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First order magnetic transitions described by three degrees of freedom: an appropriate Clausius-Clapeyron equation and application to MnAs and Gd(5)Ge(2)Si(2) compounds.

Author(s) : GAMA S., CAMPOS A. de, COELHO A. A., et al.

Summary

A magnetic material is a thermodynamic system described by at least three degrees of freedom, comprising the pairs of variables T-S, p-V and M-H. Magnetic first order transitions must obey the Gibbs phase rule, meaning that one phase fields in the phase diagrams must be separated by two phase fields. This means that these transitions occur over intervals of temperature, pressure and magnetic field and that an extended form of the Clausius-Clapeyron equation is valid. The notion of latent heat must be adapted for these transitions. Here, the authors present experimental evidence for these features of the first order transitions for the compounds MnAs and Gd(5)Ge(2)Si(2). Measurements of their magnetic properties allowed us to construct their magnetic phase diagrams, verifying the validity of the generalized Clausius-Clapeyron equation. For MnAs these results are compared with calorimetric data from the literature. The obtained good agreement indicates that this approach to the magnetic first order transitions is a sound one.

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Pages: 2009-3

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Details

  • Original title: First order magnetic transitions described by three degrees of freedom: an appropriate Clausius-Clapeyron equation and application to MnAs and Gd(5)Ge(2)Si(2) compounds.
  • Record ID : 2009-1624
  • Languages: English
  • Source: 3rd International Conference on Magnetic Refrigeration at Room Temperature
  • Publication date: 2009/05/11

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