Thickness-dependent magnetic properties of Ni81Fe19, Co90Fe10 and Ni65Fe15Co20 thin films

We present results of magnetization and magnetic anisotropy measurements in thin magnetic films of the alloys Ni₈₁Fe₁₉, Co₉₀Fe₁₀ and Ni₆₅Fe₁₅Co₂₀ that are commonly used in magnetoelectronic devices. The films were sandwiched between layers of Ta. At room temperature the critical thickness for all the films to become ferromagnetic is in the range 11–13 Å. In Co₉₀Fe₁₀ the coercivity and the anisotropy field both depend strongly on layer thickness.     

Electronic structure and magnetism of NpTAl (T=Co, Ni, Rh, Ir and Pt) and NpNiGa from first-principles calculations

First-principles calculations based on density-functional theory were performed for the first time on NpTAl (T=Co, Ni, Rh, Ir and Pt) and NpNiGa. The electronic density of states and equilibrium volume were studied using relativistic full-potential APW plus local-orbitals calculations. The magnetocrystalline anisotropy energy was estimated from total-energy calculations and the a-axis was predicted to be the easy axis of magnetization with the exception of T=Rh. Finally, we employed the LSDA+U method to mimic the orbital polarization and to obtain the correct total magnetic moments in experimental equilibrium.     

Cr、Mn、Co、Ni掺杂对Al13Fe4相稳定性和力学性能影响的第一性原理研

采用基于密度泛函理论的第一性原理计算方法,系统地研究了不同掺杂浓度下过渡族元素Cr、Mn、Co、Ni在Al13Fe4相中的占位情况、结构稳定性和机械性能. 计算得到所有的Al13(Fe24-xMx) (M=Cr、Mn、Co、Ni;X=1,2,4)相都具有良好的热力学稳定性和机械稳定性. 相同掺杂浓度化合物的形成焓按如下顺序减小：Al78(Fe24-xCrx) > Al78(Fe24-xMnx) > Al13Fe4 > Al78(Fe24-xNix) > Al78(Fe24-xCox).形成焓的降低增加了Al13Fe4相成核驱动力,Co和Ni有利于促进Al-Fe合金中Al13Fe4相形核,细化Al13Fe4相. 过渡族元素可以改善金属间化合物的脆性,增强塑性变形能力. 并且随着掺杂浓度的增加,过渡族元素的加入对脆性的改善呈先增大后减小的趋势.     

Dimensionality crossover upon magnetic saturation in Fe, Ni and Co

The magnetic saturation process of iron, nickel and cobalt single-crystal spheres is studied using neutron scattering in a vertical magnetic field. It is observed that upon magnetic saturation, the scattering intensities decrease instead of increasing. This indicates a decreasing coherent scattering with field. The spin precession around the field axis therefore can be assumed to be incoherent along directions transverse to the field. Comparison of the temperature dependence of the spontaneous magnetization measured by zero field NMR on the one hand and by the macroscopic magnetization on the other hand shows that Fe, Ni and Co are three-dimensional (3D) in the zero field ground state but one dimensional (1D) in the magnetically saturated state. The observed decrease in neutron scattering intensity is consistent with this conclusion. The change in dimensionality is associated with a crossover. Our neutron scattering study shows that the crossover occurs at a field that is smaller than the demagnetization field. The dimensionality crossover, therefore, is driven not by the field but by the associated forced magnetostriction.     

Electronic structure of the ordered ferromagnetic alloys Ni3Mn,Ni3Fe,and Ni3Co

Calculations of the band structure of the ferromagnetic alloys Ni₃Mn, Ni₃Fe, and Ni₃Co are presented. The results are compared with experimental data. Change in the electronic structure as one goes from Ni₃Mn to Ni₃Co is analyzed. The occurrence of ferromagnetism in the alloys studied and the possibility of their existence in an ordered ferromagnetic state are examined.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 82–88, June, 1988.     

高压下Ni3Al热力学性质的第一性原理研究

运用第一性原理方法结合准谐Debye-Grüneisen模型研究了高压下Ni3Al的热力学性质,拟合了Ni3Al的状态方程,计算了不同压强下Ni3Al的弹性模量及吉布斯自由能等热力学性质随温度的变化关系. 计算结果表明：采用七阶Birch-Murnaghan方程拟合的晶格常数与实验测量结果吻合较好;零压下弹性模量、吉布斯自由能、焓、熵、热容和体膨胀系数随温度的变化与实验值符合较好;在特定压强下,Ni3Al的弹性模量和吉布斯自由能随温度升高而减小,焓、熵随温度升高而增加;预测的德拜温度约为500K,与实验值符合较好.     

Magnetism of Fe,Co, and Ni nanowires encapsulated in carbon nanotubes

We have investigated the electronic and magnetic properties of Fe, Co, and Ni nanowires encapsulated in carbon nanotubes (CNTs) using spin polarized ab initio calculation. The incorporated systems with hollow region between the nanowire and the C shell have the enhanced magnetic moments compared to the ferromagnetic nanowires tightly wrapped by CNTs. The Co nanowire encapsulated in CNTs is a strong ferromagnet and has high spin polarization regardless of the distance between the nanowire and the C shell. The results show that the Co-filled CNTs are useful for spin polarized transport nanodevice.     

The electrical resistivity of liquid Fe,Co, Ni and Pd

The electrical resistivity of Fe, Co, Ni and Pd has been measired at high temperatures in the solid and liquid state. We discuss the results in the light of recent ideas on the Ziman theory and the spin-disorder scattering of liquid transition metals.     

Defects in hexagonal-AlN sheets by first-principles calculations

Theoretical calculations focused on the stability of an infinite hexagonal AlN (h-AlN)sheet and its structural and electronic properties were carried out within the frameworkof DFT at the GGA-PBE level of theory. For the simulations, an h-AlN sheet model systemconsisting in 96 atoms per super-cell has been adopted. For h-AlN, we predict an Al-N bondlength of 1.82 Å and an indirect gap of 2.81 eV as well as a cohesive energy which is by6% lower than that of the bulk (wurtzite) AlN which can be seen as a qualitativeindication for synthesizability of individual h-AlN sheets. Besides the study of a perfecth-AlN sheet, also the most typical defects, namely, vacancies, anti-site defects andimpurities were also explored. The formation energies for these defects were calculatedtogether with the total density of states and the corresponding projected states were alsoevaluated. The charge density in the region of the defects was also addressed.Energetically, the anti-site defects are the most costly, while the impurity defects arethe most favorable, especially so for the defects arising from Si impurities. Defects suchas nitrogen vacancies and Si impurities lead to a breaking of the planar shape of theh-AlN sheet and in some cases to the formation of new bonds. The defects significantlychange the band structure in the vicinity of the Fermi level in comparison to the bandstructure of the perfect h-AlN which can be used for deliberately tailoring the electronicproperties of individual h-AlN sheets.     

Lifetimes of excited electrons in Fe and Ni: first-principles GW and the T-matrix theory

We present the results of an ab initio calculation of excited electron lifetimes in ferromagnetic materials which incorporates non-spin-flip and spin-flip processes within GW and T-matrix approaches. The method we develop is applied to low-energy electron excitations in Fe and Ni. It is found that the spin-wave generation in Fe essentially reduces the lifetimes of the spin-minority d states whereas the free-electron-like spin-minority states and all the spin-majority states are affected much less. The influence of spin-flip scattering on the lifetimes in Ni appears to be weak. The T-matrix non-spin-flip processes are important for the lifetimes of excited spin-minority states.     

Lifetimes of excited electrons in Fe and Ni: first-principles GW and the T-matrix theory

We present the results of an ab initio calculation of excited electron lifetimes in ferromagnetic materials which incorporates non-spin-flip and spin-flip processes within GW and T-matrix approaches. The method we develop is applied to low-energy electron excitations in Fe and Ni. It is found that the spin-wave generation in Fe essentially reduces the lifetimes of the spin-minority d states whereas the free-electron-like spin-minority states and all the spin-majority states are affected much less. The influence of spin-flip scattering on the lifetimes in Ni appears to be weak. The T-matrix non-spin-flip processes are important for the lifetimes of excited spin-minority states.     

Table of hyperfine fields for impurities in Fe,Co, Ni and Gd

All data available in the literature for the impurity hyperfine fields in Fe, Co, Ni and Gd matrices are collected and tabulated. The literature search was carried out for all references listed in Physics Abstracts on papers published till the end of December 1978. The present work is an extension of similar earlier compilations [1–6]. The data are arranged in ten columns as explained below:     

Theoretical calculations on atomistic behaviors in transition metals (Fe, Co, Ni)-Al multilayer system: ab initio approach

The energetics and the structural characteristics of atomistic behaviors for transition metal (TM; Fe, Co and Ni)-Al multiplayer systems were quantitatively investigated using ab initio calculations. The energy barriers for the surface diffusion of adatom were calculated to be 0.89, 1.01 and 1.98 eV for Fe, Co and Ni on Al (0 0 1) systems, respectively. For Al/TM (0 0 1) systems, however, the energy barriers turned out to be relatively smaller than those for the corresponding opposite systems. It could be verified that the incorporation process for TM/Al (0 0 1) system can be occurred much easier than that for the Al/TM (0 0 1) systems due to relatively small energy barriers and positive energy gains.     

Magnetic behavior of na films with Fe, Co, and Ni impurities

Thin films of Na with Fe, Co, and Ni impurities are investigated. The magnetization of the impurities is measured by means of the anomalous Hall resistance. Fe and Co show a moment of about 6mu(B), while for Ni no moment is detected. Furthermore, the magnetic dephasing of the conduction electrons is measured by means of weak localization. The dephasing rate 1/tau(phi) of the 3d impurities differ qualitatively. For Fe impurities, 1/tau(phi) is so large that it cannot be measured. For Co, 1/tau(phi) has a moderate value while Ni shows hardly a dephasing effect at all.