Low frequency 1f noise in doped manganite grain-boundary junctions.pdf
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Low frequency 1/ f noise in doped manganite grain-boundary junctions
J. B. Philipp, L. Alff, A. Marx,
?
and R. Gross
Walther-Meissner-Institut, Bayerische Akademie der Wissenschaften,
Walter-Meissner-Stra?e 8, D-85748 Garching, Germany
(Dated: February 1, 2008)
We have performed a systematic analysis of the low frequency 1/ f -noise in single grain boundary junctions
in the colossal magnetoresistance material La
2/3Ca1/3MnO3?δ . The grain boundary junctions were formed
in epitaxial La
2/3
Ca
1/3
MnO
3?δ
films deposited on SrTiO
3
bicrystal substrates and show a large tunneling
magnetoresistance of up to 300% at 4.2 K as well as ideal, rectangular shaped resistance versus applied magnetic
field curves. Below the Curie temperature T
C
the measured 1/ f noise is dominated by the grain boundary. The
dependence of the noise on bias current, temperature and applied magnetic field gives clear evidence that the
large amount of low frequency noise is caused by localized sites with fluctuating magnetic moments in a heavily
disordered grain boundary region. At 4.2 K additional temporally unstable Lorentzian components show up in
the noise spectra that are most likely caused by fluctuating clusters of interacting magnetic moments. Noise due
to fluctuating domains in the junction electrodes is found to play no significant role.
PACS numbers: 75.30.Vn, 73.50.Td, 72.70.+m
I. INTRODUCTION
Doped manganites have attained large interest in recent
years because of the interesting interplay of charge, spin, or-
bital and structural degrees of freedom in these materials
1
and
their potential use in magnetoresistive devices. It was found
early that the introduction of artificial grain boundaries (GB)
into epitaxial manganite thin films leads to localized struc-
tural distortions at the GB entailing significant modifications
of the magnetotransport properties of the GB
2,3,4,5,6,7,8,9
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