Double exchange model and the unique properties of the manganites

Izyumov, Yu. A.; Skryabin, Yu. N.

doi:10.1070/pu2001v044n02abeh000840

Cited by 96 publications

(50 citation statements)

References 107 publications

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“…These materials are difficult to describe for precisely the very same reason that they are interesting; namely that they exhibit a complex interplay between lattice, charge, orbital and spin degrees of freedom. This gives rise to a very rich phase diagram, exhibiting different magnetic, orbital and charge orders, and both metallic and insulating behaviour as a function of temperature, pressure, applied field and doping 1,2,4 . Even within the "simple" low temperature ferromagnetic phase, the mechanism for the metal-insulator transition which occurs as ferromagnetic order breaks down remains controversial.…”

Section: Introductionmentioning

confidence: 99%

Quantum spin dynamics of the bilayer ferromagnet La $ \mathsf {_{1.2}}$ Sr $ \mathsf {_{1.8}}$ Mn $ \mathsf {_2}$ O $ \mathsf {_7}$

Shannon

Chatterji

Ouchni

et al. 2002

The European Physical Journal B - Condensed Matter

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We construct a theory of spin wave excitations in the bilayer manganite La 1.2 Sr 1.8 Mn 2 O 7 based on the simplest possible double-exchange model, but including leading quantum corrections to the spin wave dispersion and damping. Comparison is made with recent inelastic neutron scattering experiments. We find that quantum effects account for some part of the measured damping of spin waves, but cannot by themselves explain the observed softening of spin waves at the zone boundary. Furthermore a doping dependence of the total spin wave dispersion and the optical spin wave gap is predicted.

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Section: Introductionmentioning

confidence: 99%

Quantum spin dynamics of the bilayer ferromagnet La $ \mathsf {_{1.2}}$ Sr $ \mathsf {_{1.8}}$ Mn $ \mathsf {_2}$ O $ \mathsf {_7}$

Shannon

Chatterji

Ouchni

et al. 2002

The European Physical Journal B - Condensed Matter

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“…Below we show that within such a model, the compensation affects the magnetic interactions in a surprising way: the maximum Curie temperature is obtained not for zero compensation, but rather for a partially compensated system with 0.5 holes per substitutional Mn. We derive this result starting from a Zener doubleexchange Hamiltonian for the motion of holes in a narrow impurity band [15],…”

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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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“…where brackets mean the averaging of corresponding contributions to the conductivity  over the ensemble of granules, G is the conductance averaged over the sample,  300K the resistivity at 300 K. As is known, the systems of (Re) SCO type (Re is a trivalent rare-earth element) are double-phase systems [3]. One of the phases, matrix ReCO, can be characterized by a thermally activated mechanism of conductivity of semiconductor type,  sm (for example, of the Mott type [5]) while the conductivity of the other phase is that of SCO sublattice,  DE , due to the mechanism of double ferromagnetic exchange between cobalt ions of different valence by means of the conduction electrons [4].…”

Section: Resultsmentioning

confidence: 99%

“…The samples were cut out in the shape of rectangular parallelepipeds with the sizes close to 0.15 × 0.3 × 0.5 cm 3 . Contact pads for current and potential probes were put using the method of ultrasonic soldering of ultrapure In.…”

Section: Methodsmentioning

confidence: 99%

“…In this family, the effects of correlation of conduction electrons operated by doping can be treated as intrinsic conductivity mechanisms. The level of doping sets the size and sign of exchange interactions as parameters of correlation between local ionic magnetic moments and spins of delocalized conduction electrons [1][2][3]. These quantities define the type of interaction, including ferromagnetic, when electrons are transmitted in accordance with the scheme of double exchange [4].…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Transition Metal-Nonmetal in Conductivity of Ceramic Hole-Doped Cobaltites

Chiang¹,

Dzyuba²,

Шевченко³

et al. 2010

JMP

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In bulk granulated cobaltite La 1-x Sr x CoO 3 with the size of granules of order of 1 micron at strontium hole doping with replacement factor x = 0.35, a transition "metal-nonmetal" in the conductivity was revealed, presumably connected with AFM ordering of the moments of granules. The assumption is proved by the agreement between the experiment and results of calculation within the limits of a model offered for electron transport based on the account of in-granule double exchange Zener mechanism and intergranule mechanism of spin-polarized tunneling on the nearest neighbours with AFM exchange interaction. The calculation differs in that conductivities within granules are summarized, while total resistance of the system is represented as a sum of resistances of the granules. In addition, the existence of AFM interaction between granules is supported by the observed insensitivity of conductivity to a low external magnetic field (up to 5 kOe).

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Double exchange model and the unique properties of the manganites

Cited by 96 publications

References 107 publications

Quantum spin dynamics of the bilayer ferromagnet La $ \mathsf {_{1.2}}$ Sr $ \mathsf {_{1.8}}$ Mn $ \mathsf {_2}$ O $ \mathsf {_7}$

Quantum spin dynamics of the bilayer ferromagnet La $ \mathsf {_{1.2}}$ Sr $ \mathsf {_{1.8}}$ Mn $ \mathsf {_2}$ O $ \mathsf {_7}$

Self-Compensation in Manganese-Doped Ferromagnetic Semiconductors

Transition Metal-Nonmetal in Conductivity of Ceramic Hole-Doped Cobaltites

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