Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Suppression of spin-density-wave transition and emergence of
  ferromagnetic ordering of Eu$^{2+}$ moments in EuFe$_{2-x}$Ni$_{x}$As$_{2}$   We present a systematic study on the physical properties of
EuFe$_{2-x}$Ni$_{x}$As$_{2}$ (0$\leq$\emph{x}$\leq$0.2) by electrical
resistivity, magnetic susceptibility and thermopower measurements. The undoped
compound EuFe$_{2}$As$_{2}$ undergoes a spin-density-wave (SDW) transition
associated with Fe moments at 195 K, followed by antiferromagnetic (AFM)
ordering of Eu$^{2+}$ moments at 20 K. Ni doping at the Fe site simultaneously
suppresses the SDW transition and AFM ordering of Eu$^{2+}$ moments. For
$x\geq$0.06, the magnetic ordering of Eu$^{2+}$ moments evolves from
antiferromagnetic to ferromagnetic (FM). The SDW transition is completely
suppressed for $x\geq$0.16, however, no superconducting transition was observed
down to 2 K. The possible origins of the AFM-to-FM transition and the absence
of superconductivity in EuFe$_{2-x}$Ni$_{x}$As$_{2}$ system are discussed.

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The categories of this paper are: patt-sol
12
The categories of this paper are: nucl-th
26
The categories of this paper are: bayes-an
19
The categories of this paper are: eess
9
The categories of this paper are: nlin
0
The categories of this paper are: hep-ph
30
The categories of this paper are: q-alg
37
The categories of this paper are: supr-con
7
The categories of this paper are: hep-th
1
The categories of this paper are: cs
6
The categories of this paper are: astro-ph
10
The categories of this paper are: q-bio
17
The categories of this paper are: q-fin
18
The categories of this paper are: econ
21
The categories of this paper are: adap-org
34
The categories of this paper are: chem-ph