The attraction of m + to O 2- : using muons to study oxides

1. The attraction of m+ to O2-:using muons to study oxides Steve Blundell Clarendon Laboratory, Dept. Physics, University Of Oxford, UK

2. Why muons? • Susceptibility is a bulk measurement • measures “volume-averaged” magnetic • properties • Muon-spin rotation is a local measurement • measures magnetic properties at a • local level • …so what is a muon?

3. Particle properties

4. we=geBe wm=gmBm wp=gpBp

5. STEP 1:

6. STEP 2: implantation 4

8. STEP 3: decay 2.2 ms

10. Muon decay Muon decays into a positron: Positron decay is asymmetric with respect to the initial muon-spin polarization because of parity violation (weak interaction) (see S.J. Blundell, Contemp. Phys. 40, 175 (1999)) MUON POSITRONNEUTRINOS

12. Muon experiment MUON IMPLANTATION SPIN PRECESSION SPIN PRECESSION AND DECAY

13. Experimentsat ISIS pulsed muon facility Experiments here

14. Experiments at PSImuon facility Paul Scherrer Institute, Villigen, Switzerland

15. GPS spectrometer

16. In the presence of magnetic order, muons sense the internal magnetic field in a material, measured at the muon stopping site. The muon spin precession frequency, ωμ=2πνμ, is given by ωμ=γμBμ. This allows us to follow the temperature dependence of the magnetic order.

17. EuB6 A ferromagnet M.L. Brooks, T. Lancaster, S.J. Blundell and F.L. Pratt in preparation.

19. mSR and ordered organic ferromagnets and antiferromagnets Ferromagnet Antiferromagnet

20. mSR and ordered organic ferromagnets and antiferromagnets

21. Uniformly weakly magnetic Non-magnetic, with strongly magnetic impurities or Susceptibility gives average information and therefore can give the same response for the situations sketched above (hence many false claims of room temperature organic ferromagnetism…) mSR gives local information and therefore can distinguish between these two situations.

23. AFM order in LiVGe2O6 SJB et al.Phys Rev. B 67, 224411 (2003)

24. LiVGe2O6 2 clear frequencies persist below the so-called ordering temperature... SJB et al.Phys Rev. B 67, 224411 (2003)

25. LiVGe2O6 SJB et al.Phys Rev. B 67, 224411 (2003)

27. Dipole-dipole field

28. Dipole-dipole field

29. Dipole-dipole field Problem: 0

30. Dipolar fields Dipolar field calculations:

39. For cuprates, kill AFM with a few % of dopant and achieve maximum superconductivity at x~0.15. The normal state is a (weird) metal. For these nickelates, only metallic at x~1. No superconductivity. Evidence for 2D ordered array of holes below ~230 K. mSR used to find ground state for 0<x<1.

40. PRB 59 3775 (1999)

41. PRB 59 3775 (1999)

42. Sr2CuO3 Chains of -Cu-O-Cu-O-Cu-O-Cu- along x-axis superexchange through oxygen anions chains well separated and J’/J small J ~ 1300 K, TN=5 K

43. Muon data Sr2CuO3 Ca2CuO3 Kojima et al PRL 78 1787 1997

44. (ingenious chemistry by Rosseinsky, Hayward et al - Liverpool)

45. Muon data LaSrCoO3H0.7 Our data: Science 295 1882 2002 Oscillations imply static, large, local field corresponding to the whole of the sample

46. Muon data The internal magnetic field is very high (~0.5 T) which is much greater than in Sr2CuO3 (~0.01 T) TN is well above room T in our compound, much greater than ~5 K in Sr2CuO3 and ~10 K in Ca2CuO3

47. Conclusion: LaSrCoO3H0.7 contains the hydride ion H- (1s2) Hydride ions can transmitexchange interactions very effectively! This leads to the separated chains being bridged, raising the transition temperature of our compound to well above room temperature!

48. Sr2CuO3 Chains of -Cu-O-Cu-O-Cu-O-Cu- along x-axis superexchange through oxygen anions chains well separated and J’/J small