Short-range antiferromagnetic correlations in the superconducting state of filled skutterudite alloys Pr1−xEuxPt4Ge12

Abstract

Motivated by current research efforts towards exploring the interplay between magnetism and superconductivity in multiband electronic systems, we have investigated the effects of Eu substitution through thermodynamic measurements on the superconducting filled skutterudite alloys Pr1−xEuxPt4Ge12. An increase in Eu concentration leads to a suppression of the superconducting transition temperature consistent with an increase of magnetic entropy due to Eu local moments. While the low-temperature heat capacity anomaly is present over the whole doping range, we find that in alloys with x ≤ 0.5 the Schottky peaks in the heat capacity in the superconducting state appear to be due to Zeeman splitting by an internal magnetic field. Our theoretical modeling suggests that this field is a result of the short-range antiferromagnetic correlations between the europium ions. For the samples with x > 0.5, the peaks in the heat capacity signal the onset of antiferromagnetic (AFM) ordering of the Eu moments.

Magnetic field dependence of the Schottky anomaly in filled skutterudites Pr1−xEuxPt4Ge12

“…1(c We note that a superconducting transition at a temperature T c is clearly seen in the heat capacity of the samples with 0 ≤ x ≤ 0.3 [22]. The superconducting jump becomes broader and T c shifts to lower temperatures, as expected, with increasing H ext and increasing Eu concentration [22]. The samples with 0.3 < x ≤ 0.5 show a superconducting transition only in resistivity measurements [25], while the samples with x > 0.5 do not display a superconducting transition for temperatures down to T = 0.5 K.…”

“…The effective field has, hence, two contributions: H eff ≡ H int +H ext . The internal field H int is due to the net magnetic moment m present as a result of short-range antiferromagnetic correlations between the nearest-neighbor Eu ions [22]. These short-range antiferromagnetic correlations co-exist with superconductivity in these lower Eu substituted samples (see Fig.…”

“…1 of ref. [22], in order to determine γ n and B. We then subtracted the phonon contribution to the specific heat for all the measured samples of Pr 1−x Eu x Pt 4 Ge 12 .…”

“…Nevertheless, once the AFM transition is suppressed below the lowest measured temperature of 0.5 K, the maximum of the Schottky anomaly shifts to higher temperatures with further increase in H ext [ Fig. 1(c We note that a superconducting transition at a temperature T c is clearly seen in the heat capacity of the samples with 0 ≤ x ≤ 0.3 [22]. The superconducting jump becomes broader and T c shifts to lower temperatures, as expected, with increasing H ext and increasing Eu concentration [22].…”

“…We performed lowtemperature specific heat measurements on samples of Pr 1−x Eu x Pt 4 Ge 12 in magnetic field. Our detailed and systematic analysis indicates that the upturns in the heat capacity are caused by the splitting of the octet degenerate states of Eu 2+ due to the internal magnetic field produced by the net magnetic moment m present as a result of short-range antiferromagnetic correlations between the nearest-neighbor Eu ions [22]. We have also systematically analyzed the effect of applied magnetic field on the temperature T max of the maximum of the Schottky anomaly.…”