Safarabadi, Mahboobeh: Ab initio calculation for Co nanoparticles, Fe2CoO4 and Co2FeO4 spinels, and Ni-Mn-Ga and Ni-Mn-Sn Heusler alloys. 2014
Inhalt
- 1 Introduction
- 2 Density Functional Theory (DFT)
- 2.1 Hartree-Fock Approximation
- 2.2 Electron Correlation
- 2.3 Exchange Interaction
- 2.4 Pseudopotentials
- 3 SPRKKR Method
- 4 DOS Calculations for Co, Fe2CoO4 and Co2FeO4
- 4.1 Cobalt characterization in different Phases
- 4.2 DOS Calculation for Cobalt in three Phases
- 4.3 Spinel Ferrites Compounds
- Figure 4-12. (Color online) Co-Fe-O phase diagram, red dots show the stable phases and purple dot the unstable Co2FeO4 one.
- Figure 4-13. Difference of either total energy from the total energy of the most stable phase Co2FeO4-inverse vs. the absolute magnetization in (μB /unit cell).
- Figure 4-20. Density of states for Co2FeO4 inverse spinel vs. energy (eV) for spin up and down electrons close to Fermi level.
- Conclusion- According to these results Fe2CoO4 in both structures is an insulator with a gap about 0.21 eV for Normal structure which is in a good agreement with [4] and 0.24 eV for Invesre one which does not correspond to [4] with a gap of 0.8 eV, while Co2FeO4 is a half-metal which corresponds to the expriments of Anna-Lena Wolff. As the data in Table 4-III shows the calculated magnetic moments in comparison to Table 4-II, taken magnetic moments as reference, the magnetic moments for Co are overestimated
- 5 Heusler Alloys and Shape Memory Effect
- 5.1 Structural Properties of Magnetic Heusler Alloys
- 5.2 Magnetic field effect on Strain
- 5.3 Jahn-Teller effect
- 5.4 Slater-Pauling rule
- 6 Shape Memory Effect in Ni2MnGa
- 6.1 Martensitic structure of Ni2MnGa
- 6.2 Composition and Temperature dependence of the Crystal Structure of Ni–Mn–Ga alloys
- Figure 6-2. a sector of the ternary phase diagram of Ni–Mn–Ga showing the critical range of 7.67 < e/a < 7.7 of the coupled magnetostructural phase transitions (- - - -). The figure lists experimental data for TC < TM (□), TC = TM (●) and TC > TM (■). The arrows in the figure mark the theoretical prediction for preferred transformation to modulated 5M and 7M and non-modulated tetragonal T structures, respectively. The yellow dot marks the stoichiometric compound Ni2MnGa [69].
- 6.3 Denisty of States Calculation for Ni2MnGa
- 7 Shape Memory Effect in Ni–Mn–Sn alloys
- 8 Multilayer systems consisting of Ni2MnGa and Ni2MnSn
- 9 Shape Memory Effect of Non-Stoichiometric Compounds
- 10 Summary and Conclusions
- 11 Outlook