| 1. |
- Li, Chun-Mei, et al.
(författare)
-
Magnetic ordering and physical stability of X2Mn1+xSn1-x (X = Ru, Os, Co, Rh, Ni, Pd, Cu, and Ag) Heusler alloys from a first-principles study
- 2013
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 88:1, s. 014109-
-
Tidskriftsartikel (refereegranskat)abstract
- The magnetic ordering and its effect on the physical stability of X2Mn1+xSn1-x (0 <= x <= 0.5, and X = Ru, Os, Co, Rh, Ni, Pd, Cu, and Ag) Heusler alloys are investigated systematically by the use of first-principles method. It is found that the ferromagnetic (FM) coupling between Mn on Mn sublattice (Mn-1) and Mn on Sn sublattice (Mn-2) is favorable over the antiferromagnetic (AFM) coupling for X with the number of valence electrons [N-v(X)] of 8 and 9, and vice versa for X with N-v(X) = 10 and 11, originated from the competition of the exchange interactions between X-Mn-2 and Mn-1-Mn-2. In comparison with the FM Mn-1-Mn-2 coupling, the AFM coupling decreases significantly the shear elastic constant C' but increases slightly C-44, which results in increasing elastic anisotropy (A = C-44/C') and consequently may facilitate the tetragonal shear lattice deformation. The hybridization of the minority electronic states between X d and Sn p plays a dominant role on the orientation of the magnetic coupling. The smaller change of the density of states in the Fermi level, induced by the lattice distortion for C', corresponds to the softer C' as well as the larger A in the AFM state than the FM one.
|
|
| 2. |
- Li, Wei, et al.
(författare)
-
The effect of Al on the 475 degrees C embrittlement of Fe-Cr alloys
- 2013
-
Ingår i: Computational materials science. - : Elsevier BV. - 0927-0256 .- 1879-0801. ; 74, s. 101-106
-
Tidskriftsartikel (refereegranskat)abstract
- Aluminum addition to ferritic stainless steels was found to effectively suppress the deleterious 475 degrees C embrittlement resulting from the phase decomposition in concentrated Fe-Cr alloys. With the aim of revealing the mechanism behind this prosperous phenomenon, here we investigate the effect of Al on the interfacial energy and formation energy of Fe-Cr solid solutions. The interface between the decomposed Fe-rich alpha and Cr-rich alpha' phases carries a positive excess energy, which is of significant importance on determining the process of phase separation. Using ab initio alloy theory, we show that for the alpha-Fe70Cr20Al10/alpha'-Fe100-x-yCryAlx (0 <= x <= 10, 55 <= y <= 80) interface, the Al content (x) barely changes the interfacial energy. However, for the alpha-Fe100-x-yCryAlx/alpha'-Fe10Cr90 (0 <= x <= 10, 0 <= y <= 25) interface, the interfacial energy increases with Al content due to the variation of the formation energies of the Fe-Cr alloys upon Al alloying. Our ab initio results are supported by CALPHAD calculations, and suggest that the beneficial effect of Al on ferritic steels is mainly due to its thermodynamical effect on the alpha' phase.
|
|
| 3. |
- Lu, Song, et al.
(författare)
-
First-principles study of fcc-Ag/bcc-Fe interfaces
- 2013
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 87:22, s. 224104-
-
Tidskriftsartikel (refereegranskat)abstract
- Ab initio calculations are employed to determine the lower and upper bounds of the interfacial energy and work of separation of a fcc-Ag/bcc-Fe interface. The strain-free interfacial energy of the coherent interface is taken as the lower bound and the interfacial energy of the commensurate incoherent interface as the upper bound of the interfacial energy of a realistic semicoherent interface. The latter is estimated by applying an averaging scheme based on the interfacial energies obtained for the coherent interfaces. Similar calculations are performed for determining the bounds of the work of separation. We justify the use of the averaging scheme by carrying out large supercell calculations for a semicoherent interface. For a Fe(110)/Ag(111) semicoherent interface, we show that taking either Fe or Ag as the underlying lattice, our averaging scheme can yield a reasonable estimation of the work of separation of the semicoherent interface. However, when taking Ag as the underlying lattice, the averaged interfacial energy of the semicoherent interface is significantly underestimated due to the magnetism. The structure and magnetism at the coherent and semicoherent interfaces are discussed.
|
|
| 4. |
- Luo, Hu-Bin, et al.
(författare)
-
Magnetic properties and temperature-dependent half-metallicity of Co2Mn(Ga(1-x)Z(x)) (Z = Si, Ge, Sn) from first-principles calculation
- 2013
-
Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 25:15, s. 156003-
-
Tidskriftsartikel (refereegranskat)abstract
- Using the first-principles exact muffin-tin orbitals method in combination with the coherent potential approximation, we investigated the magnetic properties, exchange interactions, and temperature-dependent half-metallicity of the Co2Mn(Ga(1-x)Z(x)) (Z = Si, Ge, Sn) alloys. The total magnetic moment follows perfectly a previously proposed Slater-Pauling relation, i.e., mu(0) = N-t - 24, with N-t being the number of valence electrons. The Co-Mn and Co1-Co2 (inter-sublattice) interactions are dominated by direct exchange, whereas the Co1-Co1 (intra-sublattice) interaction is characterized by superexchange. The Mn-Mn exchange interaction in Co2MnGa is of long-ranged RKKY-type. However, the Mn-Mn exchange interactions in Co(2)MnZ are relatively localized and can be attributed to superexchange. The Co-Mn, Co1-Co2 and Co1-Co1 total exchange interactions increase with x, whereas the Mn-Mn total exchange interactions show convex behavior. The calculated Curie temperature (T-C) increases with x. The ability of Z to enhance T-C follows the sequence of Si > Ge > Sn, in agreement with the experimental findings. The temperature dependence of the spin polarization at the Fermi level [P(T)] is investigated based on the disordered local moment model. P(T) drops abruptly at temperatures much lower than T-C. At temperatures higher than 200 K, the composition with higher TC generally corresponds to larger P(T).
|
|
| 5. |
- Wang, Guisheng, et al.
(författare)
-
Ab initio investigation of the elastic properties of Ni3Fe
- 2013
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 88:17, s. 174205-
-
Tidskriftsartikel (refereegranskat)abstract
- Ab initio alloy theory, formulated within the exact muffin-tin orbitals method in combination with the coherent-potential approximation, is used to determine the elastic properties of Ni-Fe alloys with Fe:Ni ratio 1:3. The interplay between magnetic and chemical effects is investigated by computing the lattice parameters and the single-and polycrystal elastic moduli for different partially ordered structures in the ferro-and paramagnetic states. It is found that the influence of long-range chemical order on the bulk properties strongly depends on the magnetic state. The largest magnetic-order-induced changes are obtained for the chemically ordered L1(2) phase. The ferromagnetic L1(2) system possesses similar to 5.4% larger elastic Debye temperature than the paramagnetic L1(2) phase, which in turn has a similar Theta(D) as the chemically disordered face-centered cubic phase in either the ferro-or paramagnetic state. It is concluded that magnetic ordering has a substantially larger impact on the bulk parameters of Ni3Fe than chemical ordering. The calculated trends are explained based on the electronic structure of nonmagnetic, ferromagnetic, and paramagnetic ordered and disordered phases.
|
|
| 6. |
- Wang, Gui-Sheng, et al.
(författare)
-
The effect of long-range order on the elastic properties of Cu3Au
- 2013
-
Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 25:8, s. 085401-
-
Tidskriftsartikel (refereegranskat)abstract
- Ab initio calculations, based on the exact muffin-tin orbitals method are used to determine the elastic properties of Cu-Au alloys with Au/Cu ratio 1/3. The compositional disorder is treated within the coherent potential approximation. The lattice parameters and single-crystal elastic constants are calculated for different partially ordered structures ranging from the fully ordered L1(2) to the random face centered cubic lattice. It is shown that the theoretical elastic constants follow a clear trend with the degree of chemical order: namely, C-11 and C-12 decrease, whereas C-44 remains nearly constant with increasing disorder. The present results are in line with the experimental findings that the impact of the chemical ordering on the fundamental elastic parameters is close to the resolution of the available experimental and theoretical tools.
|
|
