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Current Status and perspective of ferromagnetic semiconductors : GaMnAs and beyond
Manipulation of the magnetization vector is one of the key processes in devices which are applied in spintronics. In ferromagnetic multilayers it enables the modification of the relative orientation of the magnetizations in adjacent layers used in TMR, GMR, and spin-torque based devices. In the context to better integrate such devices with microelectronics, diluted ferromagnetic semiconductors 3-5 semiconductors doped with magnetic ions are studied intensively. The possibility of varying the concentration of the magnetic dopant and the charge carrier concentrations as well as the strain, during and after their growth, privilege them as model systems which offer a large variation of parameters not attainable with metallic systems. Epitaxial GaMnAs thin films grown by MBE on GaAs substrates are the most interesting members of the family of diluted ferromagnetic semiconductors. They present a uniform ferromagnetic state with a highest observed Curie temperature of 200K [1]. Mn 3d-shell electrons provide the system with magnetic moments which are coupled ferromagnetically via the holes introduced to the GaAs valence band by the same dopant. The presence of a large spin-orbit coupling results in the projection of the anisotropy of the GaAs valence band on the magnetic properties of GaMnAs [2]. One of the most powerful tools to investigate magnetic properties of a ferromagnetic system is the ferromagnetic resonance spectroscopy (FMR) for which recently new approaches have be developed. Adapted to different sample configurations and the concerned parameters to investigate, they enable one to determine and analyze different magnetic parameters in systems varying from bulk materials to nanostructures. This presentation is dedicated to the FMR investigation of the influence of the hole concentration [3], the strain [4], and interlayer magnetic coupling on the magnetic properties of GaMnAs. It will be shown how such studies revealed the possibility of tailoring the magnetization anisotropy and have been a base for further device fabrication [5-7]. In addition, the future developments of both the ferromagnetic semiconductors and FMR will be discussed.
[1] M. Wang et al, APL 93, 132103, (2008)
[2] T. Jungwirth et al, Rev. Mod. Phys. 78, 809, (2006)
[3] Kh. Khazen et al, PRB, 77, 165204 (2008)
[4] M. Cubukcu et al. PRB (rapid com.), 81, 041202 (2010)
[5] S.W. Reister et al, APL, 94, 0635094 (2009)
[6] M. Sawicki et al, Nature phys, 6, 22 (2009)
[7] M. Cubukcu, JAP, 105, 07C506 (2009)