Description in a local model of the magnetic field distributions of Fe1−<i>x</i>Ni<i>x</i> disordered alloys

Restrepo, J.; Alcázar, G. A. Pérez; Bohórquez, A.

doi:10.1063/1.365564

Cited by 23 publications

(16 citation statements)

References 12 publications

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“…However, the observed spectral shape for S1 and S2 are quite similar to that of a disordered Fe 100−x Ni x alloy for x < 10. The corresponding H h f values also agree with those reported in the literature at this nickel concentration in Fe-Ni alloys [16][17]. Therefore, for S3 one observes a change in the relative intensity of the inner lines of the sextets with respect to the outer lines, as well as the presence of a small paramagnetic component (doublet) at the center of the spectrum.…”

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confidence: 80%

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A Mössbauer effect study of the Soledade meteorite

Paduani

Pérez²,

Ardisson

2005

Braz. J. Phys.

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We performed a Mössbauer spectroscopy study of the iron meteorite Soledade. This meteorite, which consists of a metallic matrix, is an octahedrite with polycrystalline troilite, cohenite, schreibersite and rhabdites as major constituents. A chemical analysis indicates 6.78 % Ni, 0.46% Co, besides traces of Cu, Cr, Ga, Ge, As, Sb, W, Re, Ir and Au. No traces of silicates have been found and no oxygen was detected. Iron is appearing in the austhenitic phase and alloyed with nickel. An analysis of the Mössbauer spectra at room temperature indicates that the Fe-Ni phase is homogeneously distributed in the matrix, although variations in the composition between different regions are observed.Since the early studies of the microstructure and chemical composition of meteorites the formation of magnetic phases has attracted the attention of metallurgists [1][2][3][4][5][6][7][8][9][10][11]. Most of the metallic specimens presented high contents of nickel and iron as major constituents, and thus the Fe-Ni alloys formed under such special conditions have been the subject of several investigations with a variety of experimental techniques. This is not an easy task considering the weathering process and the distribution of oxides in the metallic matrix, which in some cases varies in composition from one region to another. However, the complexity of the mechanism of formation of the alloys in meteorites, which can take cooling rates as long as 1 K/Ma, is an interesting subject, and its comprehension may shed some light on the metastability of alloys.The category of iron meteorites corresponds to about 5 % of the modern meteorite falls. In the study of Fe-Ni-bearing meteorites, there is a recent discussion about the formation of a low-moment Fe-rich γ phase which differs from the ordinary high-spin γ phase in the electronic structure and a lower lattice parameter, but has the same crystal structure, same degree of atomic order and same composition of ordinary taenite. In fact, this has been claimed to be a new mineral called antitaenite which is common in slowly cooled meteorites [12][13][14]. This low-spin phase is proposed to occur in a thin epitaxial intergrowth with tetrataenite (ferromagnetic atomically ordered FeNi). Actually, metastable precipitates of this low-spin phase in a matrix of high-spin Fe-Ni phase of the same controlled composition have been synthetically produced near the Invar composition (≈ 35 at% Ni).In this work we applied x-ray diffraction (XRD) and Mössbauer spectroscopy (MS) to study the iron-bearing phases detected in the iron meteorite called Soledade, which is a massive metallic block [15]. Although no one knows precisely when this specimen was found, it received the name of the locality from where it proceeded near the city of Passo Fundo in the state of Rio Grande do Sul in Brazil. The first studies indicate that this metallic meteorite is an octahedrite, with polycrystalline troilite, cohenite, schreibersite and rhabdites as major constituents. It consists of a solid block weighing 68 kg, with a...

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“…The lattice parameters determined from these samples correspond to bcc Fe-Ni alloys, which are similar to pure iron up to 10 at. % Ni [16]. Traces of iron oxide are detected for the S3 sample, collected from the coating at the surface of the specimen.…”

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confidence: 99%

A Mössbauer effect study of the Soledade meteorite

Paduani

Pérez²,

Ardisson

2005

Braz. J. Phys.

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“…Meanwhile, the Ni local moment seems to be insensitive. Thus, upon alloying ironnickel, if one considers the occupation of the immediate neighborhood following a probability distribution mechanism, the present results indicate that the Fe moment is expected to vary only slowly with composition in iron-rich alloys [16]. However, at higher Ni contents the local symmetry seems to play a major rule.…”

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confidence: 81%

Electronic structure and magnetic properties of bcc Fe–Ni alloys

Paduani

2003

Physica Status Solidi (b)

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In this work we present first-principles electronic structure calculations with the molecular cluster discrete variational method to study Fe-Ni alloys in the bcc phase. The spin-polarized calculations are based on a local-density approximation of the density-functional theory. The local moments are obtained for several configurations in 51-atoms clusters, which include four shells of neighbors to study the behavior of the magnetic moments upon alloying iron-nickel. The calculations indicate that the local Fe moment increases slightly at lower concentrations, but decreases at higher Ni contents, whereas the Ni moment is practically constant. The calculated hyperfine field (Fermi contact term) decreases by increasing the nickel concentration in the alloys. In layered systems a first investigation indicates that the Ni atoms at the inner layers show an enhanced moment relative to surface layers, as verified by experiment. In the source is a populational effect, which arises from a depleted occupation in the minority spin channel.

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“…Restrepo et al [11] extended the binomial distribution treatment until the NNN to simulate the chemical disorder in many phases of the Fe-Ni system. In another way Sedov and Tsigel'nik [12] have had success in simulating the collapse of the magnetic moment in the INVAR region by using a binomial model taking into account the two spin states known as Weiss' model [5].…”

Section: Introductionmentioning

confidence: 99%