SEM identification of the amorphous state of Fe−B ribbons

Based on X-ray diffraction and electron microscopy data on morphological inhomogeneities at the interfaces in Fe?B ribbons, the boundary boron concentration separating the crystal and amorphous states upon spinning (~10 at %) is established. A modulated isotropic stochastic wave structure is detected, the relaxation of which can be presented as spinodal decomposition.     

Elasticity of the B2 phase and the effect of the B1–B2 phase transition on the elasticity of MgO

A study of the high-pressure anisotropy of MgO was conducted using first-principles calculations based on density functional theory within the generalized gradient approximations. The pressure dependence of the elastic stiffness coefficients and the anisotropy parameters, in both B1 and B2 phases, shows that for high-hydrostatic compression the easiest deformation is the shear along (100) plane and the the material's response to deformation and to shearing strains is quite the same. According to the calculations of the velocities of propagation of elastic waves, we deduced that MgO develop an elastic anisotropy, especially, in the B1 phase. We present the B2 phase elastic properties which are not already studied under high pressure.     

Mössbauer effect studies of the Dy12Fe82B6 system

The Mössbauer measurements of both⁵⁷Fe and¹⁶¹Dy in Dy₁₂Fe₈₂B₆ system are reported. The presence of B exceeds the magnetic hyperfine fields at both⁵⁷Fe and¹⁶¹Dy nuclei as compared to corresponding pure metals Fe and Dy respectively. The only small excess of the hyperfine field at⁵⁷Fe nucleus is observed. The excess at¹⁶¹Dy nucleus is about 12% of the free ion Dy³⁺ value.     

Hysteresis of nanocrystalline R–Fe–B

The energetic model of ferromagnetic hysteresis calculates the magnetic state of materials by minimizing the total energy function for statistical domain behavior. The approach shows good agreement with the magnetization curves of mechanically alloyed Pr₉Fe₈₅B₆ powder, heat treated at different temperatures.     

Effect of Co on the thermal stability and impact toughness of sintered Nd–Fe–B magnets

The effect of Co on the thermal stability and impact toughness of sintered Nd–Fe–B magnets has been investigated. The results showed that the addition of Co decreased the intrinsic coercivity and the temperature coefficient of remanence (α), and increased the temperature coefficient of coercivity (β) for sintered Nd–Fe–B magnets. The impact toughness of sintered Nd–Fe–B magnets with the addition of Co first decreases, reaches a minimum, and then starts to increase. The possible reasons for increasing the temperature coefficients of coercivity (β) for sintered Nd–Fe–B magnets were analyzed, and the relations between the microstructure and impact toughness of sintered Nd–Fe–B magnets were studied.     

Effect of optimized aging processing on properties of the sintered Dy-doped Nd–Fe–B permanent magnet

We investigate the effect of the optimized aging processing on magnetism and mechanical property of the sintered Dydoped Nd–Fe–B permanent magnet. The experimental results show that the magnetism, especially intrinsic coercivity, of the optimized aged Dy-doped Nd–Fe–B magnet is more excellent than that of the sintered one, but the former's strength and hardness are lower than that of the latter. It was observed that the optimized aged Dy-doped Nd–Fe–B magnet have more uniform grain size, thinner(Nd, Dy)-rich boundary phase. By means of the EBSD technology, the number of larger angle grain boundaries in the optimized aged Dy-doped Nd–Fe–B magnet is more than that of the sintered one. The reasons for the increased intrinsic coercivity and decreased mechanical properties of the optimized aged Dy-doped Nd–Fe–B magnet are also discussed.     

The temperature dependence of the Mössbauer hyperfine parameters in Nd2Fe14B

We have determined the temperature dependence of the internal hyperfine field, isomer shift, and quadrupole shift at each of the six iron sites in Nd₂Fe₁₄B. The hyperfine parameters are consistent with the local iron site environments. The quadrupole and isomer shifts and their temperature dependences support our assignments of the relative ordering of the internal hyperfine fields as j₂>k₂>ck₁>j₁>c. We obtain a Mössbauer temperature of 390 K for Nd₂Fe₁₄B, which compares well with the Debye temperature of 420K for pure iron.     

Determination of the sites of Fe atoms in Fe-substituted Mn12

In this paper neutron diffraction experiments were performed for Fe-substituted Mn12 in order to determine the sites of Fe atoms. The results of structure refinements for the sample with our accessed highest Fe content showed that all Fe atoms occupied Mn（3） sites in the Mn12 skeleton. The x-ray absorption fine structure experiments as well as multiple scattering simulations gave the same result. Thus we concluded that Fe atoms only occupied Mn（3） sites. This conclusion also means that Fe-substituted Mn12 series only includes the four single-molecule magnets of [Mn12-xFexO12（CH3COO）16（H2O）4]·2CH3COOH·4H2O （x = 1, 2, 3, and 4）, denoted by Mn11Fe1, Mn10Fe2, MngFe3, and Mn8Fe4, respectively.     

Role of the chemical ordering on the magnetic properties of Fe–Ni cluster alloys

The spin and orbital moments of fcc Fe-Ni cluster alloys are determined within the framework of a d-band Hamiltonian including the spin-orbit coupling non perturbatively. Different sizes (up to 321 atoms), compositions, and chemical configurations (random alloys as well as core-shell arrays of iron and nickel atoms) are considered in order to reveal the crucial role played by local order and stoichiometry on the magnetic moments of the clusters. Interestingly, we have found considerably reduced average magnetizations for Fe-Ni clusters with Fe cores compared to that of the bulk alloy with the same composition. Indeed, in these configurations not only antiparallel arrangements between the local moments of some Fe atoms within the iron core are found, but also the total magnetization of the surface Ni atoms is significantly quenched. On the opposite, the disordered and Ni-core cluster alloys are characterized by high magnetizations resulting from saturated-like contributions from both Ni and Fe atoms, in agreement with recent ab-initio calculations. In general, the local orbital magnetic moments are strongly enhanced with respect to their bulk values. Finally, the variation of the orbital-to-spin moment ratio with the chemical order is discussed.     

Hyperfine interactions of interstitial12B in Fe,V and Ta studied by use of the asymmetric β decay

Magnetic hyperfine fields and spin-lattice relaxation times of interstitial and substitutional¹²B nuclei in Fe are studied in a temperature range, 100 K<T<1200 K, by use of the asymmetric decay from the spin polarized nuclei and NMR detection. In order to infer information regarding the location of¹²B nuclei and expansion in the nearest Fe surrounding following recoil implantation, hyperfine interactions of¹²B in non-magnetic bcc V and Ta crystals are studied.     

Effects of underlayer materials and substrate temperatures on the structural and magnetic properties of Nd2Fe14B films

Thin films of Nd_2Fe_{14}B were fabricated on heated glass substrates by dc magnetron sputtering. Different material underlayers (Ta, Mo, or W) were used to examine the underlayer influence on the structural and magnetic properties of the NdFeB films. Deposited on a Ta buffer layer at 420℃, the 300 nm thick NdFeB films were shown to be isotropic. But when the substrate temperature T_s was elevated to 520℃, the Nd_2Fe_{14}B crystallites of (00l) plane were epitaxially grown on Ta (110) underlayer. In contrast, Mo (110) buffer layer could not induce any preferential orientation in NdFeB film irrespective of the substrate temperature or film thickness. The W buffer layer was found to be most effective for the nucleation of Nd_2Fe_{14}B crystallites with c-axis alignment perpendicular to the film plane when T_s<490℃. But at T_s=490℃ the magnetic layer became isotropic. The maximum coercivity obtained was about 995 kA/m for the 100nm film deposited on W underlayer at 490℃. These variations were tentatively explained in terms of the lattice misfit between the underlayer and the magnetic layer, combined with the considerations of underlayer morphologies.     

Effect of Tb on the intrinsic coercivity and impact toughness of sintered Nd–Dy–Fe–B magnets

The effect of Tb on the coercivity and impact toughness of sintered Nd–Dy–Fe–B magnets has been investigated. The results showed that the addition of Tb enhanced the intrinsic coercivity, reduced the remanence and improved the impact toughness of sintered magnets. The optimum impact toughness of sintered magnets was achieved when 1.0 at% Tb was incorporated. The possible reasons for increasing the intrinsic coercivity and improving impact toughness of sintered magnets were analyzed, and the relations between the microstructure and impact toughness of sintered magnets were studied.     

Temperature dependence of the Mössbauer spectra of amorphous and nanocrystallized Fe86Zr7Cu1B6

Mössbauer measurements have been performed on amorphous and nanocrystalline alloy ribbons of nominal composition Fe₈₆Zr₇Cu₁B₆. The nanocrystalline samples were obtained by annealing the as-quenched alloy at different temperatures in the range between 650 and 870 K. Mössbauer spectra of the as-quenched amorphous sample have been recorded at 77 K, room temperature and above the Curie temperature (330 K) at 360 K. We have also performed Mössbauer measurements at room temperature in the nanocrystalline alloys to characterize the phases that appear after the annealing and their relative concentration. The as-quenched sample spectra reveal the existence of two inequivalent sites for Fe. Such a feature is also observed in the remaining amorphous phase of the annealed samples. In the first steps of crystallization, -Fe precipitates and its concentration increases with the annealing temperature. The experimental results suggest that the composition of the whole amorphous phase does not suffer large changes during crystallization.     

Studying the properties of Fe and Fe–Co nanotubes in polymer ion-track membranes

Iron and iron–cobalt nanostructures are probed by means of Mössbauer spectroscopy combined with scanning electron microscopy, energy-dispersion analysis, and X-ray diffraction. The obtained nanostructures are single-phase Fe_{1 ? x}Co _x (0 ≤ x ≤ 1) nanotubes that have high degrees of polycrystallinity and a bcc lattice 12 μm long and 110 ± 3 nm in diameter, with walls 21 ± 2 nm thick. A random distribution of the orientations of the magnetic momenta of Fe atoms are observed for Fe nanotubes, while Fe–Co nanotubes are characterized by a magnetic texture along their axes.     

On the control of microstructure in rapidly solidified Nd–Fe–B alloys through melt treatment

Rapidly solidified (RS) Nd₂Fe₁₄B alloys were prepared by melt-spinning under different melt treatment conditions i.e., the melt temperature was varied prior to ejection onto the quenching wheel. X-ray diffraction, transmission electron microscopy, thermal analysis and magnetic measurement were conducted on the as-quenched alloys to investigate their structural and magnetic characteristics. RS Nd₂Fe₁₄B alloys may display a variety of microstructures depending upon the thermal history of the melt before ejection: it was possible to synthesize an entirely amorphous structure, a partially amorphous structure containing nuclei and/or nanophases and a nanocrystalline structure. The relationship between the formation of crystalline nuclei or nanophases and the thermal history of the melt was studied. A lower melt ejection temperature produced a nanocrystalline microstructure, while higher melt ejection temperatures (T>1723 K) largely eliminated the presence of nuclei and associated nanophases and produced an amorphous product. The experimental results indicated that optimization of the melt treatment conditions will produce rapidly solidified Nd–Fe–B alloys with a more uniform microstructure.     

Calculation of the electronic structure and hyperfine fields for Fe1 − x Co x B and (Fe1 − x Co x )2B compounds by the Korringa-Kohn-Rostoker method

The magnetic properties of Fe_{1 ? x} Co _x B and (Fe_{1 ? x} Co _x )₂B disordered compounds were investigated using first-principles calculations of the electronic structure in the framework of the density functional theory with the Korringa-Kohn-Rostoker method. The concentration dependences of the magnetic moments and the electron density were calculated for the Fe_{1 ? x} Co _x B solid solutions. The results obtained were used to analyze in detail and to interpret the transition from a magnetic phase to a nonmagnetic phase, which was previously revealed from the experiments in the compounds under investigation. The performed analysis of the calculated hyperfine fields induced by the electronic shells at the iron and cobalt atoms in the (Fe_{1 ? x} Co _x )₂B borides made it possible to explain the experimentally observed magnetic anisotropy.     

Properties of Some Bound States of the 56Fe Nucleus Excited by the 55Mn(p,γ)56Fe Reaction

Radiative decay of 21 resonances in the ⁵⁵Mn(p,)⁵⁶Fe reaction was studied in the proton beam energy region E _p = (1.3-1.8) MeV. Properties of bound states in the final ⁵⁶Fe nucleus have been deduced from accurately measured very complex -ray spectra. About 150 levels have been firmly established for excitation energy up to 8 MeV and 93 of them have been observed for the first time or their established energy is substantially more accurate than in former publications or some other information is new. For each of the 57 levels, there has been established its decay and firmly observed at least one decay branch. Spin and parity have been newly determined or appreciated for 35 levels and for 35 levels the mean lifetime has been newly established by the DSAM method. Crude comparison of the observed level density with the statistical Fermi model prediction has been also performed.     

Effect of the temperature of megaplastic deformation on the redistribution of carbon in Fe–Ni–C austenite

Structural phase transitions induced by megaplastic deformation at temperatures of 80–573 K are investigated in high-carbon Fe–Ni austenite of the invar range of compositions. Phase transformations change their direction from the nonequilibrium dissolution of graphite particles upon low-temperature (80 and 293 K) deformation and the activation of carbon precipitation from the fcc matrix to graphite upon high-temperature (373–573 K) deformation, due to the structure being saturated with point defects.