Investigation of Pressure Effect on YbInCu 4

1. Investigation of Pressure Effect on YbInCu4 M1 Colloquium 2008 10/29 Shimizu Group Kazuki KASANO

2. Outline • Background • Purpose • Results & Discussion • Summary & My study

3. Background • What is “ Pressure effect ” ? • Macroscopic view Pressure makes material’s density higher. • Microscopic view Lattice parameter changes. Electronic parameter also changes. • Exotic properties • For example… • Metal-Insulator transition • Valence transition

4. Background • YbInCu4 • Crystal structure • C15b structure • Phase transition • Phase transition occurs at 42 K • at ambient pressure. • From magnetic susceptibility measurement, • T > 42 K : Curie-Weiss paramagnetic • T < 42 K : Pauli paramagnetic Magnetism changes at 42 K ! Tsuneaki Goto, et al., Journal of Magnetism and Magnetic Materials 272-276 (2004)

5. Background • Valence transition Valence transition at 42 K Tv (= 42 K) High Temperature phase Yb3+ (4f13) Localized magnetic moment Curie-Weiss paramagnetic Low Temperature phase Yb2+ (4f14) No localized magnetic moment Pauli paramagnetic Magnetism changes between two states ! Note Not all Yb ion changes valence. Averaged valence is non-integer valence. (For example, Yb changes from 3+ to 2.9+ in YbInCu4)

6. Background • Change of lattice parameter at Tv (Note) DL/L : standardized by lattice parameter at low temperature Tv Pauli paramagnetic state Curie-Weiss paramagnetic state The lattice parameter expands at Tv. Tsuneaki Goto, et al., Journal of Magnetism and Magnetic Materials 272-276 (2004)

7. Background • Pressure effect in YbInCu4 Under pressure At ambient pressure Curie-Weiss Paramagnetic phase Curie-Weiss Paramagnetic phase Tv Tv Pauli Paramagnetic phase Pauli Paramagnetic phase Curie-Weiss phase is stabilized by pressure.

8. Background • P-T phase diagram Curie-Weiss paramagnetic phase Temperature Tv dTv / dP ~ -20 K / GPa Pauli paramagnetic phase Pressure 1.5 GPa • Interesting points of YbInCu4 • How does Tv change at higher pressure … ? • Critical pressure isn’t so high … ? • At higher pressure, what happen … ?

9. Purpose • Purpose of this presentation • Pressure effect on valence transition of YbInCu4 • Investigation at higher pressure region • Reference • “ Effect of pressure on the electrical resistivity of a single crystal of YbInCu4 “ Ahimusa Uchida, et al., Physica B 312-313 (2002) 339-340 • “ Magnetic ordering in the pressure-stabilized high-temperature phase of YbInCu4 ” T. Mito, et al., Physical Review B 67 224409 (2003) • “ Evidence for the pressure induced magnetic ordering in YbInCu4 ” T. Mito, et al. Journal of Magnetism and Magnetic Materials 272-276 (2004) e47-e48

10. Experimental method • Sample • Single-crystal YbInCu4 • (Made by In-Cu flux method) • Measurements • Electrical resistivity • AC magnetic susceptibility • Pressure cell • Piston cylinder pressure cell (up to 2.58 GPa)

11. Results Tv = 42 K at ambient pressure • Electrical resistivity Valence transition disappears ! • At ambient pressure • Valence transition at Tv = 42 K • Under pressure • Tv shifts toward lower temperature. • Above 2.3 GPa • Valence transition disappears ! Ahimusa Uchida, et al., Physica B, 312-313 (2002) 339-340

12. Results • Precise view around 2.3 GPa • Electrical resistivity • Sharp drop at around 7 K • Magnetic susceptibility • Small decrease below 7 K T. Mito, et al., Physical Review B 67 224409 (2003) • Valence transition remains at 2.21 GPa.

13. Results • Precise view around 2.3 GPa • Electrical resistivity • Broadened step at around 3.5 K • Magnetic susceptibility • Small decrease at around 3.5 K • Sharp peak at around 2.4 K T. Mito, et al., Physical Review B 67 224409 (2003) • Coexistence of the valence transition and new magnetic order • Critical pressure is around 2.4 GPa.

14. Results • Precise view around 2.3 GPa • Electrical resistivity • Small kink at around 2.4 K • Magnetic susceptibility • Clear peak at around 2.4 K T. Mito, et al., Physical Review B 67 224409 (2003) • Valence transition is completely suppressed. • New magnetic ordering (Ferromagnetism) below 2.4 K occurs.

15. Summary P < 1.5 GPa dTv / P ~ -20 K / GPa P > 2 GPa dTv / P ~ 18.5 K / GPa T. Mito, et al., Journal of Magnetism and Magnetic Materials 272-276 (2004) e47-e48 • Pressure effect on valence transition • Valence transition is suppressed by pressure. • Tv decreases linearly up to around 2.4 GPa. • Investigation at higher pressure region • Coexistence of valence transition and magnetic ordering at 2.39 GPa • Critical pressure is around 2.4 GPa. • New ferromagnetic ordering occurs above critical pressure.

16. My study • Let’s connect to my study ! • YbInCu4 • Valence transition • Pressure effect • Not so high critical pressure • New magnetism at higher pressure region • YbPd • Valence transition • Pressure effect These are similar to YbInCu4. Different & interesting point Mysterious magnetic ordering in YbPd

17. My study • What is mysterious magnetic ordering ? High Temperature phase Yb3+ (4f13) Localized Magnetic moment Curie-Weiss paramagnetic Low Temperature phase Yb2+ (4f14) No localized magnetic moment Pauli paramagnetic In YbPd… Magnetic ordering appears at low temperature under ambient pressure !

18. My study • Purpose of my study Magnetic ordering appears R. Pott, et al., Physical Review Letters, 54, 1985 • I want to investigate… • Pressure effect on valence transitions in YbPd • What happen at low temperature ?

19. Appendix

20. Appendix1 : Electrical resistivity • Matthiessen rule • r0 : residual resistivity • rphonon : scattering by lattice vibration • relectrons : scattering between electrons • rmagnetic : magnetic scattering This term changes with magnetic change.

21. Appendix2 : Localized magnetic moment • Magnetic moment LS coupling law • J : Total angular momentum • L : Total orbital angular momentum • S : Total electronic spin angular momentum • Yb state becomes near Yb2+(4f14). • 4f orbit is filled. • L and S become 0. • J becomes 0. • No localized magnetic moment.