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تسجيل مستخدم جديدShort-range antiferromagnetic correlations in the superconducting state of filled skutterudite alloys Pr$_{1-x}$Eu$_x$Pt$_4$Ge$_{12}$
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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 Pr$_{1-x}$Eu$_x$Pt$_4$Ge$_{12}$. 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 $xleq0.5$ 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.
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By performing a series of thermodynamic measurements in an applied magnetic field $H_{textrm{ext}}$, we investigated the effects of Eu substitution on the Pr sites in filled skutterudite compound Pr$_{1-x}$Eu$_x$Pt$_4$Ge$_{12}$ ($ 0 leq x leq 1$). A
heat capacity Schottky anomaly is present over the whole doping range. For the samples with $x > 0.5$, these Schottky anomaly peaks shift to lower temperature with increasing $H_{textrm{ext}}$. We argue that this behavior reflects the antiferromagnetic (AFM) ordering of the Eu moments, as the AFM transition is suppressed by $H_{textrm{ext}}$. The Schottky peaks in the samples with $x leq 0.5$ shift to higher temperatures with increasing magnetic field, signaling the presence of an internal magnetic field due to short-range AFM correlations induced by magnetic moments of neighboring Eu sites. In low $H_{textrm{ext}}$, the Schottky gaps show a non-linear relationship with $H_{textrm{ext}}$ as the magnetic moments become weakly magnetized. In high $H_{textrm{ext}}$, the magnetic moments of Eu sites become completely aligned with $H_{textrm{ext}}$. Thus, increasing $H_{textrm{ext}}$ does not further increase the magnetization, hence the Schottky gaps increase linearly with $H_{textrm{ext}}$
We report on systematic study of superconducting characteristics and Pr crystalline-electric-field (CEF) levels of filled-skutterudite pra ($T_{rm c}$ = 2.33 K). The temperature dependences of the upper critical field $H_{rm c2}$ and the Ginzburg-Lan
dau (Maki) parameter $kappa_2$ suggest an s-wave clean-limit superconductivity. The electronic specific heat coefficient $gamma sim 95$ mJ/K$^2$mol, being $sim 1.5$ times larger than that for lra, indicates $4f$-originating quasiparticle mass enhancement. Magnetic susceptibility $chi(T)$ indicates that the CEF ground state is a $Gamma_1$ singlet and a $Gamma_4^{(1)}$ triplet first excited state lies at $Delta_{rm CEF}sim 30$ K above. Systematic comparison among pos, prs, pra and La-based reference compounds suggests that inelastic exchange- and aspherical-charge-scatterings of conduction electrons from CEF-split $4f$ levels play an essential role for the quasiparticle mass enhancement and the value of $T_{rm c}$ in the Pr-based filled skutterudites.
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