abstract
The charge ordered La1/3Sr2/3FeO3-delta (LSFO) in bulk and nanocrystalline forms are investigated using ac and dc magnetization, Mossbauer, and polarized neutron studies. A complex scenario of short-range charge and magnetic ordering is realized from the polarized neutron studies in nanocrystalline specimen. This short-range ordering does not involve any change in spin state and modification in the charge disproportion between Fe3+ and Fe5+ compared to bulk counterpart as evident in the Mossbauer results. The refinement of magnetic diffraction peaks provides magnetic moments of Fe3+ and Fe5+ are about 3.15 mu(B) and 1.57 mu(B) for bulk, and 2.7 mu(B) and 0.53 mu(B) for nanocrystalline specimen, respectively. The destabilization of charge ordering leads to magnetic phase separation, giving rise to the robust exchange bias (EB) effect. Strikingly, EB field at 5 K attains a value as high as 4.4 kOe for average size similar to 70 nm, which is zero for the bulk counterpart. A strong frequency dependence of ac susceptibility reveals cluster-glass-like transition around similar to 65 K, below which EB appears. Overall results propose that finite-size effect directs the complex glassy magnetic behavior driven by unconventional short-range charge and magnetic ordering, and magnetic phase separation appears in nanocrystalline LSFO.
keywords
EXCHANGE BIAS; IRON-OXIDES; NANOPARTICLES; DISPROPORTIONATION; TEMPERATURE; SCATTERING
subject category
Physics
authors
Sabyasachi, S; Patra, M; Majumdar, S; Giri, S; Das, S; Amaral, VS; Iglesias, O; Borghols, W; Chatterji, T
our authors
Vitor Brás Sequeira Amaral
Full professoracknowledgements
S.G. acknowledges Council of Scientific & Industrial Research (CSIR), India (Project No. 03(1167)/10/EMR-II), for financial support and DST Nanoscience unit of IACS, Kolkata for TEM and MPMS facilities. S.S. also thanks CSIR, India, for the Junior Research Fellowship. S.D. acknowledges Foundation of Science and Technology of Portugal for the postdoctoral grant. O.I. acknowledges funding of the Spanish MICINN through Grant No. MAT2009-08667 and Integrated Spanish-Portuguese Action under Grant No. AIB2010PT- 00099, European Union FEDER funds (