hf12N11 films were deposited to investigate their intrinsic damping mechanisms due to scattering of itinerant electrons, which carry the magnetic moment of the ferromagnetic transition elements. The films were produced by reactive r.f. magnetron sputtering using a 6 in. Fe37Co46Hf17 target. They were annealed at 400 °C in a static magnetic field, in order to induce in-plane uniaxial anisotropy. Subsequently, the films can be considered as uniformly magnetised. A ferromagnetic resonance frequency (FMR) of around 2.3 GHz could be attained, which was determined by measuring the real and imaginary parts of the frequency dependent permeability up to 5 GHz. The imaginary part, which represents a typical resonance curve, was utilised to obtain its full-width at half-maximum Δfeff (FWHM) for the total damping behaviour characterisation. Thereby, it is possible to extract the intrinsic Gilbert damping parameter αint, which in turn can be decomposed into two additional damping terms αsf and αos allocated to “spin-flip” and “ordinary scattering”, respectively. This result is correlated and discussed in terms of a verified theoretic model, to identify whether damping due to spin-flip scattering and/or ordinary scattering is dominant. 相似文献
4.
The CMOS compatible ferromagnetic Fe-Co-(M)-N (M=Ta, Hf) films were investigated with regard to their grain size-dependent frequency behaviour. Predominantly Fe33Co40Ta10N17 films were deposited by reactive r.f. magnetron sputtering. These films were compared to Fe36Co44Hf9N11 films. In order to induce an in-plane uniaxial anisotropy Hu as well as to investigate the grain growth behaviour, the films were annealed in a static magnetic field. The in-plane uniaxial anisotropy field of around 4 mT as well as a good soft magnetic behaviour with a saturation polarisation of approximately 1.2-1.4 T could be observed after heat treatment. Ferromagnetic resonance frequencies (FMR) of approximately up to 2.4 GHz could be achieved according to the Kittel theory. Depending on the heat treatment, high-frequency losses through energy dissipation was made conspicuous by means of the full-width at half-maximum (FWHM) Δfeff of the imaginary part of the frequency-dependent permeability which was between 0.4 and 1 GHz. This FWHM was basically discussed in terms of two-magnon scattering theories, in combination with the Herzer random anisotropy model. In order to correlate the resonance line broadening with a phenomenological damping parameter αeff, which ranged from about 0.0125 to 0.028, the modified Landau-Lifschitz-Gilbert equation was used to fit and describe the permeability spectra of the ferromagnetic films. 相似文献
5.
A new implant assisted-magnetic drug targeting approach is introduced and theoretically analyzed to demonstrate its feasibility. This approach uses ferromagnetic particles as seeds for collecting magnetic drug carrier particles at the desired site in the body, such as in a capillary bed near a tumor. Based on the capture cross section (λc) approach, a parametric study was carried out using a 2-D mathematical model to reveal the effects of the magnetic field strength (μ0H0=0.01–1.0 T), magnetic drug carrier particle radius (Rp=20–500 nm), magnetic drug carrier particle ferromagnetic material content (xfm,p=20–80 wt%), average blood velocity (uB=0.05–1.0 cm/s), seed radius (Rs=100–2000 nm), number of seeds (Ns=1–8), seed separation (h=0–8Rs), and magnetic drug carrier particle and seed ferromagnetic material saturation magnetizations (iron, SS 409, magnetite, and SS 304) on the performance of the system. Increasing the magnetic field strength, magnetic drug carrier particle size, seed size, magnetic drug carrier particle ferromagnetic material content, or magnetic drug carrier particle or seed saturation magnetization, all positively and significantly affected λc, while increasing the average blood velocity adversely affected it. Increasing the number of seeds or decreasing the seed separation, with both causing less significant increases in λc, verified that cooperative magnetic effects exist between the seeds that enhance the performance. Overall, these theoretical results were encouraging as they showed the viability of this minimally invasive, implant assisted-magnetic drug targeting approach for targeting drugs or radiation in capillary beds. 相似文献
6.
C. Liu Z.Y. Gao X. An M. Saunders H. Yang H.B. Wang L.X. Gao W. Cai 《Journal of magnetism and magnetic materials》2008
A Ni54Mn25.7Ga20.3 ferromagnetic shape memory alloy thin film has been fabricated by using the RF magnetron-sputtering technique. The structure and magnetic properties of the film were systematically investigated. The results show that the film is in ferromagnetic martensite state at room temperature with the Curie temperature (Tc) of about 370 K. The saturation magnetization (Ms) of the film reaches 45 emu/g at 300 K, which is about 80% as large as that of Ni–Mn–Ga bulk material. The magnetization hysteresis loops significantly depend on temperatures. The residual magnetization (Mr) and the coercive force (Hc) increase with decreasing temperatures. The grains homogeneously distribute in the film. The microstructure of the film consists of martensite plates. The interface between the martensite variants is clear and straight, indicating a good mobility. 相似文献
7.
S.S. Kalyan Kamal P.K. Sahoo L. Durai P. Ghosal M. Manivel Raja S. Ram 《Journal of magnetism and magnetic materials》2012
Small crystallites of a metastable phase Co0.5Pt0.5 are precipitated by heating a rheological liquid precursor of cobalt–hydrazine complex and platinum chloride H2PtCl6·xH2O in polymer molecules of poly(vinylpyrrolidone) (PVP) in ethylene glycol. The hydrazine co-reduces nascent atoms from the Co2+ and Pt4+ that recombine and grow as Co0.5Pt0.5. The PVP molecules cap a growing Co0.5Pt0.5 as it achieves a critical size so that it stops growing further in given conditions. X-ray diffraction pattern of a recovered powder reveals a crystalline Co0.5Pt0.5 phase (average crystallite size D∼8 nm) of a well-known Fm3m-fcc crystal structure with the lattice parameter a=0.3916 nm (density ρ=14.09 g/cm3). A more ordered L10 phase (ρ=15.91 g/cm3) transforms (D≥25 nm) upon annealing the powder at temperature lesser than 700 °C (in vacuum). At room temperature, the virgin crystallites bear only a small saturation magnetization Ms=5.54 emu/g (D=8 nm) of a soft magnet and it hardly grows on bigger sizes (D≤31 nm) in a canted ferromagnetic structure. A rectangular hysteresis loop is markedly expanded on an optimally annealed L10 phase at 800 °C for 60 min, showing a surface modified coercivity Hc=7.781 kOe with remnant ratio Mr/Ms=0.5564, and Ms=39.75 emu/g. Crystallites self-assembled in an acicular shape tailor large Hc from ideal single domains and high magnetocrystalline anisotropy of a hard magnet L10 phase. 相似文献
8.
Bilayered Fe65Co35 (=FeCo)/Co films were prepared by facing targets sputtering with 4πMs∼24 kg. The soft magnetic properties of FeCo films were induced by a Co underlayer. Hc decreased rapidly when the Co underlayer was 2 nm or more. The films showed well-defined in-plane uniaxial anisotropy with the typical values of Hce=10 Oe and Hch=3 Oe, respectively. High frequency characteristics of the films show the films can work at 0.8 GHz with real permeability as high as 250. 相似文献
9.
Huaping Zuo Zhenkun Wang Yuhua Xiao Dongsheng Yao Yanbo Li 《Journal of magnetism and magnetic materials》2009,321(20):3453-3456
Discontinuous [FeCoSi (d)/native-oxide]50 multilayer films were fabricated by DC magnetron sputtering without any post-deposition treatment. The films exhibit good soft magnetic properties with initial permeability μi larger than 100, the saturation magnetization 4πMs and the in-plane uniaxial anisotropy field Hk increase as the magnetic FeCoSi layer thickness d is increased from 5.5 to 20.5 Å. As a consequence, the ferromagnetic resonance frequencies fr of the films increase from 2.0 to 3.9 GHz. The combination of high fr and large μi makes these films potential candidates for magnetic devices applied in the high-frequency range. The origin of the excellent high-frequency properties in discontinuous FeCoSi/native-oxide multilayer films is discussed. 相似文献
10.
Ferromagnetic Fe-Co-Hf-N nanocomposite films were investigated concerning their microstructure-dependent frequency behaviour. To modify the composition, the films were deposited by reactive RF magnetron sputtering by using three different 6 in. targets with various Hf fractions. The films were post-annealed up to 600 °C in a static magnetic field to induce an in-plane uniaxial anisotropy and to obtain different crystal sizes. Depending on the annealing temperature, high-frequency losses were investigated by considering the full-width at half-maximum (FWHM) Δfeff of the imaginary part of the frequency-dependent permeability which showed a resonance frequency fFMR of 2.3 GHz for an in-plane uniaxial anisotropy field Hu of 4 mT. The FWHM in correlation with the damping parameter αeff is discussed, e.g., in terms of two-magnon scattering. Damping occurs due to film inhomogeneity in magnetisation and uniaxial anisotropy caused by a magnetocrystalline anisotropy Ha and/or non-magnetic phases. This will result in homogenous or even inhomogeneous resonance line broadening if additional and resonance as well as precession frequencies of independent grains arise. 相似文献
11.
M. Belmeguenai F. Zighem Y. Roussigné K. Westerholt 《Journal of magnetism and magnetic materials》2009,321(7):750-753
Co2MnGe films of 30 and 50 nm in thickness were grown by RF-sputtering. Their magnetic anisotropies, dynamic properties and the different excited spin wave modes have been studied using conventional ferromagnetic resonance (FMR) and Microstrip line FMR (MS-FMR). From the in-plane and the out-of-plane resonance field values, the effective magnetization (4πMeff) and the g-factor are deduced. These values are then used to fit the in-plane angular-dependence of the uniform precession mode and the field-dependence of the resonance frequency of the uniform mode and the first perpendicular standing spin wave to determine the in-plane uniaxial, the four-fold anisotropy fields, the exchange stiffness constant and the magnetization at saturation. The samples exhibit a clear predominant four-fold magnetic anisotropy besides a smaller uniaxial anisotropy. This uniaxial anisotropy is most probably induced by the growth conditions. 相似文献
12.
Fernando M.F. Rhen Paul McCloskeyTerence O’Donnell Saibal Roy 《Journal of magnetism and magnetic materials》2008
We have investigated CoNiFe and CoNiFe–C electrodeposited by pulse reverse plating (PRP) and direct current (DC) techniques. CoNiFe(PRP) films with composition Co59.4Fe27.7Ni12.8 show coercivity of 95 A m−1 (1.2 Oe) and magnetization saturation flux (μ0Ms) of 1.8 T. Resistivity of CoNiFe (PRP) is about 24 μΩ cm and permeability remains almost constant μr′ ∼475 up to 30 MHz with a quality factor (Q) larger than 10. Additionally, the permeability spectra analysis shows that CoNiFe exhibits a classical eddy current loss at zero bias field and ferromagnetic resonance (FMR) when biased with 0.05 T. Furthermore, a crossover between eddy current and FMR loss is observed for CoNiFe-PRP when baised with 0.05 T. DC and PRP plated CoNiFe–C, which have resistivity and permeability of 85, 38 μΩ cm, μr′=165 and 35 with Q>10 up to 320 MHz, respectively, showed only ferromagnetic resonance losses. The ferromagnetic resonance peaks in CoNiFe and CoNiFe–C are broad and resembles a Gaussian distribution of FMR frequencies. The incorporation of C to CoNiFe reduces eddy current loss, but also reduces the FMR frequency. 相似文献
13.
Xu YangJian-Qiang Wei Xing-Hua LiLu-Qian Gong Tao Wang Fa-Shen Li 《Physica B: Condensed Matter》2012,407(3):555-559
In this work, the thickness effect of Fe52Co48 soft magnetic films with in-plane anisotropy on static and microwave magnetic properties was investigated. The hysteresis loop results indicated that the static in-plane uniaxial anisotropy field increased from almost 0-60 Oe with increasing film thickness from 100 to 540 nm and well-defined in-plane uniaxial magnetic anisotropy can be obtained as the thickness reached 540 nm or larger. Based on Landau-Lifshitz-Gilbert (LLG) equation, the microwave complex permeability spectra were analyzed and well fitted. The LLG curve-fitting results indicated that the initial permeability increased from 106 to 142 and the resonant frequency was shifted from 4.95 to 4.29 GHz as the film thickness was varied from 540 to 1500 nm. Moreover, it was found that there was a discrepancy between the static and the dynamically determined anisotropy field, which can be explained by introducing an additional effective isotropic ripple field. The decreased ripple field was suggested to result in a significant decrease of damping coefficient from 0.109 to 0.038. 相似文献
14.
P.S. Keatley V.V. Kruglyak R.J. Hicken J.R. Childress J.A. Katine 《Journal of magnetism and magnetic materials》2006
A modified scanning Kerr microscope has been used as a static Kerr magnetometer to acquire in-plane vector hysteresis loops from square Si/Ta(50 Å)/Co80Fe20(40 Å)/Ni88Fe12(108 Å)/Ta(100 Å) elements with size ranging from 123 nm to 10 μm. The nanoscale elements were arranged in square arrays of 4 μm size. The laser beam was focused to a sub-micron spot, while polarization changes were recorded with an optical bridge detector containing a beam-splitting polarizer and two quadrant photodiodes. The coercive field exhibited a non-monotonic increase from 11 Oe in the 10 μm element to 170 Oe in the 123 nm elements. Loops acquired with the field applied parallel to the easy and hard in-plane uniaxial anisotropy axes were observed to become more similar in shape as the element size decreased. 相似文献
15.
Yu-Ming KuoJenq-Gong Duh 《Applied Surface Science》2011,257(15):6387-6390
High permeability magnetic films can enhance the inductance of thin-film inductors in DC-DC converters. In order to obtain high permeability, the uniaxial anisotropy and coercivity should be as low as possible. This study employed dc reactive magnetron sputtering to fabricate nanocrystalline FeHfN thin films. The influence of the nitrogen flow on the composition, microstructure, and permeability characteristics, as well as magnetic properties was investigated. Increasing the nitrogen content can alter FeHfN films from amorphous-like to crystalline phases. The magnetic properties and permeability depend on variations in the microstructure. With the optimum N2/Ar flow ratio of 4.8% (N2 flow: 1.2 sccm), low anisotropy (HK = 18 Oe), low coercivity (HC = 1.1 Oe) and high permeability (μ′ > 600 at 50 MHz) were obtained for fabrication of a nanocrystalline FeHfN film with a thickness of around 700 nm. Such as-fabricated FeHfN films with a permeability of over 600 should be a promising candidate for high-permeability ferromagnetic material applications. 相似文献
16.
Microstructure, static magnetic properties and microwave permeability of sputtered FeCo films were examined. Fe60Co40 films (100 nm in thickness) deposited on glass substrates exhibited in-plane isotropy and a large coercivity of 161.1 Oe. When same thickness films were deposited on 2.5 nm Co underlayer, well-defined in-plane anisotropy was formed with an anisotropy field of 65 Oe. The sample had a static initial permeability of about 285, maximum imaginary permeability of 1255 and ferromagnetic resonance frequency of 2.71 GHz. Cross-sectional TEM image revealed that the Co underlayer had induced a columnar grain structure with grain diameter of 10 nm in the FeCo films. In comparison, FeCo films without Co underlayer showed larger grains of 70 nm in diameter with fewer distinct vertical grain boundaries. In addition, the Co underlayer changed the preferred orientation of the FeCo from (1 0 0) to (1 1 0). The improvement in soft magnetic properties and microwave behavior originates from the modification of the film microstructure, which can be well understood by the random anisotropy theory. 相似文献
17.
The magnetic properties of strontium hexaferrite (SrFe12O19) films fabricated by pulsed laser deposition on the Si(100) substrate with Pt(111) underlayer have been studied as a function of film thickness (50–700 nm). X-ray diffraction patterns confirm that the films have c-axis perpendicular orientation. The coercivities in perpendicular direction are higher than those for in-plane direction which indicates the films have perpendicular magnetic anisotropy. The coercivity was found to decrease with increasing of thickness, due to the increasing of the grain size and relaxation in lattice strain. The 200 nm thick film exhibits hexagonal shape grains of 150 nm and optimum magnetic properties of Ms=298 emu/cm3 and Hc=2540 Oe. 相似文献
18.
We present a theoretical interpretation of recent data on the conductance near and farther away from the metal–insulator transition in thin ferromagnetic Gd films of thickness b≈2–10 nm. For increasing sheet resistances a dimensional crossover takes place from d=2 to d =3 dimensions, since the large phase relaxation rate caused by scattering of quasiparticles off spin wave excitations renders the dephasing length L??b at strong disorder. The conductivity data in the various regimes obey fractional power-law or logarithmic temperature dependence. One observes weak localization and interaction induced corrections at weaker disorder. At strong disorder, near the metal–insulator transition, the data show scaling and collapse onto two scaling curves for the metallic and insulating regimes. We interpret this unusual behavior as proof of two distinctly different correlation length exponents on both sides of the transition. 相似文献
19.
The uniaxial in-plane and out-of-plane anisotropies of [Co/SiO2] × 10 multilayers have been studied by ferromagnetic resonance, magnetometry and transmission electron microscopy. The surface and volume anisotropy constants are in the range of values typical for multilayers with Co and transition metals of the iron group. The influence of the intermixed Co-SiO2 region is discussed. 相似文献
20.
By spin-spray ferrite plating, an aqueous process, we prepared ZnxFe3−xO4 (0?x?0.97) films at 90 °C on polyimide and glass substrates, on which complex permeability (μ=μ′–jμ″) was measured. As Zn content x increases from 0 to 0.70 static permeability, μs, increases from 14 to 119, but natural resonance frequency, fr, reduces from 1 GHz to 200 MHz. This is because magnetic anisotropy field decreases more rapidly than saturation magnetization. With increasing x DC electric resistivity, ρ, increases, exceeding 50 Ω cm (a measure of the lower limit for the high-frequency application) when x>0.15. Film with x=0.70 has relatively high μ′≈119 and μ″=0 up to 20 MHz, and is promising to be used as MHz core inductors. Film with x=0.36 has relatively high μ′=80 and μ″=0 up to 100 MHz, and it may be used as inductors at the ten MHz range and noise suppression sheets at the hundred MHz range. 相似文献