Study of Electronic Structures and Thermoelectric Properties of Half Metal

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1 MEMOIRS OF SHONAN INSTITUTE OF TECHNOLOGY Vol. 39, No. 1, 2005 * ** Study of Electronic Structures and Thermoelectric Properties of Half Metal Yukio YUTOH* and Sunao SUGIHARA** Electronic structures and magnetic structures of one of half metal material, Sr 2 FeMoO 6 were studied using the ab initio calculation of molecular orbital method and they were compared with the experimental results. As for calculation, magnetic structures drastically changed with the position of oxygen atom. The Crystal 98 and the DV-Xa were used to find out a total energy by the former and covalent bonding by the latter. Furthermore, the substance was explained in terms of ferrimagnetic with Fe, m B and Mo, m B which were similar to the experimental values of 3.9 m B and 0.37 m B. Seebeck coefficient was mv/k and electrical resistivity, the order of 10 4 W m and the thermal conductivity was 2 to 3 W/m K according to our experiment. Sr 2 FeMoO 6 indicated to be metallic increasing with temperature, which agreed with electronic structure of down spin crossing the Fermi energy level and without energy gap (E f ) (DOS) Fig. 1 up spin DOS E f down spin La Sr Mn O Sr 2 FeMoO 6 1) Mn 2) (Ga,Mn)As 3) NiMnSb 4) CrAs 5) 2 3 (Giant Magneto Resistance: GMR) (Tunneling Magneto Resistance: TMR) 1.2 Sr 2 FeMoO 6, Sr 2 FeWO 6, Ca 2 FeMoO 6, Ba 2 FeMoO 6, Sr 2 FeSmO 6 Fe Mo * ** Fig. 1. DOS for half metallic structure. 63

2 39 1 Fig. 2. Crystal structure of Sr 2 FeMoO 6. Fig. 3. Ferrimagnetism structure. Fe 3d (Ferrimagnetism) GMR TMR Sr 2 FeMoO 6 B Fe Mo 2 (Fig. 2) Fe Mo 100% 100% Fe 2.5 6),7) Fe 2 Mo 6, Fe 3 Mo 6 2 6) Cubic Tetragonal K Tetragonal 8) 1.3 (Ferrimagnetism) A, B Fig. 3 (Fe 3 O 5 ) Fig. 4 p n Seebeck Peltier (T c ) (T h ) DT V V a(t h T c ) (1) a [V/K] Q Q pi (2) p p at (3) Fig. 4 (10 25 m 3 ) Z 64

3 Fig. 4. Principle of Thermoelectric Module. Z a 2 /kr (4) a (V/K) k (W/m K) r (W m) (a) a (b) k (c) r ) ZnO 10),11), Y 2 O 12) 3, Ca(Mn,In)O 13) 3, NaCo 2 O 14) 4 NaCo 2 O K Zn Ca /K NaCo 2 O W/m K Na NaCo 2 O 4 Na 16) 1.6 DT E f (adt) DT E f a α S (5) e S e (g) S k B ln g (6) k B 65

39 1 Sr 2 FeMoO 6 CRYSTAL98 DV-Xa Sr 2 FeMoO 6 Sr 2 FeMoO 6 2. 2.1 Sr 2 FeMoO 6 Fig. 2 Sr 2 FeMoO 6 FM- 3M cubic a 7.8973 Å Fe(0,0,0), Mo(0,0,0.5), Sr(0.25,0.25, 0.25), O(u,0,0) u 0.

4 39 1 Sr 2 FeMoO 6 CRYSTAL98 DV-Xa Sr 2 FeMoO 6 Sr 2 FeMoO Sr 2 FeMoO 6 Fig. 2 Sr 2 FeMoO 6 FM- 3M cubic a Å Fe(0,0,0), Mo(0,0,0.5), Sr(0.25,0.25, 0.25), O(u,0,0) u CRYSTAL98 Sr 2 FeMoO 6 17) a u 2.2 Discrete Variational (DV)-Xa DV-Xa 18) 3 V xc () 1 3α () 1 4π ρ 13 / r a (7) Fig. 5. Cluster model of (Sr 7 Fe 4 Mo 4 O 60 ) 74. a 0.7 φi*( 1) φj*( 2)( 1/ r12) φj( 1) φi( 2) dν2 νex() 1 φ *( 1) φ ( 1) f i i 4 (7) V(1) V z r eff () 1 ν ν 1 ν n n Z n 1 2 φ () 1 C χ () 1 l il i i (8) (9) (10) c i i i ρ( 2) dν2 r 12 V xc 66

5 Table 1. Characteristics of structure optimization. Before After a (Å) u Fig. 6. Center of cluster. XPS (X-ray Photoelectron Spectroscopy; X EELS Electron Energy Loss Spectroscopy; XAFS X-ray Absorption Fine Structure; X XANES X- ray Absorption Near Edge Structure; X DV-Xa Sr 2 FeMoO 6 DV-Xa DV-Xa 3. Fig. 7. Density of states before or after substitution; 0 ev is Fermi level. DV-Xa c i DV-Xa Xa a a 3.1 CRYSTAL98 Sr 2 FeMoO 6 1),20) 22) Table 1 2 3% 1% Fe Mo m B, m B Fe Mo 19) 67

6 39 1 Fe Mo 3.9 m B 0.37 m B Sr 2 FeMoO 6 Fig. 8(a) Fe Mo a Fe, Mo Fig. 8(b) Fe Mo O u u O Mo Fe u Fe, Mo Fig. 8(c) O u Mo O a O u Mo O Mo Sr 2 FeMoO 6 Fe Mo O Fe, Mo, O 3 Fe O, Mo O O u O u Mo O (6) g (5) (6) A, 3.2 DV-Xa DV-Xa Fig. 5 Sr Fig. 8. Dependence of magnetic moment of Fe and Mo on a-axis and coordinate u of O. DV-Xa (DOS) Fig. 7 DOS Sr 2 FeMoO 6 up spin 2.57 ev down spin 68

7 Fig. 9. Effective charges for Sr 2 FeMoO 6. Atomic positions correspond to Fig. 6. Fig. 11. X-ray photoelectron spectroscopy for calculation and experiment. Fig. 10. Covalent bonding for Sr 2 FeMoO 6. 0 Fig. 9 Fe, Mo, Sr, O 2.04, 2.59, 1.83, 1.31 Mo 2.59 Mo 5.5 DV-Xa Fe Mo m B, m B CRYS- TAL98 CRYSTAL98 Fig. 10 Fe O Mo O Sr O Sr 2 FeMoO 6 Fe O Mo O DV-Xa XPS XPS Fig. 11 0eV Ef 3.3 Sr 2 FeMoO 6 XRD SrCO 3 Fe 2 O 3 MoO 3 24 Ar H C 2 Ar H C 24 XRD mm XRD Fig. 12 Sr 2 FeMoO 6 Fig. 11 XPS Fig. 13 Sr 2 FeMoO 6 (a) (r) a n a r a 69

39 1 4. Fig. 13. Fig. 14. Fig. 12. XRD pattern for Sr 2 FeMoO 6.

Thermal conductivity against temperature. r 10 5 (W m) r down spin Fig.

8 Fig. 13. Fig. 14. Fig. 12. XRD pattern for Sr 2 FeMoO 6. Seebeck coeffcient and electrical resistivity against temperature. Thermal conductivity against temperature. r 10 5 (W m) r down spin Fig. 14 k 2 3 (W/mK) FeSi (/K) BiTe 3 4 Sr 2 FeMoO 6 a Sr 2 FeMoO 6 Fe, Mo Sr 2 FeMoO 6 Fe O Mo O Sr O Sr 2 FeMoO 6 Fe O Mo O CRYSTAL98 O u Mo a XPS XPS Fig. 11, DV-Xa, Frozen phonon 70

9 1) K. I. Kobayashi et al., Nature, 395 (1998) ) J.-H. Park, E. Vescovo, H.-J. Kim, C. Kwon, R. Ramesh and T. Venkatesan, Nature, 392 (1998) ) Manish Jain, Leeor Kronic, R. Chelikowsky and Vitaliy V. Godlevsky, Phys. Rev. B, 64 (2001) ) R. A. Groot, F. M. Mueller, P. G. van Engen and K. H. J. Buschow, Phys. Rev. Lett., 50 (1983) ) H. Akinaga, T. Manago and M. Shirai, Jpn. J. Appl. Phys., Part 2, 39 (2000) L ) J. Linden, T. Yamamoto, M. Karppinen, H. Yamauchi and T. Pietari, Appl. Phys. Lett., 76 (2000) ) D. D. Sarma et al., Solid State Communications, 114 (2000) ) O. Chmaissem et al., Phys. Rev. B, 62 (2000) ) M. Ohtaki, et al., Thermoelectric Properties and Applicability of In 2 O 3 -based Mixed Metal Oxides for Thermoelectric Conversion at High Temperature, Proceedings of 12th International Conference on Thermoelectrics, K. Matsumura ed., Yokohama, XII (1993) p ) T. Tsubota et al., Thermoelectric Properties of ZnO Doped with the Group 13 elements, Proceedings of The 16th International Conference on Thermoelectrics, Organized by Institute of Solid State and Materials Research Dresden, XVI (1997) p ) M. Ohta, M. Kazeoka, W. S. Seo and K. Koumoto, Thermoelectric Properties of Layer-Structured (ZnO)mIn 2 O 3 (m integer) Improved by Elemental Substitution, Proc, of 17th International Conference on Thermoelectrics, Nagoya, XVII (1998) ) K. Koumoto, W. S. Seo and S. Ozawa, Huge Thermoelectromotive Force Generated by Porous Ceramics of Y 2 O 3, Proceeding of The 16th International Conference on Thermoelectrics, Organized by Institute of Solid State and Materials Research Dresden, XVI (1997) p ) M. Ohtaki, et al., Hopping Carrier Mobilities and Thermoelectric Properties of Oxide Materials with Perovskite-Related Structure, Proceedings of the 16th International Conference on Thermoelectrics, Organized by Institute of Solid State and Materials Research Dresden, XVI (1997) p ) I. Terasaki, Y. Sasago, and K. Uchinokura, Large thermoelectric power of NaCo 2 O 4 single crystals, Phys. Rev. B, 56 (1997) ) DV Xa ) Vol. 70 (2000) ) 15 19) D. Sánchez, J. A. Alonso, M. García-Hernández, M. J. Martínez-Lope and J. L. Martínez, Phys. Rev. B, 65 (2002) ) D. D. Sarma, Priya Mahadevan, T. Saha-Dasgupta, Sugata Ray, and Ashwani Kumar, Phys. Rev. Lett., 85 (2000) ) Horng-Tay Jeng and G. Y. Guo, Phys. Rev. B, 67 (2003) ) P. Petrone and A. A. Aligia, Phys. Rev. B, 66 (2002)

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