Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Effect of size reduction on the ferromagnetism of the manganite
  La1-xCaxMnO3 (x = 0.33)   In this paper we report an investigation on the ferromagnetic state and the
nature of ferromagnetic transition of nanoparticles of
$\mathrm{La_{0.67}Ca_{0.33}MnO_3}$ using magnetic measurements and neutron
diffraction. The investigation was made on nanoparticles with crystal size down
to $15$ nm. The neutron data show that even down to a size of $15$ nm the
nanoparticles show finite spontaneous magnetization ($M_S$) although the value
is much reduced compared to the bulk sample. We observed a non-monotonic
variation of the ferromagnetic to paramagnetic transition temperature $T_C$
with size $d$ and found that $T_C$ initially enhances on size reduction, but
for $d < 50$ nm it decreases again. The initial enhancement in $T_C$ was
related to an increase in the bandwidth that occured due to a compaction of the
Mn-O bond length and a straightening of the Mn-O-Mn bond angle, as determined
form the neutron data. The size reduction also changes the nature of the
ferromagnetic to paramagnetic transition from first order to second order with
critical exponents approaching mean field values. This was explained as arising
from a truncation of the coherence length by the finite sample size.

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The categories of this paper are: chem-ph
7
The categories of this paper are: hep-th
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The categories of this paper are: plasm-ph
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The categories of this paper are: stat
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The categories of this paper are: adap-org
15
The categories of this paper are: nucl-ex
18
The categories of this paper are: econ
9
The categories of this paper are: nlin
11
The categories of this paper are: hep-lat
3
The categories of this paper are: physics
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The categories of this paper are: dg-ga
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The categories of this paper are: q-alg
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The categories of this paper are: supr-con
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The categories of this paper are: cs
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The categories of this paper are: solv-int
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The categories of this paper are: math-ph