Eur. Phys. J. B 78, 359-365 (2010)
https://doi.org/10.1140/epjb/e2010-10683-9

Influence of the carbon substitution on the critical current density and AC losses in MgB₂ single crystals

¹ Polish Academy of Sciences, Institute of Low Temperature and Structure Research, ul. Okólna 2, 50-422 Wrocław, Poland
² Solid State Physics Laboratory, ETH, 8093 Zürich, Switzerland

Corresponding author: ^a M.Ciszek@int.pan.wroc.pl

Received: 7 September 2010
Revised: 19 October 2010
Published online: 29 November 2010

Abstract

The DC magnetization and AC complex magnetic susceptibilities were measured for MgB₂ single crystals, unsubstituted and carbon substituted with the composition of Mg(B_0.94C_0.05)₂. The measurements were performed in AC and DC magnetic fields oriented parallel to the c-axis of the crystals. From the DC magnetization loops and the AC susceptibility measurements, critical current densities (J_c were derived as a function of temperature and the DC and AC magnetic fields. Results show that the substitution with carbon decreases J_c) at low magnetic fields, opposite to the well known effect of an increase of J_c at higher fields. AC magnetic losses were derived from the AC susceptibility data as a function of amplitude and the DC bias magnetic field. The AC losses were determined for temperatures of 0.6 and 0.7 of the transition temperature T_c, so close to the boiling points of LH₂ and LNe, potential cooling media for magnesium diboride based composites. The results are analyzed and discussed in the context of the critical state model.