Ferromagnetic Ge_1−xM_x (M = Mn, Fe, and Co) Nanowires

Abstract

We synthesized Ge and Ge 1-x M x (M ) Mn, Co, and Fe, x e 0.4) nanowires using the thermal vapor transport method. All of the nanowires consisted of single-crystalline Ge nanocrystals grown uniformly with the [111] direction. High-resolution X-ray diffraction showed no metal cluster formation for any of the Ge 1-x M x nanowires, and the reduction of the lattice constant for the Mn-substituted nanowires. X-ray absorption spectroscopy and X-ray magnetic circular dichroism measurements revealed that the Mn 2+ ions preferentially occupy the tetrahedral sites, substituting for Ge. The magnetic moment of the Mn ions reaches a maximum for x ) 0.1, which is much larger than that of the Fe or Co ions. The magnetic hysteresis confirms the room-temperature ferromagnetism of the Ge 1-x Mn x nanowires, which is also maximized at x ) 0.1. We suggest that the Mn ions produce dopant-acceptor hybridization with host defects in the p-type Ge nanowires. The Mn substitution is more effective to form significant ferromagnetic Ge nanowires, compared to the Fe or Co substitution.

Organization of matter into one-dimensional units on designed media

“…The XRD results revealed the unaffected crystalline lattice parameter ( ) of the new alloy material GeDy 2 , ≈ 0 5661 nm, similar to the results in Ref. [17] for the GeMn 5 nanowires. This seems attainable at low concentrations of the dopant, even when its atomic radius (R Dy ) is substantially larger than that of Ge, in the case:…”

“…The growth techniques employed for the Au seeds vary in the literature [2,[14][15][16][17]. For example, in Ref.…”

“…[16] thermal evaporation of Au is applied, in Ref. [17] -sputtering, and in Refs. [2,14] -electron beam evaporation.…”

“…[2,14] -electron beam evaporation. The analyses for homogeneity of size and shape of the fabricated Au islands by various techniques conclude in favor of electron beam evaporation as the most adequate [2,[14][15][16][17], and this is therefore also applied in this work.…”

Magnetic MnxGe1-x Dots for Spintronics Applications

“…Among them, (Ga,Mn)As became the first and the mostly studied DMSs since 1996 (Lu and Lieber, 2006); but to our knowledge, some studies lacked the threshold doping profile to push its curie temperature to room temperature and above (currently around 190 K (Lyu and Moon, 2003, van der Meulen et al, 2008, Maekawa, 2006, Wang et al, 1995). Since then, substantial research has been carried out in III-V and II-VI semiconductors to improve the T c by increasing the solubility limit and meanwhile minimizing self-compensation effect of magnetic structures, using radical techniques such as delta doping of modulation doped quantum structures (Bhatt et al, 2002, Cho et al, 2008, Berciu and Bhatt, 2001, Lauhon et al, 2002. Another approach to achieve high-T c DMS is to use transition metal doped wide bandgap nitrides and oxides, such as GaN, AlN, ZnO, TiO 2 .…”