3 GLYPH<s48> GLYPH<s50>GLYPH<s53> GLYPH<s53>GLYPH<s48> GLYPH<s55>GLYPH<s53> GLYPH<s49>GLYPH<s48>GLYPH<s48> GLYPH<s50>GLYPH<s46> GLYPH<s48> GLYPH<s50>GLYPH<s46> GLYPH<s50> GLYPH<s50>GLYPH<s46> GLYPH<s52> GLYPH<s48>GLYPH<s46> GLYPH<s48>GLYPH<s53> GLYPH<s48>GLYPH<s46> GLYPH<s53> GLYPH<s48>GLYPH<s46> GLYPH<s49> GLYPH<s49> GLYPH<s48> GLYPH<s49>GLYPH<s48> GLYPH<s50>GLYPH<s48> GLYPH<s51>GLYPH<s48> GLYPH<s48>GLYPH<s46>GLYPH<s48>GLYPH<s48> GLYPH<s48>GLYPH<s46>GLYPH<s48>GLYPH<s50> GLYPH<s48>GLYPH<s46>GLYPH<s48>GLYPH<s52> GLYPH<s48> GLYPH<s50> GLYPH<s52> GLYPH<s54> GLYPH<s56> GLYPH<s48> GLYPH<s50>GLYPH<s53> GLYPH<s53>GLYPH<s48> GLYPH<s55>GLYPH<s53> GLYPH<s49>GLYPH<s48>GLYPH<s48> GLYPH<s48>GLYPH<s46>GLYPH<s48> GLYPH<s48>GLYPH<s46>GLYPH<s49> GLYPH<s48>GLYPH<s46>GLYPH<s53> GLYPH<s49>GLYPH<s46>GLYPH<s48> GLYPH<s40>GLYPH<s98>GLYPH<s41> GLYPH<s103>GLYPH<s45>GLYPH<s102>GLYPH<s97>GLYPH<s99>GLYPH<s116>GLYPH<s111>GLYPH<s114> GLYPH<s32> GLYPH<s84> GLYPH<s32>GLYPH<s40>GLYPH<s75>GLYPH<s41> GLYPH<s69>GLYPH<s117> GLYPH<s48> GLYPH<s46>GLYPH<s53> GLYPH<s75> GLYPH<s48> GLYPH<s46>GLYPH<s53> GLYPH<s70>GLYPH<s101> GLYPH<s50> GLYPH<s65>GLYPH<s115> GLYPH<s50> GLYPH<s32> GLYPH<s32> GLYPH<s32> GLYPH<s69>GLYPH<s83>GLYPH<s82> GLYPH<s32>GLYPH<s40>GLYPH<s101>GLYPH<s109>GLYPH<s117>GLYPH<s47>GLYPH<s109>GLYPH<s111>GLYPH<s108>GLYPH<s101>GLYPH<s41> GLYPH<s84> GLYPH<s67> GLYPH<s32>GLYPH<s32> GLYPH<s69>GLYPH<s83>GLYPH<s82> GLYPH<s40>GLYPH<s97>GLYPH<s41> GLYPH<s32> GLYPH<s100> GLYPH<s99> GLYPH<s32>GLYPH<s40>GLYPH<s101>GLYPH<s109>GLYPH<s117>GLYPH<s47>GLYPH<s109>GLYPH<s111>GLYPH<s108>GLYPH<s101>GLYPH<s41> GLYPH<s32>GLYPH<s32>GLYPH<s32> GLYPH<s100> GLYPH<s99> GLYPH<s84> GLYPH<s67> GLYPH<s40>GLYPH<s72> GLYPH<s114> GLYPH<s101> GLYPH<s115> GLYPH<s45>GLYPH<s72> GLYPH<s105>GLYPH<s110> GLYPH<s115> GLYPH<s41> GLYPH<s45> GLYPH<s49> GLYPH<s32> GLYPH<s40>GLYPH<s79> GLYPH<s101> GLYPH<s45> GLYPH<s49> GLYPH<s41> GLYPH<s32> GLYPH<s32> GLYPH<s32> GLYPH<s49>GLYPH<s47> GLYPH<s100> GLYPH<s99> GLYPH<s32> GLYPH<s40>GLYPH<s109>GLYPH<s111>GLYPH<s108> GLYPH<s101>GLYPH<s47> GLYPH<s101>GLYPH<s109>GLYPH<s117>GLYPH<s41> GLYPH<s32> GLYPH<s32> GLYPH<s32> GLYPH<s32> GLYPH<s68>GLYPH<s47>GLYPH<s65> GLYPH<s84> GLYPH<s67> GLYPH<s32> GLYPH<s32> GLYPH<s32> GLYPH<s40> GLYPH<s47> GLYPH<s84> GLYPH<s67> GLYPH<s41> GLYPH<s48> GLYPH<s46>GLYPH<s53> GLYPH<s48> GLYPH<s50>GLYPH<s53> GLYPH<s53>GLYPH<s48> GLYPH<s55>GLYPH<s53> GLYPH<s49>GLYPH<s48>GLYPH<s48> GLYPH<s48>GLYPH<s46>GLYPH<s53> GLYPH<s49>GLYPH<s46>GLYPH<s48> GLYPH<s50>GLYPH<s48> GLYPH<s51>GLYPH<s48> GLYPH<s52>GLYPH<s48> GLYPH<s53>GLYPH<s48> GLYPH<s50> GLYPH<s51> GLYPH<s52> GLYPH<s53> GLYPH<s72> GLYPH<s32>GLYPH<s40>GLYPH<s107>GLYPH<s79>GLYPH<s101>GLYPH<s41> GLYPH<s84> GLYPH<s32>GLYPH<s40>GLYPH<s75>GLYPH<s41> GLYPH<s69>GLYPH<s117> GLYPH<s48>GLYPH<s46>GLYPH<s53> GLYPH<s75> GLYPH<s48>GLYPH<s46>GLYPH<s53> GLYPH<s70>GLYPH<s101> GLYPH<s50> GLYPH<s65>GLYPH<s115> GLYPH<s50> GLYPH<s126>GLYPH<s84> GLYPH<s49>GLYPH<s46>GLYPH<s48> GLYPH<s126>GLYPH<s84> GLYPH<s49>GLYPH<s46>GLYPH<s53> GLYPH<s49>GLYPH<s47>GLYPH<s84> GLYPH<s69>GLYPH<s83>GLYPH<s82> GLYPH<s49> GLYPH<s40>GLYPH<s49>GLYPH<s48> GLYPH<s57> GLYPH<s47>GLYPH<s115> GLYPH<s41> GLYPH<s32> GLYPH<s84> GLYPH<s67> FIG. 4: (Color online) Temperature dependence of the ESR linewidth Δ H . The solid line indicates the linear Korringa law. Inset: Temperature dependence of 1 /T ESR 1 on a double- logarithmic scale and linear fits indicating the power-laws in the normal and SC states. FIG. 3: (Color online) (a) Temperature dependence of the ESR intensity compared to the magnetic DC susceptibility (solid line) measured in a magnetic field of 0.3 T, i.e. well above the lower critical field H c1 in Eu 0$_{.}$5 K 0$_{.}$5 Fe 2 As 2 . Inset: Temperature dependence of the dispersion to absorption ra- tio D/A compared to the square root of the normalized DC conductivity (solid line). (b): Temperature dependence of the g -factor of the ESR line. Inset: Inverse shift of the resonance field H res from its insulator value H ins given by g ins = 1 . 993 compared to the inverse static susceptibility. cause the conductivity of these regions can be anticipated to be unchanged. Thus, the ratio of the skin depth to the diameter of the flux tubes is larger than the ratio of the skin depth to the full sample diameter, which can result in a decrease of the D/A ratio. However, detailed electro dynamical considerations are necessary to clarify this ob- servation. The consecutive increase of the D/A ratio on decreasing temperature can be related to the reentrant Eu magnetism which leads to an increase of the normally conducting volume fraction. Finally, the peak at about 8 K marks the onset of short-range order. 24,25 The temperature dependence of the g value depicted in the lower frame of Fig. 3 is only slightly affected by the onset of superconductivity. The g -value is about 2 above T$_{c}$ and starts to increase strongly below 25 K. The inset compares the corresponding inverse shift of the res- onance field from its value in an insulating environment determined by g$_{ins}$ = 1 . 993 (see Ref. 29) to the inverse static susceptibility. Both quantities approximately co- incide showing that the resonance shift is dominated by demagnetization fields resulting from the large Eu mag- netization similar to observations in systems like GdI$_{2}$ or YBaMn$_{2}$O$_{6}$. 30,31 Only the small kink at T$_{c}$ in both the reciprocal susceptibility and the resonance shift can be regarded as an effect of the superconducting state due to the opening of the excitation gap in the electronic density of states at the Fermi-level and corresponding reduction of the Pauli contribution to the susceptibility. tor of 3 when crossing T$_{c}$ with decreasing temperature. After the anticipated onset of enhanced magnetic fluctu- ations of the Eu ions at about 25 K it starts to increase again up to 8 K, below which D/A decreases again. The drop of intensity on passing T$_{c}$ can be understood due to the fact that magnetic resonance is observed only from the volume fraction of the sample which is penetrated by the magnetic flux, i.e. the surface within the Lon- don penetration depth and – in superconductors of type II – the magnetic flux tubes with normal conductivity. The concomitant drop of the D/A ratio is difficult to ex- plain, because the superconductivity strongly reduces the skin depth and, hence, is naively expected to increase the D/A ratio. The observed decrease may presumably result from the change of the effective geometry of the normal- state regions, i.e. the flux tubes in the superconducting matrix instead of a homogeneously conducting state, be- The g shift at elevated temperature Δ g = g − g$_{ins}$ = J$_{CE}$$_{−}$$_{Eu}$ (0) N ( E$_{F}$ ) ≈ 0 . 02 results from the homogenous polarization of the conduction electrons in the external field (Pauli susceptibility) and is comparable to usual metals. 32 Now we will turn to the temperature dependence of the ESR linewidth shown in Fig. 4. Note that in metallic sys- tems the ESR linewidth is determined by the spin-lattice