Complex magnetic phase diagram of ferromagnetic CeNiSb3 V.A.Sidorov et.al., Phys. Rev. B 71 094422 (2005) Katsuya TOKUOKA Shimizu-Group 1 Contents Introduction about… Ce Compounds, magnetic order , QCP,… etc. Experimental results and discussion Summary 2 4f – electron in Ce compounds Lanthanides 4f-electrons La3+ Ce3+ Pr3+ … 0 1 2 4f - electron is localized. Direct spin interaction between 4f-electrons is hard to occur. |r R(r)|2 Closed shell 5s25p6 r (a.u.) http://www.phy.saitama-u.ac.jp/~saso/saso.html 3 RKKY interaction (Ruderman-Kitel-Kasuya-Yoshida) Conduction electrons Exchange interaction Long-range order appeared ! 4f - electrons 4 Indirect f-f interaction is mediated by conduction electrons. Kondo effect Conduction electrons Spin singlet S=0 4f - electrons Magnetic moment is screened by hybridization between conduction electrons and f electrons. f-electrons are itinerant . 5 Heavy fermion state ! (重い電子状態） Pressure effect RKKY interaction Kondo effect Delicate balance Heavy Fermi liquid behavior Magnetic ordering TRKKY ∝ Jcf2 TK ∝ exp(-1/Jcf) P RKKY interaction is dominant ( f-localized ) 局在 Kondo effect is dominant ( f-itinerant ) 遍歴 Tune by pressure 6 Motivation CeNiSb3 Ferromagnetic ground state Tc = 6 K Applying pressure… How does ferromagnetism change ? R. T. Macaluso et al., J.Solid State Chem. 177 293 (2004) Where is the quantum critical point ? What happens near the critical point ? 7 Crystal structure of CeNiSb3 CeNiSb3 Orthorhombic structure Space group Pbcm (#57) a (Å) = 12.6340 b (Å) = 6.2037 c (Å) = 18.3698 Specific heat coeffecient （電子比熱係数） R. T. Macaluso et al., J.Solid State Chem. 177 293 (2004) γ = 50 mJ / mol K2 (γis proportional to effective mass.) Ferromagnetic ground state TC = 6 K 8 Temperature dependence of electrical resistivity in CeNiSb3 Double peak T ~ 100K Crystal field T ~ 10K Kondo effect ρincreases as the pressure increases. 9 Second transition TM2 TM1 Tc first increases. A second transition appeared P >39.5 kbar. Both anomaly decreases as the pressure increases. And TM2 disappeared at 55.2 kbar. Tc 10 The first derivative dρ/dT TM2 TM1 P > 39.5 kbar Shape of the peak at TM1 changes. → like shoulder And second transition TM2 appears. → sharp peak P = 55.2 kbar, Peak at TM2 disappears. Peak at TM1 becomes broader. Tc 11 Magnetic phase diagram Tc first increased. TM1 and TM2 appeared P > 35 kbar. TM2 disappears P = 55 kbar. They can’t reach the quantum critical point because of the 12 pressure cell. (P < 60kbar) Fermi liquid and Non fermi liquid At low temperature region… Fermi liquid ρ-ρ0 = AT2 Non fermi liquid ρ-ρ0 = ATn n<2 At the quantum critical point Magnetic order region ρ-ρ0 = ATn 2 < n < 3 13 Fermi liquid behavior Fermi liquid behavior recovered at P = 55.2 kbar. Kadowaki-Woods relation A / γ2 = 1×10-5μΩcm (mol K / mJ)2 γ = 300 mJ / mol K2 6 times heavier than value at 14 ambient pressure ! Complex magnetic phase diagram and etc. n value approaches to 2 . →Fermi liquid behavior is recovered. To non fermi liquid P > 60 kbar In some Ce Compounds, A and ρ0 has a sharp peak. Sign of near the quantum critical point. 15 Summary Complex magnetic phase diagram ・Tc first increases, and second magnetic phase appeared P > 35kbar. ・Critical pressure for the suppression of the low temperature phase is estimated Pcmag2 ~ 55 kbar. ・Quantum critical point associated with the higher temperature phase is estimated Pcmag1 ~ 60 kbar. 16 My sample CePdSb3 My experimental sample CePdSb3 Orthorhombic structure Space-group Pbcm a = 12.780 Å b = 6.330Å c = 12.453 Å Co Ni Cu Rh Pd Ag Antiferromagnetic ground state TN = 3 K 17 My sample CePdSb3 40 TM1 5 4 30 3 20 T (K) (cm) TM2 10 1 kbar 10 kbar 17 kbar 22 kbar TN 2 1 0 0 0 1 2 TN increases. 3 T (K) 4 5 TN Tm1 Tm2 6 0 1 2 3 P (GPa) 4 5 6 Second transition appeared with applying pressure. With our pressure cell (DAC), we will be able to reach the quantum critical point ! 18
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