Diffusion of Fe,Co, Nd,and Dy in R2(Fe1−xCox)14B where R=Nd or Dy

Transition metal and rare earth diffusion coefficients at 1323 K in Dy_2−yNd_y(Fe_1−xCo_x)₁₄B were determined by field emission energy dispersive spectroscopy compositional analysis of diffusion couple specimens. Various arrangements of component materials and temperatures were examined in order to understand the mechanisms affecting diffusion of the components and to predict the stability of functionally graded microstructures consisting of a dysprosium-rich (Dy_2−yNd_y(Fe_1−xCo_x)₁₄B) outer layer and a neodymium-rich (Nd₂(Fe_1−xCo_x)₁₄B) interior. Estimates of the mutual interdiffusion coefficients of Dy, Nd, Fe, and Co in this system were obtained from the preparation of arc melted and annealed polycrystalline specimens, assuming that the diffusion coefficients were independent of concentration (Grube solution). Fifteen diffusion couples were prepared and heat treated at 1323 K for various times in order to provide data for calculation of the diffusion coefficients. The results indicate that the diffusion coefficients of Fe and Co (D_Fe=3.28×10⁻¹⁰ cm²/s and D_Co=7.63×10⁻¹⁰ cm²/s) were significantly higher at 1323 K in this system than those for Dy and Nd (D_Nd=2.3×10⁻¹² cm²/s and D_Dy=2.9×10⁻¹² cm²/s).     

FORMATION AND MAGNETIC PROPERTIES OF NEW COMPOUNDS R3Fe29-xCrx(R=Y,Ce,Nd,Sm,Gd,Tb,and Dy)

A systematic investigation of structure and magnetic properties of the new R₃Fe_29-xCr_x compounds(R=Y,Ce,Nd,Sm,Gd, Tb,and Dy)has been performed. The Curie temperature of R₃Fe_29-xCr_x increased with increasing atomic number fromR=Ce to Gd and de creased from Gd to Dy. The saturation magnetization of R₃Fe_29-xCr_x at 4.2 K decreased gradually with increasing atomic number from R=Y to Dy,except for Ce. The spin reorientations of the easy magnetization d irection were observed at around 230 K for Nd₃Fe_24.5Cr_4.5 and 180 K for Tb₃Fe_28.0Cr_1.0,and the magnetohistory effects were obser ved for Nd₃Fe_24.5Cr_4.5 and Sm₃Fe_24.0Cr_5.0 in a low field of about 0.04 T. First order magnetization process occurs in magnetic field of around 2.3 T at room temperature for Tb₃Fe_28.0Cr_1.0. The saturation magnetization of Y₃Fe_27.2Cr_1.8 at 4.2 K is 52.2μ_B/f.u., which corresponds to an average magnetic moment of 1.92μ_B per each Fe atom.     

Hyperfine interactions in R x Gd1− x Fe3 intermetallics R = Tb,Y

The structural and magnetic properties of rare earth iron intermetallic compounds Tb _x Gd_1?x Fe₃ and Y _x Gd_1?x Fe₃ (x = 0. 0, 0. 1, 0. 2, 0. 4, 0. 5, 0. 6, 0. 8, 1. 0) was studied by X-ray diffraction, the ⁵⁷Fe Mössbauer effect and SQUID measurements. All investigated compounds crystallize in the rhombohedral PuNi3-type of crystal structure. The investigation of magnetic properties of R _x Gd_1?x Fe₃ proved their ferrimagnetic behavior. The Curie temperature of the investigated compounds decreases with the increase of R concentration from 721K (GdFe₃) to 655K (TbFe₃) and 533K (YFe₃). The saturation magnetic moment MS in the R _x Gd _1?x Fe₃ system increase with x parameter. The Mössbauer spectra are analyzed using four sextets, corresponding to three crystallographically (b, c, h) and four magnetically (b, c, h₁, h₂) inequivalent sites for iron. The mean hyperfine magnetic field increases with increase of the Gd concentration     

Theoretical Calculations of Thermal Broadenings and Transition Probabilities of R, R＇ and B Line-Groups for Ruby

On the basis of the unified calculation of the thermal shifts of R1 line, R2 line and ground-state-splitting transition probabilities of direct and Raman processes have theoretically been calculated. The thermal broadenings of R,The theoretically predicted transition probabilities are in good agreement with the experimental ones.PACS numbers: 71.70.Ch, 78.20.Nv, 63.20.Mt, 63.20.Kr     

Magnetocaloric effects in RT X intermetallic compounds(R = Gd–Tm,T = Fe–Cu and Pd,X = Al and Si)

The magnetocaloric effect(MCE) of RT Si and RT Al systems with R = Gd–Tm, T = Fe–Cu and Pd, which have been widely investigated in recent years, is reviewed. It is found that these RT X compounds exhibit various crystal structures and magnetic properties, which then result in different MCE. Large MCE has been observed not only in the typical ferromagnetic materials but also in the antiferromagnetic materials. The magnetic properties have been studied in detail to discuss the physical mechanism of large MCE in RT X compounds. Particularly, some RT X compounds such as Er Fe Si,Ho Cu Si, Ho Cu Al exhibit large reversible MCE under low magnetic field change, which suggests that these compounds could be promising materials for magnetic refrigeration in a low temperature range.     

Huge positive hyperfine fields for Sn impurity atoms on R sites of R–T intermetallic compounds (R=rare-earth,T=Fe,Co)

The magnetic hyperfine field B_hf of the ¹¹⁹Sn impurity atom on the R site of the RFe₂ (R=Sm, Tb, Tm), TbCo₂, RCo₅ (R=Dy, Ho, Er), GdCo₃ and Gd₂Co₇ intermetallic compounds has been investigated by Mössbauer spectroscopy technique. At 5 K, very large hyperfine fields equal to 46–56 T were observed. The _Bhf$B_{\mathrm{hf}}$ values are several times larger than commonly observed for Sn in 3d-based magnetic hosts. The hyperfine fields are positive (that is parallel to the 3d magnetic moments direction). The results can be interpreted qualitatively in terms of the theory proposed for the impurity atoms in homogeneous ferromagnetic hosts [J. Kanamori, H. Katayama-Yoshida, K. Terakura, Hyperfine Interact. 8 (1981) 573; J. Kanamori, H. Katayama-Yoshida, K. Terakura, Hyperfine Interact. 9 (1981) 363; M. Akai, H. Akai, J. Kanamori, J. Phys. Soc. Jpn. 54 (1985) 4246; S. Blügel, H. Akai, R. Zeller, P.H. Dederichs, Phys. Rev. B 35 (1987) 3271], when it is considered that the splitting between bonding and antibonding hybrid states is strongly dependent on the interatomic distance. As the distance between the probe atom and neighboring magnetic atoms increases, the population of the antibonding states grows and, as a consequence, the corresponding positive contribution to the _Bhf$B_{\mathrm{hf}}$ increases sharply. For Sn atom the positive contribution to the _Bhf$B_{\mathrm{hf}}$ dominates when the interatomic distance exceeds 0.28–0.29 nm.     

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.     

Effects of Co substitution on structural and magnetic properties of R3(Fe1−xCox)29−yVy (R=Tb,Dy)

Synthesis of two novel series of intermetallic compounds Tb₃(Fe_1−xCo_x)_27.4V_1.6 (x=0,0.1, 0.2, 0.3, 0.4) and Dy₃(Fe_1−xCo_x)_27.8V_1.2 (x=0, 0.1, 0.2, 0.3) with the monoclinic Nd₃(Fe,Ti)₂₉-type structure (3:29) is presented. In the Dy series for x=0.4 a disordered variant of the hexagonal Th₂Ni₁₇-type structure is formed. The cell parameters decrease and the Curie temperature increases with increasing of the Co content. In the case of the Tb₃(Fe_1−xCo_x)_27.4V_1.6 series in the M(T) curve a magnetic transition is observed which is attributed to spin reorientation phenomena. This critical temperature decreases with increasing Co from 473 K for x=0.1 to 393 K for x=0.3, and was not observed in the case of 0.4. XRD patterns of magnetically aligned powder samples reveal the presence of a tilted magnetic structure.     

R3(Fe1-xCox)29-yCry(R=Gd,Sm)化合物相稳定性研究

在制备出Gd3(Fe1-xCox)29-yCry化合物基础上,成功制备出Sm3(Fe1-xCox)29-yCry化合物,通过x射线衍射和热磁分析对R3(Fe1-xCox)29-yCry(R＝Gd,Sm)化合物相稳定性进行了研究,利用原子半径的几何因素解释了高Co含量3:29型化合物必须要有较多稳定元素的原因.对于不同的稳定元素,稳定元素半径越大,所需稳定元素含量越少,可是稳定元素的半径愈大,其增大晶格常数的能力愈强,这反而不利于稳定3:29相.通过对R3(Fe1-xCox)29-yCry(R=Gd,Sm)化合物相稳定性的研究,成功地制备出具有室温单轴磁晶各向异性的Gd3(Fe1-xCox)29-yCry(0.4≤x≤1.0;4.0≤y≤6.5)及新的Sm3(Fe1-xCox)29-yCry(0.4≤x≤1.0;4.5≤y≤7.5)化合物.     

Magnetic hysteretic characterization of the irradiation-induced embrittlement of Fe,Fe–Cu model alloys,and reactor pressure vessel steel

Neutron irradiation is known to cause embrittlement of iron-based materials; in the nuclear industry, this effect can be detrimental for reactor pressure vessel steels. In this paper, we investigate the variations of the magnetic hysteretic behavior due to neutron irradiation, for four materials, i.e. nominally pure Fe, Fe-0.1 wt% Cu and Fe-0.3 wt%Cu model alloys, and a reactor pressure vessel steel, JRQ A533-B. Two parameters related to the magnetization loop shape, i.e. maximum relative differential permeability and peak intensity of local interaction field distribution, are measured as a function of neutron fluence. For all materials both parameters decrease with increasing fluence, due to the irradiation-induced formation of nano-size defects. This decreasing trend in magnetic parameters during embrittlement is noticeable regardless the origin of the embrittlement, which can be only Cu-precipitation (thermal aging of Fe–Cu), only matrix damage (irradiation of pure Fe), or both mechanisms (irradiation of Fe–Cu or steel). The magnetic parameters relatively change up to 40%, which indicates the potential of magnetic characterization to assess irradiation-induced material hardening and embrittlement.     

Local configurations and atomic intermixing in as-quenched and annealed Fe1−xCrx and Fe1−xMox ribbons

Local atomic configuration, phase composition and atomic intermixing in Fe-rich Fe_1?xCr_x and Fe_1?xMo_x ribbons (x = 0.05, 0.10, 0.15), of potential interest for high-temperature applications and nuclear devices, are investigated in this study in relation to specific processing and annealing routes. The Fe-based thin ribbons have been prepared by induction melting, followed by melt spinning and further annealed in He at temperatures up to 1250 °C. The complex structural, compositional and atomic configuration characterisation has been performed by means of X-ray diffraction (XRD), transmission Mössbauer spectroscopy and differential scanning calorimetry (TG-DSC). The XRD analysis indicates the formation of the desired solid solutions with body-centred cubic (bcc) structure in the as-quenched state. The Mössbauer spectroscopy results have been analysed in terms of the two-shell model. The distribution of Cr/Mo atoms in the first two coordination spheres is not homogeneous, especially after annealing, as supported by the short-range order parameters. In addition, high-temperature annealing treatments give rise to oxidation of Fe (to haematite, maghemite and magnetite) at the surface of the ribbons. Fe_1?xCr_x alloys are structurally more stable than the Mo counterpart under annealing at 700 °C. Annealing at 1250 °C in He enhances drastically the Cr clustering around Fe nuclei.     

Hyperfine fields and Fe magnetic moments in Fe−Ni invar alloys

Mössbauer spectra of Fe_1?x Ni _x withx=0.40, 0.35 and 0.32 were taken at various temperatures and fitted withB _hf distributions. TheP(B _hf) curves generally show a peak and a low-field tail. The peakB ^* and the average \(\bar B\) were obtained in theT→0 limit. Fe moments were deduced from these data with help of a semiempirical equation. While the average \(\bar \mu _{Fe} \) decreases withx (invar anomaly), a large fraction of Fe atoms retain the strong moment (≈ 2.7 μ_B) typical of Ni-rich alloys. This result is consistent with a two-states model for invar.     

Magnetic Thermocouples Made of Co–Fe and Ni–Fe Permalloys

Technical Physics - Magnetized and unmagnetized Co–Fe and Ni–Fe alloys fabricated on a two-high casting installation in the form of thin flexible amorphous films are promising materials...     

Die Röntgenolumineszenz der Kristalle von NaCl: Fe

Ohne Zusammenfassung

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Nacl: Fe

     

Assignment of Photoelectron Spectra of MC2 （M= V, Cr, Fe, and Co）

Hybrid density functional theory （DFT） calculations are performed to study MC2 （M= V, Cr, Fe and Co） clusters in the neutral and anionic charge states. We find that the equilibrium geometries of MC2 and their anions are all cyclic structures with C2v symmetry, which agrees well with the previous theoretical studies. The Mulliken charge and spin populations of MC2 clusters and their anions are also calculated, and it is found that the electron charge transformations from anions to neutral molecules mainly take place on the M atoms. Time-dependent DFT is used to calculate the excited states, and a theoretical assignment for the features in the experimental photoelectron spectrum is given, which are in good agreement with the available experimental data.     

Synthesis, MSssbauer Spectra and Magnetic Properties of Quasi-One-Dimensional Fe3O4 Nanowires

Quasi-one-dimensional Fe3O4 nanowires in diameter of about 200nm were assembled into anodic aluminium oxide templates via electrodepositing and heat-treating processes. The nanowires have a polycrystalline spinel structure with α=8.317А, and each nanowire is composed of fine Fe3O4 crystallites with size of about 30nm.     

Measurement of K X-ray intensity ratios in Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn employing carbon and nitrogen projectiles – VTT method

A method is suggested to effect the self absorption correction in a different way to estimate the K X-ray intensity ratios particularly when heavy ions are used as projectiles. Employing this method, the K_β/K_α intensity ratios are measured in some 3d shell elements by using Carbon and Nitrogen ions as exciting agents. The K_β/K_α intensity ratios thus obtained in the present work are compared with the intensity ratios due to some previous authors and also with Scofield theoretical values. Received 14 August 2000 and Received in final form 3 January 2001