Schottky anomaly and short-range antiferromagnetic correlations in filled skutterudites Pr${}_{1-x}$Eu${}_x$Pt${}_4$Ge${}_{12}$

Abstract

By performing a series of thermodynamic measurements in an applied magnetic field $H_{\text{ext}}$, we investigated the effects of Eu substitution on the Pr sites in filled skutterudite compound Pr${}_{1-x}$Eu${}_x$Pt${}_4$Ge${}_{12}$ ($0\le x\le 1$). 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 $H_{\text{ext}}$. We argue that this behavior reflects the antiferromagnetic (AFM) ordering of the Eu moments, as the AFM transition is suppressed by $H_{\text{ext}}$. The Schottky peaks in the samples with $x\le 0.5$ 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 $H_{\text{ext}}$, the Schottky gaps show a non-linear relationship with $H_{\text{ext}}$ as the magnetic moments become weakly magnetized. In high $H_{\text{ext}}$, the magnetic moments of Eu sites become completely aligned with $H_{\text{ext}}$. Thus, increasing $H_{\text{ext}}$ does not further increase the magnetization, hence the Schottky gaps increase linearly with $H_{\text{ext}}$

5 pages 4 figures