Structure of Ni overlayers on bcc Fe(100)

In this paper we describe studies on the low-temperature gaseous nitriding of epitaxial Ni-covered Fe layers. The epitaxial Ni/Fe bilayer system was grown by laser ablation deposition on an MgO͑001͒ substrate. Nitriding was done in an NH 3 ϩH 2 gas mixture in the 200°C-300°C temperature range. As a result of such nitriding, the main Fe-nitride phases could be produced as a pore-free material. The samples were analyzed by x-ray diffraction and conversion electron Mössbauer spectroscopy. It was observed that at the conditions applied the Fe-nitride phase formation occurs in the ␣→␣Ј, ␣Љ→␥Ј→→␥Љ,␥ٞ sequence, whereby each step is accompanied by grain refinement. The precise orientation relationships between the phases in the ␣→␣Ј, ␣Љ→␥Ј → sequence were determined. Based on the data obtained, a model is proposed that describes this transformation sequence on an atomic scale in terms of martensitic transition. Among other results, evidence is provided for two different types of orientation relationships that can occur between ␣-Fe and ␥Ј-Fe 4 N, depending on the prevailing conditions. The morphology of the Ni/Fe-N system is discussed.

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“…This implies that the Ni forms a close layer. As has been reported earlier, 14 the overall OR in the epitaxial Ni/Fe/MgO͑001͒ system is…”

Section: Methodssupporting

confidence: 78%

Phase transformations in epitaxial Ni/Fe bilayers upon low-temperature gaseous nitriding

Mijiritskii

Boerma

2001

Phys. Rev. B

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“…(iii) Density functional theory (DFT) calculations [8] suggest that the Ni film undergoes a cell rotation with respect to the Fe(001) bare substrate, at about 3-4 ML. This finding is compatible with a c(2 × 2)-like reconstruction, as mentioned above [14]. In addition, simulations based on DFT and molecular dynamics stress that the Ni/Fe interface is highly unstable above 300/400 K and that film growth needs to be carried out at low temperatures (room temperature (RT) or lower) to avoid Ni interdiffusion inside the substrate.…”

Section: Introductionsupporting

confidence: 81%

“…Above 20 ML, the satellites disappear from the LEED pattern and a clear c(2 × 2)-like reconstruction is observed, replacing the original (1 × 1) (see figure 1(g)). The c(2 × 2)-like symmetry has been reported in the literature [14] and is attributed to the development of a fcc phase for the Ni film following the martensitic transition. However, the critical thickness obtained in this work differs from those obtained by several other authors [5,[12][13][14], according to whom the martensitic transition occurs at 6 ML, although in close agreement with the homogeneous strain theory [16], which predicts a critical thickness for the bcc Ni overlayer around 25 ML.…”

Section: Resultssupporting

confidence: 54%

“…We believe that the reason for such a discrepancy has to be looked for in the sample temperature. In our measurements, we carefully kept the temperature constant at 300 K, while other strategies have been used and reported in the literature [5,14] (in other works the sample temperature might have risen above RT). Consequently, our data indicate that the bcc-fcc transition at RT takes place at a higher film thickness than previously believed, namely 20 ML instead of 6 ML, which was the commonly accepted value.…”

Section: Resultsmentioning

confidence: 99%

“…This transition is characterized by a specific c(2 × 2)-like reconstruction in the diffraction patterns (e.g. [14] high-energy electron diffraction (RHEED)), which is interpreted in terms of four different domains, each exposing the (110) plane of the fcc structure and oriented as described by the Nishiyama-Wassermann path of the martensitic transition [15]. (iii) Density functional theory (DFT) calculations [8] suggest that the Ni film undergoes a cell rotation with respect to the Fe(001) bare substrate, at about 3-4 ML.…”

Section: Introductionmentioning

confidence: 99%

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Martensitic transition during Ni growth on Fe(001): evidence of a precursor phase

Bussetti

Riva²,

Picone³

et al. 2012

New J. Phys.

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We report evidence that the body-centered cubic (bcc)-face-centered cubic (fcc) transition that occurs during Ni film growth on a Fe(001) substrate is preceded by a pre-martensitic phase, as demonstrated by low-energy electron diffraction. The corresponding film superstructure is characterized by a displacement of Ni atoms along the main 100 crystallographic axes of iron, without any rotation of the unit cell with respect to the (001) plane, in contrast with the martensitic transition that shows four fcc Ni domains with the Ni 211 crystallographic directions aligned with the Fe 110 axes. In addition, the martensitic transition is detected not at 6 ML, as previously believed, but above 20 ML if the Ni sample is rigorously kept at room temperature. The surface morphology of the bcc-fcc transition is characterized by the development of Ni mounds oriented along the 110 directions, as shown by scanning tunneling microscopy.

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Magnetic Ultrathin Films

Heinrich

Cochran

2007

Handbook of Magnetism and Advanced Magnetic Materials

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The magnetic properties of ultrathin ferromagnetic films a few monolayers thick differ from the magnetic properties of the same material in bulk form because a large fraction of the atoms in such films are located either on the surfaces or within one monolayer of the surfaces. As a result, the magnetic properties of ultrathin films are very sensitive to surface roughness and to the proximity of foreign atoms at the interfaces with a substrate or with an overlayers film. The first part of this chapter provides an overview of three main methods for the preparation of ultrathin films: thermal deposition, laser pulse deposition, and magnetron sputtering. Emphasis is placed on techniques used to prepare high‐quality films having smooth surfaces and important examples are discussed in detail. The second part reviews magnetic anisotropies in ultrathin films: measuring techniques, the theory of magnetic anisotropies, and the effect of surface roughness on thin‐film anisotropies. The chapter closes with a guide to the literature on thin‐film magnetic anisotropy data for several interesting systems: Fe, Co, Ni films grown on various substrates; Fe films grown on GaAs crystals; Fe/Pt alloys grown on MgO; and bcc Ni films grown on GaAs(001).

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Structure of Ni overlayers on bcc Fe(100)

Cited by 22 publications

References 24 publications

Phase transformations in epitaxial Ni/Fe bilayers upon low-temperature gaseous nitriding

Phase transformations in epitaxial Ni/Fe bilayers upon low-temperature gaseous nitriding

Martensitic transition during Ni growth on Fe(001): evidence of a precursor phase

Magnetic Ultrathin Films

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