微弱磁場に於ける鐵單結晶及び鐵ニッケル合金の磁化曲線の研究

Abstract

The magnetization of single crystals of iron, as well as nickel and iron-nickel alloys, in very weak fields, has not yet been measured. So the present writers prepared single crystals of iron having a large dimension ratio, such as 100, and used an astatic magnetometer of large sensibility for measuring the intensity of magnetization. At first, the magnetization of single crystals of iron in very weak fields was measured by a usual method of demagnetization by alternating fields. According to the result of measurement, the field-range of reversible initial susceptibility is very low, and the initial susceptibilities of iron single crystals in three principal directions are as follows:- κ0[100]=26.6, κ0[110]=18.7 and κ0[111]=13.9, their ratio being 1:1/1.42:1/1.90 The effect of weak stress and that of dimension ratio on the initial susceptibility were also measured, and found that the stress affects to diminish κ0[100] and to increase κ0[110] and κ0[111] and so the anisotropy diminishes as a whole, and that as the dimension ratio decreases, the anisotropy of κ0 also diminishes at first slowly and then rapidly, v_??_nishing in a dimension ratio of about 10. Next, the magnetization was measured by means of demagnetization by heating and found that the initial susceptibilities are three to four times greater than those obtained by the demagnetization by reversals, as shown below; κ0[100]=85.4, κ0[110]=46.8, κ0[111]=69.2 and κ0[100]:κ0[110]:κ0[111]=1:1/1.82:1/2.24. This large difference in initial susceptibilities obtained by these two methods of demagnetization was found to be due to the diminution of number of unstable elementary magnets present in the boundaries of magnetic domains by gradually decreasing alternate fields, or briefly by agitating effect of magnetostriction due to the alternate fields. The change in the initial susceptibility caused by the alternate fields also differs in the directions of three principal, axes of iron. It is large in a low temperature and diminishes as the temperature is raised, and vanishes at the critical temperature. The temperature-dependency of the anisotropy of initial susceptibility of iron crystals mentioned above was found to diminish with the rise of temperature, and also with the latter the ratio of initial susceptibilities in three principal directions decreases, tending to 1 just below the critical temperature. In the case of iron-nickel alloys containing 18.5% Fe, the magnetostriction of which is zero, the initial susceptibility is almost independent of temperature, and also the effect of alternate fields on the initial susceptibility is zero. The above complicated phenomena were successfully explained on the basis of Honda-Okubo's theory of magnetization.