Phase diagram and critical behavior of the random ferromagnet Ga<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mrow /><mml:mrow><mml:mn>1</mml:mn><mml:mo>−</mml:mo><mml:mi>x</mml:mi></mml:mrow></mml:msub></mml:math>Mn<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mrow /><mml:mi>x</mml:mi></mml:msub></mml:math>N

Stefanowicz, S.; Kunert, Gerd; Simserides, Constantinos; Majewski, J. A.; Stefanowicz, W.; Kruse, C.; Figge, S.; Li, Tian; Jakieła, R.; Trohidou, K. N.; Bonanni, A.; Hommel, D.; Sawicki, M.; Dietl, T.

doi:10.1103/physrevb.88.081201

Cited by 59 publications

(89 citation statements)

References 36 publications

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“…The effect of broadening on M(T ) was modelled in an approach similar to that of Kuz'min and Tishin [35] and Stefanowicz et al [29]. In these previous studies, a Gaussian distribution of magnetic impurities or T C was used.…”

Section: E the Effects Of Inhomogeneity On The Measured Remanent Magmentioning

confidence: 99%

“…A few experimental studies have tried to determine critical exponents for (Ga,Mn)As [25][26][27][28], and, as discussed later, these have generally produced imprecise and contradictory results. Stefanowicz et al [29] carried out a detailed study of critical behavior in the related dilute ferromagnetic semiconductor (Ga,Mn)N. They found that inhomogeneity played a major role in this material leading to temperature-dependent "effective critical exponents." (Ga,Mn)As has several properties that make it well suited to the study of critical behavior at the ferromagneticparamagnetic transition.…”

Section: Introductionmentioning

confidence: 99%

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Three-dimensional Heisenberg critical behavior in the highly disordered dilute ferromagnetic semiconductor (Ga,Mn)As

et al. 2016

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We present detailed studies of critical behavior in the strongly site-disordered dilute ferromagnetic semiconductor (Ga,Mn)As. (Ga,Mn)As has a low saturation magnetization and relatively strong magnetocrystalline anisotropy. This combination of properties inhibits domain formation, thus removing a principal experimental difficulty in determining the critical coefficients β and γ . We find that there are still a large number of problems to overcome in terms of measurement procedures and methods of analysis. In particular, the combined effects of disorder and inhomogeneity limit the accessible critical region. However, we find that accurate and reproducible values of the critical exponents β and γ can be obtained from Kouvel-Fisher plots of remanent magnetization and magnetic susceptibility for our (Ga,Mn)As samples. The values of β and γ obtained are consistent with those of the three-dimensional Heisenberg class, despite the very strong disorder present in this system, and they are inconsistent with mean field behavior. Log-log plots of M(H ) data for our samples are consistent with the three-dimensional Heisenberg value of the critical exponent δ, but accurate values of δ could not be obtained for our samples from these plots. We also find that accurate values of the critical exponent α could not be obtained by fitting to the measured temperature derivative of resistivity for our samples. We find that modified Arrott plots and scaling plots are not a practical way to determine the universality class or critical exponents, though they are found to be in better agreement with three-dimensional Heisenberg values than mean field values. Below the critical temperature range, we find that the magnetization shows power-law behavior down to a reduced temperature of t ∼ 0.5, with a critical exponent β ∼ 0.4, a value appreciably lower than the mean field value of β = 0.5. At lower temperatures, Bloch 3/2 law behavior is observed due to magnons.

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Section: E the Effects Of Inhomogeneity On The Measured Remanent Magmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Three-dimensional Heisenberg critical behavior in the highly disordered dilute ferromagnetic semiconductor (Ga,Mn)As

et al. 2016

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“…Third, and most recently, the ferromagnetic coupling in insulating systems was also interpreted in terms of super exchange. 33,34 In this paper, as an illustration of our formalism, we systematically study the metal-insulator transition due to localization in the ferromagnetic phase of (Ga,Mn)N. We find that (Ga,Mn)N is always insulating within the compositional limit consistent with transport measurements. 49 Our results indicate that both the second and the third models are important to explain the magnetism in this material.…”

Section: Introductionmentioning

confidence: 59%

“…33 and 34. For x > 0.03, a nonmagnetic dopant such as Zn, or e.g., the application of a gate bias, could move the chemical potential down, leading to a metallic phase with ferromagnetism induced by double exchange as well as superexchange 33,34 possibly enhancing the Curie temperature significantly.…”

Section: Resultsmentioning

confidence: 99%

“…This implies that ferromagnetism in Ga 1−x Mn x N for x ≤ 0.03 cannot be mediated by double exchange, which would require itinerant carriers in the impurity band. For larger concentrations, chemical doping or the application of a gate bias could move the chemical potential down, leading to a metallic phase with ferromagnetism induced by double exchange as well as superexchange 33,34 possibly enhancing the Curie temperature significantly.…”

Section: Discussionmentioning

confidence: 99%

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Generalized multiband typical medium dynamical cluster approximation: Application to (Ga,Mn)N

et al. 2016

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We generalize the multiband typical medium dynamical cluster approximation and the formalism introduced by Blackman, Esterling and Berk so that it can deal with localization in multiband disordered systems with both diagonal and off-diagonal disorder with complicated potentials. We also introduce a new ansatz for the momentum resolved typical density of states that greatly improves the numerical stability of the method, while preserving the independence of scattering events at different frequencies. Starting from the first-principles effective Hamiltonian, we apply this method to the diluted magnetic semiconductor Ga1−xMnxN, and find the impurity band is completely localized for Mn concentrations x < 0.03, while for 0.03 < x < 0.10 the impurity band has delocalized states but the chemical potential resides at or above the mobility edge. So, the system is always insulating within the experimental compositional limit (x ≈ 0.10) due to Anderson localization. However, for 0.03 < x < 0.10 hole doping could make the system metallic allowing double exchange mediated, or enhanced, ferromagnetism. The developed method is expected to have a large impact on first-principles studies of Anderson localization.

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