Annealing-induced enhancement of ferromagnetism and nanoparticle formation in the ferromagnetic semiconductorGeFe

Abstract

We report the annealing-induced enhancement of ferromagnetism and nano-particle formation in group-IV-based ferromagnetic-semiconductor GeFe. We successfully increase the Curie temperature of the Ge 0.895 Fe 0.105 film up to ~220 K while keeping a single ferromagnetic phase when the annealing temperature is lower than 500°C. In contrast, when annealed at 600°C, single-crystal GeFe nano-particles with stacking faults and twins, which have a high Curie temperature nearly up to room temperature, are formed in the film. Our results show that annealing is quite effective to improve the magnetic properties of GeFe for high-temperature-operating spin-injection devices based on Si or Ge.

Origin of robust nanoscale ferromagnetism in Fe-doped Ge revealed by angle-resolved photoemission spectroscopy and first-principles calculation

“…On the other hand, the narrow-band or nearly localized Fe 3d(e) electrons play an essential role in stabilizing the ferromagnetism most likely through a double-exchange-like mechanism between neighboring Fe atoms. The present picture explains the observed increase of T C with Fe concentration [9] and with the inhomogeneity of Fe distribution [11]. The same picture explains the observation of nanoscale ferromagnetic domains formed in Fe-rich regions well above the T C [15].…”

“…Group-IV FMSs are particularly important because they are compatible with mature Si-based technology. Ge 1−x Fe x (Ge:Fe) is a promising material [9][10][11][12], and indeed can be grown epitaxially on Ge and Si substrates by the low-temperature molecular beam epitaxy (LT-MBE) method without the formation of intermetallic precipitates [13]. It shows p-type conduction, but the carrier concentration of ∼10 18 cm −3 [13] is orders of magnitude smaller than that of doped Fe atoms (∼10 21 cm −3 ).…”

“…It shows p-type conduction, but the carrier concentration of ∼10 18 cm −3 [13] is orders of magnitude smaller than that of doped Fe atoms (∼10 21 cm −3 ). The Curie temperature (T C ) increases with the Fe content and with the inhomogeneity of Fe atom distribution [11,12], and reaches ∼210 K at highest by post-growth annealing [11], which is above the highest T C of (Ga,Mn)As, ∼200 K [14]. Unlike (Ga,Mn)As, the T C does not depend on carrier concentration [13].…”

Important role of the non-uniform Fe distribution for the ferromagnetism in group-IV-based ferromagnetic semiconductor GeFe

“…This difference in the lattice constant may be attributed to the difference in the density of the stacking-fault defects along the (111) plane observed in the GeFe films. 5,6 In face-centered cubic crystals, the (004) diffraction peak shifts to the higher angle side with an increase in the density of the stacking-fault defects along the (111) plane. 28,29,30 We observe many stacking-fault defects especially in the locally high-Fe-concentration regions.…”

“…3,4,5,6 In this paper, we present the growth temperature (T S ) dependence of T C and the lattice constant of GeFe, that are investigated by magnetic circular dichroism (MCD) and the X-ray diffraction (XRD) measurements.…”