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

Abstract

We have experimentally determined the magnitude of the in-plane magnetocrystalline anisotropy of monatomic Fe steps on the surface of nanopatterned Fe/ Ag͑001͒ films. The films have been nanopatterned by the ion-sculpting technique, in which grazing-incidence ion sputtering is exploited to induce the formation of nanometer-scale surface ripples oriented along the ion-beam direction. We quantitatively assessed the ripple morphology in order to determine the density of Fe monatomic steps parallel to the ripple ridges. By correlating the morphology with the measured uniaxial magnetic anisotropy, we obtained the strength of the magnetocrystalline anisotropy of Fe monatomic steps u mc = ͑6.5± 1.5͒ ϫ 10 −10 erg/ cm.

Exchange bias in self-organized nanopatterned Cr/Fe junctions

“…Under these conditions, the Fe ripples are not separated but rather represent a regular and coherently oriented undulation of an otherwise continuous Fe film. 16 From the mean value of ripple wavelength and side-wall slope reported above, an average of approximately ten exposed Fe layers within each ripple can be expected.…”

“…In particular we notice that whereas loop "a" is square, loop "b" exhibits a very characteristic split shape, with zero remanence and two semiloops symmetrically shifted by approximately 75 Oe with respect to the H = 0 axis. Such a peculiar shape, as shown in a number of studies, 16,[20][21][22] is indicative of a total system's MAE given by the superposition of a biaxial anisotropy contribution ͑K c ͒, having an easy axis of magnetization pointing along the ͓100͔ Fe and crystallographic equivalent directions, and a uniaxial ͑K u ͒ contribution favoring the magnetization alignment parallel to ͓100͔ Fe . In our case, the K c and K u contributions, respectively, arise from the effective in-plane biaxial anisotropies of the combined Fe and Cr films, and from the step-induced interface anisotropy due to the nanoripples.…”

“…Epitaxial Fe films of thickness t FM = 30 Å were deposited by molecular-beam epitaxy onto a clean and flat Ag͑001͒ according to established procedures. 15,16 Fe grows on Ag with epitaxial relations ͓100͔ Fe ʈ ͓110͔ Ag and ͓001͔ Fe ʈ ͓001͔ Ag . 17 Once deposited, the self-organized formation of surface ripples onto the Fe surface was induced by means of the well-established ion sculpting technique, 13 irradiating the film at T = 350 K by means of a defocused beam of 1 KeV Ar + ions incident at 70°from the surface normal and along the ͓100͔ Fe direction, 16 as schematically shown in Fig.…”

“…After 5 ϫ 10 12 ions/ cm 2 fluence, the Fe surface morphology, as determined in Ref. 16 by means of spot-profile-analysis lowenergy electron diffraction ͑LEED͒, consisted of ripples with ridges oriented along ͓100͔ Fe with mean wavelength ⌳ Ϸ 9 nm, whose side walls consisted of crystalline facets at a mean angle ␣ Ϸ 14°with respect to the surface normal. Under these conditions, the Fe ripples are not separated but rather represent a regular and coherently oriented undulation of an otherwise continuous Fe film.…”

“…In our case, the K c and K u contributions, respectively, arise from the effective in-plane biaxial anisotropies of the combined Fe and Cr films, and from the step-induced interface anisotropy due to the nanoripples. 16,18,23 Both loops exhibit very sharp irreversible transitions, thereby suggesting that the magnetization reversal process proceeds by transitions between single-domain Fe states mediated by DW nucleation and subsequent propagation. 24 For systems with the above-described MAE, when the externally applied field is H ext ʈ ͓100͔ Fe ͑H ext ʈ ͓010͔ Fe ͒ directions, the magnetization reversal takes place via propagation of 180°͑90°͒ DWs.…”