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Magnetism and superconductivity in EuFe2As2 synthesized under high pressure



We have synthesized polycrystalline samples of EuFe2As2 by melting the stoichiometric mixture of constituent components at a high pressure (HP) of 8 GPa and measured the properties of HP-synthesized samples at ambient and high pressure up to 6 GPa. SDW-type antiferromagnetism appears below 150 K and Eu-related antiferromagnetism appears below 16 K in all HP synthesized samples. Also, all HP-synthesized samples exhibit superconductivity with Tc = 20–30 K at ambient pressure, though a zero-resistance state has not been observed. This superconductivity is very robust against application of magnetic field (dHc2/dT = −3.2 T K−1) and pressure (a tiny signal of superconductivity is still detectable below 2.5 K at 5.8 GPa). SDW antiferromagnetism is suppressed under pressure and is not observed above 1.7 GPa and below 60 K. The temperature of the magnetic ordering of Eu2+ moments increases under pressure. Specific heat measurements in a magnetic field reveal an increase of this temperature in field, therefore indicating field-induced ferromagnetism in the Eu sublattice.