The Distribution of the Heat Emission in the Magnetic Hysteresis Cycle

Abstract

Warburg has shown that for a complete magnetic hysteresis cycle an amount of energy equal to the area of the $I$-vs-$H$ loop is dissipated and appears as heat. But for a part of a cycle theory only states that $\mathrm{energy}=\ensuremath{\int}{H}^{H+\ensuremath{\Delta}H}\mathrm{HdI}$ is supplied to the iron. Part of this energy appears as heat, while the rest is stored as magnetic potential energy and is released in another part of the cycle. The distribution of the heat emissions for successive steps along the hysteresis cycle was obtained experimentally from the rises in temperature produced in the iron or steel. The corresponding values of $\ensuremath{\int}\mathrm{HdI}$ were obtained from the hysteresis loop. The difference between these quantities gave the potential energy throughout the cycle. The potential energy was greatest for $H={H}_{\mathrm{max}}$, zero for $H=0$. The heat emission was zero from $H={H}_{\mathrm{max}}$ to $H=0$, increased up to a little beyond $H=\ensuremath{-}{H}_{c}$, (${H}_{c}=\mathrm{the}\mathrm{coercive}\mathrm{force}$), and then decreased to $H=\ensuremath{-}{H}_{\mathrm{max}}$. A cooling was never observed. The results are discussed in connection with a recent theory of atomic behavior in ferromagnetic metals.