Abstract
It has been demonstrated in several laboratories that the heat capacity of cerium magnesium nitrate is anomalous above 20 mK. The origin of the anomaly is unknown. We have measured the heat capacity of three samples of cerium magnesium nitrate from 0.15 to 0.6 K. The samples were: (a) from a cloudy region of a large single crystal grown from nominally 95% starting material, (b) from an optically clear region of the same single crystal, and (c) from a single crystal grown from 99.9% starting material. Within the scatter of the data the three heat capacity determinations showed the same anomaly as observed elsewhere; after subtracting an appropriate lattice contribution, the heat capacity above 0.1 K is more than twice that expected for a set of interacting magnetic dipoles on a regular lattice. The “cloudy sample versus clear sample” results ruled out crystal growth problems as the source of the anomaly. Chemical analysis by neutron activation analysis, mass spectrographic analysis, and optical absorption spectroscopy all showed the presence of approximately 0.06% praseodymium to cerium ratio in the two single crystals. The heat capacity arising from the hyperfine splitting of the non-Kramers doublet ground state of that concentration of praseodymium ions in cerium magnesium nitrate accounts for the heat capacity anomaly in magnitude and temperature dependence. No serious consequences are expected regarding the use of cerium magnesium nitrate as a primary thermometric substance.
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Supported by the National Research Council of Canada.
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Folinsbee, J.T., Harrison, J.P. & McColl, D.B. The anomalous heat capacity of cerium magnesium nitrate. J Low Temp Phys 27, 25–35 (1977). https://doi.org/10.1007/BF00654635
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DOI: https://doi.org/10.1007/BF00654635