We have revisited the epitaxial growth modes of Fe on W(110) and Mo(110), and propose an overview or our contribution to the field. We show that the Stranski-Krastanov growth mode, recognized for a long time in these systems, is in fact characterized by a bimodal distribution of islands for growth temperature in the range ∼ 250 − 700 • C. We observe firstly compact islands whose shape is determined by Wulff-Kaischev's theorem, secondly thin and flat islands that display a preferred height, i.e. independant from nominal thickness and deposition procedure (1.4 nm for Mo, and 5.5 nm for W on the average). We used this effect to fabricate self-organized arrays of nanometers-thick stripes by step decoration. Self-assembled nano-ties are also obtained for nucleation of the flat islands on Mo at fairly high temperature, i.e. ∼ 800 • C. Finally, using interfacial layers and solid solutions we separate two effects on the preferred height, first that of the interfacial energy, second that of the continuouslyvarying lattice parameter of the growth surface.

We have fabricated 5 nm-high Fe(110) stripes by self-organized (SO) growth on a slightly vicinal R(110)/Al203(1120) surface, with R=Mo, W. Remanence, coercivity and domain patterns were observed at room temperature (RT). This contrasts with conventional SO epitaxial systems, that are superparamagnetic or even non-magnetic at RT due to their flatness. Our process should help to overcome superparamagnetism without compromise on the lateral size if SO systems are ever to be used in applications.Arrays of epitaxial nanometer-sized (1-50 nm) magnetic structures can be grown by self-organization (SO). However such structures are superparamagnetic or even non-magnetic at room temperature (RT) [1,2,3]. Indeed the energy barrier opposing spontaneous magnetization flipping roughly scales with KV , with K the magnetic anisotropy per unit volume, and V the system's volume. 3D clusters of similar lateral size can overcome superparamagnetism at RT by increasing K[4]. This seems not sufficient in epitaxial SO [3,5,6] because SO deposits are generally very flat, implying a very small V . Therefore, beating superparamagnetism in SO deposits without compromising on the lateral density seems to imply increasing their thickness t.One way to force SO deposits to grow vertically and overcome superparamagnetism at RT is sequential deposition [7,8]. We proposed a second route, that consists in annealing a thin continuous film deposited on a vicinal surface to form an array of several atomic layers (AL)-thick stripes [8,9]. In the early reports, concerning Fe/Mo(110) stripes, a stable thickness t = 6 AL (∼ 1.2 nm) was observed above 1-2 ALs of wetting. Yet this was not thick enough to observe static coercivity at RT, which could be obtained only for multidisperse assemblies of islands and stripes, thicker on the average. In this Letter we report the growth of thicker stripes, in the case of Fe/W(110): t ∼ 25 AL (∼ 5 nm). Such stripes display at RT functional features of magnetic materials: coercivity, remanence and domains, unlike conventional SO systems. The microscopic origin of the self-organization process is also unravelled.The samples are epitaxially grown by pulsed laser deposition in a multi-chamber ultra-high vacuum setup (base pressure 7 × 10 −9 Pa), with in situ STM, RHEED and Auger spectroscopy [10]. Commercial (1120) sapphire wafers with a residual miscut angle ǫ < 0.1 • are buffered with refractory metal films (Mo or W, < ∼ 10 nm-thick), whose surface consists of an array * Olivier.Fruchart@grenoble.cnrs.fr of atomically-flat terraces of width ∼ 200 nm, separated by mono-atomic steps [9]. Fe is then deposited at 150 • C and annealed at 400 − 450 • C, covered with 1 nm Mo for controlling the magnetic anisotropy, and finally capped by 4 nm Al as a protection against oxidation. AFM (PSI Autoprobe CP) and hysteresis loops (QD MPMS-XL) were performed ex situ. Samples were then dc-demagnetized ex situ with the field applied perpendicular to the stripes. Magnetic and chemical imaging was performed under zero external field using ...