We measure 119Sn Mössbauer spectrum of a (110) face of chromium and demonstrate that it can be properly described in terms of sinusoidally or snoidally modulated spin-density-waves (SDW) if ∼ 2% contribution of the third harmonic of SDW is taken into account.

Using theSn Mossbauer eKect we show that the crystalline boundaries have a profound in-Buence on the shape of Mossbauer spectra. Based on the newly developed method of the harmonic analysis of the Mossbauer spectra, we analyze the measured spectra in terms of higher-order harmonics and reveal a relationship between the harmonics and the size of grains: the smaller the size, the greater the contribution of the harmonics, with the third-order one being negative and dominating. We also demonstrate that the present results support the up-to-date picture of the spin-density waves in the form of single Q domains.Chromium metal owes its scientific attraction to socalled spin-density waves (SDW's) which originate &om itinerant 8and d-like electrons, and demonstrate a variety of interesting properties (see Ref. 1 and references therein). Between the Neel temperature of Ttv = 311 K and the spin-Hip temperature of TsF = 123 K, SDW's are transversely polarized; i.e. , their wave vector Q is perpendicular to their polarization vector p. Below TSF the polarization is longitudinal, i.e. , Q~~p. SDW s are incommensurate with the periodicity of the lattice, i.e. , Q g -, a being the lattice constant.Theoretically, basic properties of SDW's can be explained in terms of the band structure of pure chromium and the Coulomb interaction between the electron and the hole surfaces is responsible for their existence. SDW's can be also described by the snoidal function or a series of odd harmonicspqi being an amplitude of the ith harmonic of the CDW and b a phase shift between the CDW's and the SDW's. According to a theoretical estimation, p2/po should be of the order of 10 -10 . A recent estimation based on an x-ray diffraction experiment yields for p2 the value where n = Q . r (r being the position vector).Experimentally, evidence of S3 was found from neutron diffraction and. Sn Mossbauer-effect experiments on single-crystal samples of chromium. Recently, the authors of the present paper found evidence of S5 and possibly of S7 &om the Sn Mossbauer spectrum registered at room temperature on a (110) face of chromium. s According to theory, the Coulomb interaction between the two hole surfaces induces a charge-density wave (CDW). As the CDW order parameter is proportional to the square of the SDW order parameter, CDW's can be described in terms of a series of even harmonics as follows: of 0.003 -0.02 electrons per atom and our analysis of the (110) face Cr~~9 Sn Mossbauer spectrum gives the value of 0.02 for the maximum amplitude of the CDW.It is also of interest in searching for SDW's to know the preferred relative orientation of SDW polarizations. A single SDW Q may have one or more SDW's with symmetry-equivalent wave vectors Q. For instance, in lead it has been found. that a cubic family of 12 SDW's is required in order to explain its various properties.A question arises whether various SDW's overlap with each other in certain regions of samples in which they exist. Theoretical calculations concerning the problem of such interference of ...

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RksurnB. -En utilisant plusieurs modkles diffkrents on a montrk que parmi les modeles en deux couches employks pour lisser les spectres Mossbauer des alliages Fe-Cr, le mieux appropriC est celui qui inclut uniquement les contributions des atomes de Cr situks dans les deux premikres sphkres de coordination. Utilisant ce modde pour lisser les spectres Mossbauer d'alliages Fe-Cr avec diffkrentes concentrations de chrome (1-15 at % Cr) on a montrk que la variation du champ magnktique hyperfin au site de 57Fe(AHl) produite par une impuretk dans la premikre sphkre de coordination est supkrieure a celle (AH2) produite par une impuretk qui est un second proche voisin.Le rapport R = AHllANz depend de la concentration et les lissages par moindre carrk de nos donnees montrent qu'on peut le mettre sous la forme R = 1,24 + 0,03 c pour le modkle M 12 ou R = 1,24 + 0,02 c pour le modkle M 12 BW.On a aussi ktudik le problkme de l'additivitk des effets dus aux atomes de Cr aussi bien sur les champs magnktiques hyperfins au site des noyaux 57Fe que sur les dkplacements isomkriques. On observe une additivitk partielle et totale pour le champ magnktique hyperfin, alors que pour le dkplacement isomerique il n'y a qu'une additivitk totale avec d'assez grandes erreurs expkrimentales.Abstract. -Using several different models it has been shown, that among the two-shell models employed for fitting the Mossbauer spectra of Fe-Cr alloys the most adequate is the one, which includes only contributions from those Cr atoms which occupy the first two coordination spheres. Employing then this model for fitting the Mossbauer spectra of Fe-Cr alloys having different chromium concentration (1-15 at % Cr) it has been revealed, that the change of the hyperfine magnetic field at 57Fe nuclei, AH,, due to an impurity atom in the first coordination sphere is higher than the change, AH2, due to a second-nearest neighbour impurity.The ratio R = AH IIAHz turns out to be concentration dependent and least-squeres fits to our data show that it may be expressed as R = 1.24 + 0.03 c for the M 12-model or R = 1.24 + 0.02 c for the M 12 BW-model. The problem of the additivity of the observed effects of Cr atoms both on the hyperfine magnetic fields at 57Fe nuclei and on the isomer shifts was also investigated. For the hrnf partial and total additivity is observed, whilst for the IS only total additivity occurs within rather high experimental errors.