Hydrostatic pressure effects on the static magnetism in Eu(Fe0.925Co0.075)2As2

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.

Doping dependence and high-pressure studies on Eu x Ca1 − x Fe2As2 (0 ≤x ≤ 1)

“…The resistance reaches zero when applied pressure reaches ∼ 13 kbar at T c ∼ 14 K. It should be noted that the resistance goes to zero even though there still exists a fingerprint of the SDW transition at T SDW = 88 K, as indicated by the arrow. The coexistence of superconductivity and SDW order has been observed also in other 122 systems [20,41]. Superconductivity is suppressed if we increase a pressure higher than 12.7 kbar.…”

Spiral magnetic ordering of the Eu moments in EuNi2As2

“…13? ,14 This magnetic configuration of Eu is stable with respect to chemical substitutions at small doping levels, 15,16 but the Eu 2+ spins start to cant out of the ab plane at intermediate doping levels 9,[17][18][19] and become ferromagnetically aligned along the c axis at relatively high doping levels. [20][21][22][23] Interestingly, the ferromagnetism from the Eu sublattice was found to be compatible with the SC induced by either chemical doping or hydrostatic pressure, 9,18,22 making the "ferromagnetic superconductors" in the EuFe 2 As 2 -based system very attractive research subjects.…”

Spin reorientation of the Fe moments in Eu0.5Ca0.5Fe2As2 : Evidence for strong interplay of Eu and Fe magnetism

“…[20][21][22][23][24][25][26][27] As a special member of the "122" system, EuFe 2 As 2 has drawn tremendous attention, due to the strong spin-charge-lattice coupling and doping-or pressure-induced coexistence of SC and strong ferromagnetism. [28][29][30][31][32][33][34][35] In a purely ionic picture, the S -state (orbital moment L = 0) Eu 2+ rare-earth ion has a 4f 7 electronic configuration and a total electron spin S = 7/2, corresponding to a theoretical total effective magnetic moment of µ ef f = g S(S + 1) = 7.94 µ B (with the Landé factor g = 2). 36 The non-superconducting parent compound EuFe 2 As 2 undergoes a structural phase transition from a tetragonal to an orthorhombic phase at 190 K, concomitant with a SDW ordering of the itinerant Fe moments.…”