A very low-temperature calorimeter with a (3He+4He) dilution refrigerator The heat capacity of trans-bis(ethylenediamine)-bis(isothiocyanato)nickel(II)
1987; Elsevier BV; Volume: 19; Issue: 12 Linguagem: Inglês
10.1016/0021-9614(87)90005-x
ISSN1096-3626
AutoresShigemi Murakawa, Tomio Wakamatsu, Motohiro Nakano, Michio Sorai, Hiroshi Suga,
Tópico(s)Magnetism in coordination complexes
ResumoA calorimeter with a (3He+4He) dilution refrigerator capable of measuring heat capacity between 20 mK and 25 K has been constructed. The calorimeter works under three operational modes in accordance with the temperature region suitable for heat-capacity measurements: the isoperibol low-temperature mode covers the range below 200 mK, the adiabatic high-temperature mode is used in the range from 0.2 to 25 K, and the isoperibol third mode is adopted when the thermal relaxation time of a sample is long. The accuracy of the calorimeter has been determined indirectly by comparing heat capacities of a common sample with those measured by a 3He calorimeter whose accuracy has been established on the basis of the 1965 Calorimetry Conference Copper Standard. The heat capacity of a paramagnetic nickel complex [Ni(en)2(NCS)2] (en = H2NCH2CH2NH2) has been measured between 0.3 and 20 K. A Schottky anomaly centred around 3.3 K was detected. This anomaly was well accounted for in terms of the zero-field splitting of a single nickel ion arising from the crystalline-field anisotropy. The best fit between theory and experiment was obtained for Dk = 8.98 K and |E|k = 1.62 K (or |E|D = 0.18) where D and E are the uni- and bi-axial crystalline-field anisotropy parameters, respectively, and k is the Boltzmann constant. The heat-capacity anomaly can likewise be accounted for in terms of different set of the parameters (Dk = −6.92 K and |E|k = 3.67 K or |ED| = 0.53) because both the sets bring about identical splitting with respect to the spin energy-level.
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