Fe on W(001) from continuous films to nanoparticles: Growth and magnetic domain structure

Abstract

The evolution of the structural and magnetic properties of Fe films during growth on the W(001) surface have been studied with low energy electron diffraction, real-time low energy electron microscopy, and quasi-real-time, spin-polarized low energy electron microscopy in the absence of a magnetic field (virgin state). Depending on the growth temperature, different growth modes are observed: growth of atomically rough and highly strained (10.4% tensile) pseudomorphic films at room temperature, kinetically limited layer-by-layer growth (quasi-Frank-van der Merwe growth mode) of smooth pseudomorphic films up to 4 monolayers at around 500 K and growth of fully relaxed three-dimensional Fe islands on top of a thermodynamically stable 2-monolayer-thick wetting layer (Stranski-Krastanov growth mode) at and above 700 K. Around 500 K, layered growth is terminated by partial (2 monolayers) dewetting of the metastable Fe film and formation of thin, partially relaxed, elongated islands on a thermodynamically stable 2 monolayer film. Ferromagnetic order is first detected during growth at room temperature at 2.35 monolayer Fe film thickness. The magnetization is in-plane with a thickness-dependent direction, rotating from the substrate 110 directions at 3 monolayers toward the 100 directions at 4 monolayers and back again toward the 110 directions at about 8 monolayers. The in-plane spin reorientation that occurs at room temperature is accompanied by significant changes of the magnetic domain structure. In the Frank-van der Merwe growth regime, large magnetic domains are observed in metastable 3 and 4 monolayer films. The isolated three-dimensional Fe islands that form in the Stranski-Krastanov regime have vortex, quasi-single domain (C state), or single magnetic domain structures, depending on their size and shape. The detailed results that are obtained with high thickness, lateral and azimuthal angular resolution with spin-polarized low energy electron microscopy are compared with earlier laterally averaging and laterally resolving magnetic studies, and discrepancies are explained.

Effect of the Sputtering Power on the Structure, Morphology and Magnetic Properties of Fe Films

“…When the threshold is exceeded, the coercive force increases as the film thickness increases; Tripathi et al's study further verified this conclusion [20]. Regarding the research on iron thin films, most of them focus on the deposition time (thickness) [21], growth temperature [22], substrate selection, etc. There are few reports pertaining to the influence of the sputtering power on the structure, morphology and magnetic properties of iron thin films [17,23].…”

Finite-size Kosterlitz-Thouless transition in 2DXY Fe/W(001) ultrathin films

“…The growth of Fe/W(001) films has been studied by a number of groups. [23][24][25][26][27] After some initial uncertainty, it has been established that 2ML of Fe on W(001) are thermally stable up to 700 K, whereas thicker films are stable to lower temperatures. This permits a straightforward thickness calibration of films grown by evaporation in UHV using the Auger electron spectroscopy (AES) signal from the W substrate during deposition.…”

Modeling solid-state dewetting of a single-crystal binary alloy thin films

“…can be related to the familiar Hamaker constant A H : p ∼ A H /12πs 2 , where A H ∼ 10 −14 − 10 −12 erg [31], and s ∼ 10 −7 cm [32,34]. This gives p…”