Effects of proton irradiation on the magnetic superconductor EuFe₂(As_1 − x P _x )₂

Abstract

We report on the effects of 3.5 MeV proton irradiation on single crystals of the magnetic superconductor EuFe 2 (As 1 − x P x ) 2 , investigated at microwave frequencies by a coplanar waveguide resonator technique. We studied the relative strength of the two collective phenomena by analyzing the dependence of their onset temperatures on different perturbations: magnetic fields and structural disorder. Results suggest that superconductivity and magnetism in this material are two competing orders: as the former is suppressed by irradiation or by excess P doping, the latter reinforces and manifests itself at higher temperatures. The ability to modulate superconductivity and magnetism in EuFe 2 (As 1 − x P x ) 2 by disorder and in-plane magnetic field, respectively, offers the chance to tailor, even on a local scale, their relative weights. This could be useful for the aim of engineering this material for specific applications.

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

“…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 coplanar-waveguide-resonator technique allows determination of the complex permeability of small samples coupled to the resonator, within a cavity perturbation approach [73,74]. The presence of the sample coupled to the resonator induces changes in the resonance frequency and quality factor of the CPWR, that are related to the real and imaginary parts of the total AC susceptibility, respectively [66]:…”

“…Protons also introduce largely point like defects and, in addition, nanometric clusters, which slightly reduce the efficiency of the overall produced defects acting as scattering centers. Detailed account of the effects of disorder by doping and proton irradiation in EuFe 2 (As 0.77 P 0.23 ) 2 is given elsewhere [66].…”

“…For CPWR data, hollow symbols were obtained from a crystal with additional doping-induced disorder (x = 0.23). The way the effective disorder has been estimated and its data merged to that of the x = 0.20 was discussed in [66].…”

“…Due to relative rarity of magnetic superconductors, there is limited experimental information on the effects of disorder simultaneously on the superconductivity and magnetism. While we are not aware of such studies in magnetic borocarbides, in IBS the effect of disorder on magnetism and superconductivity was studied in several works [62][63][64][65], but none of them on the ferromagnetic Eu-based 122 compounds, except for a recent study of the effect of proton irradiation on the subject compound by some of the authors [66].…”