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SHIMIZU Group KANEMASA Taisuke

Magnetic phase diagram of the ferromagnetic compound CeAgSb 2 under high pressure V. A. Sidorov et al ., PHYSICAL REVIEW B 67 , 224419 (2003). SHIMIZU Group KANEMASA Taisuke. Contents. Introduction Experiment Results and discussion Summary. Introduction. Magnetic behavior

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SHIMIZU Group KANEMASA Taisuke

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  1. Magnetic phase diagram of the ferromagnetic compound CeAgSb2 under high pressure V. A. Sidorov et al.,PHYSICAL REVIEW B 67, 224419 (2003) SHIMIZU Group KANEMASA Taisuke

  2. Contents • Introduction • Experiment • Results and discussion • Summary

  3. Introduction Magnetic behavior is determined by a balance between RKKY interaction and Kondo effect Ce-compounds P The relation of RKKY interaction and Kondo effect

  4. Interaction between f-electrons Hi,j∝ －J (Ri,j) ・Si・Sj J > 0 → Si・Sj > 0 ferromagnetism J < 0→Si・Sj < 0 antiferromagnetism Si Sj Ri,j Ce-compound Ferromagnetic order is rare. Magnetic phase diagram is complex. P

  5. Superconductivity near the QCP After magnetism is suppressed, superconductivity appears. CeIn3 S. S. Saxena et al., Nature 406, 587 (2000) N. D. Mathur et al., Nature 394, 39 (1998) Quantum critical point (QCP) : 量子臨界点

  6. Motivation • What happens ? superconductivity or antiferromagnetism or… Ferromagnetic Ce compound T ? FM ? P

  7. Crystal structure CeAgSb2The family of RAgSb2compounds (R = La–Tm) • Tetragonal ZrCuSi2-type crystal structure • Ferromagnetic (FM) compound Curie temperature TC = 9.6 K But others are antiferromagnetic (AFM) • In this experiment, three samples labeled LANL 161, LANL 161a and UCSD, respectively, were used. Lanthanides La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

  8. Ambient-pressure measurements • Magnetic susceptibility (磁化率) T : from 1.8 K to 300 K H : 0.1 T sample : LANL 161 • Specific heat (比熱) T : from 0.3 K to 300 K sample : LANL 161 H c a

  9. High pressure measurements • Electrical resistivity Sample LANL 161 UCSD P up to ~ 50 kbar up to ~ 80 kbar pressure cell toroidal anvil cell Bridgman anvil cell • AC-calorimetry P : up to~36.5 kbar sample : LANL 161a ○ Hydrostatic pressure Toroidal anvil cell Bridgman anvil cell

  10. AC-calorimetric measurements AC-electronic heater Thermometer Sample Chromel (Ni-Cr) – Constantan (Cu-Ni) thermocouple ΔT Bath thermocouple : 熱電対

  11. Results and discussion Ambient-pressure • Magnetic susceptibility χ(T ) • increases sharply below ~10 K • (b) The ferromagnetic • transition at TC= 9.6 K a) χ (≡M/H ) vs T in H =0.1 T b) C/T vs T

  12. Temperature dependence of electrical resistivity The maximum sharpens with pressure and shifts slightly.

  13. Temperature dependence of electrical resistivity TC : 9.6 K → 2.4 K ( (32.6 kbar) Phase transition

  14. Temperature derivative of ρ There are shoulders at ~ 4 K Antiferromagnetic transition ? Lattice parameters are close to those of PrAgSb2

  15. Magnetic phase diagram ・FM order is suppressedat ~ 35 Kbar ・AFM order is appears at ~ 28 Kbar ●TC ○TN ○ ○

  16. Unique behavior in QCP ρ0 and A exhibit a sharp maximum at ~35 kbar Fits of ρ(T ) to ρ(T ) = ρ0+AT2 (LANL 161) 10 20 30 40 50 P (kbar) (a) A vs P (b) ρ0 vs P

  17. AC-calorimetric measurements Ferromagnetic transition (P ≦ 16.6 kbar) Antiferromagnetic transition (P ≧ 31.2 kbar)

  18. Magnetic phase diagram ・PC = 35kbar ・AFM is suppressed a at ~50 kbar LANL 161 — closed symbols UCSD — open symbols

  19. Summary • The FM order is suppressed at PC= 35 kbar. • Superconductivity is not observed, but a new ordered phase emerges near the QCP. • The second magnetic phase (AFM) appears above 27 kbar and is suppressed at ~50 kbar.

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