黄鉄鉱の熱分解生成物に関する研究

FeS_1+xの磁気的性質

抄録

Thermal decomposition products, FeS_1+x, were prepared by the decomposition of FeS₂ in the atmosphere of N₂, between 625°C and 900°C.
Thermomagnetic properties and the crystal structure of these thermal decomposition products were studied by the method of thermomagnetic analysis and X-ray. And the change of thermomagnetic properties of thermal decomposition products in vacuo or in air at the elevated temperature was discussed. Results obtained were summarized as follow:
1. The composition of thermal decomposition products varies with the decomposition temperature. Of such decomposition products, FeS_1.13 (prepared as 625°C) and FeS_1.11 (prepared at 650°C) were ferromagnetic and their ferromagnetic Curie point was found to be 295°C; FeS_1.09 (prepared at 675°C) and FeS_1.08 (prepared at 700°C) were antiferromagnetic and their antiferromagnetic Curie point was found to be about 220°C; FeS_1.06 (prepared at 750°C), FeS_1.05 (prepared at 800°C) and FeS_1.00 (prepared at 900°C) are paramagnetic. Crystal structure of these FeS_1+x belongs to hexagonal system whose axial ratio, c/a, is 1.66-1.68. Lattice parameter a, c and axial ratio decreases with increasing the content of sulfur in FeS_1+x. These results coincide with that of H. Haraldsen.
2. When antiferromagnetic or paramagnetic decomposition products are heated, their thermomagnetic properties change under heating conditions, such as oxygen partial pressure of the atmosphere, heating temperature, etc.: That is, thermomagnetic properties of antiferromagnetic samples remain unchanged when they are heated to about 300°C in vacuum sealed silica capsule, or in vacuo of 5×10^-5mmHg. However, when they are heated to the same temperature in vacuo of about 10^-3mmHg, or in air, it changes to ferromagnetic one whose Curie point is 295°C. Paramagnetic samples change also to ferromagnetic, and the formation of small amount of Fe₃O₄ was detected by X-ray measurement, when they are heated in air to about 430°C. By this change, latticeparameter or axial ratio of FeS_1+x change to that of ferromagnetic one. From these results, it may be concluded that such changes from antiferromagnetism or paramagnetism to ferromagnetism is due to the initial stage of oxidation of Fes_1+x, and that at the initial stage of oxidation, paramagnetic or antiferromagnetic FeS_1+x changes to ferromagnetic FeS_1+x whose composition is near the upper limit of solubility of sulfur.