Thermomagnetic Alloy

Thermomagnetic Alloy

 

(or temperature-sensitive alloy), any of various ferromagnetic alloys whose magnetization in a given magnetic field is strongly dependent on temperature. This property appears in a specific range of temperatures near the Curie points, between 0° and 200°C for thermomagnetic alloys.

Three main groups of thermomagnetic alloys are known: (1) the copper-nickel alloys (containing 30–40 percent Cu), (2) the iron-nickel alloys (30 percent Ni), and (3) the iron-nickel alloys (30–38 percent Ni) containing up to 14 percent Cr, up to 1.5 percent Al, and up to 2 percent Mn. Typical examples of these groups are Calmalloy, Thermalloy, and compensators. Copper-nickel alloys may be used at temperatures between –50° and 80°C, but they have the disadvantage of low magnetization. Iron-nickel alloys are designed for use from 20° to 80°C; a change in their crystallographic structure, accompanied by a rise in the Curie point and a drop in the temperature coefficient of magnetization, is possible at negative temperatures. Iron-nickel alloys, which can be used in narrow or wide temperature ranges (–20° to 35°C or –60° to 170°C, respectively), depending on their composition, are the most common. Iron-nickel alloys are used as substrates for multilayer thermomagnetic materials with better magnetic characteristics than the base alloys.

Thermomagnetic alloys are used mainly as thermal compensators and controllers of magnetic fluxes in measuring instruments, such as galvanometers, power meters, and speedometers. The compensators and controllers are produced in the form of shunts that divert to themselves some of the flux generated by the permanent magnets. The operation of such a shunt is based oil a rapid decrease in magnetization with increasing temperature, as a result of which the current increases in the magnet gap. This compensates for the instrument error caused by temperature changes in the induction of the magnet, the electrical resistance of the meter windings, and the stiffness of the counteracting springs. Thermomagnetic alloys are also used in temperature sensitive relays.

REFERENCES

Zaimovskii, A. S., and L. A. Chudnovskaia. Magnitnye materialy. Moscow-Leningrad, 1957. Pages 142–44.
Pretsizionnye splavy: Spravochnik. Edited by B. V. Molotilov. Moscow, 1974. Pages 156–64.

A. I. ZUSMAN