Magnetic properties of amorphous alloys

The magnetic properties of existing amorphous iron based materials, i.e., Fe--metalloid, Fe--early transition metals and Fe--rare earth alloys, are briefly discussed for some representative alloys. The spin orientation of amorphous Fe--metalloid alloys has been determined by the angular dependence of hyperfine interactions. It is shown that in iron--early transition metals ferromagnetic order is not long-ranged, but determined by magnetic clusters. The magnetic hyperfine field distributions of Fe-rich iron--early transition metals consist of a high and a low field tail. The magnetic structure has been investigated for two representative Fe--RE (RE = Er, Ce) amorphous alloys. For the first time, the magnetic coupling phenomenon in amorphous/crystalline multilayers has been discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Studies on cryoprotectant toxicity to zebrafish (Danio rerio) ovarian tissue fragments

Cryopreservation of ovarian tissue is a viable alternative to cryopreservation of oocytes and embryos in many species but it has not been studied in fish. Selection of cryoprotectant is an important step in designing cryopreservation protocols. In order to identify the optimum cryoprotectant (CPA) in a suitable concentration for zebrafish ovarian tissue cryopreservation, studies on toxicities of five commonly used cryoprotectants methanol, ethanol, dimethyl sulfoxide (DMSO), ethylene glycol (EG) and propylene glycol (PG) were carried out. Experiments were conducted on ovarian tissue fragments consisting of stage I and stage II ovarian follicles. Ovarian tissue fragments were incubated in 90% L-15 medium (pH 9) containing 1-4M cryoprotectants for 30min at 22°C. Three different tests were used to assess ovarian tissue fragment viability: trypan blue (TB) staining, fluorescein diacetate (FDA) combined with propidium iodide (PI) staining and adenosine 5′- triphosphate (ATP) assay. Results from these tests showed that ATP assay was more sensitive than FDA+PI or TB staining for assessing cryoprotectant toxicity to follicles in tissue fragments. Methanol and ethanol were the least toxic cryoprotectants tested. Cryoprotectant toxicity increased in the order of methanol/ethanol, DMSO, PG and EG. Ethanol was used for zebrafish ovarian tissue for the first time and the results showed that the effect of methanol and ethanol on ovarian tissue fragments were comparable. As methanol has been shown to be the most effective cryoprotectant for zebrafish ovarian follicles in our laboratory, the use of ethanol will also be considered in assisting future freezing protocol design. The present study also showed that stage II ovarian follicles are more sensitive to cryoprotectant treatment than stage I follicles in tissue fragments. The results obtained in this study provided useful information for ovarian tissue fragment cryopreservation protocol design in the future.     

Mössbauer Studies of Nanosize CuFe2O4 Particles

⁵⁷Fe Mössbauer spectra of pulsed-laser deposited (PLD) films of CoFe₂O₄ of 0.3 µm thickness is investigated using transmission geometry is reported. Mössbauer parameters were determined for the tetrahedral (A) and octahedral (B) sites. The PLD processed films gave measurable spectra with no visible evidence of clustering or multiple phases present. Results on the films agreed with those of the bulk material. The films exhibited magnetic hyperfine and quadruple splittings similar to that of bulk CoFe₂O₄. This work demonstrates that measurable transmission Mössbauer spectra may be obtained for PLD deposited CoFe₂O₄ thick films.     

Mössbauer study of ultrafine amorphous Fe−B alloys

The chemical composition of ultrafine amorphous Fe−B powders prepared by a chemical reduction depends on the mixed molar ratio of KBH₄ to Fe ions. We propose the following reaction processes for the formation of ultrafine Fe−B powders: (1) 4Fe²⁺+2BH₄₋+6OH⁻→2Fe₂B+6H₂O+H₂ and (2) 4Fe²⁺+2BH₄₋+7OH⁻→2Fe₃B+Fe+BO₂+5H₂O+5/2H₂.     

Mössbauer study of amorphous Fe2RE (RE=Ce,Er) alloys

Among amorphous Fe₂RE (RE=Er, Ce, Gd, La, Pr, Sm, Dy, Ho) alloys, Fe₂Ce exhibits a tendency toward short range order, while the other Fe₂RE compounds show clustering. However, we have almost no information about environments around Fe atoms. Using Mössbauer spectroscopy we have determined the quadrupole splitting distributionsP(QS) of two representative amorphous Fe₂RE (RE=Ce, Er) alloys, leading to local environments of Fe atoms. The analysis of the mixed magnetic dipole and quadrupole interactions in Fe₂Er shows two kinds of electrical field gradients (EFT) with the positive and negative signs in the sample, indicating a random packing of Fe atoms. Furthermore, the analyzed quadrupole splitting distributionP(QS) of Fe₂Er also supports random packing in this amorphous alloy. On the other hand, the amorphous Fe₂Ce alloy shows two kinds of distributions of quadrupole splitting; the major component indicating random packing and the minor component Ce-rich Ce-Fe clusters.     

Body-centered-cubic structure as a basis for deriving the intermetallic crystal structures

Hyperfine Interactions - Dioximes as ligands are used as analytical reagents and serve as models for biological systems as well as catalysts in chemical processes. A number of novel mixed complexes...     

Spin transition in a chainlike supramolecular iron(II) complex

A one-dimensional supramolecular head-to-tail N+ -H...N-type hydrogen-bonded chain of the complex [FeII(L)2H](ClO4)3.MeOH [L = 4'-(4'-pyridyl)-1,2':6'1'-bis(pyrazolyl)pyridine] exhibits a reversible, thermally driven spin transition at 286 K with a hysteresis loop of ca. 2 K.     

Vibrations of balanced fault-free ball bearings

This paper investigates the vibrations of balanced fault-free ball bearings. A lumped mass-damper-spring model is adopted including the use of the Hertzian contact theory to represent the stiffness of the bearing rolling elements. We found that the equilibrium point of the bearing undergoes a supercritical pitchfork bifurcation as the bearing internal clearance increases. We developed closed-form expressions for the frequency-response functions of the horizontal and vertical motions of bearings with small internal clearance (below the bifurcation point). We also developed a chaos map to describe the locations and intensity of chaos in the internal clearance-shaft speed parameter space for bearings with larger internal clearance (beyond the bifurcation point).     

Antiferromagnetic exchange coupling in amorphous Fe–Sc alloys

Results of ⁵⁷Fe Mössbauer, AC and DC susceptibility, grazing incidence X-ray diffraction, resistivity and Rutherford-backscattering measurements on the amorphous alloys ${\text{Fe}}_{100 - x} {\text{Sc}}_x (8 \leqslant x \leqslant 70)$ give for the first time convincing evidence for the antiferromagnetic exchange coupling between Fe-moments. The antiferromagnetic coupling between Fe-moments is for $(8 \leqslant x \leqslant 70)$ limited to certain regions (magnetic clusters) of the sample. The nature of the coupling is of the Heisenberg type. For $8 \leqslant x < 20$ , the magnetic coupling between Fe-moments is across nonmagnetic Sc-atoms. The conduction electrons mediate an indirect magnetic interaction between the Fe-moments. The magnetic exchange coupling between Fe-moments across Sc-atoms is negative. The antiferromagnetic coupling between Fe-moments can be explained by the Ruderman-Kittel-Kasuya-Yosida, RKKY, interaction by taking into account the damped oscillatory behavior of the RKKY interactions.     

Ab initio study of ternary radical–molecule complexes between HCN(HNC) and HO(HS) species

MP2 calculations with the cc-pVTZ basis set were used to analyze the intermolecular interactions in ternary radical–molecule complexes between HCN(HNC) and HO(HS) species, in gas phase and in water media. Particular attention was given to parameters such as the cooperative energies and many-body interaction energies. The results indicate that hydrogen bonding between two HCN(HNC) molecules gives more stability to triads than hydrogen bonding between HCN(HNC) and OH(SH) species. The electronic properties of the complexes were analyzed using the parameters derived from the atoms in molecules methodology. The water media has an enhancing influence on the stabilities of studied clusters versus the ones obtained in gas phase.