YFe 2 Al 10. unravelling the origin of quantum criticality

Transcription

1 YFe Al unravelling the origin of quantum criticality André Strydom Physics Department, University of Johannesburg

2 Acknowledgements Frank Steglich (MPI CPfS, Dresden) Michael Baenitz and co workers (MPI CPfS, Dresden) Meigan Aronson (BNL & Stony Brook Univ., USA) Devashibhai Adroja and Adrian Hillier (ISIS, UK) Pararajasingham Peratheepan (Eastern Univ., Sri Lanka)

3 Overview of properties of the :: series Data on YFe Al : a candidate for criticality of T= ferromagnetism?

4 Ferromagnetic quantum criticality: an enigmatic rarity Examples of itinerant ferromagnets tuned into quantum criticality by doping (UNi x Co x Si, Ca x Sr x RuO 3, CeRu x Fe x PO, ) or pressure (ZrZn, MnSi, UGe ) role of superconductivity? is the end point continuous or not? quantum critical fluctuations above T C = 3K in UCoGe but magnetic field always seems malevolent to ferromagnetic quantum criticality!

5 Ferromagnetic quantum criticality: an enigmatic rarity Case of NbFe : proximity to ferrimagnetism proposed mechanism of vanishing carrier velocity competing q= and q instabili es producing non Fermi liquid critical exponents and the key role of chemical doping Haynes et al., PRB 85 () 537 Neal et al., PRB 84 () 8533 Tompsett et al., PRB 8 () 5537 Alam and Johnson, PRL 7 () 64

6 Ferromagnetic quantum criticality: a rarity Tuning of a ferromagnet turns out to be more complex FM QCP reached through a tricritical point Belitz, Kirkpatrick, Rollbühler PRL 94 (5) 475 YFe Al : a candidate for accidental criticality of T= ferromagnetism?

7 RT Al : (R=Y, La, Ce, Yb, Lu; T=Fe, Ru, Os) [] CeRu Al : a collection of very unusual properties [] Al Orthorhombic Cmcm, unique sites for Ce, Ru Ce Ce Ce: 5. Å Ru. Thiede, Ebel, Jeitschko, J Mater Chem 8 (998). Strydom, Physica B 44 (9) 98

8 Two different anisotropic Kondo insulators CeRu Al T N = 7 K ; ord =.34 B ; k=(,,) [3] 8 mev spin gap [4] with strong c f hybridization; depletion of magnetic moment and low electrical conductivity along b axis easy magnetization along a axis yet ordered moment and high conductivity along c axis favours description in terms in terms of ac plane dimensionality CeFe Al Strong and highly anisotropic c f hybridization, pseudogap from NMR mev [5] or from neutrons 5meV [6] 3. Khalyavin et al, Phys Rev B 8 () Robert et al, Phys Rev B 8 () Chen & Lue, Phys Rev B 8 () Adroja et al., unpublished

9 CeRu Al A phase transition with a common thread in resistivity, specific heat, and susceptibility Strydom, Physica B 44 (9) 98

10 CeRu Al Characteristic Kondo Insulator (or Heavy Fermion semiconducting) susceptibility Nishioka et al., J. Phys. Soc. Japan 78 (9) 375

11 YFe Al Exploratory susceptibility [] and Mössbauer [7] reported absence of magnetic ordering above K Our studies exposed T and B dependencies in various properties below 5 K Sample quality : elemental purity > wt. % homogeneity and composition using WDX: Y : Fe : Al =.() :.() : 9.55(3) a=8.97 Å, b=.5 Å, c=9. Å powder XRD profile refinement Mössbauer to check for single species of Fe 7. Waerenborgh et al, J. Alloys Comp () 78

12 YFe Al Sample quality (continued) nearest neighbour Fe Fe : 4.48 Å Fe in octahedral site symmetry

13 YFe Al Sample quality (continued) : recent single crystal analysis [8] reported no significant deviation from ideal Fe and Al site compositions through refinement of site occupations Y environment Fe environment 8. Kerkau et al., Z. Kristallogr. NCS 7 () 89

14 YFe Al : physical properties: Thermal behaviour Susceptibility Curie Weiss at high T (> K), eff.4 B ac shows no frequency dependence ( Hz) Strydom & Peratheepan, PSS RRL 4 () 356

15 YFe Al : physical properties: Thermal behaviour Susceptibility Park et al., PRB 84 () 9445 Strydom & Peratheepan, PSS RRL 4 () 356

16 YFe Al : physical properties: Thermal behaviour Susceptibility (T ) T.8 (T ) T.8 Park et al., PRB 84 () 9445

17 YFe Al : physical properties: Thermal behaviour Susceptibility Key results of Park et al.: YFe Al can be tuned into a Fermi liquid using magnetic field, (T ) T.8 Susceptibility scaling exponents are not reconcilable with either mean field nor with disorder or impurity models Park et al., PRB 84 () 9445

18 YFe Al : physical properties: Thermal behaviour Magnetization Continuous curvature towards T= yet / is still finite at.5 K Strydom & Peratheepan, PSS RRL 4 () 356

19 YFe Al : physical properties: Thermal behaviour Magnetization T=.78 K Strydom et al., J. Phys. Soc. Japan 8 () SA43

20 YFe Al : physical properties: Thermal behaviour Magnetization 6 Al NMR : suppression of spin fluctuations commences from B T T=.78 K Strydom et al., J. Phys. Soc. Japan 8 () SA43

21 YFeAl physical properties: Magnetism Inelastic neutron scattering T=4K T = K mar7975.spe, symd(,,3), s=4, Ei=5 mev < Q <7, <Energy< mar7977.spe, symd(,,3), s=4, Ei=6 mev < Q <3.5, <Energy< Q (Å ) Adroja & Strydom (5 3 Oct, ISIS, UK) Energy (mev) Energy (mev) Ei = 6 mev 4 - Q (Å ) mar7976.spe, symd(,,3), s=4, Ei=6 mev < Q <3.5, <Energy<5 3 Q (Å ) Energy (mev) Energy (mev) 6 Ei = 5 mev mar7978.spe, symd(,,3), s=4, Ei=5 mev < Q <7, <Energy< Q (Å )

22 YFeAl physical properties: Magnetism Inelastic neutron scattering T=4K T = K mar7975.spe, symd(,,3), s=4, Ei=5 mev < Q <7, <Energy< mar7977.spe, symd(,,3), s=4, Ei=6 mev < Q <3.5, <Energy<5 Further experiments: lower T, E, Q Q (Å ) Adroja & Strydom (5 3 Oct, ISIS, UK) Energy (mev) Energy (mev) Ei = 6 mev 4 - Q (Å ) mar7976.spe, symd(,,3), s=4, Ei=6 mev < Q <3.5, <Energy<5 3 Q (Å ) Energy (mev) Energy (mev) 6 Ei = 5 mev mar7978.spe, symd(,,3), s=4, Ei=5 mev < Q <7, <Energy< Q (Å )

23 YFe Al physical properties: Magnetism 6 Al NMR:. Baenitz et al.,

24 YFe Al physical properties: Magnetism Muon spin resonance T =.5 K B L = 5 G G 5G G 5 G 5 G G Adroja, Hillier, Strydom, (7 8 Oct, ISIS, UK)

25 YFe Al physical properties: Magnetism Muon spin resonance absence of cooperative magnetic effects confirmed down to.5 K Complete absence of small field induced effects Are spin fluctuations at 5 mk still too short lived for the ISIS SR time window? Adroja, Hillier, Strydom, (7 8 Oct, ISIS, UK)

26 YFe Al : physical properties: Thermal Specific heat : low T Below K, C p (T )/T =.38() T.3()

27 YFe Al : physical properties: Thermal Specific heat : the role of Fe stoichiometry

28 YFe Al : physical properties: Thermal Specific heat : the role of Fe stoichiometry Far from stoichiometric Fe Fermi liquid

29 YFe Al : physical properties: Thermal Specific heat : the role of Fe stoichiometry Far from stoichiometric Fe Fermi liquid At stoichiometric Fe non Fermi liquid

30 YFe Al : physical properties: Thermal Specific heat : the role of Fe stoichiometry Far from stoichiometric Fe Fermi liquid At stoichiometric Fe non Fermi liquid Near stoichiometric Fe spin fluctuating C P (T )/T = + bt + [dt. ln(t/t sf )], T sf = 5() K

31 YFe Al : physical properties: Thermal Specific heat : the role of Fe stoichiometry Far from stoichiometric Fe Fermi liquid At stoichiometric Fe non Fermi liquid Near stoichiometric Fe spin fluctuating non Fermi liquid behaviour does not scale with Fe concentration

32 YFe Al : physical properties: Thermal Electrical resistivity T K K.cm, RRR 3 (polycrystal) 75.cm, RRR (single crystal) [Aronson et al.]

33 Conclusions YFe Al is a good metal, paramagnetic at room temperature No magnetic ordering found down to.5k Correlated phenomena develop below K in electronic specific heat, or below K in electrical resistivity Notions of itinerant FM quantum criticality: Specific heat : C p (T )/T T.33 (D clean FM ) Susceptibility : (T ) T 4/3 (3D clean FM ). Moriya & Takimoto, JPSJ 64 (995) 96, Lonzarich, The Electron (997) Cambridge. Hertz PRB 4 (976) 65, Millis PRB 48 (99) 783

34 Questions How to reconcile the dimensionality issue? Is there magnetic ordering below T = 5 mk? or is the observed nfl scaling merely a spectator segment en route to a very low T Fermi liquid? Current work (T) and (T) under pressure (T) at low temperatures

35 THANK YOU!!