Seijiro Maeda

On the Ferrimagnetism of Iron Selenides

The thermomagnetic properties of iron selenides FeSe x with various selenium contents x were measured as functions of temperature. The thermomagnetic curves obtained belong to the ordinary Weiss type. It was also found that the magnetization at the boiling temperature of liquid nitrogen increases with the selenium content, reaches its maximum value. 35 gauss, at x =1.23, and then decreases again with further increase of x . The Neel temperature was approximately 150°C in the range of x from 1 to 1.26 whereas it decreases gradually with further increase of x and approaches to its lowest value 30°C at x =1.35. The origin of the magnetization of this substance was discussed based on the theory of ferrimagnetism.

On the Magnetic Properties of the System MnSb-CrSb

The change of magnetic properties due to the replacement of manganese by chromium in manganese antimonide (MnSb), which is of the NiAs structure, was investigated. It was found that, with the increase of the concentration of chromium, the magnetic behaviour of these compounds (Mn 1- x Cr x )Sb changes as follows: (1) at x =0 (MnSb), the temperature-magnetization curve shows typical behaviour of ferromagnetic substance, (2) in the range 0.1≤ x ≤0.7, it deviates remarkably from the Weiss curve in proportion with the chromium content, and the temperature dependence of the reciprocal susceptibility above the Curie point is of a ferrimagnetic type. (3) In the range 0.8≤ x ≤0.9 a transition from ferrimagnetic to antiferromagnetic was observed, and finally (4) at x =1 (CrSb) a typical antiferromagnetism could be seen. A short discussion of such transitions is given.

Thermal Analysis of Iron Sulfides at the Temperature Range of β-transformation

The measurements of specific heat was performed at the temperature range of β-transformation in iron sulfides with various sulfur contents x ranging from x =1 to x =1.12. A peak in specific heat versus temperature curve is found at 315°C, and this temperature as well as the jump in specific heat, 0.05 cal gr. -1 deg. -1 in value, is almost independent of sulfur contents. The mechanism of transformation is discussed, based upon the theory of ferrimagnetism, and it is concluded that the present experimental results accord well with the theoretical ones.

On the Magnetic Anisotropy of a Pyrrhotite Crystal

Measurement of the magnetic anisotropy energy of a single crystal of natural pyrrhotite in c-plane was made by means of the torque method at room temperature up to a magnetic field of 20000 oe and at low temperature in a constant field. It was found that the easy axis lay along [2\bar10] direction above -80°C which, however, changed to [100] direction below that temperature. The torque curves in c-plane were composed of two- and six-fold symmetric parts. It was also found that in the range of strong magnetic fields the six-fold symmetric part at room temperature decreased with the inverse square of the applied field; such a field dependence is explained assuming a triad structure for the single crystal of pyrrhotite. A remark is also given on the origin of the two-fold symmetric torque.

On the Magnetic Properties of Chromium Sulfides

The thermomagnetic properties of chromium sulfide CrS 1.17 were studied. The spontaneous magnetization of this compound, which is probably of the ferrimagnetic origin, suddenly disappears during cooling at -120°C. A slight heat absorption was observed at this transition point. By X-ray analysis excess diffraction lines besides those of the ideal crystal lattice of the nickel arsenide type were observed at room temperature, which shows a super-lattice structure with parameters of twice c and \(2\sqrt{3}\) times of a , a and c being those of the original lattice. It was also found by X-ray analysis that there was no change of the crystal lattice at the magnetic transition temperature, -120°C. This compound showed a ferrimagnetic behavior with the asymptotic Curie temperature at 150°K. A peak in susceptibility vs . temperature curve was found by the thermomagnetic measurement in the temperature range from the liquid helium temperature to -120°C. Basing on these data, a short discussion on the nature of the a...

On the \(\varLambda\)-shaped Ferrimagnetism of FeS1.10

A \(\varLambda\)-shaped change in the thermomagnetic curve in iron sulfide FeS 1.10 (γ-transformation) was investigated experimentally. It was found that the height of peak was increased by decreasing the heating speed of the specimen. Temperature hysteresis in the thermomagnetic curves were also found at the low temperature side of the peak. Excess specific heat corresponding to the thermomagnetic anomaly was observed; the amount of anomalous heat absorption during the transformation was of the order of 100 cal/mol. It was concluded that the change of magnetism at the transformation is due to the ferrimagnetic distribution of ferrous and ferric ions and the change of vacant site distribution at the transformation.