Magnetic solids warm and cool under the application and removal of a magnetic field. Such effects have been used for nearly fifty years to produce cooling near absolute zero for low temperature physics research. Two technological developments have made magnetic heating and cooling in the vicinity of room temperature technically feasible. These are the bulk separation of the rare earth elements and the development of superconducting magnets that can produce very strong magnetic fields with very low power expenditure. With these developments and a combination of known, but previously unassociated principles, it is appropriate to evaluate this new method of heating and cooling that differs rather fundamentally from methods now in use. A major feature of the magnetic cycle is that, in an ideal embodiment, it would pump heat with the maximum theoretically-possible efficiency, i.e., the Carnot efficiency.

The efficacy of the regenerative cycle has been shown in a reciprocating laboratory device by the production of a substantial span of temperature between the heat absorbing end and the heat discharge end. However, no device that would qualify as a commercial prototype has yet been constructed, and a substantial amount of development. work, parametric study of alternative configurations, and economic evaluation must be done. The basic principles of magnetic heat pumping have been presented and are fairly simple.

Several possible variations of the overall form of the magnetic heat pump have been presented, as well as some alternative forms of the magnetic refrigerant core. Other new configurations may well be conceived to utilize the attractive characteristics of magnetic thermodynamic cycles effectively.