Anisotropic Phase Separation through the Metal-Insulator Transition in Amorphous Alloys

Abstract

The characteri=tion of nanometer-de phase sepamtion in sputterd amorphous meti-Ge and Fe-Si films has led to the observation of a new microstructure that extends through the meti-insulator transition. The phase separated regions, which are depndent on deposition conditions, are well-correlated and of the order of 1 nm in the growth plane but poorly-correlated and 1.5-2.0 nm in the growth direction. The resdts suggest that fluctuations during film growth play a pivoti role in preventing anticipate columnar structures, probably l~ing to unusti percolation properties.-. Vapor-depositi amorphous meti-germanium and meti-silicon films have been the subject : of extensive study over the past decade. Much of the effort is aired at understanding the meMinsulator (M-I) transition, since many view the films as relatively unique examples of homogeneous materials which undergo a continuous structural transition as the meti concentration is increased:: In contrast, Kortright and Bienenstoekl inferred from their structural study of amorphous MoCGel-c that films with &c4.23 consist of aGe and a Me-modified material that coexist on a size scak of less than 4 nm. These authors were unable to confirm their supposition definitively with small-angle x-ray scattering (SAXS), however, since the observed intensity patterns could arise from either defecm or such phase separation. In addition, they reference an unsuccessful attempt to detect phase separation with transmission electron microscopy. Subsequently, Yoshizumi et al.2 and Mael et d.3 notd that their observation of a metallic low tempemture specific heat in insulating (cd. 1) amorphous MoCGel-Cfilms is consistent with the coexistence proposal. Recently, Rice et d.4 have used anomalous small-angle x-my mttering (ASAXS) to show, definitively that a variety of Ge-nch amorphous meti-germanium films have SAXS patterns that arise _from composition fluctuations or phase separation, rather than from defec~. E1-tron microscopy has been used in the past to observe composition modulations in, for example, the Work supported in part by~epartment of Energy Contract DE-AC03-76S~515.

Magnetic properties of nanoclusters formed by implantation of Fe into Ge using a metal-vapor vacuum arc ion source

“…[13][14][15] There has been a lot of effort to understand the metal-insulator transition as well as the magnetic transition in the amorphous Fe-Ge system. [12][13][14][15][16][17] The magnetic properties of nanophase materials can be tuned from soft to hard, depending on the magnetic coupling between their small crystallites. The magnetic properties of nanocrystalline Fe-Ge alloys and the change in magnetic properties upon annealing, and their correlation to changes in the structure of the materials have been studied in detail by Hamdeh et al 18 Most of the Fe-Ge amorphous alloys were prepared by the sputter deposition method.…”

“…The magnetic properties of nanocrystalline Fe-Ge alloys and the change in magnetic properties upon annealing, and their correlation to changes in the structure of the materials have been studied in detail by Hamdeh et al 18 Most of the Fe-Ge amorphous alloys were prepared by the sputter deposition method. [12][13][14][15][16][17] In this work, we report the synthesis of Fe clusters in Ge ͑110͒ by ion implantation. We report the results of magnetization and magnetoresistance measurements.…”

Zero-bias anomaly in homogeneously disordered MoGe nanowires undergoing a superconductor-insulator transition

“…, by anomalous small-angle X-ray scattering 41,42 .) Our conditions for the deposition of MoGe alloy are very similar to that used for fabrication of the samples employed in structural studies and important parameters, such as resistivity and C T , are well reproduced.…”

First principles prediction of the metastability of the Ge2Mn phase and its synthesis pathways

“…The nonprimitive unit cell contains 12 atoms; four Mn at 4͑a͒ and eight Ge at 8͑h͒ positions, the latter being further defined by the reduced parameter x. 13 This compound is inspired by experiments of Regan et al, 14 which show similar anisotropic phase separations in Fe-Ge systems as in experiments of Jamet et al, 6 the possibility of substituting Fe by Mn in the C16 structure. Such substitution by Mn ͑and Co͒ has been considered in a previous ab initio study.…”