โ Scribed by H. van Dijk; W.H. Keesom
No coin nor oath required. For personal study only.
The authors developed the technique for measuring specific heats in constant strong magnetic fields. Measurements were made in magnetic fields at liquid helium temperatures and in field zero also at temperatures obtained by demagnetization.
The specific heats of the specimen of iron ammonium alum showed an anomalous maximum at about 3.6"K. This behaviour can not be yet explained.
Values of C, -Cc were compared with a B r i 11 o II i n function on the basis of six equidistant magnetic energy levels. Within a certain region the values nearly agree with theory. Outside that region they reveal, however, considerable deviations.
5 1. Introdzlction.
Temperatures below 1 "K, obtained by demagnetization, are usually calculated from magnetic susceptibilities by extrapolating CURIE'S law. It is to be expected that the "Curietemperatures" so obtained do not coincide with thermodynamic temperatures when we come to the lowest temperatures.
Several authors pointed out and discussed methods that may be used to derive the thermodynamic temperatures for this region with a view to comparing them with the Curie-temperatures.
W. H. K e e s o m r) showed how the thermodynamic temperature can be derived from adiabatic experiments starting from a known temperature, combined with caloric measurements at both the initial temperature (in a magnetic field) and the final temperature.
C. W.
C 1 a r k ") tried this method with gadolinium sulphate octohydrate. Similar methods have been discussed and tried by G i. a u q u e and MacDougalll) andby Kiirti and Simon3). Giauque and MacDougall used gadolinium phospho-
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