Single crystal growth and basic characterization of intermetallic compounds. Eundeok Mun Department of Physics Simon Fraser University

Transcription

1 Single crystal growth and basic characterization of intermetallic compounds Eundeok Mun Department of Physics Simon Fraser University CIFAR Summer School 2015

2 Beautiful single crystals! Then What? We know how to make a noodle soup. Enjoy! Is it delicious? Is it interest? Magnetic, electronic, mechanical, thermal property, and so on If so, continue to make it, share the recipe with friends, and discuss how good it is. Collaborations - open to community and try to understand the nature of the material. If not, make another one!

3 Characterizations Quantum mechanics, electrodynamics, statistical mechanics, and solid state physics Structural! Electronic! I V R = V/I Magnetic! Thermal! Q/ T Thermodynamic and transport measurements bulk

4 Determination of crystal structure Identify crystal structure: powder and single crystal x-ray Determine crystallographic orientations: Laue back reflection 3-fold Analyze elemental compositions: EDX, WDS, EPMA, etc Ba Fe 1-x Co x As 2 : nominal and actual x Note: site-deficiency is a nature of some materials 4-fold Synchrotron and elastic neutron Micro and surface structure: SEM, TEM, etc

5 Electronic properties - resistivity Let s categorize materials like metal, semiconductor, superconductor, and insulator Metal Superconductor Semiconductor Lakeshore.com phase transition anisotropy thermometer We can get a lot of information from the temperature dependence of resistivity.

6 Electronic properties - resistivity Resistivity / Resistance In a simple way Ohm s law I = (1/R) V Electrical contact: silver/gold paste, soldering l A w J = E V t 1 ne2 m I A l R Categorize materials from (T) n: carrier density m: effective mass : relaxation time For simple metal Temperature dependence Residual resistivity Residual resistivity ratio Spin disorder scattering Fermi surface

7 Electronic properties Hall, TEP Carrier density - electron and hole N S H V T low Heat flow T high I electron hole Resistivity- even (H) = xx (H) ~ H 2 Hall resistivity- odd H (H) = xy ~ H Thermoelectric power (thermocouple) S = - V / T (V/K) S is positive when the direction of electric current is the same as the direction of thermal current. Order of ~ V/K Hall coefficient R H = xy / H carrier type (electron, hole) Hall coefficient and Thermoelectric power

8 Electronic properties - resistivity Let s categorize materials like metal, semiconductor, superconductor, and insulator Resistivity (ohm cm) semiconductor insulator Metal: Cu, Ag, Au Semiconductor: Si, Ge, InSb Superconductor: Pb, Sn, In Insulator: wood, plastic, glass This is a simple picture. superconductor metal Temperature (K) In materials - Antiferromagnetic Ferromagnetic Superconductor Metal-to-Insulator CDW SDW Meta-magnetic Topologically non-trivial Nematic phase There are more

9 Residual resistivity and RRR Resistivity (ohm cm) 0 ~T ~T 2 ~T 5 grain boundary, imperfection, dislocation, impurity Temperature (K) Metal at low temperatures e-e scattering - Fermi liquid = 0 + AT 2 Residual resistivity 0 Residual resistivity ratio RRR R(300K) / R(2K) geometric factors cancel out NOTE: the measured electrical resistivity will contain an impurity scattering term, 0 which appears additively. This is often associated with chemical impurities as well as a variety of structural defects.

10 Magnetic materials: spin disorder scattering J. MMM 205 (1999) Resistivity T M sd spin disorder scattering 0 grain boundary, imperfection, dislocation, impurity AFM order T N = 10.9 K sd 0 Temperature (K)

11 Residual resistivity and RRR Extremely pure & fully ordered 0 ~ 0.04 cm RRR ~ grain boundary, imperfection, dislocation, impurity Highly disordered : Ni site-deficiency LuNi 0.81 Ge 3 0 ~ 1 cm RRR ~ 17 0 ~ 22 cm RRR ~ 3 J. MMM 205 (1999) In general, high RRR means low 0.

12 Residual resistivity and RRR If the grown material is fully ordered, expected low 0, high RRR, and Quantum oscillations dhva Very large MR at low temperatures Quantum oscillations SdH MR: % at 2 K Simple metal (semimetal) MR ~ H 2 Kohler rule (0) F H (0) n MR ~ H 1.8

13 Quantum oscillations Fermi surface of Cu dhva-oscillations in magnetization Landau gauge: H H k^ A Hyi^ Landau level Harmonic oscillator Oscillation frequency: related to area of extremal orbit, periodic in 1/H, p=1/f~1/a Oscillation amplitude: increases as magnetic field increases decreases as temperature increases L-K formula: effective (band, renormalize) mass Dingle temperature, g-factor, and so on

14 Fermi surface of high T c cuprates Quantum oscillations SdH Nature 511, 61 (2014), samples come from UBC Fourier Transform Angle dependence mapping Fermi surface Multi-band system: PtSn 4 Complex and Difficult + + ARPES

15 CDW, SDW, magnetic superzone gap Resistivity is very sensitive to changes in the Fermi Surface: K. Myers, et al., JMMM 205, 27 (1999) E. Fawcett, Spin-density-wave antiferromagnetism in chromium, RMP 60, 209 (1988) A. Arrott, Antiferromagnetism in Metals Vol. IIB, p.295 R. Elliot, Magnetic properties of rare earth metals (1972) M. Maple, et al., PRL 56, 185 (1986) CDW (and SDW) transitions, where nested parts of the Fermi surface become gapped below T CDW. This leads to an decrease in conductivity due to a decrease S F. For a partial gapping of the F.S. the sample remains metallic and ultimately returns to (T) with positive slope.

16 Magnetism valence electron I nuclear conduction electron Magnetic susceptibility & Magnetization Atom or molecule: Na, NO,? Free atoms and ions with a partially filled shell? Exchange interactions? Larmor diamagnetism (Langevin result) Pauli paramagnetism of conduction electrons Landau diamagnetism of free electrons Curie/Langevin paramagnetism (~ 1/T) Magnetic ordering: antiferromagnetic/ferromagnetic NMR, Neutron scattering, ESR, etc.

17 Hund Rules Kittel Introduction to solid state physics The Hund rules as applied to electrons in a given shell of an atom affirm that electrons will occupy orbitals in such a way that the ground state is characterized by the following: 1. The maximum value of the total spin S allowed by the exclusion principle 2. The maximum value of the orbital angular momentum L consistent with this value of S 3. The value of the total angular momentum J is equal to L-S when the shell is less than half full and to L+S when the shell is more than half full. When the shell is just half full, the application of the first rule gives L = 0, so that J = S 2S 1 L J Fe 2+ 3d 6 L z = L = = 2 S = 1/2 * 4 = 2 J = L + S = 4 5 D 4

18 Hund Rules The Hund rules as applied to electrons in a given shell of an atom affirm that electrons will occupy orbitals in such a way that the ground state is characterized by the following: 1. The maximum value of the total spin S allowed by the exclusion principle 2. The maximum value of the orbital angular momentum L consistent with this value of S 3. The value of the total angular momentum J is equal to L-S when the shell is less than half full and to L+S when the shell is more than half full. When the shell is just half full, the application of the first rule gives L = 0, so that J = S Ce 3+ 4f 1 Gd 3+ 4f L = 3 S = 1/2 J = L - S = 5/2 2 F 5/ L = 0 S = 7/2 J = S = 7/2 8 S 7/2

19 Hund Rules The Hund rules as applied to electrons in a given shell of an atom affirm that electrons will occupy orbitals in such a way that the ground state is characterized by the following: 1. The maximum value of the total spin S allowed by the exclusion principle 2. The maximum value of the orbital angular momentum L consistent with this value of S 3. The value of the total angular momentum J is equal to L-S when the shell is less than half full and to L+S when the shell is more than half full. When the shell is just half full, the application of the first rule gives L = 0, so that J = S Exercise Dy 3+ 4f L = S = J = 2S 1 L J

20 Hund Rules The Hund rules as applied to electrons in a given shell of an atom affirm that electrons will occupy orbitals in such a way that the ground state is characterized by the following: 1. The maximum value of the total spin S allowed by the exclusion principle 2. The maximum value of the orbital angular momentum L consistent with this value of S 3. The value of the total angular momentum J is equal to L-S when the shell is less than half full and to L+S when the shell is more than half full. When the shell is just half full, the application of the first rule gives L = 0, so that J = S Exercise Dy 3+ 4f L = 5 S = 5/2 J = L+S = 15/2 6 H 15/2

21 3d and 4f electron basic level d-electrons Experiments close to S f-electrons Experiments close to J Kittel Introduction to solid state physics

22 Itinerant and localized Crystalline Electric Field (CEF) spin-orbit coupling Magnetic properties of rare earth metals R. J. Elliot 3d-electrons (CEF) > (L-S) 4f-electrons (CEF) < (L-S) Note for d-electrons most of the case considering t 2g and e g energy level splitting due to the octahedron environment. But, in general we have to consider actual local point symmetry.

23 4f-electron magnetism By controlling S, L, J as well as point symmetry (CEF) we can get a wide variety of magnetic properties: eff, sat and anisotropy.

24 Effective moment and saturated magnetization Magnetic susceptibility dm dh In the low field region, the magnetization of a paramagnetic system is linear in H. For such low field, (T) M (T ) H Effective moment p = g[j(j+1)] 2 (T ) M(T ) H Np2 2 B 3k B T C T Magnetic moment vs field Brillouin function - paramagnet Kittel Introduction to solid state physics

25 Effective moment and saturated magnetization Magnetic susceptibility Fit with Curie-Weiss Law : the temperature dependence of the magnetic susceptibility in the paramagnetic state is given by (T) C T P 0 J. MMM 205 (1999) Plot inverse magnetic susceptibility C Np2 B 2 3k B Determine p from the slop and compare to the free ion value Gd 3+ free ion value p = 7.94 from the slop 7.9 B /Gd 3+

26 Effective moment and saturated magnetization Magnetic susceptibility Fit with Curie-Weiss Law : the temperature dependence of the magnetic susceptibility in the paramagnetic state is given by (T) C T P 0 J. MMM 205 (1999) : basically temperature independent term that is the sum of core diamagnetism, Pauli paramagnetism, and Landau diamagnetism negative 1/ Weiss temperature p Temperature

27 Effective moment and saturated magnetization Magnetization isotherms - spin state of magnetic ions Multiferroicity with coexisting isotropic and anisotropic spins in Ca3Co 2 x Mn x O 6 PRB 89, (R) (2014) Mn 4+ : 3d 3 S = 3/2 Co 2+ : 3d 7 S = 3/2 or 1/2? No evidence of low-spin to high-spin transition Neutron seeing ordered moment should be complementary

28 Anisotropy in magnetic susceptibility The anisotropy can be clearly seen in 1/ CEF anisotropy NO CEF anisotropy Gd 3+ or Eu 2+ (s-state, L = 0) For rare-earth with finite L, there will be CEF splitting that can give rise to significant anisotropy, depending on local point symmetry. J. MMM 205 (1999) Exchange interaction - anisotropy

29 Magnetism Exchange interaction J Magnetic ordering and quasi-particle Direct Indirect RKKY Kondo

30 Specific heat Electron and phonon contribution Specific heat of a metal at low temperatures c T T 3 : n(e F ) density of state : Debye temperature Specific heat of Cu matter ad methods at low temperature ~0.7 mj/mol K 2 Plot C/T vs T 2 extract and Specific heat of CeAl 3 PRL 35, 1779 (1975) Heavy fermion - large! - large effective mass m* times bigger than Cu ~1620 mj/mol K 2 Note: estimate value - carefully consider all possible contributions in specific heat, especially magnetic and Schottky contributions

31 Specific heat Electron and phonon contribution Heavy fermion superconductor Specific heat of CeCu 2 Si 2 PRL 43, 1892 (1979) Specific heat jump at the T c - related to the The C p jump - not related to any other contributions like electronic schottky, nuclear, magnetic fluctuations, and all strange stuffs

32 Heavy fermion Kondo effect Phys. Rev. Lett. 94, (2005) The electronic specific heat - measure of the electron effective mass Relationship among thermodynamic and transport Specific heat Resistivity Susceptibility Thermal conductivity Thermoelectric power Thermal expansion Fermi liquid: KW, Wilson number, and more Please make summary note just for yourself Anything deviates from conventional behavior?

33 Entropy Specific heat is intimately related to entropy S C m T dt Tell us how much entropy is associated with a given state. For magnetic systems we need to use the magnetic specific heat. Remove phonon contributions: often do this by subtracting a non-magnetic analogue. C m = C p (R) C p (Y, La, Lu) Gd-compound, no CEF J(=S, L=0) = 7/2 Entropy associated with magnetic ordering Rln(8)

34 Energy level splitting CEF effect Schottky anomaly Consider a two-level system C U T k B ( / T) 2 e /T (1 e /T ) 2 ~1/T 2 Nuclear: 1 ~ 100 mk splitting, often observed below 1K Estimate effective mass Subtracting nuclear contribution by simply use ~ 1/T 2

35 Energy level splitting CEF effect Schottky anomaly Given the Hund s rule, groundstate multiplet J we would expect R ln(2j + 1) entropy associated with the magnetic state. For rare earths the spin-orbit coupling give rise to crystalline electric field (CEF) splitting. quartet Ce (J = 5/2) in cubic symmetry 2J +1 = 6 doublet PrAgSb 2 : no magnetic ordering at low temperatures can be considered as a two level system C U T k B g 1 g 2 ( / T ) 2 e /T 1 g 1 e /T g 2 2 Specific heat at low temperatures and neutron at high temperatures

36 Phase transitions We have now seen how (T), C p (T), and (T) can be used to determine magnetic ordering temperatures (as well as many other useful parameters). C m M.E. Fisher, Philos. Mag. 7 (1962) M.E. Fisher, J.S. Langer, Phys. Rev. Lett. 7 (1968) 665. M.P. Kawatra, et al., Phys. Rev. Lett. 23 (1969) 83. D.J.W. Geldart, T.G. Richard, Phys. Rev. B 12 (1975) 5175.

37 Phase transitions We have now seen how (T), C p (T), and (T) can be used to determine magnetic ordering temperatures (as well as many other useful parameters). M.E. Fisher, Philos. Mag. 7 (1962) M.E. Fisher, J.S. Langer, Phys. Rev. Lett. 7 (1968) 665. M.P. Kawatra, et al., Phys. Rev. Lett. 23 (1969) 83. D.J.W. Geldart, T.G. Richard, Phys. Rev. B 12 (1975) 5175.

38 Phase transitions Bulk transition Specific heat: good measure of bulk phase transition - superconductors Poster: QMSS-18 Hyunsoo Kim (University of Maryland) H. Kim, et al., Philosophical Magazine, 2015 Crystal growth and annealing study of fragile, non-bulk superconductivity in YFe 2 Ge 2 Jump in the specific heat!!!!

39 Guess from periodic table-tuning systems Density of state Exchange interaction

40 Thank you! Questions