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ABSTRACT: Employing first-principles density-functional-theory-based calculations, we study the electronic structure and magnetoelastic effect in difluoride compounds MF 2 (M = Mn, Fe, Co, Ni). The magnetoelastic-effect-driven cell-parameter changes across the series are found to exhibit nonmonotonic behavior in agreement with recent experimental reports. Our study reveals that this originates from the nonmonotonicity in the exchange striction of the bond-stretching phonon mode associated with the short M-F bond. Our study also uncovers the role of M-F covalency in driving the nonmonotonic behavior of the M-M exchange interaction across the series.
Physical Review B 08/2012; 8620(86):054422. · 3.69 Impact Factor
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Physical Review Letters 03/2012; 108(12):129702. · 7.37 Impact Factor
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ABSTRACT: Motivated by recent experimental results, we study the effect of size reduction on half-doped manganite, La(0.5)Ca(0.5)MnO(3), using the combination of density-functional theory (DFT) and dynamical mean-field theory (DMFT). We find that upon size reduction the charge-ordered antiferromagnetic phase, observed in bulk, is destabilized, giving rise to the stability of a ferromagnetic metallic state. Our theoretical results, carried out on a defect-free nanocluster in isolation, establish the structural changes that follow upon size reduction to be responsible for this. Our study further points out the effect of size reduction to be distinctively different from application of hydrostatic pressure. Interestingly, our DFT+DMFT study additionally reports the correlation-driven stability of the charge-orbitally ordered state in bulk La(0.5) Ca(0.5) MnO(3), even in the absence of long-range magnetic order.
Physical Review Letters 11/2011; 107(19):197202. · 7.37 Impact Factor
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ABSTRACT: Using first-principles density functional theory, we study piezoelectricity in short-period superlattices made with combinations of ferroelectric and paraelectric components that exhibit polar discontinuities. We show that the piezoelectric response of such a superlattice can be tuned in terms of sign and magnitude by the choice of components. As these superlattices with nonswitchable polarization do not undergo ferroelectric transitions, we predict them to exhibit a robust piezoelectric response with weaker temperature dependence compared to their bulk counterparts.
Journal of Applied Physics 04/2011; · 2.17 Impact Factor
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ABSTRACT: Employing first principles density functional calculations, together with
solution of the low-energy, model Hamiltonian constructed in a first principles
manner, we explored the origin of magnetism and $T_c$ trend in Cr-based double
perovskite series, Sr$_2$CrB$'$O$_6$ (B$'$=W/Re/Os). Our study shows that the
apparently puzzling $T_c$ trend in Sr$_2$CrB$'$O$_6$ (B$'$=W/Re/Os) series can
be understood in terms of the interplay of the hybridization driven mechanism
and the super-exchange mechanism.
01/2011;
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ABSTRACT: We construct an effective spin Hamiltonian for YMn2O5 through analysis of first-principles density-functional theory results. Using our first-principles-derived spin Hamiltonian we calculate the magnon dispersion of this compound and compare with the experimentally measured spectra probed using inelastic neutron scattering. Our first-principles-derived set of magnetic interaction parameters show the importance of the Mn1-Mn2 interaction along the b axis, which was ignored in the literature. We provide justification in favor of our first-principles-derived parameters.
Phys. Rev. B. 01/2011; 84(5).
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ABSTRACT: Using first-principles density functional calculations, we study the interplay of ferroelectricity and polar discontinuities in a range of 1-1 oxide superlattices, built out of ferroelectric and paraelectric components. Studies have been carried out for a varied choice of chemical composition of the components. We find that, when polar interfaces are present, the polar discontinuities induce off- centric movements in the ferroelectric layers, even though the ferroelectric is only one unit cell thick. The distortions yield non-switchable polarizations, with magnitudes comparable to those of the corresponding bulk ferroelectrics. In contrast, in superlattices with no polar discontinuity at the interfaces, the off-centric movements in the ferroelectric layer are usually suppressed. The details of the behavior and functional properties are, however, found to be sensitive to epitaxial strain, rotational instabilities and second-order Jahn-Teller activity, and are therefore strongly in uenced by the chemical composition of the paraelectric layer. Comment: 7 pages, 2 figures
04/2010;
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ABSTRACT: Using first principles density functional calculations, together with exact diagonalization of Fe-Mo Hamiltonian constructed in a first principles Wannier function basis, we studied the electronic structure of La doped double perovskite compound Sr$_2$FeMoO$_6$. Our calculation show stabilization of kinetic energy driven antiferromagnetic phase for La rich compounds, in agreement with the results obtained on the basis of previous model calculations. Comment: 11 figures. accepted for publication in Phys. Rev. B
11/2009;
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ABSTRACT: Using first-principles density functional calculations, we have computed the optical and magneto-optical properties of the Cr-based double perovskite compounds, Sr2CrB′O6 with B′ = W,Re,Os. Our computed magneto-optic spectra show substantially large Kerr rotations of about −2° to −2.5° for Sr2CrWO6 and Sr2CrReO6 and a moderately large Faraday rotation of about −0.25×106 deg/cm in insulating Sr2CrOsO6, indicating possible industrial applications. Our study should motivate experimental investigations in this yet to be explored area of Sr2CrB′O6 compounds.
Applied Physics Letters 05/2008; 92(20):201912-201912-3. · 3.84 Impact Factor
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ABSTRACT: Using first-principles density functional calculations, we study the electronic and magnetic properties of the ferromagnetic insulating double perovskite compound La2NiMnO6, which has been reported to exhibit an interesting magnetic field sensitive dielectric anomaly as a function of temperature. Our study reveals the existence of very soft infrared active phonons that couple strongly with spins at the Ni and Mn sites through modification of the superexchange interaction. We suggest that these modes are the origin for the observed dielectric anomaly in La2NiMnO6.
Physical Review Letters 05/2008; 100(18):186402. · 7.37 Impact Factor
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M Ikeda,
T Yoshida,
A. Fujimori,
M Kubota,
K Ono, Hena Das,
T. Saha-Dasgupta,
K. Unozawa,
Y. Kaga,
T Sasagawa,
H Takagi
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ABSTRACT: We have performed angle-resolved photoemission spectroscopy (ARPES) measurements and first-principles electronic structure calculations on the electron-doped high-Tc superconductors Ln1.85Ce0.15CuO4 (Ln = Nd, Sm, and Eu). The observed Fermi surface and band dispersion show such changes that with decreasing ionic size of Ln3+, the curvature of the Fermi surface or -t'/t decreases, where t and t' are transfer integrals between the nearest-neighbor and next-nearestneighbor Cu sites, respectively. The increase of t with chemical pressure is found to be significant, which may explain the apparently inconsistent behavior seen in the hole-doped La2-xSrxCuO4 under epitaxial strain [M. Abrecht et al., Phys. Rev. Lett. 91, 057002 (2003)]. A gap due to the antiferromagnetism opens even in the nodal region for the Sm and Eu compounds, and the gap size increases in going from Ln = Sm to Eu. Comment: 4 pages, 4 figures
03/2008;
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ABSTRACT: Using first-principles electronic structure calculations based on the Nth order muffin tin orbital (NMTO)-downfolding technique, we derived the low-energy spin model for CuTe2O5. Our study reveals that this compound is a 2D coupled spin-dimer system with the strongest Cu-Cu interaction mediated by two O-Te-O bridges. We checked the goodness of our model by computing the magnetic susceptibility with the Quantum Monte Carlo technique and by comparing it with available experimental data. We also present magnetization and specific heat results which may be compared with future experimental investigations. Our derived model is in disagreement with a recently proposed model for this compound [J. Deisenhofer et al, Phys. Rev. B,74 (2006) 174421]. The situation needs to be settled in terms of further experimental investigations. Comment: 8 pages, 15 figures
03/2007;
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ABSTRACT: Using Nth order muffin-tin-orbital-based downfolding technique in combination with dynamical mean field theory, we investigate the correlated electronic structure of La2CuO4 in the so-called “T” and “T′” crystal structure which serve as the parent compounds for the hole-doped and electron-doped high Tc compounds. La2CuO4, which naturally forms in T structure, has been reported to made to form in T′ structure by means of special thin-film synthesis technique of replacing La by isovalent RE (RE=Y,Lu,Sm,Gd…) ions [ A. Tsukada et al. Solid State Commun. 133 427 (2005)]. The experimental studies on T′-structured La2CuO4 reveal contrasting properties to that in T structure, which we examine by means of electronic structure calculations. Our dynamical mean field calculations show introduction of correlation effect to the one-electron band structure of T′- and T-structured La2CuO4, providing metallic solution in one case (T′) and insulating solution to another (T).
Phys. Rev. B. 79(13).
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ABSTRACT: Using first-principles density-functional calculations, we determine and analyze the Born effective charges Z(*) that describe the coupling between electric field and atomic displacements for ferromagnetic double-perovskite compound, La2NiMnO6. We find that th Born effective charge matrix of Ni in La2NiMnO6, has an anomalously large antisymmetric component, whose magnitude reduces substantially upon change in the magnetic ordering between Ni and Mn, showing it to be a magnetism-dependent electrostructural coupling. We use a local picture of the electronic structure obtained with Wannier functions,
along with its band-by-band decomposition to determine its electronic origin.
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ABSTRACT: Using first-principles electronic structure calculations based on the Nth order muffin-tin orbital (NMTO)-downfolding technique, we derived the low-energy spin model for CuTe2O5. Our study reveals that this compound is a two-dimensional coupled spin-dimer system with the strongest Cu-Cu interaction mediated by two O-Te-O bridges. We checked the validity of our model by computing the magnetic susceptibility with quantum Monte Carlo technique and comparing it with available experimental data. We also present magnetization and specific-heat results which may be compared with future experimental investigations. Our derived model provides an alternative scenario to a recently proposed model for this compound Phys. Rev. B 74 174421 (2006). The situation needs to be settled in terms of further experimental investigations.
Phys. Rev. B. 77(22).
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ABSTRACT: Using first-principles density functional calculations, we study the electronic and magnetic properties of the ferromagnetic insulating double perovskite compound La2NiMnO6, which has been reported to exhibit an interesting magnetic field sensitive dielectric anomaly as a function of temperature. Our study reveals the existence of very soft infrared active phonons that couple strongly with spins at the Ni and Mn sites through modification of the superexchange interaction. We suggest that these modes are the origin for the observed dielectric anomaly in $La_2NiMnO_6$.
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ABSTRACT: Using first-principles density-functional calculations, we determine and analyze the Born effective charges Z∗ that describe the coupling between electric field and atomic displacements for ferromagnetic double-perovskite compound, La2NiMnO6. We find that the Born effective charge matrix of Ni in La2NiMnO6, has an anomalously large antisymmetric component, whose magnitude reduces substantially upon change in the magnetic ordering between Ni and Mn, showing it to be a magnetism-dependent electrostructural coupling. We use a local picture of the electronic structure obtained with Wannier functions, along with its band-by-band decomposition to determine its electronic origin.
Phys. Rev. B. 79(14).
