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1.
A new technique, which utilizes the interlayer diffusion, for preparation of self-assembled nanodot magnetic structures has been proposed. L10-phase Pt/FeCu and Pt/FeAg films have been successfully synthesized by this technique. Both the coercivity of Pt/FeCu and Pt/FeAg films exhibited, respectively 4.1 and 8.0 kOe in perpendicular direction. Pt/Fe and Pt/FeAg films show positive values, while Pt/FeCu shows negative value in δm plot. The results indicate that the exchange coupling between the grains has been decoupled in the self-assembled nanodot structure in Pt/FeCu film.  相似文献   

2.
The deposition monolayers of L10 FePt nanoparticles via an electrospraying method and the magnetic properties of the deposited film were studied. FePt nanoparticles in a size of around 2.5 nm in diameter, prepared by a liquid process, were used as a precursor. The size of the deposited particles can be controlled up to 35 nm by controlling the sprayed droplet size that is formed by adjusting the precursor concentration and the precursor flow rate. The droplets were heated in a tubular furnace at a temperature of up to 900 °C to remove all organic compounds and to transform the FePt particles from disordered face centered cubic to an ordered FCT phase. Finally, the particles were deposited in the form of a monolayer film on a silicon substrate by electrostatic force and characterized by scanning electron microscopy. The monolayer of particles was obtained by the high charge on particles obtained during the electrospraying process. The magnetic properties of the monolayer were investigated by magneto-optic Kerr effect measurements. Coercivity up to 650 Oe for a film consisting of 35 nm L10 FePt nanoparticles was observed after heat treatment at a temperature of 800 °C.  相似文献   

3.
Anomalous magnetization processes and non-symmetrical domain wall displacements in the minor loop of L10 FePt particulate films were investigated by magnetization measurements and in situ magnetic force microscopy. Magnetization (M) decreases dramatically on increasing the magnetic field to ∼3 kOe after which M becomes small and constant in the range of 5–20 kOe as observed in the successive measurement of minor loops. The domain wall displacement is non-symmetrical with respect to the field direction. The anomalous magnetization behavior was attributed to the non-symmetrical domain wall displacement and large magnetic field required for domain wall nucleation. Energy calculations from modeling suggest that non-symmetrical domain wall displacement is caused by the existence of metastable domains in which the domain edges are stuck to the particle boundaries.  相似文献   

4.
Electron microscopy was employed to investigate the structure of magnetic field crystallized (Co1−xFex)89Zr7B4 alloys with only dilute Fe-contents (x=0, 0.025, 0.05, and 0.10). The x=0.025 and 0.05 alloys exhibit very large field induced anisotropies and multiple nanocrystalline phases (BCC, FCC, and HCP) surrounded by an intergranular amorphous phase. Correlation between the volume fraction crystallized and the measured value of HK suggests that the large KU values are associated with the crystalline phases that form. Multiple crystalline phases are present for the highest KU alloys and so the presence of FCC and/or HCP-type nanocrystals may be responsible for these observations. High-resolution transmission electron microscopy (HRTEM) illustrates a number of microstructural features including (1) high densities of stacking faults in many of the FCC and, in particular, the HCP-type nanocrystals, (2) infrequent BCC/FCC orientation relationships, and (3) nanocrystals with disordered or long period stacking sequences of close-packed planes. High densities of planar faults are suggested as a potential source of KU for the FCC and HCP-type nanocrystals, but the origin of the large values of KU found in dilute Fe-containing, Co-rich “nanocomposite” alloys is an area where further work is needed.  相似文献   

5.
A three-dimensional micromagnetic model with non-uniform grain size distribution has been built up to study the magnetization process in FePt L10 perpendicular media. A 3D model of a single FePt magnetic grain is also set up for comparison. The high magneto-crystalline anisotropy Ku results in a short exchange length lex in FePt nanograins. Therefore a magnetic grain is divided into smaller grids on the order of lex. The simulated perpendicular and longitudinal loops are consistent with experiments, and it is explained why the measured perpendicular Hc is relatively smaller compared with the saturation field of the longitudinal loop in the FePt perpendicular medium.  相似文献   

6.
FePt and FePt/Cr films were epitaxially grown on MgO (2 0 0) substrates at 350 °C by DC magnetron sputtering. The structural properties and epitaxial relationship are investigated by high-resolution X-ray diffraction (XRD). The XRD spectra revealed that both FePt and FePt/Cr films had a (0 0 1) preferred orientation. However, FePt films with Cr underlayers had a larger a and a smaller c than those of the samples without Cr underlayers. Furthermore, the FePt (0 0 1) peak characterized by its rocking curves became less pronounced when the Cr underlayer was applied. The off-spectra from the MgO (1 1 1), Cr (1 0 1) and FePt (1 1 1) demonstrated that the epitaxial relationship between the FePt film, Cr underlayer and MgO substrate was confirmed to be FePt (0 0 1)<100> || Cr (1 0 0)<1 1 0> || MgO (1 0 0)<0 0 1>. The domain size and Ms decreased when the Cr underlayer was applied due to the diffusion of Cr and the existence of the initial layer between Cr and FePt layers.  相似文献   

7.
FePt (20 nm) films with AgCu (20 nm) underlayer were prepared on thermally oxidized Si (0 0 1) substrates at room temperature by using dc magnetron sputtering, and the films annealed at different temperature to examine the disorder–order transformation of the FePt films. It is found that the ordered L10 FePt phase can form at low annealing temperature. Even after annealing at 300 °C, the in-plane coercivity of 5.2 kOe can be obtained in the film. With increase in annealing temperature, both the ordering degree and coercivity of the films increase. The low-temperature ordering of the films may result from the dynamic stress produced by phase separation in AgCu underlayer and Cu diffusion into FePt phase during annealing.  相似文献   

8.
In this paper we report results on the synthesis and magnetic properties of L10 FePt nanocomposite films. Three fabrication methods have been developed to produce high-anisptropy FePt films: non-epitaxial growth of (0 0 1)-oriented FePt:X (X=Ag, C) composite films that might be used for perpendicular media; monodispersed FePt(CFx) core–shell nanocluster-assembled films grown with a gas-aggregation technique and having uniform cluster size and narrow size distribution; and template-mediated self-assembled FePt clusters prepared with chemical synthesis by a hydrogen reduction technique, which has a high potential for controlling both cluster size and orientation. The magnetic properties are controllable through variations in the nanocluster properties and nanostructure. Analytical and numerical simulations have been done for these films, providing better understanding of the magnetization reversal mechanisms. The films show promise for development as magnetic recording media at extremely high areal densities.  相似文献   

9.
The microstructure and magnetic properties of FePt films grown on Cr and CrW underlayers were investigated. The FePt films that deposited on Cr underlayer show (2 0 0) orientation and low coercivity because of the diffusion between FePt and Cr underlayer. The misfit between FePt magnetic layer and underlayer increases by small addition of W element in Cr underlayer or using a thin Mo intermediate layer, which is favorable for the formation of (0 0 1) orientation and the transformation of FePt from fcc to fct phase. A good FePt (0 0 1) texture was obtained in the films with Cr85W15 underlayer with substrate temperature of 400 °C. The FePt films deposited on Mo/Cr underlayer exhibit larger coercivity than that of the films grown on Pt/Cr85W15 because 5 nm Mo intermediate layer depressed the diffusion of Cr into magnetic layer.  相似文献   

10.
This study has investigated the microstructure and magnetic properties of Fe40Ni38B18Mo4 at various degrees of crystallization from the amorphous state. TEM and XRD studies confirmed that phases forming after crystallization at temperatures around 414 and 522 °C were cubic (Fe, Ni, Mo)23B6 phase and FCC (Fe, Ni) solid solution. The growth behavior and morphology of the nanocrystalline phases have been studied as a function of time and temperature. Nanoparticles were lying in the size range of 10–20 nm and they were stable below 522 °C. Kissinger approach, Ozawa method and Yi Qun Gao method were employed to determine and compare the kinetic parameters of the crystallization processes. A growth mechanism of crystallizing phases was proposed on the basis of these results. Magnetic properties mainly coercivity and saturation magnetization of as-received and heat-treated samples were evaluated.  相似文献   

11.
The field dependence of spin and orbital magnetic moments of Fe in L10 FePt magnetic thin films was investigated using X-ray magnetic circular dichroism (XMCD). The spin and orbital moments were calculated using the sum rules; it was found that the spin and orbital moment of Fe in L10 FePt films are ∼2.5 and 0.2 μB, respectively. The relative XMCD asymmetry at Fe L3 peak on the dependence of applied field suggested that the majority magnetic moment of L10 FePt films resulted from Fe.  相似文献   

12.
The 57Fe Mössbauer effect measurements were made for the L10 ordered Fe-Pt alloys with 39-62 at% Pt and the effect of local atomic environment on the hyperfine structure was investigated. Furthermore, the thermal stability of magnetic order was investigated for the alloys with high Pt concentration. From the analyses of the observed Mössbauer spectra, we found that dipole-field-like anisotropic transferred hyperfine fields are mainly responsible for the large difference in hyperfine field between Fe-site and Pt-site in the Fe-rich alloys. In the Pt-rich region far from stoichiometry, the existence of many Fe-sites occupied by excess Pt atoms causes a distribution of exchange fields. Therefore, the iron atoms in different local environments may have their several hyperfine fields with different temperature dependence. The anomalous temperature dependence of the averaged hyperfine field and line broadening observed for the 61, 62 at% Pt alloys can be understood from the co-existence of various sub-spectra with different temperature dependence. As a result, the thermal stability of magnetic order is largely reduced as the Pt concentration exceeds 60 at%.  相似文献   

13.
We report a new synthesis route for preparation of single-domain barium hexaferrite (BaFe12O19) particles with high saturation magnetization. Nitric acid, known as a good oxidizer, is used as a mixing medium during the synthesis. It is shown that formation of BaFe12O19 phase starts at 800 °C, which is considerably lower than the typical ceramic process and develops with increasing temperature. Both magnetization measurements and scanning electron microscope micrographs reveal that the particles are single domain up to 1000 °C at which the highest coercive field of 3.6 kOe was obtained. The best saturation magnetization of ≈60 emu/g at 1.5 T was achieved by sintering for 2 h at 1200 °C. Annealing at temperatures higher than 1000 °C increased the saturation magnetization, on the other hand, decreased the coercive field which was due to the formation of multi-domain particles with larger grain sizes. It is shown that the best sintering to obtain fine particles of BaFe12O19 occurs at temperatures 900-1000 °C. Finally, magnetic interactions between the hard BaFe12O19 phase and impurity phases were investigated using the Stoner-Wohlfarth model.  相似文献   

14.
Ni80Fe20 permalloy nanoparticles (NPs) have been prepared by the polyol processing at 180 °C for 2 h and their particle sizes can be precisely controlled in the size range of 20-440 nm by proper addition of K2PtCl4 agent. X-ray diffraction results show that the Ni-Fe NPs are of FCC structure, and a homogeneous composition and a narrow size distribution of these NPs have been confirmed by scanning electron microscopy assisted with energy dispersion spectroscopy of X-ray (SEM-EDX). The saturation magnetization of ~440nm NPs is 80.8 emu/g that is comparable to that of bulk Ni80Fe20 alloys, but it decreases to 28.7 emu/g for ~20 nm NPs. The coercive force decreases from 90 to 3 Oe with decreasing NP size. The wide range of particle size is exploited to seek for high permeability composite particles. The planar type samples composed of the NiFe NPs exhibit low initial permeability due to the deteriorated magnetic softness and low packing density. However, when they are mixed with Fe micron particles, the initial permeability significantly increases depending on the mixing ratio and the NiFe NP size. A maximum initial permeability is achieved to be ~9.1 at 1 GHz for the Fe-10 vol%NiFe (~20 nmΦ), which is about three times that of pure Fe micron particles. The effects of Ni-Fe particle size, volume percentage and solvent on the static and dynamic permeability are discussed.  相似文献   

15.
FePt:Ag nanocomposite films were prepared by pulsed filtered vacuum arc deposition system and subsequent rapid thermal annealing on SiO2/Si(1 0 0) substrates. The microstructure and magnetic properties were investigated. A strong dependence of coercivity and ordering of the face-central tetragonal structure on both Ag concentration and annealing temperature was observed. With Ag concentration of 22% in atomic ratio, the coercivity got to 6.0 kOe with a grain size of 6.7 nm when annealing temperature was 400 °C.  相似文献   

16.
Fully dense nanocomposite magnets containing hard R2Fe14B and soft α-Fe phases were produced from both melt-spun and mechanically milled alloys by hot pressing and subsequent die upsetting. Although R-lean R–Fe–B alloys that do not contain the grain-boundary R-rich phase are known not to be susceptible to texture development by means of die upsetting, we found that small additions of Cu make the texturing possible. The resulting microstructure of oriented platelet grains is similar to that of the R-rich die-upset magnets. Properties of the Cu-containing R2Fe14B/α-Fe die-upset magnets can be further improved by adding Ga. The anisotropic Pr12Fe80Cu1Ga1B6 magnet made from mechanically milled alloy and containing 17.2 wt% α-Fe had a remanence of 13 kG and a maximum energy product of 23.4 MG Oe. The Pr11.25Fe80.75Cu1Ga1B6 magnet made from melt-spun alloy and containing 16.2 wt% α-Fe had a maximum energy product of 19.9 MG Oe. The low coercivity of 3–4 kOe typical for the Cu-containing R2Fe14B/α-Fe die-upset magnets is due to the relatively coarse α-Fe grains. The latter grains are too large for intergranular exchange interaction, but, nevertheless, they are well coupled with the R2Fe14B grains by a long-range magnetostatic interaction.  相似文献   

17.
The variation of the applied field results in a subsequent change of magnetization with time. There is a relationship between the coercivity (Hc), as the equilibrium characteristic of the system, and its magnetic stability (1/S), as a parameter characterizing the time dependence. 1/S as a function of Hc has been measured and studied for different Fe1−xCox samples. We synthesized several samples with different values of x by applying various magnetic fields during the grains’ growth, and observed a linear relationship between 1/S and Hc.  相似文献   

18.
Ribbons of nominal compositions YCo5 Cx (x = 0, 0.2, 0.4, 0.6) are prepared by melt spinning at surface velocities v = 5, 10, 15, 20, 25, 30 and 35 m/s. YCo5 ribbon is crystallized in a single YCo5 phase of hexagonal CaCu5 structure. A small quantity of YCoC2 phase appears in the ribbons with C addition besides the YCo5 phase. With the increase of x the lattice constant c increases and a along with the unit cell volume decreases. The largest values of iHc = 888 kA/m and (BH)max = 58.4 k Jim3 at present for the YCo5 ribbon system were obtained with x = 0.4 and v = 20 m/s. The improvement of the permanent magnetic properties is rooted in the refinement of the microstructure and the appearance of the YCoC2 phase which can act as domain wall pinning centers.  相似文献   

19.
Core/shell structured Mn3O4/MnO nanoparticles were prepared by arc evaporating metallic manganese in air. These nanoparticles show unconventional exchange bias phenomena, in which the Curie temperature of the ferrimagnetic Mn3O4 is lower than the Néel temperature of the antiferromagnetic MnO. The exchange bias field in Mn3O4/MnO nanoparticles is much smaller than that in Mn3O4/Mn nanoparticles, due to the weak interfacial exchange coupling. The coercivity of the Mn3O4 phase in nanoscale is almost three times greater than that of the bulk Mn3O4.  相似文献   

20.
The L10 CoPt films with (0 0 1) preferred orientation are achieved by fabricating on the glass substrates and post annealing at 600° C for 30 min. The preferred orientation of [ZrO2/CoPt]n/Ag films dependence of the Ag underlayer thickness, ZrO2 and CoPt interlayer thickness is investigated. A large perpendicular magnetic anisotropy and a nearly perfect L10 CoPt (0 0 1) texture are obtained in the [ZrO2 (3 nm)/CoPt (5 nm)]3/Ag (10 nm) film. The existence of ZrO2 plays an important role in reducing the intergranular interactions and in determining the size of CoPt grains. Magnetic reversal in textured CoPt films are close to a Stoner-Wolfarth rotation.  相似文献   

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