Abstract
EuFe2As2-based iron pnictides are quite interesting compounds, due to the two magnetic sublattices in them and the tunability to superconductors by chemical doping or application of external pressure. The effects of hydrostatic pressure on the static magnetism in Eu(Fe0.925Co0.075)2As2 are investigated by complementary electrical resistivity, ac magnetic susceptibility and single-crystal neutron diffraction measurements. A specific pressure-temperature (P-T) phase diagram of Eu(Fe0.925Co0.075)2As2 is established. The structural phase transition, as well as the spin-density-wave order of Fe sublattice, is suppressed gradually with increasing pressure and disappears completely above 2.0 GPa. In contrast, the magnetic order of Eu sublattice persists over the whole investigated pressure range up to 14 GPa, yet displaying a non-monotonic variation with pressure. With the increase of the hydrostatic pressure, the magnetic state of Eu evolves from the canted antiferromagnetic structure in the ground state, via a pure ferromagnetic structure under the intermediate pressure, finally to an “unconfirmed” antiferromagnetic structure under the high pressure. The strong ferromagnetism of Eu coexists with the pressure-induced superconductivity around 2 GPa. Comparisons between the P-T phase diagrams of Eu(Fe0.925Co0.075)2As2 and the parent compound EuFe2As2 were also made.
Highlights
The discovery of Fe-based superconductors[1] has provided new platforms to study the intriguing interplay between superconductivity (SC) and magnetism
In order to conclude how the magnetism in both sublattices develop with the external pressure and to clarify the nature of the magnetic state in possible pressure-induced superconducting phase, we have carried out complementary experiments including the electrical resistivity, ac magnetic susceptibility and neutron diffraction measurements on the Eu(Fe1−xCox)2As2 (x = 0.075) single crystal under hydrostatic pressure
Combining the results from the resistivity, ac magnetic susceptibility and neutron diffraction measurements, a phase diagram describing how the static magnetism of Eu(Fe0.925Co0.075)2As2 develops upon the application of hydrostatic pressure is established
Summary
The discovery of Fe-based superconductors[1] has provided new platforms to study the intriguing interplay between superconductivity (SC) and magnetism. For the undoped parent compound EuFe2As2, the high-pressure ac magnetic susceptibility measurement using the piston-cylinder cell suggests that the magnetic ground state of the Eu2+ moments is still an AFM order in the pressure-induced superconducting phase (with the maximum applied pressure P ~ 2.8 GPa)[17], similar to that under the ambient pressure. Complementary high-pressure muon-spin rotation (μSR) and magnetization measurements were performed on non-superconducting isovalent-substituted EuFe2(As0.88P0.12)[2], in which the Eu2+ spins were found to order in the canted AFM (C-AFM) structure in the ground state[28]. In order to conclude how the magnetism in both sublattices develop with the external pressure and to clarify the nature of the magnetic state in possible pressure-induced superconducting phase, we have carried out complementary experiments including the electrical resistivity, ac magnetic susceptibility and neutron diffraction measurements on the Eu(Fe1−xCox)2As2 (x = 0.075) single crystal under hydrostatic pressure. It is very interesting to investigate how this intermediate magnetic structure in the T − x phase diagram evolves with hydrostatic pressure, and to conclude what type of magnetic order of Eu can coexist with the pressure-induced superconducting phase
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