Indication of ferromagnetism in molecular-beam-epitaxy-derived N-type GaMnN

Overberg, M. E.; Abernathy, C. R.; Pearton, S. J.; Theodoropoulou, Nikoleta; McCarthy, Kevin; Hebard, A. F.

doi:10.1063/1.1397763

Cited by 282 publications

(170 citation statements)

References 18 publications

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“…Since experimental values for T C in Ga 1−x Mn x N are quite controversial (reported values range from 0K to 940K 4,26,27,28,29,30 ), we refrain from a comparison here. However, the Curie temperatures we calculated are quite low compared to earlier mean-field estimates (e.g.…”

Section: Resultsmentioning

confidence: 99%

Magnetism in (III,Mn)-V diluted magnetic semiconductors: Effective Heisenberg model

Hilbert

Nolting

2005

Phys. Rev. B

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The magnetic properties of the diluted magnetic semiconductors (DMS) (Ga, Mn)As and (Ga, Mn)N are investigated by means of an effective Heisenberg model, whose exchange parameters are obtained from first-principle calculations. The finite-temperature properties of the model are studied numerically using a method based upon the Tyablikov approximation. The method properly incorporates the effects of positional disorder present in DMS. The resulting Curie temperatures for (Ga, Mn)As are in excellent agreement with experimental data. Due to percolation effects and noncollinear magnetic structures at higher Mn concentrations, our calculations predict for (Ga, Mn)N very low Curie temperatures compared to mean-field estimates.

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Section: Resultsmentioning

confidence: 99%

Magnetism in (III,Mn)-V diluted magnetic semiconductors: Effective Heisenberg model

Hilbert

Nolting

2005

Phys. Rev. B

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“…On the other hand, available experimental data often contradict each other. Some reports show that high T c ferromagnetism is achievable in this system [2,3,4,5]; others show that the magnetic coupling of the Mn ions in GaMnN is actually antiferromagnetic (AFM) [6]. The exact nature of the magnetism observed in this system is also still under debate [7,8,9].…”

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confidence: 93%

Transition from ferromagnetism to antiferromagnetism in Ga1−xMnxN

Dalpian

Wei

2005

Journal of Applied Physics

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Using density functional theory, we study the magnetic stability of the Ga1−xMnxN alloy system. We show that unlike Ga1−xMnxAs, which shows only ferromagnetic (FM) phase, Ga1−xMnxN can be stable in either FM or antiferromagnetic phases depending on the alloy concentration. The magnetic order can also be altered by applying pressure or with charge compensation. A unified model is used to explain these behaviors.The discovery of ferromagnetism in Mn-containing III-V semiconductors has attracted significant attention in the last decade because the interesting combination of semiconductor electronics and metallic ferromagnetism creates great potential for developing functional devices that manipulate spin, as well as charge. Among the materials that have been investigated, GaMnN is one of the most interesting systems. On one hand, original theoretical predictions suggest that high T c ferromagnetism can be achieved in the GaMnN alloy [1], which has resulted in an extensive experimental, as well as theoretical, study of its physical properties. On the other hand, available experimental data often contradict each other. Some reports show that high T c ferromagnetism is achievable in this system [2,3,4,5]; others show that the magnetic coupling of the Mn ions in GaMnN is actually antiferromagnetic (AFM) [6]. The exact nature of the magnetism observed in this system is also still under debate [7,8,9]. Some groups suggested that the observed ferromagnetism could be due to secondary phases generated during growth, and that GaMnN is a spin glass system [8]. Other groups argue that no secondary phase is observed in their single-crystal GaMnN samples that show ferromagnetism [9]. There are also discussions about whether the relevant Mn 3d state has d 4 or d 5 + h character, or whether the d levels are localized in the bandgap or inside the valence band [10].Although many of the issues are still under intensive study, recent ab initio band structure and total energy calculations [11,12,13] seem to agree that Mn 3d levels are located in the gap, and that the interaction between substitutional Mn ions is ferromagnetic (FM) at low Mn concentration. Because previous ab initio studies also find that pure MnN has an AFM ground state [14], an interesting question was raised about how the magnetic and electronic properties of Ga 1−x Mn x N evolve as a function of the Mn concentration x. Furthermore, it is now well known that the ferromagnetism observed in Mn-containing GaAs is caused by holes in the host valence-band-derived states. It would be important to understand how the mechanism changes in Mn-containing GaN, where the holes are created in the Mn d bands.In this paper, using ab initio band structure and total energy methods, we study the magnetic properties of Ga 1−x Mn x N in the low and high Mn concentration regimes. We also study the effects of pressure and charge compensation on the magnetic properties of this system. We show that unlike in GaMnAs, where p-d coupling induced level splitting at the valence band maximum (VBM)...

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“…7 Most of these systems are controversially discussed in the literature, and an unambiguous determination of the ferromagnetism has only been reported for (Zn, Cr)Te with a relatively high Cr concentration of 20% and a Curie temperature of 300 K. 8 In particular, in this class of materials (Ga, Mn)N has been frequently mentioned as the most promising high-T C DMS referring to the prediction of model calculations by Dietl et al 5 and ab initio results by Sato et al 9 Many groups have tried to fabricate ferromagnetic (Ga, Mn)N, but the experimental results are very controversial and confusing. After the observation of the ferromagnetism of (Ga, Mn)N, 10 many experiments followed; however, reported T C 's are scattered between 20 and 940 K. [10][11][12][13][14] Moreover, recently Ploog et al observed spin-glass behavior in 7% Mn-doped GaN and suggested that the ferromagnetism observed in 14% Mn-doped GaN originated from Mn-rich clusters. 15 Thus, the ferromagnetism in (Ga, Mn)N is still an open question which we reconsider in this paper.…”

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Low-temperature ferromagnetism in (Ga, Mn)N: Ab initiocalculations

et al. 2004

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The magnetic properties of dilute magnetic semiconductors (DMSs) are calculated from first-principles by mapping the ab initio results on a classical Heisenberg model. By using the Korringa-Kohn-Rostoker coherent-potential approximation (KKR-CPA) method within the local-density approximation, the electronic structure of (Ga, Mn)N and (Ga, Mn)As is calculated. Effective exchange coupling constants J ij 's are determined by embedding two Mn impurities at sites i and j in the CPA medium and using the J ij formula of Liechtenstein et al. [J. Magn. Magn. Mater. 67, 65 (1987)]. It is found that the range of the exchange interaction in (Ga, Mn)N, being dominated by the double exchange mechanism, is very short ranged due to the exponential decay of the impurity wave function in the gap. On the other hand, in (Ga, Mn)As, where p-d exchange mechanism dominates, the interaction range is weaker but long ranged, because the extended valence hole states mediate the ferromagnetic interaction. Curie temperatures (T C 's) of DMSs are calculated by using the mean-field approximation (MFA), the random-phase approximation, and the, in principle exact, Monte Carlo method. It is found that the T C values of (Ga, Mn)N are very low since, due to the short-ranged interaction, percolation of the ferromagnetic coupling is difficult to achieve for small concentrations. The MFA strongly overestimates T C . Even in (Ga, Mn)As, where the exchange interaction is longer ranged, the percolation effect is still important and the MFA overestimates T C by about 50%-100%. Dilute magnetic semiconductors (DMSs), such as (In, Mn)As and (Ga, Mn)As discovered by Munekata et al. and Ohno et al., have been well investigated as hopeful materials for spintronics. 1 Curie temperatures (T C 's) of these DMSs are well established 1-3 and some prototypes of spintronics devices have been produced based on these DMSs. The magnetism in these DMSs are theoretically investigated and it is known that the ferromagnetism in these systems, as well as (Ga, Mn)Sb, can be well described by Zener's p-d exchange interaction, due to the fact that the majority of d states lies energetically in the lower part of the valence band.4 Dietl et al. 5 and MacDonald et al. 6 explained many physical properties of (Ga, Mn)As based on the p-d exchange model, and first-principles calculations by Sato et al. showed that the concentration dependence of T C in (Ga, Mn)As was well understood by the p-d exchange interaction if a correction to the local-density approximation (LDA) is simulated by the LDA+ U method with U = 4 eV. 4 While these p-d exchange systems, in which the d states of Mn impurities are practically localized, are well understood, there exist an even larger class of systems where the d levels lie in the gap exhibiting impurity bands for sufficiently large concentrations. To these impurity band systems belong (Ga, Mn)N, (Ga, Cr)N, (Ga, Cr)As, (Zn, Cr)Te, (Zn, Cr)Se, and many others, as shown by first-principles calculations. 7Most of these systems are controversially discussed ...

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Indication of ferromagnetism in molecular-beam-epitaxy-derived N-type GaMnN

Cited by 282 publications

References 18 publications

Magnetism in (III,Mn)-V diluted magnetic semiconductors: Effective Heisenberg model

Magnetism in (III,Mn)-V diluted magnetic semiconductors: Effective Heisenberg model

Transition from ferromagnetism to antiferromagnetism in Ga1−xMnxN

Low-temperature ferromagnetism in (Ga, Mn)N: Ab initiocalculations

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