Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Doping Dependence of the Second Magnetization Peak, Critical Current
  Density and Pinning Mechanism in BaFe$_{2-x}$Ni$_x$As$_2$ Pnictide
  Superconductors   A series of high quality BaFe$_{2-x}$Ni$_x$As$_2$ pnictide superconductors
were studied using magnetic relaxation and isothermal magnetic measurements in
order to study the second magnetization peak (SMP) and critical current
behaviour in Ni-doped 122 family. The temperature dependence of the magnetic
relaxation rate suggests a pinning crossover, whereas, it's magnetic field
dependence hints a vortex-lattice structural phase-transition. The activation
energy ($U$) estimated using the magnetic relaxation data was analyzed in
detail for slightly-underdoped, slightly-overdoped and an overdoped samples,
using Maley's method and collective creep theory. Our results confirm that the
SMP in these samples is due to the collective (elastic) to plastic creep
crossover as has been observed for the other members of 122-family. In
addition, we also investigated the doping dependence of the critical current
density ($J_c$) and the vortex-pinning behaviour in these compounds. The
observed $J_c$ is higher than the threshold limit (10$^5$ A/cm$^2$) considered
for the technological potential and even greater than 1 MA/cm$^2$ for slightly
underdoped Ni-content, x = 0.092 sample. The pinning characteristics were
analyzed in terms of the models developed by Dew-Hughes and Griessen $et$ $al$,
which suggest the dominant role of $\delta l$-type pinning.

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The categories of this paper are: patt-sol
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The categories of this paper are: chao-dyn
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The categories of this paper are: stat
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The categories of this paper are: bayes-an
13
The categories of this paper are: quant-ph
12
The categories of this paper are: nucl-th
35
The categories of this paper are: mtrl-th
7
The categories of this paper are: hep-th
2
The categories of this paper are: math
36
The categories of this paper are: cmp-lg
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The categories of this paper are: gr-qc
10
The categories of this paper are: q-bio
1
The categories of this paper are: cs
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The categories of this paper are: supr-con
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The categories of this paper are: alg-geom
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The categories of this paper are: funct-an