Effect of pressure on the electric transport properties of carbon-doped

Abstract

We report about influence of external pressure on electrical resistivity of EuB 5.99 C 0.01 , the compound believed to be intrinsically inhomogeneous due to fluctuation of carbon content. Our results show that the low-temperature resistivity maximum shifts to lower temperature with applied pressure, opposite to the behavior reported for stoichiometric EuB 6. The origin of such qualitative difference we associate with the increasing volume fraction of the phase that is not compatible with ferromagnetic ordering (originating in regions with relatively higher carbon concentration) with enhancing pressure. Our results support a recent proposition [1] that carbon-rich regions strongly influence magnetotransport properties of carbon-doped EuB 6 , such as they play a role of "spacers", which prevent percolation of ferromagnetic phase.

Influence of Pressure on the Electrical Transport Properties of Carbon-Doped EuB6

“…2. With increasing pressure we see an increase of T RM which is opposite to the dependence observed in our previous work [9]. However, the result reported in this work is consistent with the influence of pressure on pure EuB 6 .…”

“…However, the result reported in this work is consistent with the influence of pressure on pure EuB 6 . As it was already shown in previous studies [1][2][3][4][5][6][7][8][9], the "sample dependence issue" is important in case of EuB 6 and carbon-doped EuB 6 . The reason for it is the very small number of intrinsic carriers, which influences considerably the physical properties of samples, and even very small deviations in stoichiometry or impurities can lead to a substantially different behaviour.…”

“…1) which points to an interplay between at least two mechanisms -one is suppressing and the other one increasing the resistivity with pressure. On the other hand, the monotonic decrease of resistivity at room temperature (ρ 300 K , not shown) by 7%, from 163 µΩcm to 151.7 µΩcm, can be explained by an increase of the concentration of charge carriers due to applied pressure [9]. In case of stoichiometric EuB 6 a decrease of ρ 300 K by about 20% was observed in the same pressure range [5].…”

“…The EuB 6−x C x single crystal was grown using the zone-floating method and we used a sample from the same batch as in work [9], where the content of carbon was estimated by microprobe to be x = 0.01. Measurements of ac-resistivity have been performed by means of a four probe method utilizing lock-in amplifier and current source with active common mode rejection.…”

“…(ii) The magnetic * corresponding author; e-mail: gabriel.pristas@saske.sk polaron (MP) phase (below about 30 K [4]) in EuB 6 has two components: a highly-conducting FM phase (represented by MPs) and a poorly conducting paramagnetic phase. In case of carbon-doped EuB 6 this phase consists at least of three components [9]: a highly-conducting FM phase represented by MPs (matrix), and regions with carbon-poor and carbon-rich domains. (iii) In the magnetically ordered state EuB 6 is a homogeneous ferromagnet, while carbon-doped EuB 6 has two components: the FM matrix and heli-magnetic (HM) domains formed in carbon-rich regions [8].…”