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Register a new userStrain-Control of the magnetic anisotropy in (Ga,Mn)(As,P) ferromagnetic semiconductor layers
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Authors
Aristide Lema^itre
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A small fraction of phosphorus (up to 10 %) was incorporated in ferromagnetic (Ga,Mn)As epilayers grown on a GaAs substrate. P incorporation allows reducing the epitaxial strain or even change its sign, resulting in strong modifications of the magnetic anisotropy. In particular a reorientation of the easy axis toward the growth direction is observed for high P concentration. It offers an interesting alternative to the metamorphic approach, in particular for magnetization reversal experiments where epitaxial defects stongly affect the domain wall propagation.
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The effect of picosecond acoustic strain pulses (ps-ASP) on a thin layer of (Ga,Mn)As co-doped with phosphorus was probed using magneto-optical Kerr effect (MOKE). A transient MOKE signal followed by low amplitude oscillations was evidenced, with a strong dependence on applied magnetic field, temperature and ps-ASP amplitude. Careful interferometric measurement of the layers thickness variation induced by the ps-ASP allowed us to model very accurately the resulting signal, and interpret it as the strain modulated reflectivity (differing for $sigma_{pm}$ probe polarizations), independently from dynamic magnetization effects.
We present an experimental and theoretical study of magnetocrystalline anisotropies in arrays of bars patterned lithographically into (Ga,Mn)As epilayers grown under compressive lattice strain. Structural properties of the (Ga,Mn)As microbars are investigated by high-resolution X-ray diffraction measurements. The experimental data, showing strong strain relaxation effects, are in good agreement with finite element simulations. SQUID magnetization measurements are performed to study the control of magnetic anisotropy in (Ga,Mn)As by the lithographically induced strain relaxation of the microbars. Microscopic theoretical modeling of the anisotropy is performed based on the mean-field kinetic-exchange model of the ferromagnetic spin-orbit coupled band structure of (Ga,Mn)As. Based on the overall agreement between experimental data and theoretical modeling we conclude that the micropatterning induced anisotropies are of the magnetocrystalline, spin-orbit coupling origin.
We report single-color, time resolved magneto-optical measurements in ferromagnetic semiconductor (Ga,Mn)As. We demonstrate coherent optical control of the magnetization precession by applying two successive ultrashort laser pulses. The magnetic field and temperature dependent experiments reveal the collective Mn-moment nature of the oscillatory part of the time-dependent Kerr rotation, as well as contributions to the magneto-optical signal that are not connected with the magnetization dynamics.
The laser-induced precession of magnetization in (Ga,Mn)As samples with different magnetic anisotropy was studied by the time-resolved magneto-optical method. We observed that the dependence of the precession amplitude on the external magnetic field depends strongly on the magnetic anisotropy of (Ga,Mn)As and we explain this phenomenon in terms of competing cubic and uniaxial anisotropies. We also show that the corresponding anisotropy fields can be deduced from the magnetic field dependence of the precession frequency.
We present a systematic study on the influence of epitaxial strain and hole concentration on the magnetic anisotropy in (Ga,Mn)As at 4.2 K. The strain was gradually varied over a wide range from tensile to compressive by growing a series of (Ga,Mn)As layers with 5% Mn on relaxed graded (In,Ga)As/GaAs templates with different In concentration. The hole density, the Curie temperature, and the relaxed lattice constant of the as-grown and annealed (Ga,Mn)As layers turned out to be essentially unaffected by the strain. Angle-dependent magnetotransport measurements performed at different magnetic field strengths were used to probe the magnetic anisotropy. The measurements reveal a pronounced linear dependence of the uniaxial out-of-plane anisotropy on both strain and hole density. Whereas the uniaxial and cubic in-plane anisotropies are nearly constant, the cubic out-of-plane anisotropy changes sign when the magnetic easy axis flips from in-plane to out-of-plane. The experimental results for the magnetic anisotropy are quantitatively compared with calculations of the free energy based on a mean-field Zener model. An almost perfect agreement between experiment and theory is found for the uniaxial out-of-plane and cubic in-plane anisotropy parameters of the as-grown samples. In addition, magnetostriction constants are derived from the anisotropy data.
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