AVS 50th International Symposium
    Magnetic Interfaces and Nanostructures Friday Sessions
       Session MI+SC-FrM

Paper MI+SC-FrM1
Ferromagnetic Nano Fe-Germenide Particles in MBE-grown Ge-Fe

Friday, November 7, 2003, 8:20 am, Room 316

Session: Semiconductor Spin Injection
Presenter: R. Goswami, Geo-Centers Inc.
Authors: R. Goswami, Geo-Centers Inc.
G. Kioseoglou, Naval Research Laboratory
A.T. Hanbicki, Naval Research Laboratory
B.T. Jonker, Naval Research Laboratory
G. Spanos, Naval Research Laboratory
Correspondent: Click to Email
Ferromagnetic-semiconductors (FMSs) have attracted considerable attention due to the coexistence of semiconductor properties and long-range ferromagnetic (FM) order in these materials. Recently, ferromagnetic order was reported in alloy thin films based on Ge, which provides a simple host lattice to explore the fundamental origins of FM order. A relatively high Curie temperature,120 K, has been experimentally observed in a Ge-3.3at.% Mn film grown epitaxially on GaAs. It has been theoretically predicted very recently that Ge with Fe atoms in the lattice will be ferromagnetic semiconductors and the Curie temperature will increase as a function of Fe concentration. To date, relatively little attention has been paid to understanding the fine scale microstructural evolution within Ge-Fe thin films. It is well known that the microstructure plays a vital role in dictating the ferromagnetic properties. Fe-Ge contains different phases with magnetic properties ranging from ferromagnetic Fe to antiferromagnetic FeGe@sub2@. The purpose of the present investigation is to elucidate the phase transformations and overall microstructural evolution in epitaxial Ge- 4at.% Fe thin films deposited on (100) GaAs substrates at three different temperatures, 150°, 250° 400 ° C, in order to better understand magnetic properties in these materials. The equilibrium phases at this composition (4%Fe) are Ge with negligible amount of Fe and antiferromagnetic FeGe@sub2@. We have observed for all cases that nano-particles of ferromagnetic- Fe@sub3@ Ge@sub2@ form uniformly in a crystalline Ge-matrix. The particle size was observed to decrease with the substrate temperature. We demonstrate that a supersaturated Ge-Fe solid-solution forms initially from the vapor phase resulting in the solid state precipitation of this metastable ferromagnetic- germanide. This work was supported by the Office of Naval Research and DARPA.