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The attraction of + to O2-:using muons to study
oxides
Steve Blundell
Clarendon Laboratory, Dept. Physics, University Of Oxford, UK
Why muons?
Susceptibility is a bulk measurementmeasures “volume-averaged” magneticproperties
Muon-spin rotation is a local measurementmeasures magnetic properties at alocal level
…so what is a muon?
Particle properties
e=eBe
p=pBp
=B
STEP 1:
STEP 2:
implantation 4
STEP 3: decay
2.2 s
Muon decay
Muon decays into a positron:
Positron decay is asymmetricwith respect to the initialmuon-spin polarizationbecause of parity violation (weak interaction)
(see S.J. Blundell, Contemp. Phys. 40, 175 (1999))
MUON POSITRON NEUTRINOS
Muon experimentSPIN PRECESSION
MUON IMPLANTATION
SPIN PRECESSION AND DECAY
Experiments
at ISIS pulsed muon facility
Experiments here
Experiments at PSImuon facility
Paul Scherrer Institute, Villigen, Switzerland
GPS spectrometer
In the presence of magnetic order, muonssense 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 dependenceof the magnetic order.
EuB6
A ferromagnet
M.L. Brooks, T. Lancaster,S.J. Blundell and F.L. Prattin preparation.
SR and ordered organic ferromagnets and antiferromagnets
Ferromagnet
Antiferromagnet
SR and ordered organic ferromagnets and antiferromagnets
or
Uniformly weakly magnetic Non-magnetic, with strongly magnetic impurities
Susceptibility gives average information and thereforecan give the same response for the situations sketchedabove (hence many false claims of room temperature organic ferromagnetism…)
SR gives local information and therefore can distinguishbetween these two situations.
AFM order in LiVGe2O6
SJB et al. Phys Rev. B 67, 224411 (2003)
LiVGe2O6
SJB et al. Phys Rev. B 67, 224411 (2003)
2 clear frequenciespersist below theso-calledorderingtemperature...
LiVGe2O6
SJB et al. Phys Rev. B 67, 224411 (2003)
Dipole-dipole field
Dipole-dipole field
Dipole-dipole field
Problem:
0
Dipolar fields
Dipolar fieldcalculations:
For cuprates, kill AFM with afew % of dopant and achievemaximum superconductivityat x~0.15. The normal stateis a (weird) metal.
For these nickelates, onlymetallic at x~1. No superconductivity. Evidence for 2D orderedarray of holes below ~230 K.
SR used to find groundstate for 0<x<1.
PRB 59 3775 (1999)
PRB 59 3775 (1999)
Sr2CuO3
Chains of-Cu-O-Cu-O-Cu-O-Cu-along x-axis
superexchange throughoxygen anions
chains well separatedand J’/J small
J ~ 1300 K, TN=5 K
Muon data
Sr2CuO3
Ca2CuO3
Kojima et alPRL 78 1787 1997
(ingenious chemistry by Rosseinsky, Hayward et al - Liverpool)
Muon data
LaSrCoO3H0.7
Our data:Science 295 1882 2002
Oscillations imply static, large, local field corresponding to the whole of the sample
Muon data
The internal magneticfield is very high (~0.5 T)which is much greaterthan in Sr2CuO3 (~0.01 T)
TN is well above room Tin our compound,much greater than ~5 Kin Sr2CuO3 and ~10 Kin Ca2CuO3
Conclusion:
LaSrCoO3H0.7 contains the hydride ion
H- (1s2)
Hydride ions can transmit exchange interactionsvery effectively! This leads to the separated chainsbeing bridged, raising the transition temperatureof our compound to well above room temperature!
Sr2CuO3
Chains of-Cu-O-Cu-O-Cu-O-Cu-along x-axis
superexchange throughoxygen anions
chains well separatedand J’/J small
C.D. Ling et al PRB 62, 15096 (2000)
La2-2xSr1+2xMn2O7
C.D. Ling et al PRB 62, 15096 (2000)
La2-2xSr1+2xMn2O7
La2-2xSr1+2xMn2O7
C.D. Ling et al PRB 62, 15096 (2000)
Bilayer manganates
A. Coldea et al. PRL 89 277601 (2002)
Relaxation functionsOne caninterpolatebetweenstaticsand dynamicsusing adynamicalKubo-Toyabefunction
Muons and spin glasses
Muons that stop closerto magnetic ions“see” a wider local fielddistribution (whichextends to higherfields) than muonswhich stop at a greaterdistance
Y.J. Uemura et al,PRB 31, 546 (1985)
La1.5Sr0.5MnRhO6
ferromagnetic insulatorwith large MR, evidencefor magnetic polaronsabove Tc.
A. Coldea, I.M. Marshall, S.J. Blundell, J. Singleton, L.D. Noailles, P.D. Battleand M.J. Rosseinsky,
PRB 62, R6077 (2000)
ZnCr2O4
Gd3Ga5O12
JPCM 14 L157 (2002)
ZnCr2O4
JPCM 14 L157 (2002)
Gd3Ga5O12
JPCM 14 L157 (2002)
Kajimoto et al, PRB 67, 014511 (2003)
P.G. Freeman et al, PRB 66, 212405 (2002)
La1.5Sr0.5NiO4
La1.5Sr0.5NiO4
ChrisSteer et al.
The attraction of + to O2-:using muons to study
oxides
Thanks to members of the Oxford muon group, ICL Oxford, Chemistry in Liverpool, ISIS + many
othersand to you for your attention!