Ferromagnetism of disordered systems

Korenblit, I. Ya.; Shender, E. F.

doi:10.1070/pu1978v021n10abeh005686

Cited by 83 publications

(55 citation statements)

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“…To find the Curie temperature of the ferromagnetic phase transition, we first note that mean-field theory is not well justified because of the exponential dependence of the integrals t ij and because of the Mn positional disorder [18,19]. Instead we represent the system as a percolation network of randomly distributed sites, each occupied by either A 0 or A − , with interactions only between sites with different charges.…”

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confidence: 99%

Self-Compensation in Manganese-Doped Ferromagnetic Semiconductors

2002

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We present a theory of interstitial Mn in Mn-doped ferromagnetic semiconductors. Using densityfunctional theory, we show that under the non-equilibrium conditions of growth, interstitial Mn is easily formed near the surface by a simple low-energy adsorption pathway. In GaAs, isolated interstitial Mn is an electron donor, each compensating two substitutional Mn acceptors. Within an impurity-band model, partial compensation promotes ferromagnetic order below the metal-insulator transition, with the highest Curie temperature occurring for 0.5 holes per substitutional Mn.Ferromagnetism in dilute magnetic semiconductors is generally believed to be mediated by carriers-electrons or holes-originating from the magnetic dopants themselves. For example, an isolated Mn impurity in GaAs can substitute for Ga and contribute one hole, which is weakly bound to its acceptor core [1]. GaAs samples with Mn dopant concentrations in the range 1-2% are ferromagnetic insulators, while samples in the range 3-6% are ferromagnetic metals [2]. In the metallic phase the nominal hole concentration, p, is in principle equal to the number of Mn atoms per unit volume. Measured hole concentrations are much smaller, by factors ranging from ∼3 for MnGaAs [2] to ∼10 or more for MnGe [3]. In most theories of ferromagnetism in dilute magnetic semiconductors, reduced hole concentrations suppress the Curie temperature [4,5,6]. The reverse scenario-raising the Curie temperature by increasing the hole concentrationis therefore of great current interest. For current theoretical reviews see Refs. [5,6].Recent experiments show a strong correlation between Curie temperature, carrier concentration, and the fraction of Mn found at interstitial sites [7]. In this paper we address several questions not yet settled by experiment. (1) By what mechanism are interstitials formed, given that their calculated formation energies are considerably higher than substitutionals? (2) What determines the relative abundance of interstitials and substitutionals? (3) Under what (doping) conditions do interstitials act as compensators? (4) What role does compensation play in the ferromagnetism?To answer these questions, we use density-functional theory (DFT) to establish the following: (i) During the MnGaAs growth, Mn adatoms follow a very simple lowenergy pathway to directly form interstitial Mn near the surface. (ii) The deposition of additional As converts some of these interstitials to substitutional sites. (iii) The remaining interstitial Mn atoms act as donors, each compensating two substitutional acceptors. Finally, we show that within an impurity-band model, ferromagnetism below the metal-insulator transition is most favorable-in the sense of the highest Curie temperature-for 0.5 holes per substitutional Mn.For MnGaAs grown by MBE, recent channeling Rutherford backscattering experiments show that as much as ∼15% of the total Mn may be interstitial [7]. An open theoretical question is how interstitial Mn might be formed, under what conditions, and in what concentration. ...

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confidence: 99%

Self-Compensation in Manganese-Doped Ferromagnetic Semiconductors

2002

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“…It is interesting to notice that a discontinuous transition between liquid and glass, with coexistence of phases, has been recently found in lattice heteropolymers with random interactions 46,47 . We also mention that generalizing the present model to a two component magnetic model 53 , and including quenched disorder, further phases can be found, e.g. an antiquadrupolar phase.…”

Section: Discussionmentioning

confidence: 99%

“…In order to find further phases, e.g. an antiquadrupolar phase, 23 a generalization of the present analysis to a two component magnetic model, 53 including quenched disorder, has to be carried out.…”

Section: Analyzing the Stability Of The Rs Solution [See Eqs (2526)mentioning

confidence: 99%

Thermodynamic properties of a full-replica-symmetry-breaking Ising spin glass on lattice gas: The random Blume-Emery-Griffiths-Capel model

Crisanti

Leuzzi

2004

Phys. Rev. B

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The study of the mean-field static solution of the Random Blume-Emery-Griffiths-Capel model, an Ising-spin lattice gas with quenched random magnetic interaction, is performed. The model exhibits a paramagnetic phase, described by a stable Replica Symmetric solution. When the temperature is decreased or the density increases, the system undergoes a phase transition to a Full Replica Symmetry Breaking spin-glass phase. The nature of the transition can be either of the second order (like in the Sherrington-Kirkpatrick model) or, at temperature below a given critical value, of the first order in the Ehrenfest sense, with a discontinuous jump of the order parameter and accompanied by a latent heat. In this last case coexistence of phases takes place. The thermodynamics is worked out in the Full Replica Symmetry Breaking scheme, and the relative Parisi equations are solved using a pseudo-spectral method down to zero temperature.Since its discovery, the spin glass (SG) phase has played and still plays a fundamental role in the investigation and understanding of many basic properties of disordered and complex systems. The analysis of the mean-field approximation of theoretical models displaying such a phase has revealed different possible scenarios, including different kinds of transition from the paramagnetic phase to the SG phase, as well as different kinds of SG phases. Most of the work, however, has been concentrated on just two scenarios.In order of appearance in literature the first scenario is described by a Full Replica Symmetry Breaking (FRSB) solution characterized by a continuous order parameter function, 1 which continuously grows from zero by crossing the transition. The prototype model is the Sherrington-Kirkpatrick (SK) model, 2 a fully connected Ising-spin model with quenched random magnetic interactions.The second scenario, initially introduced by Derrida by means of the Random Energy Model (REM), 3 provides a transition with a jump in the order parameter to a stable low temperature phase in which the replica symmetry is spontaneously broken only once. The order parameter is a step function taking two values q min and the so-called Edwards-Anderson order parameter, 4 q EA , (else said self-overlap), with q min < q EA . In the paramagnetic phase they are both equal to zero. At the transition, q EA grows to a value larger than q min . No discontinuity appear, however, in the thermodynamic functions. Actually, at the transition to the one step Replica Symmetry Breaking (1RSB) SG phase, the Edwards-Anderson order parameter q EA can either grow continuously from zero or jump discontinuously to a finite value. The first case of this second scenario includes Potts-glasses with three or four states, 5 the spherical p-spin spin-glass model in strong magnetic field 6 and some inhomogeneous spherical p-spin model with a mixture of p = 2 and p > 3 interactions.7,8 The latter case includes, instead, Potts-glasses with more than four states 5 , quadrupolar glass models, 5,9 p-spin interaction spin-glass models with p...

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“…contrast to a Bloch and mean-field type M vs. T curve in the singular heterostructure). As it was shown previously this type of the temperature dependence is typical for the percolation ferromagnetic ordering [17][18][19]. The percolation model is based on the assumption that indirect exchange between magnetic centres (Mn 2+ ions) is carried out by charge carriers (holes in the case of GaAs:Mn).…”

Section: Static Magnetization Of Vicinal Heterostructuresmentioning

confidence: 99%

The influence ofδ-<Mn>-layer's magnetization on polarization of photoluminescence of quantum well in singular and vicinal InGaAs/GaAs/δ-<Mn> heterostructures

Dmitriev

Таланцев

Zaı̆tsev

et al. 2012

J. Phys.: Conf. Ser.

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The influence of δ--layer's magnetization on polarization of photoluminescence of quantum well in singular and vicinal InGaAs/GaAs/δ- heterostructures Abstract. Magneto-optical properties and spin dynamics in a p-type GaAs-based heterostructures containing an InGaAs quantum well and 2 nm thick GaAs layer doped with 5 at. % Mn (GaAs:Mn) on flat and vicinal substrates were studied between 2 and 300 K. A significant enhancement of photoluminescence circular polarization P C = 15 % was found at temperatures T < 30 K. In the non-magnetic quantum well P C = 0 %. The polarization of the InGaAs quantum well photoluminescence follows the temperature dependence of the GaAs:Mn layer magnetization. Two types of ferromagnetism were found. In the heterostructures grown on the flat substrate parallel to the (001) GaAs plane the magnetization obeys the Bloch T 3/2 temperature dependence while for the structures grown on the vicinal surface (disoriented by 3°) the magnetization follows percolation dependence. The later is attributed to the formation of strongly disordered islands of GaAs:Mn. IntroductionHeterostructures containing a quantum well and a thin layer of a diluted magnetic semiconductor (DMS) like GaAs:Mn have attracted great attention due to their possible application for injecting spin-polarized carriers in light emitting diodes [1]. The implantation of Mn into the quantum well leads to low mobility of charge carriers and suppresses radiative recombination [2]. The spatial separation of charge carriers and the GaAs:Mn layer results in a considerable increase in the mobility of charge carriers and the luminescence quantum yield [3]. This combination of optically and magnetically active structures appears promising for controlling optical properties by spin-dependent magnetic field control over the luminescence.The presence of charge carriers in the GaAs:Mn layer facilitates the indirect Ruderman-KittelKasuya-Yosida (RKKY) exchange interaction between Mn 2+ ions in hybrid structures [4][5][6][7][8]. Measurements of the luminescence polarization [8], the electric resistance and the Hall voltage [4][5][6][7] indirectly confirmed the existence of ferromagnetism in GaAs:Mn layers. The interpretation of the magnetization data, however, is difficult and usually requires additional assumptions for the separation of the contributions of the diamagnetic crystal lattice and paramagnetic structural defects, substrate, and interlayer boundaries. This problem can be solved by the electron spin resonance (ESR) technique [9] allowing the separation of contributions of above mentioned subsystems to the magnetic susceptibility of the samples.

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Ferromagnetism of disordered systems

Cited by 83 publications

References 4 publications

Self-Compensation in Manganese-Doped Ferromagnetic Semiconductors

Self-Compensation in Manganese-Doped Ferromagnetic Semiconductors

Thermodynamic properties of a full-replica-symmetry-breaking Ising spin glass on lattice gas: The random Blume-Emery-Griffiths-Capel model

The influence ofδ-<Mn>-layer's magnetization on polarization of photoluminescence of quantum well in singular and vicinal InGaAs/GaAs/δ-<Mn> heterostructures

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