Muon-spin-relaxation studies of magnetic order and dynamics of the n=2 Ruddlesden-Popper phases Sr2RMn2O7 (R = Pr, Nd, Sm, Eu, Gd, Tb, Dy, and Ho)

Bewley, R.I. and Blundell, S.J. and Lovett, B.W. and Jestädt, Th. and Pratt, F.L. and Chow, K.H. and Hayes, W. and Battle, P.D. and Green, M.A. and Millburn, J.E. and Rosseinsky, M.J. and Spring, L.E. and Vente, J.F. (1999) Muon-spin-relaxation studies of magnetic order and dynamics of the n=2 Ruddlesden-Popper phases Sr2RMn2O7 (R = Pr, Nd, Sm, Eu, Gd, Tb, Dy, and Ho). Physical Review B - Condensed Matter and Materials Physics, 60 (17). pp. 12286-12293. ISSN 01631829 (ISSN). (The full text of this publication is not currently available from this repository. You may be able to access a copy if URLs are provided)

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Abstract

Zero field muon spin relaxation (μSR) has been used to study the magnetic properties of n=2 Ruddlesden-Popper phases Sr2RMn2O7, where R = Pr, Nd, Sm, Eu, Gd, Tb, Dy, and Ho. The results show that the size of the lanthanide ion is crucial in determining the magnetic state and dynamics of the system. Because muons are implanted throughout the bulk of the sample, impurity phases contribute only according to their volume fraction. Hence in the case of biphasic samples the data are dominated by the majority phase. Although none of our samples has a ferromagnetic ground state, colossal magnetoresistance (CMR) is observed over a wide temperature range, 4 K<T<150 K, for both the Pr and Nd compounds. The μSR results show that the magnetic transition in both these samples is broad. Ordered, but fluctuating, regions form at �150 K, the reported onset of CMR, with the fluctuation rates gradually decreasing with temperature. Even at 5 K, fluctuations are still observed. The ferromagnetic double exchange between Mn ions becomes weaker as the size of the lanthanide ion decreases. Sr2SmMn2O7 shows weak clustering at a much reduced temperature of 30 K whereas Sr2EuMn2O7 shows spin-glass-like behavior. For all lanthanide ions smaller than Eu no long range magnetic ordering of the spins is observed and the observed relaxation rates follow an activated dependence. The technique allows us to extract the effective activation energy associated with the magnetic fluctuations of the lanthanide moments in samples with R = Sm, Eu, Gd, Tb, Dy, and Ho. CMR is only observed where μSR measurements show a broad magnetic transition associated with fluctuations. We therefore believe that these fluctuating ordered regions are responsible for the extended temperature regime in which CMR has been observed in these nonferromagnetic n=2 Ruddlesden-Popper phases. ©1999 The American Physical Society.

Item Type: Article
Additional information: Unmapped bibliographic data: LA - English [Field not mapped to EPrints] J2 - Phys. Rev. B Condens. Matter Mater. Phys. [Field not mapped to EPrints] AD - Clarendon Laboratory, University of Oxford, Parks Road, Oxford OX1 3PU, United Kingdom [Field not mapped to EPrints] AD - Inorganic Chemistry Laboratory, Department of Chemistry, University of Oxford, South Parks Road, Oxford OX1 3QR, United Kingdom [Field not mapped to EPrints] AD - ISIS, RAL, Chilton, Didcot OX11 0QX, United Kingdom [Field not mapped to EPrints] AD - RIKEN-RAL, Rutherford Appleton Laboratory, Chilton, Didcot OX11 0QX, United Kingdom [Field not mapped to EPrints] AD - Department of Physics, Lehigh University, 16 Memorial Drive East, Bethlehem, PA 18015, United States [Field not mapped to EPrints] DB - Scopus [Field not mapped to EPrints]
Subjects: Q Science > QC Physics > QC173.45 Condensed Matter
Q Science > QD Chemistry > QD478 Solid State Chemistry
Divisions: Faculties > Sciences > School of Physical Sciences > Functional Materials Group
Depositing User: Giles Tarver
Date Deposited: 21 Oct 2015 13:54 UTC
Last Modified: 21 Jan 2016 11:21 UTC
Resource URI: https://kar.kent.ac.uk/id/eprint/51148 (The current URI for this page, for reference purposes)
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