Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Crystalline C60 fulleride with metal inside   Endohedral metallofullerenes have been extensively studied, since the first
experimental observation of La@C60 in a laser-vaporized supersonic beam in
1985. However, all of these studies have been carried out on metallofullerenes
larger than C60 such as (metal)@C82, and there are no reported purified
C60-based metallofullerenes except for [Li@C60]+(SbCl6)- salt. Pure (metal)@C60
has not been obtained because of their extremely high chemical reactivity. We
report here the first isolation, structural determination and electromagnetic
properties of crystalline C60-based metallofullerenes, Gd@C60(CF3)5 and
La@C60(CF3)5. Synchrotron X-ray single-crystal diffraction reveals that La and
Gd atoms are indeed encapsulated in the Ih-C60 fullerene. The HOMO-LUMO gaps of
Gd@C60 and La@C60 are significantly widened by an order of magnitude with
addition of CF3- groups. Magnetic measurements show the presense of a weak
antiferromagnetic coupling in Gd@C60(CF3)3 crystals at low temperatures. Gd@C60
and La@C60 might exhibit superconductivity as the electronic structures
resemble those of superconducting alkali-doped C60 fullerides.

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The categories of this paper are: math
34
The categories of this paper are: chem-ph
33
The categories of this paper are: plasm-ph
11
The categories of this paper are: hep-lat
29
The categories of this paper are: funct-an
35
The categories of this paper are: mtrl-th
30
The categories of this paper are: q-alg
22
The categories of this paper are: chao-dyn
6
The categories of this paper are: astro-ph
9
The categories of this paper are: nlin
32
The categories of this paper are: atom-ph
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The categories of this paper are: cs
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The categories of this paper are: econ
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The categories of this paper are: gr-qc
36
The categories of this paper are: cmp-lg
23
The categories of this paper are: solv-int