Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The effect of Fe and Ru substitution for Ni on the thermopower in
  MgCNi_3   The intermetallic perovskite MgCNi3 is a superconductor with a Tc=7 K.
Substitution of Fe and Ru for Ni decreases Tc monotonically as the doping
concentration is increased. Here we report thermopower measurements, S(T), on
MgCNi3, MgCNi3-xFex and MgCNi3-xRux. For MgCNi3, the thermopower is negative, -
12.5 mikroV/K, at 300 K. The absolute value of S decreases as x increases in
MgCNi3-xFex and MgCNi3-xRux. The sign of S changes from negative to positive at
low temperatures for values of x > 0.01. These data show that the carriers in
MgCNi3 are electrons, and by increasing x and decreasing temperature, the
participation of hole carriers clearly increases. The influence of the magnetic
moments of the Fe atoms on the thermopower is not visible.

30
The categories of this paper are: q-alg
35
The categories of this paper are: mtrl-th
19
The categories of this paper are: eess
9
The categories of this paper are: nlin
22
The categories of this paper are: chao-dyn
7
The categories of this paper are: hep-th
31
The categories of this paper are: ao-sci
36
The categories of this paper are: cmp-lg
5
The categories of this paper are: gr-qc
34
The categories of this paper are: chem-ph
3
The categories of this paper are: physics
29
The categories of this paper are: funct-an
33
The categories of this paper are: plasm-ph
1
The categories of this paper are: cs
12
The categories of this paper are: nucl-th
6
The categories of this paper are: astro-ph