Magnetization process of Fe layers in Fe/Nd multilayered films investigated by57Fe Mössbauer spectroscopy

The magnetization process of Fe and Nd layers at 5K in Fe/Nd multilayered films with strong perpendicular magnetic anisotropy is elucidated from a comparison of⁵⁷Fe Mössbauer spectra in the presence of the external field applied parallel to the film plane with total magnetization. At zero external field, the film has a magnetic multi-domain structure. The Nd layer moment is perpendicular to the film plane and the Fe layer moment points in the out-of-plane direction. The Fe layer moment monotonically rotates to the in-plane direction with increasing external field parallel to the film plane, while the Nd layer moment is oriented to the film normal direction up to the external field of 10kOe, above which the Nd layer moment gradually turns to the direction of the external field.     

Magnetic anisotropy in Fe/rare‐earth multilayers

Magnetic anisotropy of Fe/RE multilayers (RE=Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu) was studied using ⁵⁷Fe Mössbauer spectroscopy. Perpendicular magnetic anisotropy was observed in Fe/Pr, Fe/Nd, Fe/Tb, and Fe/Dy multilayers. The external field dependence of the direction of magnetic moments was also examined for Fe/Tb multilayers. The results imply that the perpendicular magnetic anisotropy originates from the single ionic anisotropy of RE at the interfaces.     

Magnetic and structural properties of FeX/Tb15 Å multilayers

Magnetic domains in Fe/Tb sputter-deposited multilayer films are studied magneto-optically using a Kerr microscope. These observations together with other experimental measurements (vibrating sample- and torque magnetometry) showed the important role of the iron-layer thickness d_Fe on the magnetic properties of the films. At certain combinations of the layer thicknesses both perpendicular and in-plane anisotropies are present in the film. The structural investigations indicate that a gradual increase of the iron-layer thickness d_Fe leads to a phase transition of iron from amorphous to crystalline at certain thicknesses of the iron layer, which is also reflected in the magnetic behavior of the films. The differences between the magnetic properties of the investigated multilayered Fe/Tb films and those of amorphous FeTb films are discussed as well.     

The interaction of Fe on MgO(1 0 0) surfaces

The atomic interaction and magnetic properties of ultrathin Fe films grown on cleaved and polished MgO(1 0 0) surfaces were studied by conversion electron Mössbauer spectroscopy (CEMS). ⁵⁷Fe layers were deposited as probe atoms in different layer positions in 10 ML thick Fe films. Fe layers of different thicknesses were formed on polished and cleaved substrate surfaces at RT deposition. The analysis of the spectra showed no Fe-O^2- interaction in MgO/Fe interface. FeO phase formation was excluded. The Mössbauer spectrum of 5 ML ⁵⁷Fe sample showed enhanced internal magnetic field at 80 K. No interdiffusion of ⁵⁷Fe and ⁵⁶Fe atoms was observed between the layers at room temperature.     

Interface magnetism of Fe/Nd multilayers studied by Mössbauer spectroscopy

Fe/Nd multilayers with⁵⁷Fe enriched interfaces are prepared to investigate crystal structure and magnetism at the interface by Mössbauer spectroscopy. The intermixture at the interface is less than two atomic layers. The magnetic moments of interface Fe atoms align collinear and turn at a certain temperature or at a certain magnetic field with keeping the collinear structure. By annealing, the interface component with smaller hyperfine field decreases and the perpendicular magnetic anisotropy increases.     

Ab initio calculations of interfacial magnetism in Fe/Mo superlattices

Ab initio calculations have been performed on Fe/Mo(1 0 0) superlattices in order to study the interfacial magnetic properties and layer thickness effect on the magnetic moments. In most cases, the magnetic moments of interfacial Fe monolayers are always smaller than those of the inner layers, and the induced magnetic moments of interfacial Mo monolayers oriented in the opposite direction. Calculation results show that the Fe layers are ferromagnetic when n = 3. As the thickness of the Mo layers increases, the influence of the Mo layer increases and the magnetic state of the Fe layer gradually changes into an antiferromagnetic or non-magnetic state. The change of magnetic moments of Fe/Mo superlattices is in agreement with the experimentally observed oscillation periods.     

Nd2Fe14B的价电子结构分析和磁性计算

应用固体与分子经验电子理论计算了Nd₂Fe₁₄B的价电子结构、磁矩和居里温度,计算结果与实验值相符.计算表明:该合金的磁性与3d磁电子数成正比.从Fe(c)晶位到Fe(k₂)晶位磁矩增加,其机理源于价电子、哑对电子和3d磁电子之间的转化,有78%的哑对电子和18%的3d共价电子转化成了磁电子.居里温度和磁矩与Fe原子配位数成正比,与加权等同键数I^σ成反比,Nd原子 关键词： 2Fe₁₄B')" href="#">Nd₂Fe₁₄B 价电子结构 居里温度     

Theoretical study of magnetism and electronic structure of Fe3/Crn(1 1 0) superlattices

The electronic structure and magnetism of Fe₃/Cr_n(1 1 0) (n=1, 3, 5) superlattices (SL) with varying layer thickness have been studied using the full-potential linearized augmented plane-wave (FLAPW) method within the first-principle formalism. The results show that the ferromagnetic state is the preferable phase in the ground state. The magnetic moments of the Fe layers are slightly modified by the presence of the Cr layers. The Cr magnetic moments alternate direction from layer to layer, and an antiferromagnetic coupling between Fe and Cr at the interfacial layer is seen. The magnetic moments of the Cr layers are suppressed because there is a strong hybridization between d-states of both Fe and Cr atoms. Only a small moment is found in the Cr layer. The Cr moment alignment is determined by a delicate balance between the different magnetic interaction.     

Local magnetic states and hyperfine interactions in Fe/Ti magnetic superlattices

Multilayer Fe/Ti films are synthesized by deposition in a Penning discharge. Measurements are made of thhe static hysteresis loops and Mössbauer spectra on Fe⁵⁷ nuclei. The hyperfine magnetic field distribution functions are calculated. It is established that the spontaneous magnetization of Fe/Ti magnetic superlattices undergoes very strong oscillations as a function of the Ti layer thickness. Three groups of peaks are noted in the hyperfine field distribution functions, corresponding to three nonequivalent states of the Fe ions, in one of which these ions do not have a characteristic magnetic moment. These results also agree with measurements of the temperature dependence of the magnetization in weak magnetic fields. For some Ti interlayer thicknesses the saturation magnetization scaled to the Fe content is much higher than the saturation magnetization of bulk Fe.     

The spin texture in Fe/Tb multilayers

Fe/Tb multilayers (ML) have been prepared in UHV. The layer thickness for Fe was varied from 10 to 80 Å with Tb-layer thicknesses of 3.5, 7, 14 and 26 Å. Different substrate temperatures T_s between T_s=130 K and RT have been used. The magnetic spin texture was studied by⁵⁷Fe-Mössbauer spectroscopy from T=4.2 K to 670 K. The ferrimagnetic coupling between Fe and Tb moments was observed by Mössbauer studies in external fields up to 5 T.     

非晶态RE—TM(RE=Nd,Pr,TM=Fe,Co,Ni)薄膜的磁性和Pr的变价行为

本文通过对非晶态轻稀土Pr,Nd和过渡族金属Fe,Co,Ni薄膜合金的低温磁性研究,分别得到了(Pr,Nd)_x-(Fe,Co,Ni)_1-x合金中Pr,Nd和Fe,Co,Ni金属磁矩随成份x的变化,并且通过对磁矩的研究得到Pr离子的4f电子可能有退局域化的结论。 关键词：     

Magnetic and Mössbauer studies of Fe/Mo multilayered thin films

Fe(x)/Mo(y), multilayered thin films (MLF) with y=7.0 nm and x=0.7, 1.3, 2.6, 3.6, 13.0 nm were fabricated by radio frequency (RF) sputtering. X-ray diffraction evidences that these films have a good periodicity and bcc structure for both Fe and Mo layers. Mössbauer spectra at room temperature (RT) are used to investigate the structure and the local magnetic properties of the interfaces between Fe and Mo layers. It is found that the interfaces present alloying features, i.e. the Fe atoms are randomly substituted by Mo atoms. Magnetic anisotropy which forces magnetic moments to lie in the film plane and reduced magnetic moments in interface region were observed. The specific magnetization of the films exhibits a BT^3/2 dependence with very large values of B which can be attributed to the distribution of exchange interaction in the interfaces.     

Iron spin-reorientation transition in NdFeAsO

The low-temperature magnetic structure of NdFeAsO has been revisited using neutron powder diffraction and symmetry analysis using the Sarah representational analysis program. Four magnetic models with one magnetic variable for each of the Nd and Fe sublattices were tested. The best fit was obtained using a model with Fe moments pointing along the c-direction, and Nd moments along the a-direction. This signals a significant interplay between rare-earth and transition metal magnetism, which results in a spin-reorientation of the Fe sublattice upon ordering of the Nd moments. All models that fit the data well, including collinear models with more than one magnetic variable per sublattice, were found to have an Fe moment of 0.5 μ(B) and a Nd moment of 0.9 μ(B), demonstrating that the low-temperature Fe moment is not substantially enhanced compared to the spin-density wave state.     

Magnetic structure and preferential occupation of Fe in the composite compound Nd2Co6Fe

The crystal and magnetic structures of the composite compound Nd₂Co₆Fe have been investigated by high-resolution neutron powder diffraction and X-ray powder diffraction. The compound crystallizes in the hexagonal Ce₂Ni₇-type structure consisting of Nd(Co,Fe)₂ and Nd(Co,Fe)₅ structural blocks alternately stacked along the c-axis. Multi-pattern Rietveld refinement of neutron diffraction and X-ray diffraction data at room temperature reveal that substitution of Fe for Co occurs exclusively in the Nd(Co,Fe)₅ structural blocks. The preferential occupation of the Fe atoms in the structure is discussed based on the mixing enthalpy between Nd and Fe atoms and on the lattice distortions. In agreement with the reported magnetic phase diagram of the Nd₂Co_7−xFe_x compounds, magnetic structure models with the moments of all atoms in the ab plane at 300 K and along the c-axis at 450 K provide a satisfactory fitting to the experimental neutron diffraction data. The refinement results show that the atomic moments of (Co,Fe) atoms within the Nd(Co,Fe)₅ blocks decrease slightly with temperature, whereas the atomic moments of Nd in the compound and of (Co,Fe) atoms at the interface between the Nd(Co,Fe)₂ and Nd(Co,Fe)₅ blocks are reduced significantly.     

Superconductivity of MgB 2 Thin Films Prepared By CoEvaporation and Magnetism of MgB 2 /Fe Multilayers Studied By Mössbauer Spectroscopy

MgB 2 thin films and MgB 2 /Fe multilayers have been prepared by vapor deposition of the elements in vacuum. X-ray diffraction studies of the MgB 2 samples show preferred c -axis growth along the film normal direction. Superconducting transition temperatures of 18 K and 22 K have been measured before and after annealing, respectively, of an MgB 2 film of 1575 Å thickness. Atomic force microscope images show island growth of the films leading to a rough surface. Mössbauer spectroscopy on MgB 2 /Fe/MgB 2 multilayers of various Fe layer thicknesses indicates superparamagnetic behavior. Evidence is provided for the formation of interfacial amorphous (a-) Fe 3 B. The magnetic ordering of Fe and a-Fe 3 B and the size effect in MgB 2 are assumed to be the cause for the destruction of the superconductivity in the as-grown multilayers.     

Effect of composition on phase formation,microstructure and magnetic properties of Nd–Fe–B thin films

Nd–Fe–B hard magnetic thin films were deposited on a combined Cr/Ta buffer layer on heated MgO(1 0 0) substrates by pulsed laser deposition. The effect of composition on phase formation, morphology and magnetic properties was investigated. For a quantification of phase formation, hysteresis measurements along the hard axis are used. Optimum phase formation is obtained at a Nd/Fe ratio around 0.3. For this Nd content an excellent magnetic texture and a coercivity up to 1 T can be obtained; however, remanence is reduced and the films have a granular microstructure with high roughness. Also a certain B surplus is of benefit. However, with a too-high B or Nd surplus phase formation is more difficult.     

Structure and magnetic properties of magnetron-sputtered [(Fe/Pt/Fe)/Au]n multilayer films

Using dc magnetron sputtering, Fe/Pt/Au multilayer films were prepared, and the effects of Au layer thickness and annealing temperature on structure and magnetic properties of the Fe/Pt/Au multilayer films were investigated. The as-deposited Fe/Pt/Au multilayer films have good periodic structure with composition modulation along the growth direction. The stress stored in the as-deposited films promoted the ordering of the films annealed at 400 °C. When the films were annealed at 500 °C, the thicker Au layer could restrain the order-disorder transformation region volume and lead to the decrease of the ordered volume fraction with Au layer thickness increasing.     

Thickness dependence of X-ray absorption and photoemission in Fe thin films on Si(0 0 1)

To investigate the initial growth of Fe films on Si(0 0 1) and the Fe/Si interface, Fe films at various thicknesses have been systematically studied by soft X-ray absorption spectroscopy (XAS) and X-ray photoemission spectroscopy (XPS). The Fe L edge XAS spectrum shows a strong thickness dependence with broader line-width for thinner films. Detailed analysis of the Fe absorption signal as a function of the thickness shows that the broad linewidth of Fe L edge XAS spectra is mostly contributed by the first Fe layer at the Fe/Si interface. In contrast to XAS, Fe 2p photoemission spectra for these films are identical. However, valence band photoemission also shows a strong thickness dependence. Comparing the valence band photoemission spectra of the thin Fe/Si(0 0 1) films with that of pure Si and the thickest Fe film, the difference spectra at all thicknesses show almost identical shape indicating the same origin: the Fe/Si interface. Thus, it is mainly the first Fe layer at Fe/Si layer that is reactive with the Si substrate changing its electronic structure.     

Magnetisation and remagnetisation peculiarities of Fe/Cr multilayer films caused by instability of Cr layers magnetic structure

A model to describe the magnetic properties of Fe/Cr/Fe films with nanometer-thick layers of Fe and Cr is proposed. The model rests on the assumption that there exists a magnetic order of the linearly polarized spin-density wave type in a chromium interlayer with thicknesses even less than its wavelength. This only assumption proved to be enough to describe the following characteristics, experimentally observed, of the magnetic properties of the multilayer Fe/Cr films: the existence of short and long periods, dependences of their magnetic properties on the chromium layer thickness, noncollinear orientation of the magnetizations of neighboring iron layers, the existence of the magnetization curves beyond the hysteresis loops of magnetization.     

Electronic structure and magnetism of R(Fe,Si)12 (R = Y, Nd)

The newly developed full-potential linearized augmented plane wave (LAPW) and local orbitals (lo) based on standard APW methods are briefly introduced, and the structure and magnetic properties of R(Fe, Si)12 compounds (R = Y, Nd) are calculated using the method. The distribution of Si at different sites is analyzed based on total energy of one crystal unit with structure having been optimized. The characters of magnetic moments, total density of states (TDOS) and partial density of states (PDOS) for different crystal sites Si occupies are obtained and analyzed. The results show that the total magnetic moments of RFe10Si2 (R = Y, Nd) are larger than those of RFe10M2 (M = Ti, V, Cr, Mn, Mo and W) and the hybridization mechanism is seen as follows. Si(8j) reduce the magnetic moments of Fe at three sites, however, Si(8f) mainly reduce the magnetic moments of Fe(8i) and Fe(8j) atoms. The Curie temperature is markedly enhanced by the introduction of Si atoms according to spin fluctuation of DOS at Fermi level.