Ce3Pt2Pb4: a new quasi-two dimensional ferromagnet

We have synthesized single crystals of Ce_3Pt_2Pb_4, which is found by single crystal x-ray diffraction measurements to form in the hexagonal Fe_2P structure. Arrott plots of the magnetization indicate the formation of a spontaneous moment approaching 1 μ_B per Ce at 3.5 K for H||c, but no moment is found above 1.8 K for fields in the basal plane. The specific heat is featureless at 3.5 K, while a sharp lambda-like anomaly is found in the specific heat at 0.8 K. We propose that long range ferromagnetic correlations develop in the basal plane for temperatures below 3.5 K, but three dimensional ferromagnetic order is only achieved at 0.8 K. Magnetic fields broaden and shift the specific heat anomaly to temperatures as large as 1.6 K in 5 T. The temperature dependent susceptibility obeys the Curie-Weiss law above 20 K, with Ce moments of 2.3 μ_B, suggesting that the Kondo effect has little effect in this system. Our measurements indicate that Ce_3Pt_2Pb₄ is a quasi-two dimensional ferromagnet, where the Ce moments are highly localized.