A Study of Epitaxial Films of Bcc Nickel on FE{001} with leed Intensity analysis and Total Energy Band Calculations

Abstract

Analysis of LEED intensities of thin films of Ni grown epitaxially on bcc FeJ001 1 establishes that the structure is bcc up to six layers, but with a contraction of 5 % of the first layer spacing and expansion of 5% of the second layer spacing. At thicknesses above six layers there is a gradual change to a new surface and bulk structure with increasing disorder. Spin-polarized total-energy band calculations show that the bcc Ni film is stretched 1.4% from its equilibrium value and thereby changed from nonmagnetic to ferromagnetic. The calculated results on stable and metastable phases of Fe, Co, Ni and Cu show that the equilibrium lattice parameters and differences in binding energies favor mutual epitaxy for any bcc or fcc pair. There are six pairs in which a possible metastable phase is grown epitaxially on a stable substrate.

Magnetism in ultrathin film structures

“…Paduani [830] studied the electronic and magnetic properties of bcc FeNi alloys based on a non-relativistic spin-polarized method in the LSD approximation; the results predict a magnetic moment per Ni atom of 0.74 µ B /atom for a 1ML bcc Ni embedded in a bcc Fe matrix; for a 3 ML bcc Ni they found for the magnetic moment of Ni at the centre a value of 1.14 µ B /atom, which is surprisingly large. Shawagfeh and Khalifeh [695] have also performed first principle calculations (LMTO-ASA) to determine the electronic and magnetic properties of Ni/Fe(0 0 1) overlayers; from the energy calculation of bulk bcc Ni, they obtained an equilibrium lattice constant of 2.79 Å and a Ni magnetic moment of 0.585 µ B /atom at the equilibrium lattice constant, in good agreement with the calculations of other authors [764,766,803,829,830,1150]. For a bcc Ni layer sandwiched between bcc Fe, they found a Ni magnetic moment of 0.89 µ B /atom for the thick Fe slabs (7 to 11 ML), while for the bcc Ni bilayer, the magnetic moment of Ni is 0.76 µ B /atom at the surface layer and 0.59 µ B /atom at the interface.…”

“…The bcc phase of Ni is not usually found in nature, but it was shown by Moruzzi et al [764,766,829,1150] that it corresponds to a metastable phase with an equilibrium lattice constant of a bcc Ni eq = 2.78 Å, with a nearby non-magnetic-toferromagnetic transition with increasing atomic volume (see also [830]); for a bcc Ni = 2.78 Å, the magnetic moment of Ni is predicted to be around 0.41 µ B /atom [829], and given the small lattice mismatch between the equilibrium lattice constant of bcc Ni (2.78 Å) and that of bcc Fe (2.866 Å), η = −3.0%, it may be expected that bcc Ni could be grown on Fe(0 0 1). This Ni phase was indeed obtained by means of molecular beam epitaxy by Heinrich et al [823,1144,[1151][1152][1153] and Wang et al [1150,1154]. These experimental results suggest that bcc Ni can be grown homomorphically on the bcc Fe(0 0 1) surface up to 3-6 ML, depending on substrate conditions; above this thickness the lattice constant expands by ≈2% and develops a c(2 × 2) surface reconstruction [823,1154].…”

Occasional “long-range” nonequilibrium body-centered-cubic structures in NiFe/Cu spin valves

“…In the present study, the value of the lattice parameter of the bcc Cu measured from the FFTs is approximately 0.29 nm, close to calculated values of 0.287 and 0.296 nm. 23,24 This suggests that significantly more relaxation of the bcc Cu has taken place in the present study than in the Nb/Cu multilayers examined by Mitchell and co-workers. 18,22 Further, it is interesting to note that the bcc structures investigated here display a significant degree of stability.…”