Limits...
Lattice dynamics of Ga1-xMnxN and Ga1-xMnxAs by first-principle calculations.

Leite Alves HW, Scolfaro LM, da Silva EF - Nanoscale Res Lett (2012)

Bottom Line: The dependence of the calculated phonon frequencies with the Mn content was analyzed, and the results indicate that the phonon frequencies decrease with the increasing of Mn composition, leading to the false impression that they obey the Vegard rule in some cases.Moreover, the hexagonal Ga1-xMnxN alloys are elastically unstable for Mn concentrations at the order of 20%, which explains in part the experimentally observed deterioration of these alloys.These findings can be used in future technologies as a guide for the synthesis of spintronic nanostructured devices, such as nanowires, based on these materials.

View Article: PubMed Central - HTML - PubMed

Affiliation: Departamento de Ciências Naturais, Universidade Federal de São João del Rei, Praça Dom Helvécio, 74, São João del Rei, 36301-160, MG, Brazil. hwlalves@ufsj.edu.br.

ABSTRACT
In this work, we present theoretical results, using first-principle methods associated to the virtual crystal approximation model, for the vibrational mode frequencies of both the Ga1-xMnxN (in both cubic and hexagonal structures) and the Ga1-xMnxAs alloys, with the Mn contents in the range of 0% to 20%. The dependence of the calculated phonon frequencies with the Mn content was analyzed, and the results indicate that the phonon frequencies decrease with the increasing of Mn composition, leading to the false impression that they obey the Vegard rule in some cases. Moreover, the hexagonal Ga1-xMnxN alloys are elastically unstable for Mn concentrations at the order of 20%, which explains in part the experimentally observed deterioration of these alloys. These findings can be used in future technologies as a guide for the synthesis of spintronic nanostructured devices, such as nanowires, based on these materials.

No MeSH data available.


Related in: MedlinePlus

Calculated phonon frequencies for the hexagonal Ga1−xMnxN alloy as function of the Mn concentration.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC3526471&req=5

Figure 4: Calculated phonon frequencies for the hexagonal Ga1−xMnxN alloy as function of the Mn concentration.

Mentions: In Figure 4, we show the calculated phonon frequency dependence on the Mn concentration for the hexagonal Ga1−xMnxN alloy. From this figure, we note that, except for the A1(TO) phonon, all the other modes have their frequencies decreasing with the increase of Mn content. These findings are, qualitatively, in good agreement with the experimental data[8,12] and also follow the same features obtained for cubic alloys. Additionally, from the results depicted in Figure 4, we observe that the E2(low) mode became softer with the increase of Mn concentration, and when this content is greater than 20%, this mode has a negative frequency. From the lattice dynamics point of view, this is a clear indication that there is an elastic instability of the hexagonal Ga1−xMnxN alloy, leading to some structural phase transition, as observed for the cubic HfO2 and ZrO2 compounds[21]. This is an indication to explain the deterioration in the Ga1−xMnxN lattice[7]. Moreover, as the obtained E2(low) mode frequency becomes 135.1 cm−1, a value close to Eu which is one of the face-centered tetragonal MnN mentioned above, we can infer that this deterioration can be assigned to the rearrangement of the N atoms bonded to Mn that change the local symmetry around the metal, from the hexagonal to the tetragonal (or cubic) structure. These N atom rearrangements are increased as the Mn content increases, leading to the observed deterioration of the hexagonal lattice. However, as the crystal is viewed in a well-ordered alloy in the VCA model, our current results cannot describe, accurately, this observed deterioration. Thus, a good physical picture of this effect can only be described using total energy and phonon mode calculations where the local environment of the Mn atoms is taken into account. Such calculations are currently under way.


Lattice dynamics of Ga1-xMnxN and Ga1-xMnxAs by first-principle calculations.

Leite Alves HW, Scolfaro LM, da Silva EF - Nanoscale Res Lett (2012)

Calculated phonon frequencies for the hexagonal Ga1−xMnxN alloy as function of the Mn concentration.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3526471&req=5

Figure 4: Calculated phonon frequencies for the hexagonal Ga1−xMnxN alloy as function of the Mn concentration.
Mentions: In Figure 4, we show the calculated phonon frequency dependence on the Mn concentration for the hexagonal Ga1−xMnxN alloy. From this figure, we note that, except for the A1(TO) phonon, all the other modes have their frequencies decreasing with the increase of Mn content. These findings are, qualitatively, in good agreement with the experimental data[8,12] and also follow the same features obtained for cubic alloys. Additionally, from the results depicted in Figure 4, we observe that the E2(low) mode became softer with the increase of Mn concentration, and when this content is greater than 20%, this mode has a negative frequency. From the lattice dynamics point of view, this is a clear indication that there is an elastic instability of the hexagonal Ga1−xMnxN alloy, leading to some structural phase transition, as observed for the cubic HfO2 and ZrO2 compounds[21]. This is an indication to explain the deterioration in the Ga1−xMnxN lattice[7]. Moreover, as the obtained E2(low) mode frequency becomes 135.1 cm−1, a value close to Eu which is one of the face-centered tetragonal MnN mentioned above, we can infer that this deterioration can be assigned to the rearrangement of the N atoms bonded to Mn that change the local symmetry around the metal, from the hexagonal to the tetragonal (or cubic) structure. These N atom rearrangements are increased as the Mn content increases, leading to the observed deterioration of the hexagonal lattice. However, as the crystal is viewed in a well-ordered alloy in the VCA model, our current results cannot describe, accurately, this observed deterioration. Thus, a good physical picture of this effect can only be described using total energy and phonon mode calculations where the local environment of the Mn atoms is taken into account. Such calculations are currently under way.

Bottom Line: The dependence of the calculated phonon frequencies with the Mn content was analyzed, and the results indicate that the phonon frequencies decrease with the increasing of Mn composition, leading to the false impression that they obey the Vegard rule in some cases.Moreover, the hexagonal Ga1-xMnxN alloys are elastically unstable for Mn concentrations at the order of 20%, which explains in part the experimentally observed deterioration of these alloys.These findings can be used in future technologies as a guide for the synthesis of spintronic nanostructured devices, such as nanowires, based on these materials.

View Article: PubMed Central - HTML - PubMed

Affiliation: Departamento de Ciências Naturais, Universidade Federal de São João del Rei, Praça Dom Helvécio, 74, São João del Rei, 36301-160, MG, Brazil. hwlalves@ufsj.edu.br.

ABSTRACT
In this work, we present theoretical results, using first-principle methods associated to the virtual crystal approximation model, for the vibrational mode frequencies of both the Ga1-xMnxN (in both cubic and hexagonal structures) and the Ga1-xMnxAs alloys, with the Mn contents in the range of 0% to 20%. The dependence of the calculated phonon frequencies with the Mn content was analyzed, and the results indicate that the phonon frequencies decrease with the increasing of Mn composition, leading to the false impression that they obey the Vegard rule in some cases. Moreover, the hexagonal Ga1-xMnxN alloys are elastically unstable for Mn concentrations at the order of 20%, which explains in part the experimentally observed deterioration of these alloys. These findings can be used in future technologies as a guide for the synthesis of spintronic nanostructured devices, such as nanowires, based on these materials.

No MeSH data available.


Related in: MedlinePlus