arXiv subjects

S. M. Dubiel

Publications and source records attributed to S. M. Dubiel.

At least 19 recordsLinked to original sources

arXiv2019

Site-resolved hyperfine and lattice dynamical properties of a single-crystal Fe3Si

A single-crystal sample of a DO3-ordered Fe3Si compound was studied by means of the 57Fe Mössbauer spectroscopy. Spectra have been recorded in a transmission geometry in the temperature range between 5 and 850 K. They have been analyzed either in terms of five sextets or five hyperfine field distribution curves. Concerning the former three sub spectra have been attributed to Fe atoms occupying the B sites and having 8Fe, 7Fe1Si and 6Fe2Si atoms in the first coordination shell (1NN), respectively, and two have been attributed to Fe atoms residing on the A and C sites and having 4Fe4Si and 3Fe5Si atoms in the 1NN, respectively. Based on the temperature dependence of the center shifts values the Debye temperature, T_D, have been determined. TD was found to be equal to 491 (11) K for the sites A and C, and to 403 (3) K the site B. The smaller value of T_D coincides with the smaller values of the hyperfine field, H. Changes in H caused by one Si atom present in the 1NN have been determined as ca.13 kOe for Fe atoms occupying the A and C sites and ca.54 kOe for Fe atoms present on the B sites. These changes have been also expressed in terms of the underlying number of polarized s-like electrons, dNs. For the Fe atoms situated on the A and C sites dNs=0.03 was found while for those occupying the B sites dNs=0.17.

cond-mat.str-el↗

arXiv2019

On the magnetic phase diagram of a sigma-phase Fe47Re53 compound in the H-T plane

Sigma-phase Fe47Re53 compound was investigated by means of in-field DC and AC magnetization measurements. Field cooled, MFC, and zero-field cooled, MZFC, DC magnetization curves were recorded in the magnetic field, H, up to 1000 Oe. AC magnetization measurements were performed at the constant frequency of 1465 Hz in the field up to H=500 Oe. Both types of measurements gave evidence in favor of a re-entrant character of magnetism in the studied sample. Based on characteristic temperatures determined from the measurements magnetic phase diagrams have been outlined in the H-T plane. The diagrams are similar but not identical. The main difference is that in the diagram constructed based on the DC data there is an intermediate antiferromagnetic-like phase which is absent in the AC diagram. Furthermore, the border lines (irreversibility, cross-over and Curie temperature) follow the power law but with correspondingly different exponents. The studied sample was also characterized by determining the effect of H on the degree of irreversibility and that of frustration.

cond-mat.str-el↗

arXiv2018

Effect of 0.25 and 2.0 MeV He-ion irradiation on short-range ordering in model (EFDA) Fe-Cr alloys

The effect of He+ ion irradiation on a distribution of Cr atoms in model (EFDA) Fe(100-x)Cr(x) (x=5.8, 10.75, 15.15) was studied by means of conversion electrons Mossbauer spectroscopy. The alloys were irradiated to the dose of 1.2E16 ions per cm2 (7.5 dpa) with He+ of 0.25 and 2.0 MeV. The distribution of Cr atoms within the first two coordination shells around the probe Fe atoms was expressed in terms of the Warren-Cowley short-range order parameters alpha1 (first-neighbour shell, 1NN), alpha2 (second-neighbour shell, 2NN) and alpha12 (1NN+2NN. In non-irradiated alloys alpha1 was positive and alpha2 was negative for all three samples which indicates an ordering of Cr atoms. Yet, the value of alpha12 were close to zero, i.e. the distribution of Cr atoms averaged over the first two coordination shells around the probe Fe atoms, was random. The effect of the irradiation of the Fe5Cr sample is similar for the two energies of the He+ projectiles viz. increase of number of Cr atoms in the 1NN and decrease in the 2NN shell. Consequently, the degree of the ordering increased. For the other two samples, the effect of the irradiation depends on the composition, and it is stronger for the less energetic ions where, in the case of Fe10Cr, the disordering disappeared and some traces of Cr clustering (alpha12 weakly positive) can be seen. In the Fe15Cr sample the clustering is clear. In the samples irradiated with 2.0 MeV ions the ordering also survived in the samples with x=10.75 and 15.15, although its degree became smaller than in the Fe5Cr sample. Small changes in the magnetic texture were revealed.

cond-mat.mtrl-sci↗

arXiv2018

Mössbauer study of Eu0.57Ca0.43Fe2As2 and Eu0.73Ca0.27(Fe0.87Co0.13)2As2: A comparison to 122 iron-based superconductors parent compounds EuFe2As2 and CaFe2As2

57Fe and 151Eu Moessbauer spectra were obtained versus temperature for Eu0.57Ca0.43Fe2As2 compound with 3d and 4f magnetic order and Eu0.73Ca0.27(Fe0.87Co0.13)2As2 re-entrant superconductor, where the finite resistivity reappears while approaching the ground state. They were compared with previously obtained spectra for parent compounds EuFe2As2 and CaFe2As2. It was found that substitution beyond the Fe-As layers does not lead to the rotation (canting) of the Eu2+ magnetic moments and does not generate Eu3+ states. On the other hand, re-entrant superconductor exhibits rotation (canting) of the Eu2+ moments on the c-axis of the unit cell leading to the transferred hyperfine magnetic field on iron nuclei. Divalent europium orders magnetically within the bulk of the re-entrant superconducting phase. The re-entrant superconductor remains in the inhomogeneous state close to the ground state with about 27 % of the volume being free of 3d magnetism, while the remainder exhibits weak spin density wave. Those two regions slightly differ by the electric field gradient and electron density on iron nuclei.

cond-mat.supr-con↗

arXiv2018

On the magnetism of the C14 Nb0.975Fe2.025 Laves phase compound: Determination of the H-T phase diagram

A C14 Nb0.975Fe2.025 Laves phase compound was investigated aimed at determining the H-T magnetic phase diagram. Magnetization, M, and AC magnetic susceptibility measurements were performed. Concerning the former field-cooled and zero-field-cooled M-curves were recorded in the temperature range of 2-200K and in applied magnetic field, H, up to 1000 Oe, isothermal M(H) curves at 2 K, 5 K, 50 K, 80 K and 110 K as well as hysteresis loops at several temperatures over the field range of -10 to +10kOe. Regarding the AC susceptibility, both real and imaginary components were registered as a function of increasing temperature in the interval of 2 K - 150 K at the frequencies of the oscillating field, f, from 3 Hz up to 999 Hz. An influence of the external DC magnetic field, H, on the temperature dependence of the AC susceptibility was investigated, too. The measurements clearly demonstrated that the magnetism of the studied sample is weak, itinerant and has a reentrant character. Based on the obtained results a magnetic phase diagram has been constructed in the H-T coordinates.

cond-mat.str-el↗

arXiv2017

The giant effect of magnetic ordering on a sound velocity in a sigma-Fe55Cr45 alloy

We studied atomic dynamics of sigma-Fe(100-x)Cr(x) (x=45 and 49.5) alloys using nuclear inelastic scattering of synchrotron radiation. For the sigma-Fe55Cr45 alloy, the derived reduced iron-partial density of phonon states reveal a huge difference in the low-energy region between magnetic and paramagnetic states. The latter implies a ca.36% increase of the sound velocity in the magnetic phase, which testifies to a magnetically-induced hardening of the lattice.

cond-mat.str-el↗

arXiv2016

Magnetism of a sigma-phase Fe60V40 alloy: magnetic susceptibilities and magnetocaloric effect studies

Magnetic properties of a sigma-phase Fe60V40 intermetallic compound were studied by means of ac and dc magnetic susceptibility and magnetocaloric effect measurements. The compound is a soft magnet yet it was found to behave like a re-entrant spin-glass system. The magnetic ordering temperature was found to be T_C ca.170 K, while the spin-freezing temperature was ca.164 K. Its relative shift per decade of ac frequency was 0.002, a value smaller than that typical of canonical spin-glasses. Magnetic entropy change, DeltaS, in the vicinity of T_C was determined for magnetic field, H, ranging between 5 and 50 kOe. Analysis of DeltaS in terms of the power law yielded the critical exponent, n, vs. temperature with the minimum value of 0.75 at T_C, while from the analysis of a relative shift of the maximum value of DeltaS with the field a critical exponent Delta=1.7 was obtained. Based on scaling laws relationships values of other two exponents viz. betha=0.6 and gamma=1 were determined.

cond-mat.str-el↗

arXiv2016

Effect of 2 MeV Fe3+ irradiation on Fe atom site population in a sigma-phase Fe-Cr compound

A sigma-Fe54.5Cr45.5 samples irradiated in vacuum with 2 MeV Fe3+ ions at 300, 400, 475 and 700 deg C to the maximum dose of 12.5 dpa were studied with the conversion electron Mössbauer spectroscopy (CEMS). The analysis of the room temperature CEMS spectra revealed an irradiation-induced redistribution of Fe atoms viz. their number on B and D sites decreased while on A, C and E sites increased. The degree of the redistribution was found to be proportional to the number of Fe atoms present on the lattice sites in the non-irradiated samples. The highest degree of the redistribution was revealed in the sample irradiated at 300 deg C. No change in the site occupancy was found in the sample irradiated at 700 deg C.

cond-mat.mtrl-sci↗

arXiv2016

Distribution of Cr atoms in a strained and strain-relaxed Fe89.15Cr10.75 alloy: Mössbauer effect study

A Fe89.15Cr10.75 alloy in a heavily strained (by cold rolling) and strain-relaxed states was studied by means of the conversion electrons Mössbauer spectroscopy (CEMS). Analysis of the spectra in terms of a two-shell model revealed significant differences between the studied samples, in particular, in values of the hyperfine field, a distribution of Cr atoms within the first two neighbor-shells, the latter was expressed in terms of the short-range order parameters, and in the magnetic texture.

cond-mat.mtrl-sci↗

arXiv2016

Phase decomposition in an Fe-Cr alloy at 402 deg C: Mössbauer spectroscopic study

Phase separation in strained and strain-free samples of Fe84.85Cr15.15 induced by an isothermal annealing at 402 deg C up to 3888 h was studied by means of the Mossbauer spectroscopy. The measured Fe-site spectra were analyzed with two different procedures viz. a hyperfine field distribution and a two-shell superposition methods. Information relevant to the kinetics of the separation process, concentration of Cr in Fe-rich phase, short-range ordering and magnetic texture was obtained based on values of spectral parameters. In particular, the following quantities pertinent to the kinetics were found: the activation energy, equal to 1666 kJ per mol for the strained sample, and to 1388 kJ per mol for the strain-relaxed one, the Avrami exponent n=2.5(2) for both samples, the rate constant equal to 0.0011(1) for the strained and to 0.0028(1) per hour for the strained-free samples, respectively. The concentration of Cr in the Fe-rich phase was revealed to be 11.6(4) at. % for the strained sample, and to 13.2(4) at.% for the strain-free one. Significant differences in the values of the short-range parameters were revealed for the two samples. An average angle between the magnetization vector and the normal to the sample surface was equal to 52.7 deg for the strained sample, and to 57.5 deg for the strain-relaxed one.

cond-mat.mtrl-sci↗

arXiv2016

Magnetic phase diagrams in the H-T plane of the magnetically strongest sigma-phase Fe-V compounds

Magnetization measurements were performed on two sigma-phase samples of Fe(100-x)V(x) (x=35.5, 34.1) vs. temperature, T, and in DC magnetic field, of various amplitudes. Using three characteristic temperatures, magnetic phase diagrams in the H-T plane have been designed testifying to a re-entrant character of magnetism. The ground magnetic state, a spin glass (SG), was evidenced to be composed of two sub phases: one with a weak irreversibility and the other with a strong irreversibility. Two critical lines were reconstructed within the SG state. Both of them show a crossover from the Gabay-Toulouse behavior (low field) to a linear and/or quasi-Almeida-Touless behavior. A strong difference in the effect of the applied magnetic field on the SG phase in the two samples was revealed.

cond-mat.str-el↗

arXiv2015

Dynamics of Fe atoms in Fe-gluconate as seen by Mössbauer spectroscopy

Fe-gluconate was studied by means of the Mössbauer spectroscopy in the temperature interval of 80-305K. The measured spectra were analyzed in terms of two subspectra and, alternatively, two distributions of the quadrupole splitting. The major component (ca.85%) was identified as due to high-spin Fe2+ ions while the identification of the minor component (ca.15%) was not unique: some characteristics are in favour of the high-spin Fe3+ state while other ones are consistent with the low-spin Fe2+ state. Values of the Debye temperature were determined for both phases from a temperature dependence of the center shift as well as from that of the spectral area. The force constant for the high-spin ferrous atoms was evaluated to be equal to 44 N/m (243 cm-1).

cond-mat.mtrl-sci↗

arXiv2015

Evidence for a re-entrant character of magnetism of sigma-phase Fe-Mo alloys: non-linear susceptibilities

Non-linear ac magnetic susceptibility terms viz. quadratic, chi2, and cubic, chi3, were measured versus temperature and frequency for a series of the sigma-phase Fe(100-x)Mo(x) (47<x<53) compounds. Clear evidence was found that the ground magnetic state of the samples is mixed i.e. constituted by two phases: a spin glass (SG) and a ferromagnet (FM), hence the magnetism of the investigated samples can be regarded as re-entrant (RSG). Based on the present data, previously reported magnetic phase diagram has been upgraded [J. Przewoznik, S. M. Dubiel,J. Alloy. Comp., 630 (2015) 222].

cond-mat.str-el↗

arXiv2015

Mössbauer spectroscopic study of a sigma-Fe65.9V34.1 alloy: Curie and Debye temperatures

Sigma-phase Fe65.9V34.1 alloy was investigated with the Mössbauer spectroscopy. Mössbauer spectra were recorded in the temperature interval of 80-300 K. Their analysis in terms of the hyperfine distribution protocol yielded the average hyperfine field, , the average center shift, , and the spectral area, A. The magnetic ordering temperature, T_C=312.5(5) K was determined from the temperature dependence of , and the Debye temperature, T_D, from the temperature dependence of and the relative spectral area. The value obtained from the former was 403(17) K and that from the latter 374(2) K. The value of the force constant was determined. The lattice dynamics of Fe atoms was described in terms of the kinetic, E_k, and the potential energy, E_p.

cond-mat.str-el↗

arXiv2015

Debye temperature of nanocrystalline Fe-Cr alloys obtained by mechanical alloying

A series on nanocrystalline Fe100-xCrx alloys prepared by mechanical alloying was investigated with X-ray diffraction (XRD), scanning electron microscopy (SEM) and Mössbauer spectroscopy (MS) techniques. XRD and SEM were used to structurally characterize the samples whereas MS permitted phase analysis as well as determination of the Debye temperature, Theta_D. Concerning the latter, an enhancement relative to bulk Theta_D-values was revealed in the range of ca. 40 < x <50. In a sample of Fe55.5Cr44.5 two phases were detected viz. (1) crystalline and magnetic with Theta_D=572(56) K and (2) amorphous and paramagnetic with Theta_D=405(26) K.

cond-mat.str-el↗

arXiv2015

On the magnetism of sigma-Fe54Cr46 alloy: AC and DC susceptibility studies

Sigma-phase intermetallic compound of Fe54Cr46 was investigated using DC and AC magnetic susceptibility techniques. A clear-cut evidence was found that the sample orders magnetically at Tc=23.5 K and its ground magnetic state is constituted by a spin glass. The temperature at which the zero-field cooled magnetization has its maximum decreases with an external magnetic field in line with the Gabay-Toulouse prediction. The temperature at which the AC magnetic susceptibility has its maximum does not depend on frequency which, in the light of the mean-field theory, testifies to very long magnetic interactions.

cond-mat.mtrl-sci↗

arXiv2014

Magnetism of sigma-phase Fe-Mo alloys: ac magnetic susceptibility study

A series of four sigma-Fe(100-x)Mo(x) samples was investigated with ac magnetic susceptibility measurements. An evidence was found that the ground magnetic state of the samples is constituted by a spin glass (SG) with the spin glass temperature ranging between ca. 34K for x=47 and ca. 16K for x=53. The SG state is heterogeneous and it can be divided into a weak-irreversibility and a strong-irreversibility domains. Its figures of merit are typical of metallic (canonical) spin glasses.

cond-mat.str-el↗

arXiv2014

Magnetism of sigma-phase Fe-Mo alloys: its revealing and characterization

A low-temperature magnetism was revealed in a series of sigma-Fe(100-x)Mo(x) alloys (x=45-53). Its characterization has been done using vibrating sample magnetometry, Mössbauer spectroscopy, and ac magnetic susceptibility. The magnetic ordering temperature was determined to lie in the range of 46 K for x=45 and 22K for x=53, and the ground magnetic state was found to be typical of a spin-glass.

cond-mat.str-el↗