EuFe${}_2$As${}_2$ under high pressure: an antiferromagnetic bulk superconductor

Abstract

We report the ac magnetic susceptibility ${\chi }_{ac}$ and resistivity $\rho$ measurements of EuFe${}_2$As${}_2$ under high pressure $P$. By observing nearly 100% superconducting shielding and zero resistivity at $P$ = 28 kbar, we establish that $P$-induced superconductivity occurs at $T_c\sim$~30 K in EuFe${}_2$As${}_2$. $\rho$ shows an anomalous nearly linear temperature dependence from room temperature down to $T_c$ at the same $P$. ${\chi }_{ac}$ indicates that an antiferromagnetic order of Eu${}^{2+}$ moments with $T_N\sim$~20 K persists in the superconducting phase. The temperature dependence of the upper critical field is also determined.

To appear in J. Phys. Soc. Jpn., Vol. 78 No. 8

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