Landolt-Börnstein - Group III Condensed Matter Introduction


This chapter provides an introduction to the properties and aspects of Invar alloys. Such alloys are very important for precision measuring instruments in the fields of electronic and optical systems. The linear thermal expansion coefficient of common metals and alloys is usually the order of magnitude of 10-5K-1. In the case of the cancellation of the anharmonic term by the spontaneous volume magnetostriction, the thermal expansion coefficient becomes zero. Therefore, Invar characteristics are observed when the hypothetical paramagnetic linear thermal expansion below the magnetic transition temperature and the spontaneous volume magnetostriction are comparable in magnitude but with different sign. The Invar characteristics have been observed not only in several kinds of Fe-rich fcc alloys but also in various Fe-based amorphous alloys, and in Cr-based and Mn-based crystalline alloys. A large value of ωs is often observed in weak ferromagnetic materials in which the exchange splitting is not so large so that the Fermi surface appears in both spin sub-bands of the d-states. When the spin fluctuation effect becomes dominant, the Invar effect is not always correlated with the magnetic long range order, namely, TC and TN, and a small thermal expansion coefficient is obtained in the spin glass state. The shrinkage often occurs even above TC due to the same effect.

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Title Introduction
Book Title
Magnetic Alloys for Technical Applications. Soft Magnetic Alloys, Invar and Elinvar Alloys
7.1.4 Invar alloys
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Landolt-Börnstein - Group III Condensed Matter
  • H. P. J. Wijn
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  • K. Fukamichi
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