Spontaneous Magnetization — Techniques and Measurements

Measurements on the temperature variation of spontaneous magnetization by both the magnetothermal and magnetic methods have hitherto been confined to nickel; the extension of these measurements, calling for greater sensitivity, is discussed. To the direct method devised by Weiss and Forrer has been added a direct current amplifier, which allows a small magnetocaloric rise of temperature to be measured accurately. The original ferromagnetic balance devised by Sucksmith has been improved and now is capable of wider application to measurements of magnetic intensity in fields which are due to either air core coils or electromagnets. The method is not complicated by the presence of any image effect so that measurements of $\frac{d\sigma }{\mathrm{dH}}$ in high fields can be made with considerable precision.

Measurements on a copper-nickel alloy (27.5 percent Cu) have been made, and it is shown that the two methods give identical results except in the immediate neighborhood of the Curie temperature, where the thermal measurements give a steeper descent to the temperature axis with little "tail," while the magnetic data indicate a higher Curie temperature with a significant tail. Below the Curie temperature the linear relationship between the magnetocaloric rise of temperature and the square of the intensity magnetization is found as in nickel and iron; above this temperature there is pronounced curvature.

Measurements have also been carried out on a mixed ferrite (MgO ZnO 2${\mathrm{Fe}}_2$${\mathrm{O}}_3$). Satisfactory agreement between the results by the two methods are obtained, both curves differing markedly from the law of corresponding states for the ferromagnetic elements.