Microwave analysis of the interplay between magnetism and superconductivity in EuFe2(As1−xPx)2

Abstract

We report on the microwave analysis of the interplay between magnetism and superconductivity in single crystals of EuFe 2 (As 1−x P x) 2 , accomplished by means of a coplanar waveguide resonator technique. The bulk complex magnetic susceptibility χ m extracted through a cavity perturbation approach is demonstrated to be highly sensitive to the magnetic structure and dynamics, revealing two distinct magnetic transitions below the superconducting critical temperature. By a comparison with magnetic force microscopy maps, we ascribe the χ m peak observed at about 17 K to the transition from the ferromagnetic domain Meissner phase to the domain vortex-antivortex state, with the subsequent evolution of the domain structure at lower temperatures. The second χ m peak observed at 11 K reflects a specific high-frequency feature, connected to vortex-antivortex dynamics and eventual spin reorientation transition of the Eu 2+ canted ferromagnetic subsystem. The two peaks merge and vanish upon application of an in-plane magnetic field, which is compatible with the presence of a quantum critical point below 1 T.

Effect of Controlled Artificial Disorder on the Magnetic Properties of EuFe2(As1−xPx)2 Ferromagnetic Superconductor

“…Of course, the physics around ferromagnetic transition is significantly affected by the proliferation of spontaneous (vortex-antivortex) phases as was determined in the comprehensive microscopic study [81]. This scenario has been further explored in [76,82] Similarly, effects of spontaneous vortex phase was investigated both experimentally and theoretically in already mentioned 1144 sibling compound, RbEuFe 4 As 4 [30,31,83,84].…”

“…For comparison, the data in panels (a) and (b) were normalized to extrapolate to χ = −1 at the lowest T, whereas panel (c) shows the calibrated data. All three susceptibility curves clearly show superconducting transition near T c ≈ 24 K and ferromagnetic transition at T m ≈ 18 K. The microwave-frequency CPWR data show extra features and a detailed analysis of the measurements is given elsewhere [66,76], while we are interested in a comparison of the transition temperatures. Below T c diamagnetic susceptibility is rather broad compared to much sharper transitions of nonmagnetic superconductors.…”

“…The overall real and imaginary parts of the susceptibility for ferromagnetic superconductors are given by a bulk magnetic contribution and by a screening given by the superconducting condensate. The superconducting transition temperature T c corresponds to the onset of the diamagnetic signal (onset of an increase of the resonance frequency upon cooling), while the magnetic transition temperature T m is defined as the onset of a positive contribution to the bulk susceptibility [76].…”

Tuning the Intrinsic Anisotropy with Disorder in the CaKFe4As4 Superconductor

“…The London penetration depth is measured by means of a coplanar-waveguide-resonator (CPWR) technique that has already been applied to study other IBS crystals [16][17][18][19]. The resonator consists of an YBa 2 Cu 3 O 7−x coplanar waveguide to which the sample is coupled.…”

Eliashberg Theory of a Multiband Non-Phononic Spin Glass Superconductor

“…The discovery of the new iron-based superconductor family based on EuFe 2 As 2 [1][2][3][4][5][6][7][8] allowed to investigate more deeply the interplay of magnetism and superconductivity. Compared to the past, there is now a new aspect to be considered: magnetism not only competes with superconductivity but also can be involved in the mechanism of superconductivity itself, as in the case of cuprates, heavy fermions and iron-based superconductors.…”