The thermal energy changes occurring in cyclic magnetization of a 4% nickel-silicon alloy (Curie temperature approximately 34 °C) were determined at 20 °C and 30 °C. The total thermal energy change at 30 °C was about a quarter of that at 20 °C. An equation given previously by Davis is used to show that the changes are almost entirely due to the ordinary magnetocaloric effect with small components due to magnetic potential energy and He dI. Results are tabulated.

Energy changes in magnetization of a nickel - silicon alloy

In observing the energy changes occurring during magnetization of ferromagnetics and ferrimagnetics three effects referred to as the `dip', `low-field rise' and `kink' have been reported at low fields by Bates and his co-workers, but have remained unexplained hitherto. They are investigated in the present paper for a hypothetical specimen by means of the general energy equation previously given by Davis. The `kink' is shown to be due to the large magnetostriction energy change at fields comparable with Hc. The `dip' is due to the long narrow hysteresis loop making changes of magnetization large at small values of external field. The `low-field rise' is due to the remanent magnetization making the energy curve slightly asymmetrical. Three curves are given.

Energy changes in magnetization of ferromagnetics and ferrimagnetics: an interpretation of three reported effects

An equation is derived which gives the total energy variation of a ferromagnetic during virgin and cyclic magnetization, and makes possible a detailed analysis of the distribution of energy variation over the various processes involved, and its dependence on magnetizing field and intensity of magnetization. The method is first to calculate for small changes of magnetizing field the total energy made available within the specimen by the current source, by the ordinary magnetocaloric effect and by conversion of magnetic potential energy. From this there are then subtracted the major quantities of energy stored as potential energy: namely, in the demagnetizing and external fields of the specimen, and as magnetocrystalline energy and work done in magnetostriction against internal stresses. Energy changes due to other processes are considered but found to be small. The theory gives calculated curves agreeing well in shape with the observed curves for nickel of Bates and Davis. Discrepancies in magnitude are shown to be largely due to understimation of magnetocrystalline energy. A method is given which, in so far as it is valid, gives a messure of the actual total magnetocrystalline energy and internal work of magnetostriction. It is concluded that the thermal energy curves of Bates and Davis are, in fact, curves of total magnetic and magnetomechanical energy variation.

J H Davis

Papers

Energy changes in magnetization of ferromagnetics in low and moderate fields