Spin Diffusion in Double-Exchange Manganites

Chernyshev, A. L.; Fishman, Randy

doi:10.1103/physrevlett.90.177202

Cited by 12 publications

(28 citation statements)

References 26 publications

(30 reference statements)

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“…The interacting DOS per spin is defined by It is also possible to explicitly evaluate the DOS at ω = 0 for any q: N(ω = 0, q) = (8/πW 2 (1 − q))Re J 2 c − J 2 , which vanishes when J > J c ≡ W (1 − q)/2. In a NM, the critical value required to split the band is J c = W/4, as found earlier [13]. In an AF, J c = 0 since a gap forms for any nonzero coupling constant.…”

Section: The De Hamiltonian Issupporting

confidence: 66%

Short-range ordered phase of the double-exchange model in infinite dimensions

et al. 2006

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Using dynamical mean-field theory, we have evaluated the magnetic instabilities and T = 0 phase diagram of the double-exchange model on a Bethe lattice in infinite dimensions. In addition to ferromagnetic (FM) and antiferromagnetic (AF) phases, we also study a class of disordered phases with magnetic short-range order (SRO). In the weak-coupling limit, a SRO phase has a higher transition temperature than the AF phase for all fillings p below 1 and can even have a higher transition temperature than the FM phase. At T = 0 and for small Hund's coupling J H , a SRO state has lower energy than either the FM or AF phases for 0.26 ≤ p < 1. Phase separation is absent in the J H → 0 limit but appears for any non-zero value of J H .

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Section: The De Hamiltonian Issupporting

confidence: 66%

Short-range ordered phase of the double-exchange model in infinite dimensions

et al. 2006

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“…By adapting also the DMFT, the spin diffusion at any temperature down to the ferromagnetic transition point in manganites has been calculated. 12 A qualitative agreement of the theoretically calculated spin diffusion constant with the experimental data was also observed. 12 Developing from these achievements, in the present work we focus on the spin dynamical properties in the DMSs based on the DMFT.…”

Section: Introductionsupporting

confidence: 68%

“…12 A qualitative agreement of the theoretically calculated spin diffusion constant with the experimental data was also observed. 12 Developing from these achievements, in the present work we focus on the spin dynamical properties in the DMSs based on the DMFT. We construct a microscopic model for DMSs, in which the randomness of the doped magnetic ions is taken into account.…”

Section: Introductionsupporting

confidence: 68%

Spin dynamics in paramagnetic diluted magnetic semiconductors

Phan

Tran

2015

Phys. Rev. B

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Microscopic properties of low-energy spin dynamics in diluted magnetic semiconductor are addressed in a framework of the Kondo lattice model including random distribution of magnetic dopants. Based on the fluctuation-dissipation theorem, we derive an explicit dependence of the spin diffusion coefficient on the single-particle Green function which is directly evaluated by dynamical mean-field theory. In the paramagnetic state, the magnetic scattering has been manifested to suppress spin diffusion. In agreement with other ferromagnet systems, we also point out that the spin diffusion in diluted magnetic semiconductors at small carrier concentration displays a monotonic $1/T$-like temperature dependence. By investigating the spin diffusion coefficient on a wide range of the model parameters, the obtained results have provided a significant scenario to understand the spin dynamics in the paramagnetic diluted magnetic semiconductors.Comment: 6 pages, 4 figure

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“…Perhaps more importantly, the behavior of n h < x holes in the impurity band of a DMS with x < 1 Mn atoms per site is very similar to that of a DE model with filling p = n h /x < 1 [21]. So as long as J c is sufficiently large to produce a well-defined impurity band, the qualitative results of this model should be independent of the precise magnitude of J c /W [19]. As we shall see, a generalized DE model with one local moment per site and large J c also has the distinct advantage that analytic results are possible for any angular momentum j of the charge carriers.…”

mentioning

confidence: 99%

“…It has since developed into one of the most powerful many-body techniques for studying electronic models such as the Hubbard [12,13] and DE [14][15][16][17][18][19] models. Since DMFT becomes exact in the dilute limit, it is a good starting point for studying DMS.…”

mentioning

confidence: 99%

Transition Temperature of a Magnetic Semiconductor with Angular Momentumj

Moreno

Fishman²,

Jarrell³

2006

Phys. Rev. Lett.

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We employ dynamical mean-field theory to identify the materials properties that optimize Tc for a generalized double-exchange (DE) model. We reach the surprising conclusion that Tc achieves a maximum when the band angular momentum j equals 3/2 and when the masses in the mj = ±1/2 and ±3/2 sub-bands are equal. However, we also find that Tc is significantly reduced as the ratio of the masses decreases from one. Consequently, the search for dilute magnetic semiconductors (DMS) materials with high Tc should proceed on two fronts. In semiconductors with p bands, such as the currently studied Mn-doped Ge and GaAs semiconductors, Tc may be optimized by tuning the band masses through strain engineering or artificial nanostructures. On the other hand, semiconductors with s or d bands with nearly equal effective masses might prove to have higher Tc's than p-band materials with disparate effective masses.The discovery of dilute-magnetic semiconductors (DMS) with current transition temperatures above 170 K[1-3] initiated an active search for the optimal material for spintronic device applications [4]. However, the ferromagnetic transition temperature of magnetic semiconductors involves many parameters that are difficult to control experimentally. To facilitate the search for new magnetic semiconductors with high transition temperatures, we evaluate T c for a double-exchange system with general angular momentum j using dynamical mean-field theory (DMFT). Surprisingly, T c is found to reach a maximum for j = 3/2 and for equal light and heavy hole masses. However, we also find that T c decreases significantly when the ratio of the masses is reduced.The notion of using magnetic semiconductors in spintronic devices dates back to the 1960's, when europium chalcogenides [5] and chromium spinels [6] were extensively studied. Before the appearance of the latest generation of III-V DMS grown by molecular beam epitaxy techniques [1,2], II-VI [7] and IV-VI [8] DMS were developed by alloying non-magnetic semiconductors with magnetic ions. Improvement in growth techniques has pushed the T c of Ga 1−x Mn x As to values above 170 K [3]. As we discuss later, the large value of T c in deltadoped GaAs [9] might be associated with the reduced magnetic frustration when the Mn ions are restricted to two-dimensional planes.In our calculation we employ the DMFT, which was formulated in the late 1980's by and Metzner and Vollhardt [11]. It has since developed into one of the most powerful many-body techniques for studying electronic models such as the Hubbard [12,13] and DE [14-19] models. Since DMFT becomes exact in the dilute limit, it is a good starting point for studying DMS. Recent work on DMS materials has used DMFT to study variants of the DE model [20,21] with less than one local moment per site. A DE model with one local moment per site and large coupling constant J c provides an upper limit to the transition temperature for a system with exchange coupling between the local moments and charge carriers. Perhaps more importantly, the behavi...

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Spin Diffusion in Double-Exchange Manganites

Cited by 12 publications

References 26 publications

Short-range ordered phase of the double-exchange model in infinite dimensions

Short-range ordered phase of the double-exchange model in infinite dimensions

Spin dynamics in paramagnetic diluted magnetic semiconductors

Transition Temperature of a Magnetic Semiconductor with Angular Momentumj

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