The specific heat of NdIn, in the temperature range 2.3 t o 27 K and in the magnetic field up to 5 T as well as the thermal expansion between 1.5 K and room temperature are measured. The low-temperature behaviour of NdIn, is governed by the energy gap in the spin wave spectrum. The specific heat at the antiferromagnetic transition reveals anomalously large critical exponents.It is shown that the specific heat anomaly a t T N contains contributions from two closely lying transitions. The influence of the magnetic field on the energy gap, on the first-order transitions found in the antiferromagnetic state, and on the NBel peak is studied. Thermal properties in the paramagnetic state are analyzed basing on the available CF data.An NdIn, werden im Temperaturbereich 2,3 bis 27 K und im Magnetfeldern bis 5 T die spezifische Warme und im Bereich zwischen 1,5 K und Raumtemperatur die thermische Ausdehnung gemessen. Das Tieftemperaturverhalten wird von einer Energieliicke im Spinwellenspektrum bestimmt. Die spezifische Warme wird in der N l h e der antiferromagnetischen Ordnung durch ungewohnlich hohe kritische Exponenten beschrieben. Es wird gezeigt, daO die Anomalie in der spezifischen Warme bei T N aus zwei nah beieinander liegenden Ubergangen besteht. Untersucht wird der EinfluB des Magnetfeldes auf die Energieliicke, die beiden ubergange 1. Art im antiferromagnetischen Ordnungszustand und auf den NBel-Peak. Die thermischen Eigenschaften im paramagnetischen Zustand werden auf der Grundlage der zur Verfiigung stehenden Kristollfeldparametern analysiert.
Low-temperature specific heat measurements on bulk technical polymer samples (polytetrafluoroethylene and polychlorotrifluoroethylene) were carried out between 2,5 and 20 K. In these experimental investigations a heat pulse method and an adiabatic vacuum calorimeter were used.The low-temperature specific heats of polytetrafluoroethylene (T4) and polychlorotrifluoroethylene (T3) have not been studied in sufficient detail [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. The extrapolation of the experimental values at 20 K down to 4 K by means of the Debye-model is inadmissible [5]. Thus, investigations of the thermal properties giving the necessary physical quantities and constants for cryogenic design of these highly crystalline polymers are quite important.In the present work, calorimetric measurements on the bulk polymer samples were made in the range 2.5-20 K. The length and diameter of the samples did not surpass 50 mm and 12 ram, respectively. By using a shield in a vacuum calorimeter [16], entirely adiabatic conditions of operation were ensured. The cooling of the calorimeter, as well as that of the sample and the shield, was effected with a mechanical heat switch [17]. The heat capacity was derived from a well-known relation between the increase of the sample temperature (A T ~ 10-2 T) and the amount of heat supplied to the sample by a 650 f2 heater, consisting of 0.050 mm diameter constantan wire. This heater gives heat impulses lasting 40 seconds. The temperatures of the samples and the shield were measured by 300~ Allen-Bradley resistors. The calibration of these resistors was performed using a germanium (NIG) substandard. The time for establishment of the heat equilibrium was a few seconds at 2.5 K, and about 15 minutes at 20 K.
ExperimentalThe temperature-dependence of the specific heat is presented in Fig. 1 for polychlorotrifluoroethylene, and in Fig. 2
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