Epitaxial growth, magnetic properties, and lattice dynamics of Fe nanoclusters on GaAs(001)

Abstract

Epitaxial bcc-Fe͑001͒ ultrathin films have been grown at ϳ50°C on reconstructed GaAs͑001͒-͑4 ϫ 6͒ surfaces and investigated in situ in ultrahigh vacuum ͑UHV͒ by reflection high-energy electron diffraction, scanning tunneling microscopy ͑STM͒, x-ray photoelectron spectroscopy ͑XPS͒, and 57 Fe conversion electron Mössbauer spectroscopy ͑CEMS͒. For t Fe =1 ML ͑monolayer͒ Fe coverage, isolated Fe nanoclusters are arranged in rows along the ͓110͔ direction. With increasing t Fe the Fe clusters first connect along the ͓−110͔, but not along the ͓110͔ direction at 2.5 ML, then consist of percolated Fe clusters without a preferential orientation at 3 ML, and finally form a nearly smooth film at 4 ML coverage. Segregation of Ga atoms within the film and on the Fe surface appears to occur at t Fe = 4 ML, as evidenced by XPS. For coverages below the magnetic percolation, temperature-dependent in situ CEMS measurements in zero external field provided superparamagnetic blocking temperatures T B of 62± 5, 80± 10, and 165± 5 K for t Fe = 1.9, 2.2, and 2.5 ML, respectively. At T Ͻ T B , freezing of superparamagnetic clusters is inferred from the observed quasilinear T dependence of the mean hyperfine magnetic field ͗B hf ͘. By combining the STM and CEMS results, we have determined a large magnetic anisotropy constant of ϳ5 ϫ 10 5 and ϳ8 ϫ 10 5 J/m 3 at t Fe = 1.9-2.2 and 2.5 ML, respectively. For t Fe ഛ 2.5 ML, our uncoated "free" Fe clusters exhibit intrinsic magnetic ordering below T B , contrary to literature reports on metal-coated Fe clusters on GaAs. Our present results demonstrate that the nature of the percolation transition for free Fe nanoclusters on GaAs͑001͒ in UHV is from superparamagnetism to ferromagnetism. From the Mössbauer spectral area, a very low Debye temperature ⌰ D of 196± 4 K is deduced for these uncoated Fe nanoclusters in UHV, indicating a strong phonon softening in the clusters.

Recipe for High Moment Materials with Rare-earth and 3d Transition Metal Composites

“…The above theoretical results are compared with two molecular beam epitaxy (MBE) grown trilayer systems GaAs(100)/Fe 15 /Sc n /Gd 30 and GaAs(100)/Fe 15 /Mn n /Gd 30 (subscripts denote the number of monolayers of each layer); one with a non-magnetic, Sc, spacer and the other with a magnetic, Mn, spacer. The reflection high energy electron diffraction (RHEED) pattern collected on the GaAs after sputter cleaning confirms earlier reports of 4 × 6 surface reconstruction in GaAs 21 . A typical RHEED intensity oscillations for the growth of Fe on GaAs(100) are shown in Fig.…”

Epitaxial Growth of FeCo Thin Films on SrTiO3 Single-Crystal Substrates

“…FeCo(100)A2 28,30,32,33) や GaAs(100) 34 XRDピーク位置から計算したエピタキシャルFeCo薄膜の膜面 垂直方向 ( Fig. 15(d-1)) および膜面内方向 ( Fig.…”

Iron on GaN(0001) pseudo-1 × 1 (1+112) investigated by scanning tunneling microscopy and first-principles theory

“…[3][4][5][6] There have been many studies of Fe on conventional semiconductor substrates, including GaAs. [7][8][9][10][11][12][13] Recent studies have confirmed that composition and bonding at the Fe/GaAs interface affect spin injection more than bulk properties of the Fe contact. 14 GaN has found important applications in electronic and optoelectronic devices.…”