Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Large irreversibility field in nanoscale C-doped MgB2/Fe tape conductors   We investigated the effect of nanoscale-C doping on the critical current
density Jc and irreversibility field Birr of Fe-sheathed MgB2 tapes prepared by
the in-situ powder-in-tube method. The tapes were heat treated at 600-950C for
1 h. Higher values of Jc and Birr were seen for 5 at.%C-doped MgB2 tapes at
higher sintering temperatures, where substantial substitution of boron for
carbon occurred. The C-doped samples sintered at 950C showed the highest Birr,
for example, at 4.2 K, the Birr reached 22.9 T. In particular, at 20 K, Birr
for the C-doped tape achieved 9 T, which is comparable to the upper critical
field of the commercial NbTi at 4.2 K. This role of nano-sized C particles can
be very beneficial in the fabrication of MgB2 tapes for magnetic resonance
imaging applications at 20 K.

13
The categories of this paper are: quant-ph
6
The categories of this paper are: astro-ph
31
The categories of this paper are: ao-sci
21
The categories of this paper are: adap-org
5
The categories of this paper are: gr-qc
32
The categories of this paper are: atom-ph
11
The categories of this paper are: hep-lat
15
The categories of this paper are: nucl-ex
30
The categories of this paper are: q-alg
25
The categories of this paper are: patt-sol
37
The categories of this paper are: supr-con
18
The categories of this paper are: econ
9
The categories of this paper are: nlin
10
The categories of this paper are: q-bio
0
The categories of this paper are: hep-ph
35
The categories of this paper are: mtrl-th