A Diamond is Forever. High Pressure Experiments using Designer Diamond Anvils. Damon Jackson

Transcription

1 A Diamond is Forever High Pressure Experiments using Designer Diamond Anvils Damon Jackson

2 Partial List of Collaborators LLNL Sam Weir Jason Jeffries Chantel Aracne Vince Malba Scott McCall UAB Yogesh Vohra Shane Catledge UCSD Brian Maple LSU Dave Young

3 Overview Description of Designer Diamonds Applications AC Magnetic Susceptibility description of technique example results Electrical Resistivity description of technique adaptation for PPMS example results

4 I V I I Ohmic heating (2000 C) I I I Electrical Resistivity AC Magnetic Susceptibility 60µm culet, 4µm line widths A Description of Designer Diamond Anvils

5 Diamond Anvil Cell: The tool for high pressure research typical sample size is ~75 µm in diameter, 50 µm thick Center-of-Earth type pressures (3.6 Mbar) are possible wonderful tool for optical measurements (x-ray, Raman)

6 Diamond Anvil Cell: The tool for high pressure research typical sample size is ~75 µm in diameter, 50 µm thick DAC capabilities are Center-of-Earth type pressures (3.6 But... Mbar) are possible limited for electrical transport, magnetic properties, etc. wonderful tool for optical measurements (x-ray, Raman)

7 Designer Diamond Anvils lithographically fabricated thin-film tungsten microprobes completely encased within epitaxial diamond µm 4-12 µm embedded leads provide electrical insulation so that metal gaskets can still be used diamond-encapsulated probes remain functional to multi-mbar pressures D.D. Jackson et al., Rev. Sci. Instrum., 74, 2467

8 Designer Diamond Anvil Fabrication Lithographic Fabrication of Microprobes laser pantography (electrical pads) and projection lithography (diamond flat) linewidths down to 1 µm Epitaxial Diamond Deposition Univ. of Alabama CVD process diamond film is typically µm thick Final Polishing and Completion microprobes are now completely encapsulated in diamond, except for the exposed ends. 300 µm

9 Lithography onto Diamond Anvils 3D Lithography required for fabrication onto the non-flat surfaces projection lithography for the diamond flat laser pantography for the contact pads Tungsten probes have a width of 5-10 µm and 0.5 µm thick Electrical Contact Pads

10 Designer Diamond Anvil Fabrication a single-crystal diamond anvil with embedded electrodes electrical contact pads rate of diamond nucleation and growth on clean metal films is low

11 Fabrication Concerns Tungsten Electrodes As a carbide former, W adheres well to diamond W has an extremely high melting point, 3410 C Low thermal coefficient of expansion, 4.5x10-6 C -1 (diamond 1 x 10-6 C -1, and most metals are double digit 10-6 C -1 ) Highly incompressible, BW=308 GPa, Bdia=442 GPa No pressure induced transition to at least 4 Mbar CVD Diamond Growth Polishing Designer Diamonds Numerous processing parameter must be precisely tuned Methane/hydrogen gas mixture (2% CH4/98% H2) Microwave power (1.1 kw magnetron at 2.45 GHZ) Substrate temperature (1200 C) Epitaxial growth rate (about 10 µm/hour) Crystallographic orientation of the diamond (100 direction) Rough diamond film must be optically polished to micron tolerances

12 AC Magnetic Susceptibility

13 Conventional Magnetic Susceptibility with a DAC T. Timofeev, et al., Fizika I Tekhnika Vysokikh Davlenii, 16, 15 (1984)

14 Conventional Magnetic Susceptibility with a DAC T. Timofeev, et al., Fizika I Tekhnika Vysokikh Davlenii, 16, 15 (1984) low sensitivity low signal to noise

15 Magnetic Susceptibility with Designer Diamond Anvils χ ac experiments are difficult because magnetic field decreases as 1/r 3 Using Designer Diamond Anvils, filling factor is drastically increased due to embedded microloops 10-turn pick-up coil coil lines are 5 µm wide and 0.35 µm thick mechanically robust high signal-to-noise sensitivity (10-2 emu/cm 3 )

16 High Sensitivity, High Signal-to-Noise Ratio Traditional coil, 2mm radius 0.5mm from Designer coil, 100 µm radius 20 µm from High filling factor results in 20x increase in signal Small radius results in 1/400 background flux 4 10 x increase in signal-to-noise ratio

17 Magnetic Susceptibility with Designer Diamonds microcoil BeCu DAC to Lock-In MP35N gasket excitation coil 50-turn excitation coil no need for a compensation coil MP35N gasket is used due to its: hardness (yield strength 20 kbar) low magnetization temperature independent resistivity (RRR=9) Be-Cu DAC

18 Piston-Cylinder DAC BeCu DAC made by Kyowa Seisakusho Straightforward alignment procedure DAC mini model About half the diameter

19 AC Magnetic Susceptibility Schematic Signal source is used to drive the excitation coil Lock-In is referenced to the signal source and measures voltage from microloop sensing coil Using a closed cycle He cryostat (15<T<300 K) Automated kinematic fiber optic system to measure pressure as a function of temperature

20 Pressure Measurements Ruby fluorescence vs P is well known, simple, and cheap Can use well-aligned microscope for individual chip Good at room temp. Can use fiberoptic system to measure ruby in-situ

21 Pressure Measurements Ruby fluorescence vs P is well known, simple, and cheap Can use well-aligned microscope for individual chip Good at room temp. Can use fiberoptic system to measure ruby in-situ

22 Example Results

23 Heavy Rare-Earth Magnetism Gd FM Tb Dy Ho Er AFM/FM helical-afm helical-afm sinusoidal-afm c-axis canted ferromagnetism c-axis ferromagnetic c-axis helical ferromagnetism basal-plane ferromagnetic helical-antiferromagnetic modulated sinusoidal antiferromagnetism type (4-3) modulated ferromagnetism modulated sinusoidal antiferromagnetism (no trans) Tm sinusoidal-afm Ambient Pressure T (K)

24 dhcp Phase Transition Gd Tb Dy Ho Er Tm Pressure (GPa)

25 Example of Results - Magnetization of Tb Peak in susceptibility GPa at FM transition Temperature (K) dt C / dp = -11 K/GPa T C (0 GPa) = 240 K Sm-Type hcp χ' (au) dhcp Sm-Type Temperature (K) GPa 2.7 GPa 4.9 GPa 8.3 GPa 300 dtc/dp = -11 K/GPa same rate as McWhan and Stevens, PRL 139, 682 (1965) 50 disappearance of FM Pressure (GPa) 8 10 phase at room temperature Sm- Type to double-hcp D.D. Jackson, et al., Phys. Rev. B, 71, (2005) structural transition

26 Example of Results - Magnetization of Dy Voltage (arb. units) Dysprosium Temperature (K) 0.6 GPa 1.6 GPa 2.7 GPa 4.6 GPa 7.2 GPa 8.3 GPa Peak in susceptibility at AFM transition dtn/dp = -6.7 K/GPa Inflection point at FM Sm-Type dhcp dtc/dp = -4.6 K/GPa disappearance of AFM phase near room temperature Sm-Type to double-hcp structural transition D.D. Jackson, et al., Phys. Rev. B, 71, (2005)

27 Magnetic Phase Diagram 300 Temperature (K) Gd (FM) Tb (FM) Dy (AFM) Ho (AFM) Er (AFM) ( AFM or FM) Tm (AFM) ( AFM or FM) For Gd-Ho, disappearance of magnetic phase is near Sm- Type to double-hcp transition (dt crit /dp)/(de Gennes) Const Pressure (GPa) 15 20

28 Universal Phase Diagram Normalize transition temps. to ambient pressure value Normalize pressure to point at which magnetism is suppressed All rare-earths are RKKY magnets T crit / T crit (P=0) Gd (FM) Tb (FM) Dy (AFM) Ho (AFM) Er (AFM) Tm (AFM) Universal behavior due to similar DOS P / P crit

29 AC Magnetic Susceptibility microcoil T crit / T crit (P=0) Gd (FM) Tb (FM) Dy (AFM) Ho (AFM) Er (AFM) Tm (AFM) P / P crit

30 Electrical Resistivity

31 Electrical Resistivity to Multi-Megabar Pressures Resistivity can be measured up to megabar pressures 1, 2, 6, 8 probe anvils Chosen for redundancy, symmetry, ultra-high pressure, etc.

32 Resistivity inside PPMS Adapted for use in the PPMS Temperature ranges: 2<T<330K Magnetic fields up to 16 T

33 Pressure vs Temperature Thermal expansion of DAC increases P Add delrin spacer above piston Pressure change 0.75 GPa

34 Pressure vs Temperature Thermal expansion of DAC increases P Add delrin spacer above piston Pressure change 0.75 GPa

35 Pressure vs Temperature Thermal expansion of DAC increases P Add delrin spacer above piston Pressure change 0.75 GPa

36 Example Results

37 Ferromagnetism in Ordered Au4V Au4V Crystal Structure Creveling, Luo, and Knapp annealed Au-20%V at 500 C for a week V atoms become crystallographically ordered Au4V alloy is FM at TC=43 K L. Creveling et al., Phys Rev. Lett., 18, 851 (1967)

38 Ferromagnetism in Ordered Au4V Magnetization of Au4V Creveling, Luo, and Knapp annealed Au-20%V at 500 C for a week V atoms become crystallographically ordered Au4V alloy is FM at TC=43 K L. Creveling et al., Phys Rev. Lett., 18, 851 (1967)

39 Electrical Resistivity of Au4V Resistivity vs Temperature In 1967, Maple et al. found a kink in R(T) at TC We analyzed the same batch of samples! Can use the kink to identify TC and track its pressure dependance M.B. Maple et al., Phys. Lett. A, 25, 121 (1967)

40 Au4V Resistivity Under Pressure Resistivity vs T, P Kink broadens as pressure increases TC increases with pressure Why not use magnetic susceptibility? Chin et al. (1968) found M sat (4.2K) quickly decreased with increasing strain M(T,P) signal too small

41 TC vs Pressure Phase Diagram Bridgeman (hydrostatic) and DAC (non-hydrostatic) results are consistent Magnetic Phase Diagram P 18 GPa, dtc/dp = 2.7 K/GPa Above 18 GPa, indication of TC became washed out not possible to accurately pinpoint TC No indication of magnetic ordering during downloading

42 CeCrSb3 - Itinerant FM Quasi-2D within b-c plane anisotropy also seen in transport properties FM Cr ordering TCr =115 K Also have magnetic anomalies at lower temperatures max (min) along Mb (Mc) at 48 K Metallic behavior for T<TCr Peak in d /dt at TCr and 18 K D. D. Jackson et al., PRB, V 76, p (2007)

43 CeCrSb3 - Itinerant FM Quasi-2D within b-c plane anisotropy also seen in transport properties FM Cr ordering TCr =115 K Also have magnetic anomalies at lower temperatures max (min) along Mb (Mc) at 48 K Metallic behavior for T<TCr Peak in d /dt at TCr and 18 K D. D. Jackson et al., PRB, V 76, p (2007)

44 CeCrSb3 - Itinerant FM Quasi-2D within b-c plane anisotropy also seen in transport properties FM Cr ordering TCr =115 K Also have magnetic anomalies at lower temperatures max (min) along Mb (Mc) at 48 K Metallic behavior for T<TCr Peak in d /dt at TCr and 18 K D. D. Jackson et al., PRB, V 76, p (2007)

45 Resistivity under pressure Measurements on a polycrystalline sample Max in peaks of d /dt locates TCr and TCe Pressure suppresses TCr Max found in TCe followed by decrease

46 CeCrSb3 - Magnetic Phase Diagram Pressure suppresses TCr Max found in TCe followed by decrease Disappearance of magnetic phase motivates search for superconductivity Data collected using PPMS

47 Superconductivity? 2K Superconductivity appears for 11 P 13.6 GPa at ~3K See drop in (T) Critical field 3 T

48 Superconductivity? 2K Superconductivity appears for 11 P 13.6 GPa at ~3K See drop in (T) Critical field 3 T

49 CeCrSb3 - An unconventional FM with hints of superconductivity Quasi-2D, anisotropic crystal structure Resistivity can detect transition temperatures Pressure suppresses TCr Max found in TCe followed by decrease Drop in (T) hints at SC

50 Electrical Resistivity

51 Summary Designer Diamond Anvil fabrication High pressure transport measurements such as AC susceptibility and electrical resistivity are powerful tools designer diamonds simplify these measurements DAC mini load in PPMS allows for investigations under extreme conditions:

52