arXiv subjects

J. Zukrowski

Publications and source records attributed to J. Zukrowski.

21 records · Page 2Linked to original sources

arXiv2009

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.

cond-mat.supr-con↗

arXiv2009

Unusual dynamics of Fe atoms in chromium matrix

57Fe site Mossbauer Spectroscopy (MS) was used to investigate a dynamics of 57Fe atoms embedded into chromium lattice as impurities. From the Mossbauer spectra recorded in the temperature range of 80 to 350 K, a temperature dependence of the Lamb-Mossbauer factor, f, was determined. The latter revealed an unusual dynamics of 57Fe atoms viz. harmonic mode below T = 145 K with a characteristic effective Debye temperature, Qeff = 185 K and anharmonic one above T o 145 K. The latter mode exists in two clearly separated temperature intervals with slightly different Qeff - values viz. (i) 156 K for 145 K < T < 240 K and the record-high anharmonic coefficient e = 18 * 10-4 K-1 and (ii) 152 K for T > 240 K and e = 13.6 * 10-4 K-1. Based on the Visscher's theory, the record-low values of relative binding force constants for Fe atoms were determined as 0.0945, 0.0673 and 0.0634, respectively. It is suggested that the unusual dynamics observed in this study might be related to the underlying spin- and charge- and strain-density waves of chromium.

cond-mat.mtrl-sci↗

arXiv2008

Anomalous binding of Fe atoms in chromium

Binding of 57Fe atoms in a metallic chromium was investigated in a Cr-Fe alloy, containing less than 0.1 at% Fe enriched to ~95 % in 57Fe isotope, using 57Fe-site Mossbauer spectroscopy. The binding force was derived from the Debye temperature, T_D, that, in turn, was calculated from the temperature dependence of the central shift of the Mossbauer spectra recorded in the range of 80 to 330 K. Following a temperature dependence of the line width that shows a minimum at ~155 K, two temperature intervals were considered: a low temperature one (LT) ranging from 80 to 155 K, and the T_D - value of 292 (12) K or 279 (34) K, and a high temperature one (HT) ranging from 155 to 330 K with the T_D - value of 399 (15) or 399 (25) K, depending on the fitting procedure. The corresponding values of the harmonic force (spring) constant are: 35.4 N/m and 66.1 N/m or 33.8 N/m and 66.1 N/m for the LT and HT, respectively. This means that in the HT range the binding force of 57Fe atoms by the Cr matrix is by a factor of ~1.9 - 2 stronger than that in the LT range. This anomaly is possibly related with a different polarization of the spin-density waves in the LT and HT "phases".

cond-mat.mtrl-sci↗