Abstract
Magnetic susceptibility χ ¯ obtained from magnetization measurement (for fields H=0.1 and 1.0 T) of polycrystalline Eu 2Ti 2O 7 shows two distinct features. Firstly, χ ¯ increases on cooling below 300 K and attains a temperature-independent constant value χ ¯ max = 7940 1 0 - 6 emu / mol ‐ EuTiO 3.5 at 68 K ( T max). 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 J cl=−0.76 K and a weak dipolar interaction D nn=0.0056 K. C P of polycrystalline sample of Eu 2Ti 2O 7 and Y 2Ti 2O 7 are measured between 1.8–35 and 1.8–120 K respectively and θ D vs. T (K) curves are calculated. At 4 K, θ D of Eu 2Ti 2O 7 shows a kink and d C P/d T curve show a maximum. Optical results show energy exchange between Eu 3+ 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 C P.
Published Version
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