Low-temperature measurements of magnetic susceptibility and specific heat of Eu2Ti2O7—An XY pyrochlore

Magnetic susceptibility χ¯ obtained from magnetization measurement (for fields H=0.1 and 1.0 T) of polycrystalline Eu2Ti2O7 shows two distinct features. Firstly, χ¯ increases on cooling below 300 K and attains a temperature-independent constant value χ¯max=794010-6emu/mol‐EuTiO3.5 at 68 K (Tmax). Secondly, χ¯ shows an antiferromagnetic increase below 4.9±0.1 K. The former behavior is explained by crystal field (CF) theory. CF levels and wave functions of ground and excited states are determined accurately from analyses of χ¯ and earlier reported Mössbauer and optical spectra. Analysis of χ¯T vs. 1/T curve at low temperatures gives the classical nearest-neighbor exchange interaction Jcl=−0.76 K and a weak dipolar interaction Dnn=0.0056 K. CP of polycrystalline sample of Eu2Ti2O7 and Y2Ti2O7 are measured between 1.8–35 and 1.8–120 K respectively and θD vs. T (K) curves are calculated. At 4 K, θD of Eu2Ti2O7 shows a kink and dCP/dT curve show a maximum. Optical results show energy exchange between Eu3+ ions at intrinsic and extrinsic (defect) sites via super-exchange interaction at low temperature which may account for the observed anomalous behavior of χ¯ and CP.