The laboratory exercise described in this paper is based on a well-known qualitative demonstration of Curie temperature.1 A long ferromagnetic wire, in the form of a spiral, is attracted to a strong permanent magnet placed near its midpoint (see Fig. 1). The temperature of the wire is increased by passing a current through it. When the temperature reaches the Curie point, the wire becomes paramagnetic and is no longer strongly attracted to the magnet. We have developed this demonstration into a quantitative experiment by providing an accurate way to determine the temperature at which the ferromagnetic-paramagnetic transition occurs.

Topics
Ferromagnetic materials, Magnetic materials, Paramagnetic materials, Phase transitions, Educational aids, Laboratories
1.
R.M. Sutton, Demonstration Experiments in Physics (McGraw-Hill, New York, 1938), p. 292.
2.
http://www.kanthal.com. This site includes specifications and physical properties of Kanthal D and other alloys.
3.
H.S. Carslaw and J.C. Jaeger, Conduction of Heat in Solids, 2nd ed. (Oxford University Press, 1959), pp 18–21.
4.
A table of physical and mechanical properties of Kanthal D as well as a number of related alloys may be found at (Propriedades Fisicas e Mecanicas Ligas Kanthal) http://www.casaferreira.com.br/aquecimento/fiosfitas/ligas.htm.
5.
600°C was below the usable range for our optical pyrometer. In order to obtain reliable temperature readings, it was necessary to work well above the Curie temperature.
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© 2007 American Association of Physics Teachers.
2007
American Association of Physics Teachers
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