M.J. Steenland

Determination of very low thermodynamic temperatures in chromium potassium alum

Abstract Thermodynamic temperatures have been measured in the region below 0.1° K by four different methods. The results are in reasonable agreement. Hysteresis sets in at 0.004° K. The lowest temperatures measured are around 0.003°K. The susceptibility and the losses are given at a frequency of 225 Hertz. At the higher temperatures the losses are proportional to r 1.7±0.15 between 225 and 525 Hertz.

Further researches on the magnetic properties of potassium chromium alum below 1 °K

Synopsis A refinement of the ballistic method for measuring susceptibilities is described. With this method measurements on a sphere ground from a single crystal CrK(SO 4 ) 2 .12H 2 O were performed in constant external fields. The results of these measurements were used to test a formula of Garrett for determining the absolute temperatures and to calculate the temperature variations along isentropics. Also the behaviour of the remanent magnetic moment in constant external fields was studied.

Some magnetic properties of chromium potassium alum below the curie-point

Abstract Details are given on the remanence and hysteresis effects occurring at very low temperatures in a sphere of chrome alum described in a previous paper. From these data a temperature determination can be derived which is in rough agreement with our former measurements.

Magnetic researches on adiabatically demagnetized chromium methylamine alum

Synopsis The magnetic susceptibility of CrCH 3 NH 3 (SO 4 ) 2 .12H 2 O has been studied first in zero external field. The influence of the amplitude and the frequency of the measuring field on the value of the susceptibility was measured. Also the hysteresis effects were investigated. In section 3 special attention has been paid to the behaviour of the susceptibility in external fields, both transverse and longitudinal, below its maximum as a function of entropy. Two marked bends have been found in the magnetization curves. In transverse fields striking anisotropies with a binary symmetry showed up. In section 5 a discussion is given of the measured curves, especially for the lowest temperatures, based on the occurrence of antiferromagnetic domains.

The magnetic behaviour of iron ammonium alum at very low temperatures

Abstract The magnetic properties of iron ammonium alum, FeNH4(SO4)2 · 12H2O, have been studied between about 0.005°K and 0.05°K. The samples investigated were a sphere of powder and a massive prolate spheroid. No difference was found in the Curie point which lies at about 0.030°K.

Temperatures obtained by adiabatic demagnetization of a diluted chromium alum

Abstract Measurements have been carried out on a powdered mixed crystal of chromium alum and aluminium alum containing 21.3 Al-ions for each Cr-ion. Even at the lowest temperatures reached no maximum of the susceptibility was found. Thermodynamic temperatures between 0.0014 and 0.019°K have been determined making use of the susceptibility as a thermometric parameter and heating by means of an oscillating magnetic field of 225 hertz.

The magnetic behaviour of copper potassium tutton salt and manganese ammonium tutton salt at very low temperatures

Abstract A first survey has been given of the thermodynamic temperatures reached by adiabatic demagnetisation of copper potassium Tutton salt and of manganese ammonium Tutton salt. Some magnetic properties of these salts at very low temperatures are described.

Chapter XIV Adiabatic Demagnetization

Publisher Summary This chapter considers the two parts of the apparatus separately. It deals with the cooling of the paramagnetic salt, the determination of its temperature and magnetic properties, and discusses the cooling down of the other materials with the salt. The method of adiabatic demagnetization consists of two stages: First, an isothermal magnetization of the paramagnetic salt at the lowest temperature that can be obtained with liquid helium; second, an adiabatic demagnetization of the salt. During the isothermal magnetization, the paramagnetic ions of the crystalline lattice are partly oriented parallel to the field. During the subsequent adiabatic demagnetization, the entropy of the salt remains constant at a low value and a final state is obtained where the entropy is lower than at the initial temperature in zero field and hence the temperature is lower. The apparatus for an adiabatic demagnetization experiment consists of two fundamental parts: First, the equipment necessary for the production, conservation, and determination of the low temperature itself, and secondly, that needed for cooling down the material under investigation with the paramagnetic salt and for making measurements on it.

The magnetic behaviour of copper potassium tutton salt at very low temperatures; A correction and an addition☆

Abstract Revision of earlier results is necessary by an error of calculation, made in Commun. No. 279c. The corrected results are compared with those of other investigations.