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1.
We have performed ferromagnetic resonance measurements on thin polycrystalline Ni 80Fe 20 (permalloy) double layers with interlayers of Cu, Cr and Pd. Furthermore, a mathematical model is presented, which allows a calculation of resonance fields in the parallel configuration. Comparison of the calculated and measured resonance field values yields an interlayer exchange coupling constant A12 as a function of interlayer thickness d. We observe exponential dependencies of A12 on d for Cr, Cu and Pd interlayers with the strongest decay for Cr. Additionally, we present FMR measurements and calculations for a Ni 80Fe 20/Cr/Co heterostructure layer system. 相似文献
2.
The anisotropic magnetoresistance (AMR) in permalloy Ni 81Fe 19 film deposited on a 1.2 nm Co 33Cr 67 buffer layer was significantly enhanced. The high-resolution electron microscopy was used to study the microstructure of Ni 81Fe 19 film with and without Co 33Cr 67 buffer layer. It was found that Co 33Cr 67 buffer layer can induce good (1 1 1) texture, while without Co 33Cr 67 buffer layer, Ni 81Fe 19 film show randomly oriented grain structure. The Δρ/ρ enhancement is attributed to the decrease in the resistivity ρ of the Ni 81Fe 19 film due to the formation of the large (1 1 1) textured grains in Ni 81Fe 19 film with Co 33Cr 67 buffer layer. However, the surface roughness of substrate may limit the (1 1 1) textured grain size and induce additional grain boundaries in Ni 81Fe 19 film with Co 33Cr 67 buffer layer, limit the enhancement of the AMR effect. 相似文献
3.
The nucleation mechanism to predict coercivity values in melt-spun exchange-coupled (Nd 1−xPr x) yFe 94−yB 6 alloys for various Nd:Pr ratios x, and Fe:RE ratios y, was tested using the dependence of the anisotropy constant K1 on Pr content x for the minimum nucleation field HNmin in the modified Brown's equation. Very good agreement was found between experimental data and theoretical values, confirming the predominance of the nucleation of reverse domains over the wall pinning process in the coercivity mechanism of melt spun REFeB alloys. 相似文献
4.
We carried out a comprehensive study of structural, magnetic and electrotransport properties of as-deposited and annealed (Ni 80Fe 20) χAg( 1−χ) heterogenous alloys prepared by sputtering. The NiFe atomic concentration was varied between 15% and 40%. These alloys consist of small magnetic particles (Ni 80Fe 20) embedded in a nonmagnetic matrix (Ag). The structures of these alloys were investigated by X-ray diffraction, scanning electron microscopy and high-resolution cross-section transmission electron microscopy. The magnetic measurements were made using SQUID magnetometry and ferromagnetic resonance. Magnetoresistance was measured with a conventional four-point probe between 1.5 K and room temperature in field range 0–6T. Three contributions to the magnetoresistance of these granular alloys have been clearly identified: the spin-valve (or giant) magnetoresistance as in multilayers, scattering on magnetic fluctuations (as in any ferromagnetic metal around its magnetic ordering temperature), and anisotropic magnetoresistance. These three contributions have their own dependences on the size of the magnetic particles, on the degree of intermixing between Ni 80Fe 20 and Ag, and on temperature. We discuss the different shapes and amplitudes of magnetoresistance versus Ni 80Fe 20 concentration or temperature and their evolution upon annealing in terms of the relative roles of these three contributions. The magnetoresistance in multilayers (current in-plane or perpendicular to the plane) and granular alloys are also compared. 相似文献
5.
Variation of the complex permeability with frequency of Ni 1−xZn xFe 2O 4 ( x=0.5, 0.6 and 0.7) prepared by a combustion method has been measured over a wide range of frequency, up to 1.8 GHz. Zn content improves permeability but moves the onset of resonance to lower frequencies. The influence on some properties of samples prepared by the insertion of small amounts of Ruthenium, Yttrium and rare-earth cations into the Ni0.5Zn0.5MxFe2−xO4 ferrite has been also investigated. Relative losses and Curie temperature of all the samples have been measured. Ferrites substituted with Ru and Gd improve microwave behavior compared to non-substituted samples. 相似文献
6.
R 2(Fe, Co) 14B compounds (R = Y, Nd and Gd) were prepared in high purity. The magnetic behavior of R 2(Fe, Co) 14B compounds is reported over the temperature range 4 to 300 K. The effects of Fe substitution by Co on the saturation magnetization, Curie temperature and anisotropy are presented. The spin-reorientation temperature is lowered as Co replaces Fe. This also results in a reduced cone angle. The R2Fe14−xCoxB alloys crystallize in the tetragonal structure over the entire concentration range of 0 x 14. When Fe is substituted by Co, the Curie temperature increases significantly, the saturation magnetization increases to a maximum value around x = 2, and the anisotropy becomes planar for R = Y and Gd. The Nd2(Fe, Co)14B systems all exhibit uniaxial anisotropy at room temperature and Nd2Co14B is strongly uniaxial at 77 K. The Nd2(Fe, Co)14B systems are conical at 77 K. 相似文献
7.
The magnetic properties of Fe–SiO 2 nanogranular composite thin films were studied as a function of film thickness and Fe concentration, f, using ferromagnetic resonance at X-band (9.4 GHz) and Q-band (35 GHz). Films with an Fe volume percent ranging from 17% to 70% were fabricated from a mosaic target using RF sputtering techniques. Film thickness was varied between 10 and 200 nm. From measurements made at room temperature with the external field applied parallel and perpendicular to the film plane, it was possible to determine an almost linear dependence of the effective anisotropy field with Fe concentration. Small differences observed between X- and Q-band, specially at low f, were attributed to the effects that the different fields applied during the experiment cause on the magnetic state of the sample. No systematic change of the effective field or the g value was observed in films of different thickness. The absorption line width, on the other hand, was found to depend on film thickness indicating a larger distribution of particle shape and size with increasing film thickness. A maximum in the line width was observed around f30–35% and is probably caused by the transition from single domain ferromagnetic clusters to superparamagnetic particles. 相似文献
8.
The roughening of interfaces as a function of layer thickness and magneto transport properties have been investigated on sputter-deposited Fe/Ni 75B 25 multilayer films. X-ray reflectivity data were recorded for Ni 75B 25(72 nm) film and for [Fe(2 nm)/Ni 75B 25(2 nm)] 16 and [Fe(4 nm)/Ni 75B 25(4 nm)] 8 multilayer films. A power law dependence of the interfacial width of growing Fe/Ni 75B 25 interfaces was observed. The resulting growth exponents β were found to be in the range of 0.55–0.58 in the initial growth stage of the multilayer with lower Fe/Ni 75B 25 repetition thickness and at approximately 0.34 for multilayer with higher repetition thickness. The growth exponents were compared with theoretical calculations. High resolution electron microscopy revealed the columnar growth of the Fe/Ni 75B 25 multilayer. Additionally, an increase of magnetoresistance was observed by the multilayering of Ni 75B 25 films with Fe interlayers. 相似文献
9.
化学共沉淀工艺制备Zn 0.2Fe 2.8O 4铁氧体颗粒,颗粒尺寸约300埃,近似呈球状,在其表面外延生长一层钴铁氧体层。测量了矫顽力、铁磁共振线宽随钴含量的变化,得到由于外延层引起的磁各向异性常数K u约为5×10 5尔格/厘米 3。由实验结果分析,主要是Zn 0.2Fe 2.8O 4颗粒表面与外延生长层相当于两个氧离子层厚所产生的相互作用。
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10.
Several magnets with different Zr contents were studied: Sm(Co balFe 0.2Cu 0.1Zr x) 8 (bal=balance; x=0, 0.02, 0.04, 0.06 and 0.08). The microstructure of the magnets includes three main phases, all crystallographically coherent: the cell phase Sm 2(Co,Fe) 17, the cell boundary phase Sm(Co,Cu) 5 and a lamellar Zr-rich phase, rhombohedral (ZrSm) 1Co 3. The hysteresis curves were compared with the Callen, Liu and Cullen (CLC) modification of the Stoner–Wohlfarth model for an isotropic distribution of interacting single-domain particles. Choosing reasonable values for the saturation magnetization Ms, the anisotropy field Ha, and the mean-field interactions of the CLC model, we were able to reproduce the main features of the hysteresis curves for the x=0.02 and 0.04 samples. For higher x values, X-ray diffraction Rietveld analysis revealed the presence of other “impurity” phases, among them cubic Zr 6(Co,Fe) 23, rhombohedral (SmZr) 5(CoFeCu) 19 and rhombohedral (SmZr) 2(CoFeCu) 7. 相似文献
11.
Single crystals of Ba, Sr M-type hexagonal ferrites were prepared by ion exchange in Ba, Sr containing molten salts from single crystals of β″ -ferrites. A fast diffusion of the divalent Ba 2+, Sr 2+ is observed leading to a non-stoichiometric M-type ferrite with chemical formula: Ba 1+xFe 10.5Co 0.25O 17+x (0 ≤ x ≤ 0.25). x depending on the exchange reaction time. Saturation magnetization ranges from 19 to 64 emu/g depending on exchange conditions. The Curie temperature is (470 ± 5)°C. An easy axis direction ( Ms c) has been determined in all cases. The observed anisotropy is considerably lower than that of M ferrite. The calculated anisotropy constants are, in 10 6 erg/cm 3, K1 = 0.8 and K2 = 1.0 at room temperature. 相似文献
12.
Magnetic and structural characteristics of Pr 2Co 17-based ternaries, in which Co is partly replaced by other transition elements, namely Fe, Mn, Cr, Cu and Al, have been investigated. The objective of the work was to explore the possibility of enhancing the anisotropy of Pr 2Co 17 to the point that it would be useful for permanent magnet fabrication. X-ray diffraction indicates that all the systems studied occur in the rhombohedral Th 2Zn 17 structure. The cell constants increase as Fe, Mn, etc., are introduced in the system, which indicates that substitution occurs in the Co sublattice. The Curie temperatures, Tc, decrease monotonically with increasing x in the order Fe < Cu < Mn < Al < Cr. The saturation magnetization, Ms, increases with increasing x for the Fe system with x 8. For x #62; 8 in the Pr 2Co 17-xFe x system and in all other ternary systems st died, Ms decreases with x, the magnitude of the effect being in the order Cr #62; Al #62; Mn #62; Cu. The rate of decrease is larger than that expected as a simple dilution except for the systems containing Cu. Significant modification of the anisotropy characteristics of Pr 2Co 17 is observed upon substitution. The planar anisotropy of Pr 2Co 17 becomes uniaxial with Fe ( x 4) and Mn ( x 2) substitutions. With Cr and Al substitutions, the plane-seeking tendency of Pr 2Co 17 is significantly weakened. 相似文献
13.
The magnetization of magnetically-aligned Gd 2Fe 14−xCo xB samples with x = 0, 2, 4, 6, 8.4, 11.2 and 14 has been measured at 4.2 K in fields up to 14 T and the anisotropy fields have been derived. The effect of substitution of Co for Fe on the magnetic properties of Gd 2Fe 14B has been investigated. 相似文献
14.
Magnetic transitions in La(Fe 1−xCo x) 11.4Si 1.6 compounds with x=0–0.08, have been studied by DC magnetic measurements and Mössbauer spectroscopy. The temperature dependence of the Landau coefficients has been derived by fitting the magnetization, M(μ 0H), using the Landau expansion of the magnetic free energy. For x0.02 there is a strongly first-order magnetic phase transition between ferromagnetic and paramagnetic (F–P) states in zero external field and a metamagnetic transition from paramagnetic to ferromagnetic (P–F) above Tc. Increasing the cobalt content drives the F–P transition towards second order and eliminates the metamagnetic transition. 相似文献
15.
The formation of tetragonal R 2(FeCo) 14C phase has been examined in as-cast and melt-spun R 14Fe 78−xCo xC 8 alloys with cobalt substitutions (R = Y, Dy, Nd). The magnetic properties over a temperature range and the microstructure have been studied as a function of cobalt content. The Curie temperature is increased with Co content but the anisotropy K is decreased. High cobalt content leads to the formation of 1:5 phase. High corecivities have been developed in as-cast and melt-spun Dy 14Fe 78−xCo xC 8 alloys with Co content at zero and 32 at %, respectively. As-cast Nd 16Fe 78−xCo xC 8 alloys did not show any permanent magnetic properties although they had the 2:14:1 phase. However, melt-spun and powdered Nd---Fe---Co---C samples showed a coercivity with the highest value corresponding to a melt-spun Nd 14Fe 78C 8 sample. Microstructure studies showed that the high HC in ribbons is due to the fine grain size which is in the range of 500–1000 Å. 相似文献
16.
An attempt is made to synthesize Nd 2Co 14C compound by mechanical alloying Nd 16Co 76B 8−xC x (0 x8) alloys and subsequent annealing. Phase formation and magnetic properties of Nd 2Fe 14B-type Nd 16Co 76B 8−xC x alloys and their hydrides are investigated. The Nd 2Co 14(B,C) phase with Nd 2Fe 14B-type structure is formed for Nd 16Co 76B 8−xC x (0 x7) alloys, while NdCo 7C δ phase with TbCu 7-type structure is observed in Nd 16Co 76C 8 alloy. The lattice parameter c of the Nd 2Co 14(B,C) phase decreases with increasing the carbon content. A limit volume of the unit cell to form the Nd 2Fe 14B-type structure is estimated to be 0.870 nm 3. The spin-reorientation temperature TSR increases with increasing the carbon content, due to an enhancement of magnetocrystalline anisotropy caused by carbon substitution for boron. After hydrogenation, the lattice expansion is observed for Nd 16Co 76B 8−xC x (0 x7) alloys. The spin-reorientation temperature of Nd 16Co 76B 8−xC xH y (0 x7) is much lower than that of the host alloys. Some structural and magnetic properties of hypothetic Nd 2Co 14C and Nd 2Co 14CH y compounds are estimated by extrapolation. 相似文献
17.
We studied the coercivity in magnets of composition R 17Fe 83−χB χ (R = Nd, Pr and χ = 8, 30), using measurements of the coercive field Hc, its angular dependence, and the magnetic viscosity coefficient Sv, for temperatures between 4.2 and 500 K. The results are discussed in relation to a model which does not specifically consider the detailed mechanisms involved in magnetization reversal, but which provides information about the magnetic properties in the activation volume v where magnetization reversal is initiated. It is concluded that the ordering temperature in v tends to be slightly smaller than in the bulk and that the room temperature anisotropy in v is not strongly reduced with respect to the bulk value. Finally, a direct evaluation of the dipolar interactions is in good agreement with results obtained from Hc( T). 相似文献
18.
Effects of titanium carbide (TiC) addition on structural and magnetic properties of isotropic (Pr,Nd)–Fe-B nanocrystalline magnetic materials have been investigated. In this work, we investigate the effect of TiC addition on a (Pr,Nd)-poor and B-rich composition, as well as on a B-poor and (Nd,Pr)-rich composition. Rapidly solidified (Pr,Nd)–Fe–B alloys were prepared by melt-spinning. The compositions studied were (Pr 1−xNd x) 4Fe 78B 18 ( x=0, 0.5, and 1) with addition of 3 at% TiC. Unlike the (Pr xNd 1−x) 9.5Fe 84.5B 6 materials that present excellent values for coercive field and energy product, the (Pr,Nd)-poor and B-rich composition alloys with TiC addition present lower values. Rietveld analysis of X-ray data and Mössbauer spectroscopy revealed that samples are predominantly composed of Fe 3B and -Fe. For the RE-rich compositions (Pr xNd 1−x) 9.5Fe 84.5B 6 ( x=0.1, 0.25, 0.5, 0.75, and 1) with the addition of 3 at% TiC, the highest coercive field and energy product (8.4 kOe and 14.4 MGOe, respectively) were obtained for the composition Pr 9.5Fe 84.5B 6. 相似文献
19.
本文通过在新固相源中添加Ni 2O 3的方法, 采用顶部籽晶熔渗生长工艺(TSIG)制备出组分为(1- x) (Gd 2O 3+1.2BaCuO 2)+ x Ni 2O 3、直径为20 mm的单畴GdBCO 超导块材(其中 x = 0, 0.02, 0.06, 0.10, 0.14, 0.18, 0.30, 0.50 wt%), 并研究了Ni 2O 3的掺杂量x对样品的表面生长形貌、微观结构、临界温度 Tc、磁悬浮力以及俘获磁通密度的影响. 研究结果表明, 当Ni 2O 3的掺杂量 x在0–0.50 wt%的范围内时, 均可制备出单畴性良好的样品, 且Ni 2O 3的掺杂对样品中Gd211粒子的分布和粒径没有明显的影响. 在Ni 2O 3的掺杂量 x从0增加到0.50 wt%的过程中, 样品的临界温度 Tc呈现下降的趋势, 从 x=0时的92.5 K下降到 x=0.50 wt%时的86.5 K, 这是由于Ni 3 +替代GdBCO晶体中Cu 2 +所致; 样品磁悬浮力和俘获磁通密度均呈现先增大后减小的变化规律, x=0.14 wt%时, 磁悬浮力达到最大值34.2 N, x=0.10 wt%时, 俘获磁通密度达到最大值0.354 T. 样品磁悬浮力和俘获磁通密度的变化规律与Ni 2O 3的掺杂量 x有密切关系, 只有当掺杂量 x合适时, Ni 3+对Cu 2 +的替代既不会造成 Tc的明显下降, 但又能产生适量的Ni 3 +/Cu 2+ 晶格畸变, 从而达到提高样品磁通钉扎能力和超导性能的效果. 相似文献
20.
The maximum solid solubility of gallium in the perovskite-type La 1−xSr xFe 1−yGa yO 3−δ ( x=0.40–0.80; y=0–0.60) was found to vary in the approximate range y=0.25–0.45, decreasing when x increases. Crystal lattice of the perovskite phases, formed in atmospheric air, was studied by X-ray diffraction (XRD) and neutron diffraction and identified as cubic. Doping with Ga results in increasing unit cell volume, while the thermal expansion and total conductivity of (La,Sr)(Fe,Ga)O 3−δ in air decrease with gallium additions. The average thermal expansion coefficients (TECs) are in the range (11.7–16.0)×10 −6 K −1 at 300–800 K and (19.3–26.7)×10 −6 K −1 at 800–1100 K. At oxygen partial pressures close to atmospheric air, the oxygen permeation fluxes through La 1−xSr xFe 1−yGa yO 3−δ ( x=0.7–0.8; y=0.2–0.4) membranes are determined by the bulk ambipolar conductivity; the limiting effect of the oxygen surface exchange was found negligible. Decreasing strontium and gallium concentrations leads to a greater role of the exchange processes. As for many other perovskite systems, the oxygen ionic conductivity of La 1−xSr xFe 1−yGa yO 3−δ increases with strontium content up to x=0.70 and decreases on further doping, probably due to association of oxygen vacancies. Incorporation of moderate amounts of gallium into the B sublattice results in increasing structural disorder, higher ionic conductivity at temperatures below 1170 K, and lower activation energy for the ionic transport. 相似文献
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