Role of conduction-electron<i>–</i>local-moment exchange in antiferromagnetic semiconductors: Ferrons and bound magnetic polarons

Mauger, A.; Mills, D. L.

doi:10.1103/physrevb.31.8024

Cited by 49 publications

(25 citation statements)

References 16 publications

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“…For the parameters given in Table I, no bound state is produced if the Coulomb term of the Hamiltonian is set to zero, in agreement with Ref. [11], which concluded theoretically that free conduction band electrons cannot form magnetic polarons in bulk EuTe. Figures 2 and 3 show the results of the calculations obtained both by the self-consistent and variational methods.…”

Section: B Ground State Of the Polaronsupporting

confidence: 67%

“…The variational calculation produces a ferromagnetic core of radius r c = 0.95a, whereas the self-consistent result is r c = 0.47a. Given that the nearestneighbor distance in the face-centered cubic EuTe lattice is 0.71a, then a small ferromagnetic core is predicted by the variational model, but no ferromagnetic core is expected in the self-consistent approximation, which characterizes the polaron as type I [11].…”

Section: B Ground State Of the Polaronmentioning

confidence: 99%

“…A better choice is Bohr's function, which will be used here, as done by other authors describing impurity-stabilized polarons [10,11] and photoinduced ones [35],…”

Section: B Ground State Of the Polaronmentioning

confidence: 99%

“…It is also assumed that the spin of the photoexcited electron is relaxed [15,27], meaning that the effective field B Xf points in the direction of the applied magnetic field, if one is present. Last but not least, the canting angle is allowed to vary continuously, which would be strictly valid only when S → ∞ but is a suitable approximation in the present case, considering the large spin S = 7/2 of the Eu atoms [11].…”

Section: A Polaron Hamiltonianmentioning

confidence: 99%

“…However, technological interest waned when it was discovered that EuTe is an antiferromagnet with a very low Néel temperature (T N = 9.6 K), which is impractical for device applications. Nevertheless, EuTe and other Eu chalcogenides remain ideal magnetic systems that can be used to test the principles of operation of spin-related devices [8], and to investigate many-body physical phenomena, e.g., spin waves [9] and magnetic polarons [2,4,[10][11][12][13][14].…”

Section: Introductionmentioning

confidence: 99%

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Luminescence properties of magnetic polarons in EuTe: Theoretical description and experiments in magnetic fields up to 28 T

et al. 2014

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The recent discovery of a polaron-associated zero phonon line in the band-edge photoluminescence of high optical quality EuTe crystals opens up the prospect of answering long-standing questions about the polaron internal structure, thermal stability, and generation efficiency. Here, a Schrödinger equation for the polaron was formulated and resolved by using both variational and self-consistent methods. The theory is in good agreement with measurements of the zero phonon line as a function of magnetic field and temperature, and it could be applied to other polaronic systems. It is deduced that, in EuTe, at 0 K, a polaron carries a magnetic moment of 610μ B , and its binding energy is 27 meV. However, this binding energy does not carry the usual meaning of thermal stability, because it decreases drastically when the sample is warmed up. For instance, at T = 100 K, the binding energy is already reduced to only 6 meV. The thermal destruction of a polaron is brought about by thermal fluctuations of the spin lattice that suppress the electron's self-energy. Photoluminescence excitation spectra of EuTe demonstrate that the photogeneration of polarons becomes increasingly inefficient when the energy of the pumping photon is increased above the band gap.

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Section: B Ground State Of the Polaronsupporting

confidence: 67%

Section: B Ground State Of the Polaronmentioning

confidence: 99%

“…A better choice is Bohr's function, which will be used here, as done by other authors describing impurity-stabilized polarons [10,11] and photoinduced ones [35],…”

Section: B Ground State Of the Polaronmentioning

confidence: 99%

Section: A Polaron Hamiltonianmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Luminescence properties of magnetic polarons in EuTe: Theoretical description and experiments in magnetic fields up to 28 T

et al. 2014

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Photoinduced Magnetism and Conduction Electrons in Magnetic Semiconductors

Nagaev¹

1988

Physica Status Solidi (b)

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MnF, antiferromagnetic system by plane-polarized light through excitation of excitons in one of the two equivalent sublattices in the AFM was the subject of an outstanding experimental study [6]. A great amount of experimental work has been carried out2) with the aim of verifying and analyzing in detail the above-mentioned effects. Basic Principles of the Magnetic Semiconductor Theory Temperature dependence of the energy spectiqum of conduction electrons in ferromagnetic systemsThe theory of magnetic semiconductors is based on the s-f model (below the differences between localized d-and f-electrons are disregarded). With charge carriers having the same sign, the Hamiltonian for this model in the nearest-neighbour approximation has the following form:The first term in (2.1) describes the conduction electrons; g is the dimensionless coordinate of the atom, A the vector connecting the nearest neighbours, (T the spin projection. The second term describes the exchange interaction between conduction electrons and localized magnetic moments; here, Sg is the operator of the localized magnetic moment for the g atom, so,, are the Pauli matrices. The third term describes the "direct" (more precisely, the superexchange) interaction between localized magnetic moments which determines the type of magnetic ordering in the crystal. For certainly, the lattice of magnetic atoms is considered to be simple cubic.Magnetic semiconductors can be classified according t o the magnitude of the parameter ASIW, where S is the magnitude of the localized spin of the atom, W the conduction band width. Among semiconductors with a wide conduction band ( W > > A S ) are, e.g., EuO and EuS ferromagnets and EuTe and EuSe antiferromagnets.Among semiconductors with a narrow conduction band are, e.g., ferromagnetic spinels CdCr,Se, and others [74]. A theory of narrow-band magnetic semiconductors was described in detail earlier [63]. Below we shall analyze the results as applied to semiconductors with wide conduction bands. Qualitatively, in both cases the physical picture is the same, but if W > AX a more detailed analysis is possible [75, 2031.

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