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Sperimagnetism in Fe(78)Er(5)B(17) and Fe(64)Er(19)B(17) metallic glasses: II. Collinear components and ferrimagnetic compensation
Magnetization measurements on an Fe(64)Er(19)B(17) glass and polarized-beam neutron scattering measurements on Fe(78)Er(5)B(17) and Fe(64)Er(19)B(17) were described in part I. The finite spin-flip neutron scattering cross sections were calculated using a sperimagnetic structure based on random cone arrangements of the magnetic moments. The temperature variation of the cross sections of Fe(64)Er(19)B(17) suggested that a compensated sperimagnetic phase existed at T(comp).
The analysis of the non-spin-flip neutron scattering cross sections is described here in part II. Two spin-dependent total structure factors S(+/-+/-). (Q) were defined from these cross sections and, despite the limited range of the data 0.5 angstrom(-1) , are zero on both sublattices in the compensated sperimagnetic structure at T(comp). The pre-peak in the spin-dependent total structure factors at 112 K showed that it originated in the atomic structure and it may involve Fe-Er-Fe 'collineations' at a radial distance of approximate to 6.0 angstrom. Finally, the RDF(+/-+/-) (r) of Fe(64)Er(19)B(17) at 180 K and of Fe(78)Er(5)B(17) at 2 K show that both glasses have the (mu(Fe) UP:mu(Er) DOWN) structure like the (Fe, Tb)(83)B(17) collinear ferrimagnets
Influence of chemical and magnetic interface properties of Co-Fe-B / MgO / Co-Fe-B tunnel junctions on the annealing temperature dependence of the magnetoresistance
The knowledge of chemical and magnetic conditions at the Co40Fe40B20 / MgO
interface is important to interpret the strong annealing temperature dependence
of tunnel magnetoresistance of Co-Fe-B / MgO / Co-Fe-B magnetic tunnel
junctions, which increases with annealing temperature from 20% after annealing
at 200C up to a maximum value of 112% after annealing at 350C. While the well
defined nearest neighbor ordering indicating crystallinity of the MgO barrier
does not change by the annealing, a small amount of interfacial Fe-O at the
lower Co-Fe-B / MgO interface is found in the as grown samples, which is
completely reduced after annealing at 275C. This is accompanied by a
simultaneous increase of the Fe magnetic moment and the tunnel
magnetoresistance. However, the TMR of the MgO based junctions increases
further for higher annealing temperature which can not be caused by Fe-O
reduction. The occurrence of an x-ray absorption near-edge structure above the
Fe and Co L-edges after annealing at 350C indicates the recrystallization of
the Co-Fe-B electrode. This is prerequisite for coherent tunneling and has been
suggested to be responsible for the further increase of the TMR above 275C.
Simultaneously, the B concentration in the Co-Fe-B decreases with increasing
annealing temperature, at least some of the B diffuses towards or into the MgO
barrier and forms a B2O3 oxide
The Unevolved Main Sequence of Nearby Field Stars and the Open Cluster Distance Scale
The slope and zero-point of the unevolved main sequence as a function of
metallicity are investigated using a homogeneous catalog of nearby field stars
with absolute magnitudes defined with revised Hipparcos parallaxes, Tycho-2
photometry, and precise metallicities from high-dispersion spectroscopy.
(B-V)-temperature relations are derived from 1746 stars between [Fe/H] = -0.5
and +0.6 and 372 stars within 0.05 dex of solar abundance; for T_e = 5770 K,
the solar color is B-V= 0.652 +/- 0.002 (s.e.m.). From over 500 cool dwarfs
between [Fe/H] = -0.5 and +0.5, Delta(B-V)/Delta[Fe/H] at fixed M_V = 0.213 +/-
0.005, with a very weak dependence upon the adopted main sequence slope with
B-V at a given [Fe/H]. At Hyades metallicity this translates into Delta
M_V/Delta[Fe/H] at fixed B-V = 0.98 +/- 0.02, midway between the range of
values empirically derived from smaller and/or less homogeneous samples and
model isochrones. From field stars of similar metallicity, the Hyades ([Fe/H] =
+0.13) with no reddening has (m-M)_0 = 3.33 +/- 0.02 and M67, with E(B-V) =
0.041, A_V = 3.1E(B-V), and [Fe/H] = 0.00, has (m-M)_0 = 9.71 +/- 0.02 (s.e.m),
where the errors quoted refer to internal errors alone. At the extreme end of
the age and metallicity scale, with E(B-V) = 0.125 +/- 0.025 and [Fe/H] = +0.39
+/- 0.06, comparison of the fiducial relation for NGC 6791 to 19 field stars
with (B-V) above 0.90 and [Fe/H] = +0.25 or higher, adjusted to the metallicity
of NGC 6791, leads to (m-M)_0 = 13.07 +/- 0.09, internal and systematic errors
included.Comment: 32 pages, 8 eps figures, latex; accepted for PAS
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Quadruple bonding between iron and boron in the BFe(CO)3- complex.
While main group elements have four valence orbitals accessible for bonding, quadruple bonding to main group elements is extremely rare. Here we report that main group element boron is able to form quadruple bonding interactions with iron in the BFe(CO)3- anion complex, which has been revealed by quantum chemical investigation and identified by mass-selected infrared photodissociation spectroscopy in the gas phase. The complex is characterized to have a B-Fe(CO)3- structure of C3v symmetry and features a B-Fe bond distance that is much shorter than that expected for a triple bond. Various chemical bonding analyses indicate that the complex involves unprecedented B≣Fe quadruple bonding interactions. Besides the common one electron-sharing σ bond and two Fe→B dative π bonds, there is an additional weak B→Fe dative σ bonding interaction. This finding of the new quadruple bonding indicates that there might exist a wide range of boron-metal complexes that contain such high multiplicity of chemical bonds
Temperature-Dependence of Magnetically-Active Charge Excitations in Magnetite across the Verwey Transition
We have studied the electronic structure of bulk single crystals and
epitaxial films of magnetite FeO. Fe core-level spectra show clear
differences between hard x-ray (HAX-) and soft x-ray (SX-) photoemission
spectroscopy (PES), indicative of surface effects. The bulk-sensitive spectra
exhibit temperature ()-dependent charge excitations across the Verwey
transition at =122 K, which is missing in the surface-sensitive spectra.
An extended impurity Anderson model full-multiplet analysis reveals roles of
the three distinct Fe-species (A-Fe, B-Fe, B-Fe) below
for the Fe spectra, and its dependent evolution. The Fe
HAXPES spectra show a clear magnetic circular dichroism (MCD) in the metallic
phase of magnetized 100-nm-thick films. The model calculations also reproduce
the MCD and identify the magnetically distinct sites associated with the charge
excitations. Valence band HAXPES shows finite density of states at for
the polaronic metal with remnant order above , and a clear gap formation
below . The results indicate that the Verwey transition is driven by
changes in the strongly correlated and magnetically active B-Fe and
B-Fe electronic states, consistent with resistivity and bulk-sensitive
optical spectra.Comment: 5 pages, 4 figures Accepted in Physical Review Letter
Isotope effect on the transition temperature in Fe-based superconductors: the current status
The results of the Fe isotope effect (Fe-IE) on the transition temperature
obtained up to date in various Fe-based high temperature superconductors
are summarized and reanalyzed by following the approach developed in [Phys.
Rev. B 82, 212505 (2010)]. It is demonstrated that the very controversial
results for Fe-IE on are caused by small structural changes occurring
simultaneously with the Fe isotope exchange. The Fe-IE exponent on
[, is the isotope mass]
needs to be decomposed into two components with the one related to the
structural changes () and the genuine (intrinsic)
one (). The validity of such decomposition is
further confirmed by the fact that coincides with
the Fe-IE exponent on the characteristic phonon frequencies as is reported in recent EXAFS and Raman experiments.Comment: 7 pages, 4 figures. The paper is partially based on the results
published in [New J. Phys. 12, 073024 (2010) = arXiv:1002.2510] and [Phys.
Rev. B 82, 212505 (2010) = arXiv:1008.4540
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