Determining the Curie Temperature of Iron and Nickel

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Erlend H. Graf, Column Editor A Department of Physics & Astronomy, SUNY–Stony Brook, for Teaching Physics Stony Brook, NY 11794; [email protected] Determining the Curie Temperature of Iron and Nickel

S. Velasco and F.L. Román, Departamento de Física Aplicada, Facultad de Ciencias, Universidad de Salamanca, Salamanca, Spain

he phenomenon of ferromag- ate experiments that investigate the point.3-6 However, most of the Tnetism is well-known to high ferromagnetic-paramagnetic phase simple classroom demonstrations of school and undergraduate students, transition by means of the analysis this phenomenon are designed essen- and its physical basis is explained in of the magnetic properties and the tially for demonstrating the existence most general physics textbooks.1-2 electrical resistance of the mate- of the Curie point. In this paper we There are some elegant undergradu- rial above and below the transition describe a rather simple demonstration experiment for determining quantitatively the Curie temperature of a ferromagnetic material. At room temperature materials such as iron and nickel are ferromagnetic, and so they are attracted to a permanent magnet. When these materials are heated above a certain characteristic temperature, they become paramagnetic and are no longer attracted to the magnet. This characteristic temperature is named the Curie temperature (T ) in honor Ferromagnetic C of the French physicist Pierre Curie, sphere 7 Glass tube Magnet who supposedly discovered it in 1892. The Curie temperature is about Thermocouple 770ºC (1043 K) for soft iron and about 358ºC (631 K) for nickel.8 A simple way to demonstrate the Computer existence of the Curie temperature is with the so-called Curie-point pendulum.9-13 In this experiment, Data logger Butane torch a little piece of a ferromagnetic material (rod, nail, coin) is attached Fig. 1. Photo and schematic of the experimental setup used to determine the Curie temperature of iron and to the end of a thin wire, which is nickel. The end of a Type K thermocouple is inserted hung vertically. A nearby magnet at- into a small hole in the sphere, the temperature of tracts the piece of material, which is which is recorded by means of a data logger con- then heated with a Bunsen burner nected to a PC.

The Physics Teacher ◆ Vol. 45, September 2007 DOI: 10.1119/1.2768702 387

Figure 1: Velasco and Román • are: Apparatus needed in our experiment. ments, and calculations that are not a number of assumptions, measure to be made. Their method requires method to allow such determinations to modify the magnet/heated wire Kizowski et al. of the Curie temperature. However, low for a quantitative determination demonstrations normally do not al magnet drops from the wire. Such it reaches its Curie temperature the an electric current through it. When wire. tached to a horizontal ferromagnetic stration employs a small magnet at the magnet. Another simple demon character and is again attracted to material recovers its ferromagnetic from the magnet. After cooling, the becomes paramagnetic and falls away material exceeds its Curie value, it flame. When the temperature of the The major items used in our setup Two small (0.8-cm diameter) fer romagnetic spheres, one iron, one 14 The wire is heated by passing

the corresponding Curie temperature (horizontal lines). (horizontal temperature Curie corresponding the indicating magnet, the onto and thermocouple the off jumps sphere the when occurs slope the in spheres. change The nickel and iron the for curves Cooling 2. Fig. Apparatus 388 15

have shown how Temperature (oC) 200 400 600 800

0 Figure 2:

5 - - - - - 770 Ve T 10 lasco andRomán o 358 the magnet is close enough (~2.5 probe should be kept aligned). When of the magnet and thermocouple brought close to the sphere (the axes temperature, the magnet is slowly properly, with everything at room bar. To ensure that the system works the end of a cylindrical stainless-steel Fig. 1). The disk magnet is placed at tally with the help of a clamp (See this assembly is positioned horizon the hole of one of the spheres, and cm) is free. This end is inserted into that only the end of the probe (0.47 and passed through the glass tube so thin layer of a thermal insulating tape • • • • ime (s) C The thermocouple is coated with a o Data logger One neodymium disk magnet, A cylindrical glass tube, 0.8 cm A Type K thermocouple (-270 1.2 cm diameter, 0.5 cm thick. o.d., 0.15 cm i.d. stainless steel probe). to 137 0.47 cm deep drilled into them. holes 0.125 cm in diameter and nickel. The spheres have radial C 15 Nickel Soft iron º C with 0.1-cm diameter 16 20 and PC. º C - The Phy The and the magnet is quickly moved mocouple. The torch is turned off, and thermal insulation for the ther nickel). The glass bar acts as a shield (~810 above the metal’s Curie temperature flame of the butane torch and raised Experiment the thermocouple. sphere is again placed on the end of back to its original position and the magnet. Then the magnet is moved impediment and jump over to the thermocouple probe without any cm), the sphere must slide off the spheres) is about 10 minutes—very periment (measurements for both inside. The total time for the ex surface cools more quickly than the ing of the sphere is not uniform—its temperature. This is because the cool can be slightly larger than the Curie the temperature indicating the jump is situated very close to the sphere, and 358 Curie temperatures, 770 nickel spheres and the corresponding the cooling curves for our iron and Curie temperature. Figure 2 shows change makes it easy to identify the of the recorded cooling curve. This ing in an abrupt change in the slope due to the surrounding air, result is then free, and it cools very quickly net. netic character and jumps to the mag T the slowly falling temperature reaches tact with the thermocouple. When perature, the sphere remains in con the material is above its Curie tem ery second. While the temperature of thermocouple temperature once ev logger/PC close to the sphere (~2 cm). The data C The sphere is heated with the , the sphere recovers its ferromag 17 The end of the thermocouple º s i C for iron and ~400 cs º C for nickel. If the magnet Te 16 ac system now records the her

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Apparatus Teach Phys. 45 Phys. Teach. Teach. Phys. 389 , 374 (May 1989). (May 374 , Physics Demonstration Demonstration Physics - -

Albert A. Bartlett (Krieger, Malabar, FL, Malabar, (Krieger,

27 Phys. Teach. Phys. . University of Colorado , edit Department of Physics Boulder, CO 80309-0390 Boulder, , 201 (April 1987). (April 201 , ture logger produced by Pico Tech Pico by produced logger ture Ltd. nology sphere the immerse we point this At water of container a in magnet and of heating excessive avoid to order in magnet. the Experiments Experiments 32-3.20. pp. 1970), nickel,” in point rie 1986). (Feb. 86–87 (L), experiment” point 25 again,” point, “Curie Wilson, D.E. Teach Phys. the “Finding Cebulski, Józef and ferromagnetic for temperature Curie materials,” 2007). (Jan. We have used the TC-08 tempera TC-08 the used have We H.F. Meiners, Meiners, H.F. Cu the “Demonstrating Barnes, G. “Curie Bilancia, E. and Levi A. F. 292. p. E-104, 9, Ref. See Budzik, Sylwia Kizowski, Czeslaw

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(McGraw-Hill, New New (McGraw-Hill, Demonstration Experi Demonstration Eur. J. Phys. Phys. J. Eur. Eur. J. Phys J. Eur. La Recherche Recherche La Phys. Teach. Phys. , 723–726 (Aug. 1986). (Aug. 723–726 , Y. Kraftmakher, “Curie point of fer of point “Curie Kraftmakher, Y. romagnets,” (1997). point?,” Physics and Chemistry of Handbook (The Weast R.C. by edited ed., 56th Cleveland, Co., Rubber Chemical E120. p. 1974), Physics in ments 291. p. E-103, 1938), York, 54 Hopkins, C. J. and Hampton, R.N. experi laboratory “Undergraduate tem Curie the determine to ment resistance a using nickel of perature technique,” (1987). transi phase ferromagnetic viewing tion,” 1994). P. Jössang, “Curie … or Pouillet Pouillet or … “Curie Jössang, P. Sutton, R.M. R.A.L. Sullivan, A. Dunk, P.J. Ford, Ford, P.J. Dunk, A. Sullivan, R.A.L. for method direct “A Lue, Chin-Shan Friday, 13 Oct Friday, 2006, http://www.bobpark.org/index.html.

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2007 - What’s New, - Am. J. Phys. Phys. J. Am.

It is forty of stories women who made major contributions to twentieth 2 September 1 45, ol. V Out of the Shadows: Contributions Centuryof Twentieth to Women Physics ◆

2. Robert L. Park, out a sense of regret at what the world lost by not having greater involvement of women in my freshman only science. physics class 10% Even today, averages women.” 1. and Gary Williams (Cambridge University Press, UK, Sept. 2006). “Out of the Shadows: Contributions of to Women Twentieth-Century Physics ed by Nina Byers and Gary Williams, is an important contribution to the history of science. century physics, written by distinguished scientists who are themselves actively engaged in the areas of physics about which they write.… It cannot be read with Women Women in Physics: New Book Tells Physics for Scientists and Scientists for Physics her s, 4th ed. (Freeman Worth, Worth, (Freeman ed. 4th s, ac the Story for the First Time

i s ferromagnetic material,” material,” ferromagnetic etcetera... 2004), pp. 949–951. pp. 2004), a of transition phase the of study “A Physics for Scientists and Engineers, Engineers, and Scientists for Physics CA, Belmont, (Thomson, ed. 6th Engineer 909–913. pp. 1999), York, New J.N. Fox, N. Gaggini, and J.K. Eddy, Eddy, J.K. and Gaggini, N. Fox, J.N. P. A. Tipler, Tipler, A. P. Jr., Jewett J.W. and Serway R.A.

3. 2. References 1. SA080/04 and SA092/04. Grants Grants FIS2006-03764 FEDER and FIS2005-05081, and by Junta de CyL-FSE of Spain under Grants We are grateful for We the finan cial support by the Ministerio de Educación y Ciencia of Spain under stration. Acknowledgments reasonable for a classroom demon classroom a for reasonable The Phy