Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Role of MgO impurity on the superconducting properties of MgB2   We address the effect of MgO impurity on the superconducting properties of
MgB2. The synthesis of MgB2 is very crucial because of sensitivity of Mg to
oxidation which may lead to MgO as a secondary phase. Rietveld refinement was
performed to determine the quantitative volume fraction of MgO in the samples
synthesized by two different techniques. Both the samples were subjected to
magnetization measurements under dc and ac applied magnetic fields and the
observed results were compared as a function of temperature. Paramagnetic
Meissner effect has been observed in a sample of MgB2 having more amount of MgO
(with Tc = 37.1K) whereas the pure sample MgB2 having minor quantity of MgO
shows diamagnetic Meissner effect with Tc = 38.8K. M-H measurements at 10K
reveal a slight difference in irreversibility field which is due to MgO
impurity along with wide transition observed from ac magnetic susceptibility
measurements. The magnetotransport measurements R(T)H using RN = 90%, 50% and
10% criterion on pure sample of MgB2 has been used to determine the upper
critical field whereas the sample having large quantity of MgO does not allow
these measurements due to its high resistance.

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The categories of this paper are: physics
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The categories of this paper are: atom-ph
9
The categories of this paper are: nlin
11
The categories of this paper are: hep-lat
2
The categories of this paper are: math
27
The categories of this paper are: comp-gas
14
The categories of this paper are: math-ph
16
The categories of this paper are: stat
20
The categories of this paper are: acc-phys
35
The categories of this paper are: mtrl-th
22
The categories of this paper are: chao-dyn
31
The categories of this paper are: ao-sci
25
The categories of this paper are: patt-sol
37
The categories of this paper are: supr-con
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The categories of this paper are: q-fin
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The categories of this paper are: quant-ph