| 1. |
- Hu, Qing-Miao, et al.
(författare)
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Magnetoelastic effects in Ni2Mn1+xGa1-x alloys from first-principles calculations
- 2010
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 81:6, s. 064108-1-064108-5
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Tidskriftsartikel (refereegranskat)abstract
- The magnetic coupling between Mn atoms on Ga sublattice (Mn-Ga) and Mn atoms on Mn sublattice (Mn-Mn) in Ni2Mn1+xGa1-x alloy and its effect on the elastic modulus of the alloy are investigated by the use of first-principles methods. It is shown that, for x = 0.25, the state with antiparallel Mn-Ga-Mn-Mn magnetic coupling is slightly more stable than that with parallel coupling, whereas for x = 0.10, both magnetic states are almost degenerated. For both antiparallel and parallel Mn-Ga-Mn-Mn magnetic couplings, the bulk modulus (B) of Ni2Mn1+xGa1-x deviates from the general e/a-B relationship with e/a being the number of valence electrons per atom. The shear modulus C' versus the martensitic transformation temperature T-M for Ni2Mn1+xGa1-x with antiparallel Mn-Ga-Mn-Mn magnetic coupling is in line with the general C'-T-M relationship for Ni2MnGa-based alloys, in contrast to the case of parallel Mn-Ga-Mn-Mn magnetic coupling.
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| 2. |
- Li, Chun-Mei, et al.
(författare)
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First-principles investigation of the composition dependent properties of Ni2+xMn1-xGa shape-memory alloys
- 2010
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 82:2, s. 024201-1-024201-9
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Tidskriftsartikel (refereegranskat)abstract
- The composition dependent lattice parameter, phase stability, elastic moduli, and magnetic transition temperature of the Ni2+xMn1-xGa shape-memory alloys are studied by using the first-principles exact muffin-tin orbital method in combination with the coherent potential approximation. The lattice parameter and tetragonal shear modulus of the cubic L-21 austenite phase decreases linearly with increasing concentration x of excess Ni atoms. The heats of formation of both cubic L-21 and tetragonal beta''' phases and their difference increase with x, indicating decreasing stability of the cubic and tetragonal phases and increasing driving force for the L-21 to beta''' martensitic transition. Investigating the electronic density of states, we find that the Ni-induced decreasing phase stability can mainly be ascribed to the weakening of the covalent bonding between minority spin states of Ni and Ga. Using the computed parameters, the composition dependence of the martensitic transition temperature is discussed. The theoretical Curie temperature, estimated from the Heisenberg model in combination with the mean-field approximation, is larger for the beta''' phase than for the L-21 phase. For both phases, the Curie temperature decreases nearly linearly with increasing x.
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| 3. |
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| 4. |
- Zhang, Hualei, et al.
(författare)
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Static equation of state of bcc iron
- 2010
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 82:13, s. 132409-
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Tidskriftsartikel (refereegranskat)abstract
- Body-centered-cubic (bcc) iron is one of the most investigated solid-state systems. Using four different density-functional methods, we show that there is a magnetic transition close to the ground-state volume of bcc Fe, which originates from the particular magnetic band structure. The common equation of state functions, used to determine the basic ground-state physical quantities from the calculated total energies, cannot capture the physics of this magnetic transition leading to serious underestimation of the Fe bulk modulus. Ignorance of the magnetic transition found here is reflected by large scatter of the published theoretical bulk moduli of ferromagnetic bcc Fe. Due to the low performance of the exchange-correlation functionals, most of the erroneous results are accidentally in good agreement with the experimental values. The present finding is of fundamental importance, especially taking into account that bcc Fe is frequently used as a test system in assessing the performance of exchange-correlation approximations or total-energy methods.
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| 5. |
- Lu, Song, et al.
(författare)
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First-principles determination of the alpha-alpha ' interfacial energy in Fe-Cr alloys
- 2010
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 82:19, s. 195103-
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Tidskriftsartikel (refereegranskat)abstract
- The interfacial energies (gamma) between the Cr-rich alpha'-FexCr1-x and Fe-rich alpha-Fe1-yCry phases (0 < x, y < 0.35) are calculated to be between similar to 0.02 and similar to 0.33 J m(-2) for the ferromagnetic state and between similar to 0.02 and similar to 0.27 J m(-2) for the paramagnetic state. Although for both magnetic states, the interfacial energy follows a general decreasing trend with increasing x and y, the fine structures of the gamma(x, y) maps exhibit a marked magnetic state dependence. The subtleties are shown to be ascribed to the magnetic interaction between the Fe and Cr atoms near the interface. The theoretical results are applied to estimate the critical grain size for nucleation and growth in Fe-Cr stainless steel alloys.
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| 6. |
- Lu, Song, et al.
(författare)
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First-principles determination of the α-α' interfacial energy in Fe-Cr alloys
- 2010
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 82:19, s. 195103-
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Tidskriftsartikel (refereegranskat)abstract
- The interfacial energies (gamma) between the Cr-rich alpha'-FexCr1-x and Fe-rich alpha-Fe1-yCry phases (0 < x, y < 0.35) are calculated to be between similar to 0.02 and similar to 0.33 J m(-2) for the ferromagnetic state and between similar to 0.02 and similar to 0.27 J m(-2) for the paramagnetic state. Although for both magnetic states, the interfacial energy follows a general decreasing trend with increasing x and y, the fine structures of the gamma(x, y) maps exhibit a marked magnetic state dependence. The subtleties are shown to be ascribed to the magnetic interaction between the Fe and Cr atoms near the interface. The theoretical results are applied to estimate the critical grain size for nucleation and growth in Fe-Cr stainless steel alloys.
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