36 research outputs found
Debye temperature of disordered bcc-Fe-Cr alloys
Debye temperature, TD, of Fe100-xCrx disordered alloys with 0<x<99.9 was
determined from the temperature dependence of the centre shift of 57Fe
Mossbauer spectra recorded in the temperature range of 80-300K. Its
compositional dependence shows an interesting non-monotonous behaviour. For
0<x<~45 as well as for ~75<x<~95 the Debye temperature is enhanced relative to
its value of a metallic iron, and at x=~3 there is a local maximum having a
relative height of ~12% compared to a pure iron. For ~45~95
the Debye temperature is smaller than the one for the metallic iron, with a
local minimum at x=~55 at which the relative decrease of TD amounts to ~12%.
The first maximum coincides quite well with that found for the spin-waves
stiffness coefficient, D0, while the pretty steep decrease observed for x>~95
which is indicative of a decoupling of the probe Fe atoms from the underlying
chromium matrix is likely related to the spin-density waves which constitute
the magnetic structure of chromium in that interval of composition. The
harmonic force constant calculated from the Debye temperature of the least
Fe-concentrated alloy (x>99.9) amounts to only 23% of the one characteristic of
a pure chromium.Comment: 15 pages, 7 figures, 26 reference
Coexistence of antiferromagnetic ordering and superconductivity in the Ba(Fe0.961Rh0.039)(2)As-2 compound studied by Mossbauer spectroscopy
The results of a Fe-57 Mossbauer spectroscopy study between 2.0 and 294 K of superconducting Ba(Fe0.961Rh0.039)(2)As-2 are reported. The main component of the electric field gradient tensor at 294 K is shown to be positive and its increase with decreasing temperature is well described by a T-3/2 power-law relation. The shape of the Mossbauer spectra below the Neel temperature T-N = 55.5(1) K is shown to result from the presence of doping-induced disorder rather than of incommensurate spin-density-wave order. The measured hyperfine magnetic field reaches its maximum value at the critical temperature T-c = 14 K and then decreases by 4.2% upon further cooling to 2.0 K. This constitutes direct evidence of the coexistence of and competition between superconductivity and magnetic order. The extrapolated value of the Fe magnetic moment at 0 K is determined to be 0.35(1) mu(B). The Debye temperature of Ba(Fe0.961Rh0.039)(2)As-2 is found to be 357(3) K
Moessbauer spectroscopy evidence for the lack of iron magnetic moment in superconducting FeSe
Superconducting FeSe has been investigated by measurements of the magnetic
susceptibility versus temperature and Moessbauer spectroscopy at various
temperatures including strong external magnetic fields applied to the absorber.
It was found that isomer shift exhibits sharply defined increase at about 105 K
leading to the lowering of the electron density on iron nucleus by 0.02
electron/a.u.^3. Above jump in the electron density is correlated with the
transition from the P4/nmm to the Cmma structure, while decreasing temperature.
Moessbauer measurements in the external magnetic field and for temperatures
below transition to the superconducting state revealed null magnetic moment on
iron atoms. Hence, the compound exhibits either Pauli paramagnetism or
diamagnetic behavior. The principal component of the electric field gradient on
the iron nucleus was found as negative on the iron site.Comment: 9 pages, 6 figures, 1 tabl
THE CHARACTER OF MAGNETIC ORDER IN Fe-Cr ALLOYS-MÖSSBAUER EFFECT STUDY
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