The magnetic susceptibilities of metallic oxides, with special reference to those of chromium and manganese

Abstract

Different workers report widely divergent results for tho magnetic susceptibilities of the transition metals. It has now been shown that, if the best values for the susceptibility are taken, the magnetic moment, as calculated from the Curie law, gives values which are of no theoretical significance, but application of Weiss's modification of this law to the oxides of chromium and manganese gives values for the magnetic moment which are in accord with theory and enable magnetic measurements to be used for the evaluation of the correct formulae of oxides. The formulae of the oxides of manganese are discussed, and the occurrence of quadrivalent chromium in a hydrated dioxide of that metal established. The magnetic susceptibility of tho various stages of decomposition of chromium trioxide has been measured, and it has been found that there is little change in the magnetic susceptibility with variation of composition in non-stoichciometric oxides. The Cr₂0₃ non-stoichciometric oxide is ferromagnetic. Samples of chromic oxide prepared by different methods have slightly different susceptibility values. It is suggested that these differences are due to the presence of impurities and, in particular, to small amounts of chemisorbed gaseous elements, The adsorption of oxygen or of hydrogen at 440° on this oxide causes definite variation in tho susceptibility value. High-temperature evacuation likewise causes a considerable fall tn the susceptibility of chromic oxide. It is suggested that activated adsorption on oxides is connected with reduction of chemisorbed oxygen, and the use of magnetic measurements is recommended as a means of following surface chemical processes on oxides.