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1.
Werner Keune 《Hyperfine Interactions》2012,204(1-3):13-45
An overview is provided on our recent work that applies 57Fe M?ssbauer spectroscopy to specific problems in nanomagnetism. 57Fe conversion electron M?ssbauer spectroscopy (CEMS) in conjunction with the 57Fe probe layer technique as well as 57Fe nuclear resonant scattering (NRS) were employed for the study of various nanoscale layered systems: (i) metastable fct-Fe; a strongly enhanced hyperfine magnetic field Bhf of ~39?T at 25?K was observed in ultrahigh vacuum (UHV) on uncoated three-monolayers thick epitaxial face-centered tetragonal (fct) 57Fe(110) ultrathin films grown by molecular-beam epitaxy (MBE) on vicinal Pd(110) substrates; this indicates the presence of enhanced Fe local moments, μFe, as predicted theoretically; (ii) Fe spin structure; by applying magnetic fields, the Fe spin structure during magnetization reversal in layered (Sm–Co)/Fe exchange spring magnets and in exchange-biased Fe/MnF2 bilayers was proven to be non-collinear and depth-dependent; (iii) ferromagnet/semiconductor interfaces for electrical spin injection; CEMS was used as a diagnostic tool for the investigation of magnetism at the buried interface of Fe electrical contacts on the clean surface of GaAs(001) and GaAs(001)-based spin light-emitting diodes (spin LED) with in-plane or out-of-plane Fe spin orientation; the measured rather large average hyperfine field of ~27?T at 295?K and the distribution of hyperfine magnetic fields, P(Bhf), provide evidence for the absence of magnetically “dead” layers and the existence of relatively large Fe moments (μFe ~ 1.8?μB) at the ferromagnet/semiconductor interface. - Finally, a short outlook is given for potential applications of M?ssbauer spectroscopy on topical subjects of nanomagnetism/spintronics. 相似文献
2.
J. Gal H. Pinto S. Fredo H. Shaked W. Schäfer G. Will F. J. Litterst W. Potzel L. Asch G. M. Kalvius 《Hyperfine Interactions》1987,33(1-4):173-190
Mössbauer effect and neutron diffraction studies on the tetragonal NpM4Al8?x (M=Cr, Fe, Cu) of the 14/mmm space group are reported. In NpFe4Al8?x, both the Np and Fe sites order magnetically at close temperatures: the Np order ferromagnetically at 115(15) K (μ(Np)) ~ 0.6 μB and the Fe moments order antiferromagnetically at 130(10) K (μ(Fe) = 1.05(15) μB) with a ++?? sequence. In NpCr4Al8?x, the Np order magnetically around 50K. From the susceptibility data we conclude possible antiferromagnetic order of both Np and Cr sites. NpCu4Al8?x does not order magnetically down to at least 2 K. The magnetic hyperfine splitting observed below 45 K is explained by slow paramagnetic relaxation. The Np isomer shifts and also its magnetic behavior point to a trivalent ion (5I4 Hund's rule ground state). The observed relaxation and magnetic phenomena are discussed in terms of crystalline electric field effects. In contrast to the isostructural rare-earth RM4Al8 compounds with practically independent order of R and M magnetic sublattices, we show that Np and M sublattices in NpM4Al8 are strongly coupled. This is caused by hybridization of both Np and M atoms with Al. 相似文献
3.
《Surface science》1986,172(2):363-371
Spin-polarized self-consistent localized-orbital (SCLO) calculations have been performed for a five-plane slab simulating Pd/Fe(100). Pd monolayers were placed in registry with both faces of a three-plane Fe(100) slab. We chose a PdFe bond length equal to the sum of metallic radii, 2.62 Å, and an FeFe bond length equal to the bulk value, 2.49 A. The computed energy bands for the Pd/Fe3/Pd slab resemble those calculated for a five-plane Fe(100) slab, except for a positive work-function shift of 0.5 eV. The Pd monolayer has a magnetic moment of 0.37μB/atom. The magnetic moment of an adjacent iron atom is 2.74μB, slightly smaller than the value 2.89μB at the surface of Fe5, but still significantly larger than the central-plane value 2.37μB. The d bands of the two metals are strongly hybridized, but very little charge transfer takes place across the interface. Compared with the isolated Pd(100) monolayer, or the clean Fe(100) slab, the surface density of states of Pd/Fe(100) is rather weak near the Fermi level, suggesting a reduced chemical reactivity for this surface. 相似文献
4.
During electrostatic bonding, anodic oxidation of the anode material, for instance silicon, is thought to be the essential step in the bonding mechanism, leading to the formation of a permanent, strong and vacuum-tight bond. Despite the perceived importance of this step in the bonding mechanism of this well-established bonding technique, there is little experimental evidence for anodic oxidation during electrostatic bonding. One reason is that a thin (approximately 10–20?nm) amorphous anodic oxide layer is difficult to detect adjacent to an amorphous cation-depleted glass. Here, silicon–Pyrex and aluminium–Pyrex electrostatic bonds are made and the anodic oxidation process is studied directly using transmission electron microscopy. The consumption of silicon is demonstrated by the movement of the crystalline–amorphous interface compared with a marker under the original silicon–Pyrex interface. The formation of an anodic silica layer can also be demonstrated using electron-energy-loss spectrometry. An amorphous reaction layer 5–20?nm thick is formed during the bonding cycle. For aluminium anode materials bonded at 450°C a nanocrystalline γ-Al2O3 reaction layer is formed, which can be readily detected by transmission electron microscopy. At a bonding temperature of 350°C, no such crystalline reaction layer can be detected between Pyrex and aluminium. 相似文献
5.
Ultrathin Fe film 200 V/4 Fe/900 V/MgO(100) has been prepared by molecular beam epitaxy (MBE). The structure parameters, such as the surface and interface roughness and the thickness of each layer, were obtained by X-ray and neutron reflectivity mea
关键词:
超薄Fe膜
磁特性
极化中子反射
分子束外延 相似文献
6.
ABSTRACTObtaining both high hardness and toughness is a challenge in B4C-nano-adhesive composites. Solving the inhomogeneous distribution of nano-adhesives in B4C and forming the chemical bonding at grain boundary is an effective method. Here, we reported that the uniform distribution of titanium diboride (TiB2)-reinforced B4C composites synthesized by high-pressure and high temperature (HPHT). It is found that HPHT sintering can effectively inhibit the grain growth and increase the relative density. Moreover, HPHT sintering can cross high reaction energy barrier and effectively promote the formation of chemical bonding at grain boundary between B4C and TiB2. The optimal hardness and toughness value reach 30.0?±?0.9?GPa and 7.87?MPa·m1/2, respectively. The improvement of hardness and toughness in the final products are ascribed to the strengthening of nanoTiB2 connection of B4C boundary and intergranular fracture mechanism. This work suggests a new way to achieve the uniform distribution of nanoTiB2 in B4C and form the chemical bonding at grain boundary, which is of great significance to the further development of TiB2-reinforced B4C composites with excellent mechanical properties. 相似文献
7.
The structures and electronic properties of ferrous nitride–fulminic acid (FeN–HCNO) clusters are investigated by using PW91 functional. The results reveal that the Fe atom of an FeN molecule prefers to be absorbed on the N–O of an HCNO molecule and it shows the highest kinetic stability. The Fe–N–C–N ring structure has the highest kinetic stability, while the FeN–HCNO chain configuration shows the highest kinetic activity. The N–Fe–ONCH chain structure displays the maximum dipole magnitude (DM) value (8.246 Debye). The Fe atom of the FeN molecule adsorbed on the C atom of the HCNO molecule has the minimum DM value (0.641 Debye). The linear FeN–HCNO configuration displays the largest total spin (2.945?μB/atom). The hybridization of sp orbital of the FeN–HCNO clusters is very important. 相似文献
8.
Die magnetische Struktur und das magnetische Verhalten von ErFe2: Eine Neutronenbeugungsuntersuchung
The magnetic structure of ErFe2 has been determined from neutron diffraction measurements on a powderd sample in the temperature region between 4.2°K and 700°K. ErFe2 exhibits ferrimagnetic ordering below 600°K with the Er- and Fe-ions being antiparallel oriented. The separate sublattice magnetisations of the Er- and Fe-sublattices have been determined. The saturation moments at 4.2°K have been found to beμ(Fe)=1.97μ B andμ(Er)=8.47μ B. The coupling between the two sublattices is by an antiparallel spin-spin interaction of the Er and Fe ions. The temperature dependence of the sublattice magnetization of the Er-ions is explained by a separation into two parts: an induced magnetization at high temperatures and a spontaneous magnetization at lower temperatures. 相似文献
9.
We report on the novel application of nanoscratch characterization to provide insight into the plasticity mechanisms responsible for the behaviour of composites. Accordingly, we conduct deformation characterization with nanoscratch testing (DCNT) to study the deformation behaviour of two B4C reinforced ultrafine grained Al alloy tri-modal composites with average B4C particle sizes of ~1–6?μm and ~500?nm, respectively. To highlight the type of mechanistic information revealed in a DCNT study of composites, we concentrate on the influence of B4C particle size on deformation mechanisms. 相似文献
10.
B. Sahoo W. A. A. Macedo W. Keune V. Kuncser J. Eisenmenger J. Nogués I. K. Schuller I. Felner Kai Liu R. Röhlsberger 《Hyperfine Interactions》2006,169(1-3):1371-1377
Two different Fe/MnF2 samples have been prepared by e-beam evaporation on MgO(001) substrates. The Fe layer in the samples includes a 10 Å thick 57Fe probe layer either at the Fe/MnF2 interface (interface sample) or 35 Å away from the interface (center sample). The samples are characterized by X-ray diffraction, conversion electron Mössbauer spectroscopy (CEMS) and SQUID magnetometry. 57Fe CEMS has been employed to study the depth dependent hyperfine interactions in Fe/MnF2 as a function of temperature between 18 K to 300 K. The hyperfine field B hf has been obtained for the interfacial and off-interfacial 57Fe layers. At the interface, besides B hf of bcc-Fe, the presence of a component with a distribution P(B hf ) is observed. The latter is assigned to interfacial 57Fe atoms, indicating some (~15%, equivalent to ~1 Fe atomic layer) intermixing at the Fe/MnF2 interface and a decrease of the average hf > by 21%. The influence of the interface disappears as the 57Fe probe layer is placed away from the interface. The temperature dependence of the average hf > of the interface has been measured. The Fe spins, at remanence, are found to lie in the film plane. 相似文献
11.
Polycrystalline Fe3?x V x Al alloys with the DO3 type structure were investigated by magnetostatic and Mössbauer methods. In alloys with 0.2<x<0.5 the ferro- and superpara-magnetic phases coexist. For alloys withx≥0.5 these investigations showed that in spite of the lack of magnetic order, they are characterized by strong nonlinear variations of the magnetization in a magnetic field over a wide temperature range. This indicates the presence of magnetic clusters of Fe atoms with very large magnetic moments. Analysis of the magnetization isotherms indicates that in these alloys a distribution of magnetic moments of clusters (μc) from 10 μB to 104 μB exists. 相似文献
12.
N. N. Delyagin A. L. Erzinkyan V. P. Parfenova S. I. Reiman G. M. Gurevich Ya. Dupak 《Physics of the Solid State》1998,40(9):1500-1505
The influence of temperature on the distribution function P(B hf) of the magnetic hyperfine fields for 57Fe in (Fe0.65Ni0.35)1?x Mnx alloys (x=0, 0.024, 0.034) are investigated by Mössbauer spectroscopy. The Mössbauer absorption spectra are measured in the temperature interval 5–300 K; in the interval 5–80 K the measurements are performed in a magnetic field of 0.2 T. Anomalies are found in the temperature curves of the intensity of the principal maximum of the functions P(B hf)[B hf=30–38 T] and the total (integrated) intensities of the low-field components [B hf=(4–13) T]. The detected anomalies in the behavior of the total intensities are interpreted as resulting from a change in the balance of competing exchange interactions due to the thermal annihilation of antiferromagnetic Fe-Fe exchange interaction. The emergence of strong satellite lines in the interval B hf=20–29 T in Mn-doped alloys is attributed to reorientation of the spins of Fe atoms under the influence of strong antiferromagnetic Mn-Fe exchange interaction. 相似文献
13.
The influence of SiCp oxidized on the interface layer and thermal conductivity of SiCp/Al composites
《Composite Interfaces》2013,20(2):107-117
In this work, oxidation of silicon carbide particles (SiCp) at elevated temperature and its influence on the interface layer and thermal conductivity of SiCp/ZL101 composites prepared using pressure infiltration process were investigated respectively. It is found that initial temperature for the oxidation of SiCp is about 850?°C, and that the oxidation increment of SiCp and the thickness of SiO2 layer increase with the increase in pre-oxidation temperature and time, when the oxidized temperature exceeds 1100?°C, or the duration time exceeds 2?h at 1100?°C, a small amount of ablation will take place on the SiCp, as well as the oxidized layer has some loss. The formation of SiO2 layer can provide certain interface reactions with interface layers (3.1–6.36?μm), and the higher the thickness of SiO2 layer, the thicker the interface layer in SiCp/Al composites. However, the thickness of SiO2 layer is more than 5.9?μm, which is not benefit for the formation of interface layer. With the increase in the thickness of interface layer, thermal conductivity declines, but is not linear. 相似文献
14.
I. S. Lyubutin Ch. R. Lin S. T. Lin 《Journal of Experimental and Theoretical Physics》1997,84(4):800-807
Novel icosahedral quasicrystals, in which Fe atoms possess a magnetic moment, have been found in Al70?x BxPd30?y Fey compounds with 5<x<10 and 10<y<20. The compounds have ferromagnetic properties, and their Curie temperature ranges between 280 and 340 K, the saturation magnetization σ s(5 K)≈7.5 emu/g. It follows from Mössbauer spectra that only a fraction of Fe atoms (12 to 15%) are magnetically ordered at 4.2 K, and the mean saturation field 〈H hf〉=96 kOe. The isomer shift values confirm that the atomic volume of magnetic Fe sites is larger than that of nonmagnetic Fe sites. The magnetic properties of these quasicrystals can be interpreted in terms of large magnetic clusters with a size of 185 to 290 Å. This size correspond to about 4×104 “unit cells,” hence the magnetic state can be described in terms of bulk parameters. The localized magnetic moment of Fe atoms is tentatively ascribed to bonding between Fe and B, similarly to that in the amorphous Fe~50B~50 alloy. 相似文献
15.
V. M. Nadutov T. Ericsson S. G. Kosintsev S. M. Bugaychuk Ye. O. Svystunov H. Annersten 《Hyperfine Interactions》2006,168(1-3):1023-1027
F.C.C. Fe–30.3%Ni and Fe–30.5%Ni–1.5%C (wt.%) alloys were studied by means of Mössbauer spectroscopy in external magnetic field B ext?=?2.5, 5, 7 T parallel to the gamma-beam. It is shown that distribution of effective magnetic field in the alloys is broad and that carbon expands the range of B eff. The external magnetic field increases B eff in the Fe–Ni alloy and decreases it more evidently in the Fe–Ni–C alloy. Antiferromagnetic spin coupling along the ferromagnetic component is proposed to explain data. 相似文献
16.
H. Fujii T. Okamoto W.E. Wallace F. Pourarian T. Morisaki 《Journal of magnetism and magnetic materials》1985,46(3):245-253
Measurements of magnetization, susceptibility and Mössbauer effect were made on Zr(Fe1?xVx)2 ternaries and their hydrides. Absorbed hydrogen leads to a large increase (20–30%) in volume without a change in the crystal structure. Ferromagnetism in the Fe-rich region is enhanced by hydrogen absorption, whereas hydrogenation leads to suppression of superconductivity in the V-rich range. The Fe moments in the Zr(Fe1?xVx)2 hydrides are remarkably larger than those in the corresponding host compounds. The Fe moment in the β-ZrFe2 hydride extrapolated reaches to 2.9μB, which exceeds the saturation value in bcc Fe. The hyperfine fields of 57Fe in both Zr(Fe0.8V0.2)2 and the hydride distribute widely, indicating that the Fe moments are very sensitive to the local environment arround the Fe atoms. Arguments are presented that it is possible to interprete the Fe moment increase by hydrogenation in terms of a decrease in occupancy of the 3d-band state due to electron transfers from Fe to hydrogen and/or vanadium. 相似文献
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19.
We have investigated the performance of a graphite–boron composite (GBC) with 3?wt % boron as a precursor for a boron-doped diamond heater in a Kawai-type apparatus at 15?GPa. We first tested a machinable cylinder of GBC sintered at 1000°C in Ar/H2 gas (99:1 molar ratio). Boron oxide (B2O3) formed during sintering frequently hindered the GBC heater from stable operation at temperatures higher than 1400°C by producing melt throughout the heater together with oxide and/or silicates. We then rinsed the GBC heater in hydrochloric acid to remove B2O3. After rinsing, we succeeded in stably generating temperatures higher than 2000°C. We also improved a molding process of different-sized GBC tubes for convenient use and tested the molded GBC heater. It was free from the B2O3 problem. The electromotive force of the W/Re thermocouple was successfully monitored up to 2400°C. 相似文献
20.
The dilute magnetic properties of SrSn1?xFexO3 (x = 0.01 ? 0.15) prepared by sol-gel and thermal decomposition methods were investigated by 57Fe Mössbauer spectrometry, magnetometry, and X-ray diffractometry. It was found that SrSnO3 doped with 2–8 % Fe show weak ferromagnetism although only paramagnetic doublets are observed in 57Fe Mössbauer spectra at room temperature (RT), whereas SrSnO3 doped with 10–15 % Fe show relatively strong ferromagnetism, and the sextets are additionally observed in the 57Fe Mössbauer spectra at RT. The weak ferromagnetism by doping 2–8 % Fe is considered to be caused by the induced magnetic defects, and the ferromagnetism by doping 10–15 % Fe are considered mainly due to the magnetic coupling between dilute Fe 3+ partially substituted at Sn 4+ sites in the orthorhombic structure of SrSnO3?δ accompanying the oxygen deficiencies. It is further remarkable that poor crystalline 8 % Fe doped SrSnO3?δ obtained by annealing at 600 °C shows relatively high saturation magnetization and low coercivity. 相似文献