Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Ferromagnetic Instability in a Doped Band-Gap Semiconductor FeGa$_{3}$   We report the effects of electron doping on the ground state of a diamagnetic
semiconductor FeGa$_{3}$ with a band gap of 0.5 eV. By means of electrical
resistivity, magnetization and specific heat measurements we have found that
gradual substitution of Ge for Ga in FeGa$_{3-y}$Ge$_{y}$ yields metallic
conduction at a very small level of $y = 0.006$, then induces weak
ferromagnetic (FM) order at $y = 0.13$ with a spontaneous moment of 0.1
$\mu_{B}$/Fe and a Curie temperature $T_{C}= 3.3$ K, which continues increasing
to $T_{C} = 75$ K as doping reaches $y = 0.41$. The emergence of the FM state
is accompanied by quantum critical behavior as observed in the specific heat,
$C/T \propto -$ln$T$, and in the magnetic susceptibility, $M/B \propto
T^{-4/3}$. At $y= 0.09$, the specific heat divided by temperature $C/T$ reaches
a large value of 70 mJ/K$^{2}$molFe, twice as large as that reported on
FeSi$_{1-x}$Ge$_{x}$ for $x_{c}= 0.37$ and Fe$_{1-x}$Co$_{x}$Sb$_{2}$ for
$x_{c}=0.3$ at their respective FM quantum critical points. The critical
concentration $y_{c}=0.13$ in FeGa$_{3-y}$Ge$_{y}$ is quite small, despite the
fact that its band gap is one order of magnitude larger than those in FeSi and
FeSb$_{2}$. In contrast, no FM state emerges by substituting Co for Fe in
Fe$_{1-x}$Co$_{x}$Ga$_{3}$ in the whole range $0 \leq x \leq 1$, although both
types of substitution should dope electrons into FeGa$_{3}$. The FM instability
found in FeGa$_{3-y}$Ge$_{y}$ indicates that strong electron correlations are
induced by the disturbance of the Fe 3d - Ga 4p hybridization.

31
The categories of this paper are: ao-sci
36
The categories of this paper are: cmp-lg
12
The categories of this paper are: nucl-th
21
The categories of this paper are: adap-org
9
The categories of this paper are: nlin
32
The categories of this paper are: atom-ph
17
The categories of this paper are: q-fin
1
The categories of this paper are: cs
33
The categories of this paper are: plasm-ph
22
The categories of this paper are: chao-dyn
37
The categories of this paper are: supr-con
8
The categories of this paper are: hep-ex
16
The categories of this paper are: stat
3
The categories of this paper are: physics
6
The categories of this paper are: astro-ph
10
The categories of this paper are: q-bio