- Correlated oxides
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You might think that compounds of oxygen, like rust, are things to be
avoided if you want nice magnets, metals and superconductors. In fact,
the highest temperature superconductors are oxides, as are some of the
most interesting conduciting and magnetic materials. Moreover, in oxides the correlations between electrons play an important role.
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Recent research
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Electrons order themselves in the charge-ordered triangular antiferromagnet AgNiO2
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The triangular lattice of nickel ions that forms the antiferromagnet
AgNiO2 prevents this material from finding a unique ground state of
both spin and orbital angular momentum. We have used implanted muons
to show that this may cause AgNiO2 to adopt an exotic "charge ordered"
state, where electrons arrange themselves on the nickel ions in a
periodic pattern. Our results, which are of unprecedented resolution,
show a highly unusual dependence on temperature and suggest that this
new state of condensed matter still has much to reveal.
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- Anomalous temperature evolution of the internal magnetic field distribution in the charge-ordered triangular antiferromagnet AgNiO2
- T. Lancaster, S. J. Blundell, P. J. Baker, M. L. Brooks, W. Hayes, F. L. Pratt, R. Coldea, T. Soergel and M. Jansen,
Phys. Rev. Lett. 100, 017206 (2008)
Link
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The frustrating triangular antiferromagnet: YMnO3
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The triangular antiferromagnet YMnO3 is geometrically frustrated;
it is not possible to
satisfy all of the magnetic interactions to find the material's ground state.
In collaboration with researchers from the Paul Scherrer Institut,
Switzerland, we have used muons to show that the ground state
adopted by YMnO3 is completely magnetically ordered. This contrasts
with earlier suggestions that the material adopts the exotic "spin
liquid" state. Using a novel
combination of hydrostatic pressure and muon measurements we
have demonstrated that
applied pressure has the unusual role of simultaneously
increasing both the frustration within the layers and the interaction
between
them. This implies that the magnetically ordered ground state is only
achieved as a result of very finely balanced interactions in this system.
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- Magnetism in Geometrically Frustrated YMnO3 under Hydrostatic Pressure Studied with Muon Spin Relaxation
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T. Lancaster, S. J. Blundell, D. Andreica, M. Janoschek, B. Roessli, S. N. Gvasaliya, K. Conder, E. Pomjakushina, M. L. Brooks, P. J. Baker, D. Prabhakaran, W. Hayes and F. L. Pratt,
Phys. Rev. Lett. 98, 197203 (2007)
Link
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An unconventional weakly ferromagnetic metal
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We present experimental evidence for small-moment magnetism below the
ferromagnetic transition temperature (183 K) in the
quasi-one-dimensional metal BaIrO3. Further, we identify rearrangement
of the local magnetic moment distribution, which leaves the bulk
magnetization unchanged, at the Mott-like transition (26 K). These
results are only possible via muon techniques, since
neutron scattering studies are hindered by the large absorption of
neutrons by Ir. The low-temperature characteristics of this compound
are unconventional, and suggest that its magnetic
properties are driven by changes occurring at the Fermi surface due to
the formation of a charge-density wave state.
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- Unconventional magnetic properties of the weakly ferromagnetic metal
BaIrO3
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M. L. Brooks, S. J. Blundell, T. Lancaster, W. Hayes, F. L. Pratt, P. P. C. Frampton
and P. D. Battle,
Phys. Rev. B 71, R220411 (2005)
Link
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Hydrogen transmits magnetism
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A new magnetic oxide material has been prepared in which for the
first time
the dominant magnetic interaction is mediated by a negatively-charged
hydrogen atom, known as a hydride ion. Many types of magnetic oxides have
been prepared before which show important magnetic, conducting and even
superconducting properties, but the new material, LaSrCoO3H0.7, is the
first where oxide and hydride ions coexist. This discovery could be the
first step to a new class of magnetic materials, and opens up a new field
of chemistry.
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- The hydride anion in an extended transition metal oxide array --
LaSrCoO3H0.7
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M. A. Hayward, E. J. Cussen, J. B. Claridge, M. Bieringer,
M. J. Rosseinsky, C. J. Kiely, S. J. Blundell, I. M. Marshall and
F. L. Pratt,
Science 295, 1882 (2002)
Link
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Spin freezing in bilayer manganites
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Electron-doped bilayer manganites have been studied using
muon-spin rotation and
spin freezing has been detected over a wide range of the phase diagram.
This included a region in which magnetic Bragg peaks were invisible using
neutron scattering.
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- Spin freezing and magnetic inhomogeneities in bilayer
manganites
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A. I. Coldea, S. J. Blundell, C. A. Steer, I. M. Marshall, J. F. Mitchell
and F. L. Pratt,
Phys. Rev. Lett. 89, 277601 (2002)
Link
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