| 1. |
- Kanchana, V., et al.
(författare)
-
Electronic structure and x-ray magnetic circular dichroism of Sr2FeMoO6 : Ab initio calculations
- 2007
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 75:22
-
Tidskriftsartikel (refereegranskat)abstract
- Theoretical investigations of the electronic structure, x-ray absorption, and x-ray magnetic circular dichroism (XMCD) at the Fe L-2,L-3 and Mo L-2,L-3 edges of Sr2FeMoO6 are carried out by means of the generalized gradient approximation. The magnetic coupling between Fe and Mo is found to be antiparallel, which gives direct confirmation of ferrimagnetic ordering and settles controversies existing between the earlier experimental reports. This is also confirmed by our good agreement of the Mo L-2,L-3 edges with experiment. Using our theoretical spectra, we recalculate the spin and orbital magnetic moments by means of the XMCD sum rules and compare the results with a direct self-consistent calculation and experiment.
|
|
| 2. |
- Kanchana, V., et al.
(författare)
-
First-principles study of elastic properties of CeO2, ThO2 and PoO2
- 2006
-
Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 18:42, s. 9615-9624
-
Tidskriftsartikel (refereegranskat)abstract
- Using first-principles density functional calculations, the structural and elastic properties of fluorite type oxides CeO2, ThO2 and PoO2 were studied by means of the full-potential linear muffin-tin orbital method. Calculations were performed within the local density approximation (LDA) as well as generalized gradient approximation (GGA) to the exchange correlation potential. The calculated equilibrium lattice constants and bulk moduli are in good agreement with the experimental results, as are the computed elastic constants for CeO2 and ThO2. For PoO2 this is the first quantitative theoretical prediction of the ground state properties, and it still awaits experimental confirmation. The calculations find PoO2 to be a semiconductor with an indirect band gap and elastic constants similar in magnitude to those of CeO2 and ThO2.
|
|
| 3. |
- Kanchana, V., et al.
(författare)
-
Lattice dynamics and elastic properties of the 4 f electron system : CeN
- 2011
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 84:20, s. 205135-
-
Tidskriftsartikel (refereegranskat)abstract
- The electronic structure, structural stability, and lattice dynamics of cerium mononitride are investigated using ab initio density-functional methods involving an effective potential derived from the generalized gradient approximation and without special treatment for the 4 f states. The 4 f states are hence allowed to hop from site to site, without an on-site Hubbard U, and contribute to the bonding, in a picture often referred to as itinerant. It is argued that this picture is appropriate for CeN at low temperatures, while the anomalous thermal expansion observed at elevated temperatures indicates entropy-driven localization of the Ce f electrons, similar to the behavior of elemental cerium. The elastic constants are predicted from the total energy variation of strained crystals and are found to be large, typical for nitrides. The phonon dispersions are calculated showing no soft modes, and the Gruneisen parameter behaves smoothly. The electronic structure is also calculated using the quasiparticle self-consistent GW approximation (where G denotes the Green's function and W denotes the screened interaction). The Fermi surface of CeN is dominated by large egg-shaped electron sheets centered on the X points, which stem from the p-f mixing around the X point. In contrast, assuming localized f electrons leads to a semimetallic picture with small band overlaps around X.
|
|
| 4. |
- Krockenberger, Y., et al.
(författare)
-
Sr2CrOsO6 : End point of a spin-polarized metal-insulator transition by 5d band filling
- 2007
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 75:2, s. 020404-
-
Tidskriftsartikel (refereegranskat)abstract
- In the search for new spintronic materials with high spin polarization at room temperature, we have synthesized an osmium-based double perovskite with a Curie temperature of 725 K. Our combined experimental results confirm the existence of a sizable induced magnetic moment at the Os site, supported by band-structure calculations, in agreement with a proposed kinetic-energy-driven mechanism of ferrimagnetism in these compounds. The intriguing property of Sr2 CrOs O6 is that it is at the end point of a metal-insulator transition due to 5d band filling and at the same time ferrimagnetism and high-spin polarization are preserved.
|
|
| 5. |
- Majewski, P., et al.
(författare)
-
Magnetic moments of W 5d in Ca2CrWO6 and Sr2CrWO6 double perovskites
- 2005
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 72:13
-
Tidskriftsartikel (refereegranskat)abstract
- We have investigated the magnetic moment of the W ion in the ferrimagnetic double perovskites Sr2CrWO6 and Ca2CrWO6 by x-ray magnetic circular dichroism at the W L-2,L-3 edges. In both compounds a finite negative spin and positive orbital magnetic moment was detected. The experimental results are in good agreement with band-structure calculations for (Sr/Ca)(2)CrWO6 using the full-potential linear muffin-tin orbital method. It is remarkable that the magnetic ordering temperature, T-C, is correlated with the magnetic moment at the nonmagnetic W atom.
|
|
| 6. |
- Reddy, P. V. Sreenivasa, et al.
(författare)
-
Evidence for the antiferromagnetic ground state of Zr2TiAl : a first-principles study
- 2017
-
Ingår i: Journal of Physics. - : Institute of Physics Publishing (IOPP). - 0953-8984 .- 1361-648X. ; 29:26
-
Tidskriftsartikel (refereegranskat)abstract
- A detailed study on the ternary Zr-based intermetallic compound Zr2TiAl has been carried out using first-principles electronic structure calculations. From the total energy calculations, we find an antiferromagnetic L1(1)-like (AFM) phase with alternating ( 1 1 1) spin-up and spin-down layers to be a stable phase among some others with magnetic moment on Ti being 1.22 mu B. The calculated magnetic exchange interaction parameters of the Heisenberg Hamiltonian and subsequent Heisenberg Monte Carlo simulations confirm that this phase is the magnetic ground structure with Neel temperature between 30 and 100 K. The phonon dispersion relations further confirm the stability of the magnetic phase while the non-magnetic phase is found to have imaginary phonon modes and the same is also found from the calculated elastic constants. The magnetic moment of Ti is found to decrease under pressure eventually driving the system to the non-magnetic phase at around 46 GPa, where the phonon modes are found to be positive indicating stability of the non-magnetic phase. A continuous change in the band structure under compression leads to the corresponding change of the Fermi surface topology and electronic topological transitions (ETT) in both majority and minority spin cases, which are also evident from the calculated elastic constants and density of state calculations for the material under compression.
|
|
| 7. |
- Vaitheeswaran, G., et al.
(författare)
-
Ab initio calculated X-ray magnetic circular dichroism of Sr2CrReO6
- 2008
-
Ingår i: Europhysics letters. - : IOP Publishing. - 0295-5075 .- 1286-4854. ; 84:4
-
Tidskriftsartikel (refereegranskat)abstract
- Ab initio calculated X-ray absorption and X-ray magnetic circular dichroism (XMCD) spectra at the Cr and Re L-2,L-3 edges for the double perovskite Sr2CrReO6 are compared with experiment. The main features of the experimental spectra are reproduced by the calculations, however, the amplitudes of several structures are significantly over- or underestimated. The calculated spin and orbital magnetic moments for Cr and Re agree with those obtained by means of XMCD sum rules, except for the Cr orbital moment, illustrating that numerical uncertainties can be large for small moments. It is also argued that the Re moments are induced and not intrinsic.
|
|
| 8. |
- Vaitheeswaran, G., et al.
(författare)
-
Elastic constants and high-pressure structural transitions in lanthanum monochalcogenides from experiment and theory
- 2007
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 75:18
-
Tidskriftsartikel (refereegranskat)abstract
- The high-pressure structural behavior of lanthanum monochalcogenides is investigated by theory and experiment. Theory comprises density-functional calculations of LaS, LaSe, and LaTe with the general gradient approximation for exchange and correlation effects, as implemented within the full-potential linear muffin-tin orbital method. The experimental studies consist of high-pressure angle dispersive x-ray-diffraction investigations of LaS and LaSe up to a maximum pressure of 41 GPa. A structural phase transition from the NaCl-type to CsCl-type crystal structure is found to occur in all cases. The experimental transition pressures are 27-28 and 19 GPa for LaS and LaSe, respectively, while the calculated transition pressures are 29, 21, and 10 GPa for LaS, LaSe, and LaTe, respectively. The calculated ground-state properties such as equilibrium lattice constant, bulk modulus and its pressure derivative, and Debye temperatures are in good agreement with experimental results. Elastic constants are predicted from the calculations.
|
|
| 9. |
- Vaitheeswaran, G., et al.
(författare)
-
Elastic properties of MgCNi3 - a superconducting perovskite
- 2007
-
Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 19:32
-
Tidskriftsartikel (refereegranskat)abstract
- The cohesive and elastic properties of the non-oxide perovskite type superconductor MgCNi3 are calculated using the full-potential linear muffin-tin orbital method with the local density approximation as well as the generalized gradient approximation for exchange and correlation. The calculated equation of state and ground state properties ( equilibrium lattice constant, bulk modulus and its pressure derivative) agree well with recent experiments. From the elastic constants the Young's modulus, shear modulus, Poisson's ratio, sound velocities and Debye temperature are obtained. By analysing the ratio between bulk modulus and shear modulus we conclude that MgCNi3 is intermediate between brittle and ductile in nature.
|
|
| 10. |
- Vaitheeswaran, G., et al.
(författare)
-
High-pressure structural, elastic, and electronic properties of the scintillator host material KMgF3
- 2007
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 76:1
-
Tidskriftsartikel (refereegranskat)abstract
- The high-pressure structural behavior of the fluoroperovskite KMgF3 is investigated by theory and experiment. Density functional calculations were performed within the local density approximation and the generalized gradient approximation for exchange and correlation effects, as implemented within the full-potential linear muffin-tin orbital method. In situ high-pressure powder x-ray diffraction experiments were performed up to a maximum pressure of 40 GPa using synchrotron radiation. We find that the cubic Pm (3) over barm crystal symmetry persists throughout the pressure range studied. The calculated ground state properties-the equilibrium lattice constant, bulk modulus, and elastic constants-are in good agreement with experimental results. By analyzing the ratio between the bulk and shear moduli, we conclude that KMgF3 is brittle in nature. Under ambient conditions, KMgF3 is found to be an indirect gap insulator, with the gap increasing under pressure.
|
|
