Effect of magnetic field on short-range antiferromagnetic correlations in the filled skutterudite Pr_1-xEu_xPt₄Ge₁₂

We have investigated the effects of Eu substitution through thermodynamic measurements on the superconducting filled skutterudite Pr_1-xEu_xPt₄Ge₁₂ in an applied magnetic field H. A heat capacity Schottky anomaly is present over the whole doping range. For the samples with x > 0.5, these peaks shift to lower temperature with increasing applied magnetic field H, hence they reveal the antiferromagnetic (AFM) ordering of the Eu moments, as the AFM transition is suppressed by H. The heat capacity peaks in the samples with x ≤ 0.5 shift to higher temperatures with increasing magnetic field. These latter Schottky peaks are a result of Zeeman splitting by internal magnetic field due to short-range AFM correlations of random magnetic moments of nearing Eu sites, thus increases with Eu concentration x. In low H, the Schottky gaps show a non-linear relationship with H as the magnetic moments become weakly magnetized. In the case of a high applied H, the magnetic moments of Eu sites become completely aligned along H. Thus, Increasing H will not increase further the magnetization, hence the Schottky gaps are a linear function of the external field H.