Correlation between magnetism and structural relaxation in thin Fe(001) films patterned by the atomic saw method

Abstract

We present detailed extended x-ray-absorption fine-structure ͑EXAFS͒ studies carried out on 50-Å epitaxial thin films grown by molecular-beam epitaxy on MgO͑001͒ substrate prior and after structuration into ribbons by the so-called ''atomic saw'' method. Because of interfacial strain due to lattice mismatch ͑ϩ3.8%͒, the crystallographic structure of the as-deposited film is demonstrated to be body-centered tetragonal with lattice constants aϭ2.915Ϯ0.015 Å and cϭ2.82Ϯ0.01 Å. This structure is 2% expanded in plane and Ϫ1.6% compressed along the surface normal as compared to the bulk Fe one. After structuration, the patterned 50-Å Fe films show a strong in-plane uniaxial magnetic anisotropy ͑close to 2.5 kOe͒. The EXAFS studies provide the clear evidence that the dislocation slipping process enhances a uniaxial relaxation ␦ϭϪ2.5% of the elastic strain field in the Fe film along the direction perpendicular to the ribbons. Through magnetoelastic effects, this relaxation is clearly demonstrated to be at the source of the observed magnetic anisotropy. This paper emphasizes the power of the ''phase derivative'' method in the analysis of EXAFS spectra for the determination of crystalline parameters in the case of bcc-type structures.

Short-range charge order inRNiO3perovskites (R=Pr, Nd, Eu, Y) probed by x-ray-absorption spectroscopy

“…An estimation of the separation value of roughly ␦r Ϸ 0.12 Å can be deduced from the beating position. This value is affected by systematic errors 21 and is slightly overestimated. The average separation found for YNiO 3 and for all heavier lanthanide compounds 6,12 is ␦r Ϸ 0.09 Å.…”

“…20 The wave number where the beating occurs ͑k b ͒ satisfies ␦r • k b Ϸ / 2, where ␦r is the separation in bond length. 20,21 This beating in the EXAFS amplitude generates a splitting in the FT amplitude ͑as seen in peak A, Fig. 1͒.…”

In situ XAFS study of Fe epitaxially grown by MBE on GaAs(001)-4×6

“…Studies have been done on the evolution of the magnetic behavior, morphology and stress of these films [9,13,14], but the body of knowledge, though extensive, still lacks an understanding of the film structure as it relates to the transition in growth modes. We have reported the development of a body-centered tetragonal (bct) distortion (from body-centered cubic (bcc)) in films near 10 ML thickness [15], as determined by both phase-derivative analysis [16,17] and more-detailed fitting [18] of extended X-ray absorption fine structure (EXAFS) data. To examine the thickness dependence of this distortion, we have used the in situ molecular beam epitaxy (MBE) capabilities at the Pacific Northwest Consortium (PNC-CAT) beamline [19] to perform in situ polarizationdependent X-ray absorption fine structure (XAFS) studies of iron on GaAs(0 0 1)-4 · 6 for thicknesses from 0.5 to 30 ML.…”

“…Polarization-dependent XAFS functions by orienting the electric field of a linearly-polarized Xray beam along (nearly along, grazing) the desired orientation of a single-crystalline material, such as an epitaxial thin film [17,[20][21][22][23][24]. The absorption of the linearly polarized X-rays causes the ejected photoelectrons to have a dipole-like distribution--high probability of the photoelectron being emitted along the direction of polarization and negligible probability perpendicular to the polarization.…”

Magnetocrystalline anisotropy of monatomic steps inFe∕Ag(001)nanopatterned films

“…Coming to the Fe/ MgO͑001͒ system, which has close analogies to Fe/ Ag͑001͒, we also find experimental studies of the uniaxial anisotropy of in-plane patterned films that, however, do not report any value of the magnetocrystalline step-induced anisotropy. 34,35 In this respect, we believe that the present work highlights the role of magnetocrystalline anisotropy of surface origin in the Fe/ Ag͑001͒ system, yielding an estimation of its magnitude free of bulklike undesired contributions.…”