Dilute Magnetic Semiconductor Ga Research Articles

Ferromagnetism and infrared electrodynamics of Ga1−xMnxAs

We report on the magnetic and the electronic properties of the prototype dilute magnetic semiconductor Ga$_{1-x}$Mn$_x$As using infrared (IR) spectroscopy. Trends in the ferromagnetic transition temperature $T_C$ with respect to the IR spectral weight are examined using a sum-rule analysis of IR conductivity spectra. We find non-monotonic behavior of trends in $T_C$ with the spectral weight to effective Mn ratio, which suggest a strong double-exchange component to the FM mechanism, and highlights the important role of impurity states and localization at the Fermi level. Spectroscopic features of the IR conductivity are tracked as they evolve with temperature, doping, annealing, As-antisite compensation, and are found only to be consistent with an Mn-induced IB scenario. Furthermore, our detailed exploration of these spectral features demonstrates that seemingly conflicting trends reported in the literature regarding a broad mid-IR resonance with respect to carrier density in Ga$_{1-x}$Mn$_x$As are in fact not contradictory. Our study thus provides a consistent experimental picture of the magnetic and electronic properties of Ga$_{1-x}$Mn$_x$As.

Bulk electronic structure of the dilute magnetic semiconductor Ga1−xMnxAs through hard X-ray angle-resolved photoemission

A detailed understanding of the origin of the magnetism in dilute magnetic semiconductors is crucial to their development for applications. Using hard X-ray angle-resolved photoemission (HARPES) at 3.2 keV, we investigate the bulk electronic structure of the prototypical dilute magnetic semiconductor Ga(0.97)Mn(0.03)As, and the reference undoped GaAs. The data are compared to theory based on the coherent potential approximation and fully relativistic one-step-model photoemission calculations including matrix-element effects. Distinct differences are found between angle-resolved, as well as angle-integrated, valence spectra of Ga(0.97)Mn(0.03)As and GaAs, and these are in good agreement with theory. Direct observation of Mn-induced states between the GaAs valence-band maximum and the Fermi level, centred about 400 meV below this level, as well as changes throughout the full valence-level energy range, indicates that ferromagnetism in Ga(1-x)Mn(x)As must be considered to arise from both p-d exchange and double exchange, thus providing a more unifying picture of this controversial material.

β-detected NMR of Li in Ga1−xMnxAs

The magnetic properties of a 180-nm-thick epitaxial film of the dilute magnetic semiconductor Ga${}_{1\ensuremath{-}x}$Mn${}_{x}$As with $x=0.054$ are investigated using beta-detected NMR of low-energy implanted ${}^{8}$Li${}^{+}$. There is a broad distribution of local magnetic fields in the Ga${}_{1\ensuremath{-}x}$Mn${}_{x}$As layer, reflecting the magnetic inhomogeneity of the system. The resonance (representing the local magnetic field distribution) is followed as a function of temperature through the ferromagnetic transition. The average hyperfine field at the ${}^{8}$Li nucleus is measured to be positive and on the order of 150 G at low temperature, implying a negative hyperfine coupling of the ${}^{8}$Li to the delocalized holes and suggesting that the holes are better described by an Mn--derived impurity band. The spin--lattice relaxation of ${}^{8}$Li shows a remarkably weak feature at the phase transition and no Korringa behavior despite metallic conductivity. No evidence is found of the microscopic magnetic phase separation that has been suggested by some low-energy muon spin-rotation measurements.

Controlled doping of single crystalline diluted magnetic semiconductor Ga 1 −xMn xN nanowires

We report on the optical and magnetic properties of single crystalline dilute magnetic semiconductor Ga 1− x Mn x N nanowires. The nanowires were fabricated by chemical vapor transport process, and had diameters of <100 nm and length of several μm. Controlled doping of manganese in the range of x = 0.01–0.08 was successfully achieved by varying the processing conditions. X-ray diffraction and transmission electron microscopy observation showed that the nanowires are single crystalline without any secondary phases. Photoluminescence emissions of all the doped nanowires were red-shifted (2.8 eV) compare to pure gallium nitride nanowires (3.3 eV) at room temperature. Ferromagnetism up to room temperature was observed in GaN 1− x Mn x N nanowires with x > 0.04.

X-MCD at twin-helical undulator beam line BL25SU of SPring-8

The use of circularly polarized light in the soft X-ray region is very powerful for the study of magnetic properties of materials. In particular, the magnetic circular dichroism of core absorption spectra (X-MCD) with high resolution and high accuracy provides useful information on the spin and orbital contribution to the magnetic moment. Information on the band structures is also obtained. Typical X-MCD results are reported for Pd–Fe alloys, Co 2 YSn( Y=Ti, Zr, Nb) Heusler alloys, Fe x TiS 2 intercalated material as well as dilute magnetic semiconductor Ga 1− x Mn x As.

Superlattices of III-V semiconductor and heterogeneous magnetic layers for CPP magnetotransport

In this report we present the fabrication of superlattices consisting of heterogeneous magnetic GaAs:MnAs layers and InGaAs spacers with equal thickness. The magnetic and structural properties of such a superlattice are described, showing that under the appropriate annealing conditions the low-temperature grown superlattice structure is preserved and that the MnAs magnetic clusters can be formed in 2D sheets separated by thin (5-20 nm) semiconductor layers of good crystalline quality. CPP magnetotransport studies only show measurable MR at low temperatures, dominated by the dilute magnetic semiconductor Ga(Mn)As host lattice of the MnAs clusters.