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The EuFe(2-x)Ni(x)As2 compounds exhibiting 3d and/or 4f magnetic order were investigated by means of 57Fe and 151Eu M\"ossbauer spectroscopy. Additionally, results for the end members of this system, i.e. EuFe2As2 and EuNi2As2, are reported for comparison. It was found that spin-density-wave order of the Fe itinerant moments is monotonically suppressed by Ni-substitution. However, the 3d magnetic order survives at the lowest temperature up to at least x = 0.12 and it is certainly completely suppressed for x = 0.20. The Eu localized moments order regardless of the Ni concentration, but undergo a spin reorientation with increasing x from the alignment parallel to the a-axis in the parent compound, toward c-axis alignment for x > 0.07. The change of the 4f spins ordering from antiferromagnetic to ferromagnetic takes place simultaneously with a disappearance of the 3d spins order what is the evidence of a strong coupling between magnetism of Eu2+ ions and the conduction electrons of [Fe(2-x)Ni(x)As2]2- layers. The Fe nuclei experience the transferred hyperfine magnetic field due to the Eu2+ ordering for Ni-substituted samples with x > 0.04, while the transferred field is undetectable in EuFe2As2 and for compound with a low Ni-substitution level. It seems that the 4f ferromagnetic component arising from a tilt of the Eu2+ moments to the crystallographic c-axis leads to the transferred magnetic field at the Fe atoms.

The BaFe2(As1-xPx)2 compounds with x = 0 (parent), x = 0.10 (under-doped), x = 0.31, 0.33, 0.53 (superconductors with Tc = 27.3 K, 27.6 K, 13.9 K, respectively) and x = 0.70, 0.77 (over-doped) have been investigated versus temperature using 57Fe M\"ossbauer spectroscopy. Special attention was paid to regions of the spin-density-wave (SDW) antiferromagnetic order, spin-nematic phase, and superconducting transition. The BaFe2(As0.90P0.10)2 compound exhibits a reduced amplitude of SDW as compared to the parent compound and preserved universality class of two-dimensional magnetic planes with one-dimensional spins. The spin-nematic phase region for x = 0.10 is characterized by an incoherent magnetic order. BaFe2(As0.69P0.31)2 shows coexistence of a weak magnetic order and superconductivity due to the vicinity of the quantum critical point. The charge density modulations in the BaFe2(As0.67P0.33)2 and BaFe2(As0.47P0.53)2 superconductors are perturbed near Tc. Pronounced hump of the average quadrupole splitting across superconducting transition is observed for the system with x = 0.33. The phosphorus substitution increases the Debye temperature of the BaFe2(As1-xPx)2 compound. Moreover, experimental electron charge densities at Fe nuclei in this material conclusively show that it should be recognized as a hole-doped system. The measured M\"ossbauer spectral shift and spectral area are not affected by transition to the superconducting state. This indicates that neither the average electron density at Fe nuclei nor the dynamical properties of the Fe-sublattice in BaFe2(As1-xPx)2 are sensitive to the superconducting transition. Theoretical calculations of hyperfine parameters determining the patterns of M\"ossbauer spectra of BaFe2(As1-xPx)2 with x = 0, 0.31, 0.5, and 1.0 are performed within the framework of the density functional theory.

A single-crystal sample of a DO3-ordered Fe3Si compound was studied by means of the 57Fe M\"ossbauer 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., Comment: 15 pages, 29 references and 6 figures

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.

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 M\"ossbauer 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., Comment: 9 pages, 5 figures, 9 references

A Fe89.15Cr10.75 alloy in a heavily strained (by cold rolling) and strain-relaxed states was studied by means of the conversion electrons M\"ossbauer 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., Comment: 9 pages, 3 figures, 10 references. arXiv admin note: text overlap with arXiv:1610.08014

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., Comment: 15 pages, 7 figures, 12 references

Transmission M\"ossbauer spectra for 14.41-keV transition in 57Fe were obtained for chalcopyrite-type (Cu-Fe-S2) ternary nanocrystals stabilized by long aliphatic chain ligands. These systems could be considered as isolated hard nano-objects dispersed in soft network of organic ligands. The main attention was paid to the behavior of the particles whose average size was varied in a controllable manner from 3 to 20 nm. It was found that the magnetic hyperfine interaction was relaxed to null to the temperatures well below liquid nitrogen temperature due to the isolation of particles. The fast dynamics could be described by two level environment. Deeper level (atomic) was practically the same as for bulk material except Debye temperature, but the higher level (particle motion) was described by the classical harmonic oscillator with the spring constant dramatically softening with increasing temperature. Such behavior led to fast decrease of the recoilless fraction with increasing temperature. Practically no spectra could be obtained above 240 K. The second order Doppler shift (SOD) had additional contribution at elevated temperatures due to the induced internal oscillations within particle by surrounding thermal bath. Slow dynamics was characterized by the thermally driven overdamped harmonic oscillator motions. In addition, the long range like diffusion of particles was seen. No significant rotation of particles was found within accessible temperature range., Comment: 14 pages, 7 figures

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., Comment: 19 pages, 11 figures, 41 references. arXiv admin note: text overlap with arXiv:1402.5612

Moessbauer transmission spectra for the 14.41-keV resonant line in 57Fe have been collected at room temperature by using 57Co(Rh) commercial source and alpha-Fe strain-free single crystal as an absorber. The absorber was magnetized to saturation in the absorber plane perpendicular to the gamma-ray beam axis applying small external magnetic field. Spectra were collected for various orientations of the magnetizing field, the latter lying close to the [110] crystal plane. A positive electric quadrupole coupling constant was found practically independent on the field orientation. One obtains the following value Vzz=+1.61(4)x10^19 V/m^2 for the (average) principal component of the electric field gradient (EFG) tensor under assumption that the EFG tensor is axially symmetric and the principal axis is aligned with the magnetic hyperfine field acting on the 57Fe nucleus. The nuclear spectroscopic electric quadrupole moment for the first excited state of the 57Fe nucleus was adopted as +0.17 b. Similar measurement was performed at room temperature using as-rolled polycrystalline alpha-Fe foil of high purity in the zero external field. Corresponding value for the principal component of the EFG was found as Vzz=+1.92(4)x10^19 V/m^2. Hence, it seems that the origin of the EFG is primarily due to the local (atomic) electronic wave function distortion caused by the spin-orbit interaction between effective electronic spin S and incompletely quenched electronic angular momentum L. It seems as well that the lowest order term proportional to the product L.LAMBDA.S dominates, as no direction dependence of the EFG principal component is seen. The lowest order term is isotropic for a cubic symmetry as one has LAMBDA=lambda.1 for cubic systems with the symbol 1 denoting unit operator and lambda being the coupling parameter.

Sigma-phase Fe65.9V34.1 alloy was investigated with the M\"ossbauer spectroscopy. M\"ossbauer 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., Comment: 14 pages, 8 figures, 14 references

Two iron-chalcogenide superconductors Li(x)[C5H5N](y)Fe(2-z)Se2 and Cs(x)Fe(2-z)Se2 in the as-prepared and annealed state have been investigated by means of the Moessbauer spectroscopy versus temperature. Multi-component spectra are obtained. One can see a non-magnetic component due to iron located in the unperturbed Fe-Se sheets responsible for superconductivity. Remaining components are magnetically ordered even at room temperature. There is some magnetically ordered iron in Fe-Se sheets perturbed by presence of the iron vacancies. Additionally, one can see iron dispersed between sheets in the form of magnetically ordered high spin trivalent ions, some clusters of above ions, and in the case of pyridine intercalated compound in the form of alpha-Fe precipitates. Pyridine intercalated sample shows traces of superconductivity in the as-prepared state, while cesium intercalated sample in the as-prepared state does not show any superconductivity. Superconductors with transition temperatures being 40 K and 25 K, respectively, are obtained upon annealing. Annealing leads to removal/ordering of the iron vacancies within Fe-Se sheets, while clusters of alpha-Fe grow in the pyridine intercalated sample.

The compound BaFe2Se3 (Pnma) has been synthesized in the form of single crystals with the average composition Ba0.992Fe1.998Se3. The Moessbauer spectroscopy used for investigation of the valence states of Fe in this compound at temperature ranging from 4.2 K till room temperature revealed the occurrence of mixed-valence state for iron. The spectrum is characterized by sharply defined electric quadrupole doublet above magnetic ordering at about 250 K. For the magnetically ordered state one sees four iron sites at least and each of them is described by separate axially symmetric electric field gradient tensor with the principal component making some angle with the hyperfine magnetic field. They form two groups occurring in equal abundances. It is likely that each group belongs to separate spin ladder with various tilts of the FeSe4 tetrahedral units along the ladder. Two impurity phases are found, i.e., superconducting FeSe and some other unidentified iron-bearing phase being magnetically disordered above 80 K. Powder form of BaFe2Se3 is unstable in contact with the air and decomposes slowly to this unidentified phase exhibiting almost the same quadrupole doublet as BaFe2Se3 above magnetic transition temperature.

A review of the magnetism in the parent compounds of the iron-based superconductors is given based on the transmission Moessbauer spectroscopy of 57Fe and 151Eu. It was found that the 3d magnetism is of the itinerant character with varying admixture of the spin-polarized covalent bonds. For the 122 compounds a longitudinal spin density wave (SDW) develops. In the case of the EuFe2As2 a divalent europium orders antiferromagnetically at much lower temperature as compared to the onset of SDW. These two magnetic systems remain almost uncoupled one to another. For the non-stoichiometric Fe(1+x)Te parent of the 11 family one has a transversal SDW and magnetic order of the interstitial iron with relatively high and localized magnetic moments. These two systems are strongly coupled one to another. For the grand parent of the iron-based superconductors FeAs one observes two mutually orthogonal phase-related transversal SDW on the iron sites. There are two sets of such spin arrangements due to two crystallographic iron sites. The FeAs exhibits the highest covalency among compounds studied, but it has still a metallic character., Comment: A contribution to XVI National Conference on Superconductivity, Zakopane, Poland, 7-12 October 2013

Iron mono-arsenide in the powder form has been investigated by transmission 57Fe Moessbauer spectroscopy in the temperature range 4.2 - 1000 K. Additional spectra have been obtained at 20 K and 100 K applying external magnetic field of 7 T. It was found that the spin spiral propagating along the c-axis leads to the complex variation of the hyperfine magnetic field amplitude with the spin orientation varying in the a-b plane. The magnitude of the hyperfine field pointing in the direction of the local magnetic moment depends on the orientation of this moment in the a-b plane. Patterns are vastly different for iron located in the [0 k 0] positions and for iron in the [0 k+1/2 0] positions within the orthorhombic cell set to the Pnma symmetry. Lattice softens upon transition to the paramagnetic state at 69.2 K primarily in the a-c plane as seen by iron atoms. This effect is quite large considering lack of the structural transition. Two previously mentioned iron sites are discernible in the paramagnetic region till 300 K by different electron densities on the iron nuclei. The anisotropy of the iron vibrations developed at the transition to the paramagnetic state increases with the temperature in accordance with the harmonic approximation, albeit tends to saturation at high temperatures indicating gradual onset of the quasi-harmonic conditions. It seems that neither hyperfine fields nor magnetic moments are correct order parameters in light of the determined static critical exponents. Sample starts to loose arsenic at about 1000 K and under vacuum.

X-ray diffraction (XRD) and M\"ossbauer spectroscopy techniques combined with theoretical calculations based on the Korringa-Kohn-Rostoker (KKR) electronic structure calculation method were used to investigate \sigma-phase Fe_{100-x}Re_{x} alloys (x = 43, 45, 47, 49 and 53). Structural data such as site occupancies and lattice constants were derived from the XRD patters, while the average isomer shift and distribution curves of the quadrupole splitting were obtained from the M\"ossbauer spectra. Fe-site charge-densities and the quadrupole splittings were computed with the KKR method for each lattice site. The calculated quantities combined with the experimentally determined site occupancies were successfully used to decompose the measured M\"ossbauer spectra into five components corresponding to the five sublattices.

Concentration of Cr in the Fe-rich alpha-phase, x, resulted from a phase decomposition caused by an isothermal annealing at T = 415 and 450 C of a non-irradiated (NR) Fe-Cr14 EFDA sample and that of a He-ions irradiated (IR) one annealed at 415 C was determined with M\"ossbauer spectroscopy. The x-value in the latter was by ~3 at% higher than the one in the NR-counterpart. The activation energy for the phase decomposition in the NR-sample was 122 kJ/mol. In the IR-sample its value was by 12 kJ/mol lower. Avrami exponents for the NR-samples were close to 0.5, and that for the IR-sample had a value of about 1., Comment: 5 pages 3 figures 1 Table

Iron-based superconductors Ba0.7Rb0.3Fe2As2 and CaFe1.92Co0.08As2 of the '122' family have been investigated by means of the 14.41-keV Moessbauer transition in 57Fe versus temperature ranging from the room temperature till 4.2 K. A comparison is made with the previously investigated parent compounds BaFe2As2 and CaFe2As2. It has been found that Moessbauer spectra of these superconductors are composed of the magnetically split component due to development of spin density wave (SDW) and non-magnetic component surviving even at lowest temperatures. The latter component is responsible for superconductivity. Hence, the superconductivity occurs in the part of the sample despite the sample is single phase. This phenomenon is caused by the slight variation of the dopant concentration across the sample (crystal)., Comment: Contribution to XV KSN, Kazimierz Dolny, Poland, October 9-13, 2011

The compound EuFe(2-x)Co(x)As2 was investigated by means of the 57Fe and 151Eu Moessbauer spectroscopy versus temperature (4.2 - 300 K) for x=0 (parent), x=0.34 - 0.39 (superconductor) and x=0.58 (overdoped). It was found that spin density wave (SDW) is suppressed by Co-substitution, however it survives in the region of superconductivity, but iron spectra exhibit some non-magnetic component in the superconducting region. Europium orders anti-ferromagnetically regardless of the Co concentration with the spin re-orientation from the a-axis in the parent compound toward c-axis with the increasing replacement of iron by cobalt. The re-orientation takes place close to the a-c plane. Some trivalent europium appears in EuFe(2-x)Co(x)As2 versus substitution due to the chemical pressure induced by Co-atoms and it experiences some transferred hyperfine field from Eu2+. Iron experiences some transferred field due to the europium ordering for substituted samples in the SDW and non-magnetic state both, while the transferred field is undetectable in the parent compound. Superconductivity coexists with the 4f-europium magnetic order within the same volume. It seems that superconductivity has some filamentary character in EuFe(2-x)Co(x)As2 and it is confined to the non-magnetic component seen by the iron Moessbauer spectroscopy., Comment: 13 pages, 8 figures, 2 tables

Parent compounds AFe2As2 (A=Ca, Ba, Eu) of the 122 family of the iron-based superconductors have been studied by 57Fe Moessbauer spectroscopy in the temperature range 4.2 K - ~300 K. Spin density waves (SDW) have been found with some confidence. They are either incommensurate with the lattice period or the ratio of the respective periods is far away from ratio of small integers. SDW shape is very unconventional i.e. differs from the sinusoidal shape. Magnetic order starts with lowered temperature as narrow sheets of the significant electron spin density separated by areas with very small spin density. Magnetic sheets are likely to be ordered in the alternate anti-ferromagnetic fashion as the material as whole behaves similarly to collinear anti-ferromagnet. Further lowering of temperature simply expands sheet thickness leading to the near triangular SDW. Finally, sheets fill the whole available space and almost rectangular shape of SDW is reached. Substantial maximum amplitude of SDW appears at the temperature just below the magnetic onset temperature, and this maximum amplitude increases slightly with lowering temperature. The square root from the mean squared hyperfine field behaves versus temperature according to the universality class (1, 2), i.e., with the electronic spin space having dimensionality equal unity and the real space having dimensionality equal two. The more or less pronounced tail above transition temperature due to the development of incoherent SDW is seen., Comment: 19 pages, 6 figures, 2 tables, accepted in Phys. Rev. B

The LiFeP sample has been prepared by means of high-temperature solid state reaction. A transition temperature to the superconducting state was found as about 5.5 K by measurements of magnetization versus temperature. The second critical field was found above 1 kOe. Moessbauer spectra of the LiFeP phase are characterized by the quadrupole split doublet having splitting of about 0.10 mm/s at room temperature and 0.12 mm/s at 4.2 K. No magnetic order occurs down to 4.2 K., Comment: 6 pages, 5 figures, 1 table

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 table

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., Comment: 11 pages, 5 figures

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"., Comment: 3 figures, 9 pages, 28 references