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M1 Colloquium Presentation

M1 Colloquium Presentation. High Pressure Study of Na x TiNCl and CeFe 2. Arora Varun 29A13106 (Shimizu Lab). Contents. Introduction Motivation Experimental Method Results Summary. Intercalated MNX Compound ( Na x TiNCl ). Introduction. MNX

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M1 Colloquium Presentation

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  1. M1 Colloquium Presentation High Pressure Study of NaxTiNCl and CeFe2 AroraVarun 29A13106 (Shimizu Lab)

  2. Contents • Introduction • Motivation • Experimental Method • Results • Summary

  3. Intercalated MNX Compound(NaxTiNCl)

  4. Introduction • MNX M : Group IV metal ( Ti, Zr, Hf ) N : Nitrogen X : Halogen ( Cl, Br, I ) • Two types of layer-structured polymorphs of MNX ： • α-form(Orthorhombic ) • β-form ( Rhombohedra ) • Superconductivity uptoTc = 25.5 K in β-form :- • Lithium doped ZrNCl : Superconductivity at 13 K (1996) • Lithium doped HfNCl : Superconductivity at 25.5 K (1998) Superconducting Nitride Halides (MNX), Christian M. Schurz et al. , Zeitschrift for Kristallographie226, 395-416 (2011)

  5. TiNCl • α-MNX type structure • Layer Structure • [MN]+ layer is sandwiched between two sheets of halide anions [X]- • Orthorhombic Structure • Sensitive to moisture • Energy Band = 1.7 eV • (Semi-conductor) Cl N Basal Spacing Ti Superconducting Nitride Halides (MNX), Christian M. Schurz et al. , Zeitschrift for Kristallographie226, 395-416 (2011)

  6. What is Inter-calation? • To insert something between elements or layers. • Dopants can be introduced through the interlayer space without substituting or disturbing the original network for electron transport. • Two types of layer structured crystals : Molecular - Van der Walls force ( eg : Graphite ) Ion – exchangeable - Redox reaction ( eg : clay minerals ) Superconducting Nitride Halides (MNX), Christian M. Schurz et al. , Zeitschrift for Kristallographie226, 395-416 (2011)

  7. Previous Research on Na0.16TiNCl Superconducting Nitride Halides (MNX), Christian M. Schurz et al. Zeitschriftfor Kristallographie226, 395-416 (2011)

  8. Motivation On applying pressure, distance between the layers “d” decreases, and so Tcshould also increase ? Superconducting Nitride Halides (MNX), Christian M. Schurz et al. , Zeitschrift for Kristallographie226, 395-416 (2011)

  9. Check for Superconductivity in Na0.16TiNCl at High Pressure • Meisner Effect • Sharp change in • AC Susceptibility ( χ ) Resistivity Measurement • Sharp Drop in Resistivity Superconducting Nitride Halides (MNX), Christian M. Schurz et al. , Zeitschrift for Kristallographie226, 395-416 (2011)

  10. AC - Susceptibility Experiment

  11. AC Susceptibility and Superconductivity Bin = μ0nI = μ0M Bout = 0 If such a sample is placed in a external magnetic field, Ha, then Ba = μ0Ha Thus, Bin(total) = μ0(Ha + M) In case of paramagnetic material, in the absence of any external magnetic field, M = 0. M is directly proportional to the external magnetic field. Thus, M = χHa(χ : AC Susceptibility ) Thus, Bin(total) = μ0 (1+χ) Ha In Case of Superconductivity , Bin(total) = 0, therefore, χ = -1 Sample can be considered as a solenoid

  12. Principle of AC Susceptibility Measurement B (Magnetic field by primary coil) : Kept small, on the order of few Oe, so as not to avoid local heating f (Frequency of the field) : Increasing frequency increases not only the signal size but also the noise. n, r (No. of turns , radius of pick up coil) : Signal size is directly proportional to number of turns and radius of coil, but there is a limitation to both of these parameter when we are dealing with high pressure experiment. Vs, Vc(Volume of sample and coil) : Increasing the ratio of Vs/Vc will make the signal stronger

  13. Setting(AC Susceptibility Measurement) • Primary Coil • Cu wire (diameter = 100 μm) • Number of turns = 350 • Pick up Coil • Cu wire (diameter = 16 μm) • Diameter of coil = 300 μm

  14. Results

  15. Setting 1 Pressure Medium : Fluorinert 70 + 77 (1:1) Sample : Na0.16TiNCl and Pb Pressure : 0.1GPa Fluctuations due to change in the heater range! Pb

  16. Setting 2 Pressure Medium : Fluorinert 70 + 77 (1:1) Sample : Na0.16TiNCl and Pb Pressure : 0.1GPa Pb

  17. Setting 3 ( No pressure medium ) Sample : Na0.16TiNCl and Pb Pressure : 0.1GPa Pb

  18. Pb Pb Heating (0.5V) Heating (1V)

  19. Resistivity Measurement( 4‐probe Method)

  20. Ruby Sample • 1GPa • 1.5 GPa Gasket Insulating Layer 500 mm

  21. Summary • Na0.16TiNCl shows superconductivity at Tc= 18.1 K at ambient pressure. • Exact reason for no superconductivity observed when pressure is applied is not known, but possible reasons which can be given are : • Sample is sensitive to air/moisture, so there is a chance that sample was contaminated while installing it between the diamonds. • Maybe on applying pressure, it undergoes some structural change, and Na0.16TiNCl does not show superconductivity.

  22. Next Plan • Try to load sample inside the cell with even more care, so that is there is absolutely no contamination with air/moisture. • Next time see the crystal structure of Na0.16TiNCl under pressure and see if there is any change in structure.

  23. CeFe2

  24. n(r) r/rB Introduction Pm La Ce Pr Nd Sm Eu Gd Tb Dy Ho Tm Yb Lu ・Lanthanide 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d104f 1 5s2 5p6 5d1 6s2 Ce Localized or delocalized Ce • Cubic C15 Laves Structure (MgCu2) • Strongly hybridized compound between Fe 3d electrons and Ce 4f electrons. Fe

  25. CeFe2 v/s other REFe2 compounds • CeFe2 has lower Tc (around 230K) than other REFe2 compounds(around 600K). • The ferromagnetic ordering temperature is higher in the REFe2 compounds because of strong Fe-Fe interaction. • In case of CeFe2 , the Fe3d - Fe3d interactions compete with Fe3d - Ce4f interactions, and thus has lower Tc. Temperature Dependence of the Electrical Resistivity of REFe2, Gratzet al. , Solid State Communication, Vol.69,No. 10 (2011)

  26. Competing Ferro-Antiferromagnetic interaction in CeFe2 Ferromagnetism in CeFe2 is unstable because of competition between Fe3d- Fe3d interaction (Ferromagnetic) and Fe3d - Ce4f interaction (Anti-ferromagnetic). Presence of such a delicate balance between Ferromagnetism and Anti-ferromagnetism in CeFe2 has been proved by two methods : Doping CeFe2 with Co or Al High Pressure Antiferromagnetic order in pure CeFe2 under pressure, Braithwaite et al, Phys Rev B 76 (2007)

  27. Previous Research(High Pressure) On applying pressure, distance between Ce and Fe decreases 3d - 4f interactions increases Anti-ferromagnetic becomes prominent Antiferromagnetic order in pure CeFe2 under pressure, Braithwaite et al, Phys Rev B 76 (2007)

  28. Motivation To know how this system behave under pressure when the 4f-3d hybridization is enhanced in CeFe2

  29. Experiment Setting Gasket 100 mm

  30. My Results Tc ( My Experiment ) Tc @ 0.25 GPa

  31. Summary • CeFe2 is a strongly hybridized in which Anti-ferromagnetic state is unstable. • Anti-ferromagnetic stability can be achieved by applying pressure or by doping pure CeFe2 with Co or Al

  32. Next Plan Apply higher pressure and study the effect of increased 3d-4f interactions in CeFe2

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