Magnetotransport properties of (Ge,Mn) ferromagnetic semiconductor grown on GaAs(001)
Date Issued
2010
Date
2010
Author(s)
Yu, Ing-Song
Abstract
By low temperature Molecular Beam Epitaxy (MBE), (Ge,Mn) thin films with ferromagnetic nanostructures are grown on two kind of GaAs substrates: epiready GaAs(001) (Ga-GeMn) and GaAs(001) with amorphous As capping layer (As-GeMn).
In the Ga-GeMn samples, we observe self-organized Mn-rich nanocolumns which, depending on the initial surface morphology, are either parallel or entangled. Magnetic measurements evidence two magnetic phases: ferromagnetic nanocolumns with Curie temperature around 150K, and the Ge matrix made paramagnetic by diluted Mn. From measurements of magnetotransport, this p-type layer exhibits anomalous Hall effect (AHE) and various magnetoresistivity (MR): negative Giant MR at low temperature, parabolic ordinary MR, and an additional positive MR at low field. The simulation of magnetotransport properties has been initiated, with some assumptions on the energy-band diagram of p-type Ge semiconductor and Mn-rich nanocolumns, and shows the way that AHE in the inclusions induces AHE in the whole layer, and a mechanism of MR which accounts for this contribution (which we call Hall MR).
In the As-GeMn samples, the outdiffusion of As atoms changes the growth mechanism, from a 2D spinodal decomposition to a 3D one with the formation of nanoprecipitates with Tc=50K and of ferromagnetic Ge3Mn5 clusters. Compensation effect between Mn (donor) and As (acceptor) dominates the transport behaviors. A highly anisotropic MR is observed in n-type (Ge,Mn) films and shown to be due to weak localization effects. Another contribution is tentatively attributed to tunneling MR due to the Schottky barrier, which forms at the interface between the metallic Mn-rich inclusions and the n-type Ge semiconductor.
Subjects
Molecular Beam Epitaxy
ferromagnetic semiconductor
anomalous Hall effect
Giant magnetoresistivity
weak localization effect,
tunneling magnetoresistivity
Type
thesis
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