Fraction Of Mn Atoms Research Articles

Structural and magnetic properties of nanoclusters in GaMnAs granular layers

Structural and magnetic properties of GaAs thin films with embedded nanoclusters were investigated as a function of the annealing temperature and Mn content. Surprisingly, the presence of two kinds of nanoclusters with different structure was detected in most of the samples independently of the thermal processing or Mn content. This proved that the presence of a given type of clusters cannot be assumed a priori as is reported in many papers. The fraction of Mn atoms in each kind of cluster was estimated from the extended X-ray absorption fine structure analysis. This analysis ruled out the possibility of the existence of nanoclusters containing a hypothetic MnAs cubic compound—only (Ga,Mn)As cubic and hexagonal MnAs clusters were detected. Moreover the bimodal distribution of Mn magnetic moments was found, which scales with the estimated fraction of Mn atoms in the cubic and hexagonal clusters.

Structural and magnetic properties of the molecular beam epitaxy grown MnSb layers on GaAs substrates

The structural and magnetic properties of MnSb layers grown on two differently oriented GaAs substrates are reported. The MnSb compounds grow nonhomogenously both on GaAs(111)B and on GaAs(100) substrates. In x-ray diffraction studies the formation of two epitaxial domains is observed depending on the crystallographic orientation of the substrate. The observed diffusion of Ga atoms from the substrate to the layers results in the formation of an additional Mn-rich cubic phase of GaMnSb. In the case of the (100) oriented substrate, the diffusion of Mn into the substrate was additionally found. Traces of other phases were also noticed. The complex morphology of the layers is found to influence their magnetic properties. Magnetic force microscopy images revealed an inhomogenous distribution of the magnetic force gradient on the surface and the formation of magnetic domains in the samples. X-ray absorption studies of the chemical bonding and local atomic structure around Mn atoms confirmed high structural and chemical disorder in the samples. The chemical bonding of the dominating fraction of Mn atoms is found, however, similar to that in the reference MnSb powder. The x-ray magnetic circular dichroism measurements reveal an enhanced orbital moment and a reduced spin moment, which is most likely caused by the presence of different phases and a Mn-rich surface in the investigated samples.

Comparison of the magnetic properties of GeMn thin films through Mn L-edge x-ray absorption

X-ray absorption spectroscopy of epitaxial GeMn thin films reveals an experimentally indistinguishable electronic configuration of Mn atoms incorporated in Ge1−xMnx nanoclusters and in precipitates of the intermetallic compound Mn5Ge3, respectively. However, the average magnetic response of thin films containing Ge1−xMnx nanoclusters is lower than the response of films containing Mn5Ge3 precipitates. This reduced magnetic response of Ge1−xMnx nanoclusters is explained in terms of a fraction of Mn atoms being magnetically inactive due to antiferromagnetic coupling or the presence of structural disorder. A determination of the role of magnetically inactive Mn atoms in the self-assembly of the thermodynamically metastable Ge1−xMnx nanoclusters seems to be an essential ingredient for an enhanced control of this promising high Curie temperature magnetic semiconductor.

Properties of Ga1−xMnxAs with high x (>0.1)

We have investigated the magnetic and the crystalline properties of a set of Ga1−xMnxAs layers with high nominal Mn compositions (x=0.101–0.198). Magnetization measurements and combined channeling Rutherford backscattering (c-RBS) and particle induced x-ray emission (c-PIXE) measurements have been performed to determine the effective Mn composition xeff and the fraction of Mn atoms at various lattice sites. Here, xeff determined from magnetization measurements, which increases with increasing x, is consistent with the results determined from c-RBS-PIXE measurements.

Coupled plasmon–LO-phonon modes inGa1−xMnxAs

The vibrational and electronic properties of ${\mathrm{Ga}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}\mathrm{As}$ layers with Mn fractions $0<~x<~2.8%,$ grown on GaAs(001) substrates by low-temperature molecular-beam epitaxy, are investigated by micro-Raman spectroscopy and far-infrared (FIR) reflectance spectroscopy. The Raman and FIR spectra are strongly affected by the formation of a coupled mode of the longitudinal optical phonon and the hole plasmon. The spectral line shapes are modeled using a dielectric function where intraband and interband transitions of free holes are included. In addition to the coupled mode, the contributions of a surface depletion layer as well as a symmetry forbidden TO phonon have to be taken into account for the Raman spectra. Values for the hole densities are estimated from a full line-shape analysis of the measured spectra. Annealing at temperatures between 250 and $500\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ results in a decrease of the hole density with increasing annealing temperature and total annealing time. Simultaneously, a reduction of the fraction of Mn atoms on Ga lattice sites is deduced from high-resolution x-ray diffraction.

Local structure about Mn atoms in In1-xMnxAs diluted magnetic semiconductors.

X-ray-absorption fine-structure measurements were performed at the Mn [ital K] edge on In[sub 0.88]Mn[sub 0.12]As diluted magnetic semiconductors prepared by molecular-beam epitaxy. It has been found that in the high-growth-temperature samples ([ital T][sub [ital s]]=280 [degree]C), Mn atoms are primarily incorporated in the form of MnAs clusters with NiAs structure. No significant disorder is observed. In the low-growth-temperature samples ([ital T][sub [ital s]]=210 [degree]C), the majority of Mn atoms form small ([ital r][similar to]3 A), disordered, sixfold-coordinated centers with As. The presence of disorder in MnAs centers for the latter case is established using the method of cumulants. Only a very small fraction of Mn atoms may substitute for In in the zinc-blende InAs structure. Effective valency and coordination of Mn atoms deduced from the near-edge structure are the same for both the high- and low-growth-temperature In[sub 1[minus][ital x]]Mn[sub [ital x]]As films. The formal valency is lower than +3. The local structures established in the present work are consistent with the observed difference in magnetic behavior for samples prepared at different substrate temperatures.

Electron Channelling Enhanced Microanalysis on Ni–Al–Mn and Al–Mn–Si

Atom location by channelling enhanced microanalysis (ALCHEMI) was performed for Ni–Al–Mn compounds and Al–Mn–Si quasicrystals. For Ni75Al25−xMnx (x=5, 9) with the L12-type structure, an occupation fraction of Mn atoms at the Ni site was quantitatively determined using planar channelling conditions. The occupation fraction increases with the Mn concentration or by quenching the compound from high temperature. In quasicrystals of Al74Mn20Si6 and Al68Mn20Ru8Si4, axial channelling conditions were used to locate Si and Ru, respectively. It was shown that Si atoms occupy the Al site in Al74Mn20Si6 whereas Ru atoms occupy the site different from that of Al in Al68Mn20Ru8Si4.