Step-decorated Ferromagnetic Fe Nanostripes on Pt(997)

Abstract

We investigate the step decoration growth and magnetic properties of Fe grown on a Pt͑997͒ vicinal single crystal by means of reflection high energy electron diffraction ͑RHEED͒, scanning tunneling microscopy ͑STM͒, and the surface magneto-optical Kerr effect ͑SMOKE͒. Pt͑997͒ has 2 nm wide, ͑111͒-oriented terraces separated by ordered, monoatomic steps along the ͓110͔ direction. The Fe is grown at room temperature as wedges with thickness ranging from 0 to 4 monolayers ͑ML͒. RHEED and STM show that Fe stripes form at low coverage due to step decoration. SMOKE data taken along a wedge indicate that the Fe is ferromagnetic above 0.2 ML with its magnetic easy axis canted from surface normal direction. As temperature is increased near the Curie temperature, there is an irreversible spin reorientation to the perpendicular out-of-plane direction. The canting can be understood as arising from a competition between an in-plane, step-induced magnetic anisotropy and a perpendicular surface anisotropy associated with extended terraces due to the polarization of the proximal Pt. Above 1.7 ML the perpendicular easy axis reorients to in-plane, along the step direction, due to the dominance of the shape anisotropy. The magnetic anisotropy energy is extracted by fitting the temperature dependence of the coercivity data.

Structure and magnetism of atomically thin Fe layers on flat and vicinal Pt surfaces

“…For this thickness range, ferromagnetic hysteresis loops can again be obtained by cooling the sample below 200 K. Note that the found crit is almost twice as large as the value reported in Ref. 13.…”

“…13,[19][20][21][22] Particular focus has been on the preparation of Fe on stepped Pt͑997͒ since it allows one to form linear nanostructures and even chains of single Fe atoms. Our available data 22,46 obtained by thermal energy helium atom scattering ͑TEAS͒ can be summarized to the following picture: At deposition temperatures between 200 and 400 K, Fe atoms preferentially decorate the Pt substrate steps at the initial growth stage.…”

“…Our available data 22,46 obtained by thermal energy helium atom scattering ͑TEAS͒ can be summarized to the following picture: At deposition temperatures between 200 and 400 K, Fe atoms preferentially decorate the Pt substrate steps at the initial growth stage. 13,22 With increasing Fe coverage, Fe , the step decoration is continued, resulting in step flow growth mode. It is expected that for Fe Ͼ 1 ML, the film overgrows the substrate steps, leading to vertical mismatch and increasing disorder.…”

“…[1][2][3][4][5][6][7][8] To account for the dependence of the magnetism of epitaxial films on electronic and structural film properties, phenomenological quantities, such as magnetocrystalline, magnetoelastic, interface, or step anisotropy energies have been introduced and applied successfully during the past 2 decades of research. 3,7,[9][10][11][12][13] These parameters are chosen to reflect the symmetry of the observed magnetic anisotropy and usually hide details of the sample structure. The immense effort in determining such anisotropy contributions experimentally has partly distracted from gaining a better understanding of the role of the local atomic structure itself.…”

Complex magnetic phase in submonolayer Fe stripes on Pt(997)

“…Measurements at intermediate coverages, not displayed here, demonstrate that the transition from superparamagnetism to blocking happens at coverages around x = 0.4 ML. A similar blocking behavior was reported by Cheng et al 16 who studied comparable Fe/Pt͑997͒ systems using the magneto-optical Kerr effect ͑MOKE͒ technique. The known limited sensitivity of MOKE compared to XMCD confines their magnetic measurements to coverages larger than x = 0.5 ML.…”