Invar effect

Lagarec K, Rancourt DG (2000) FesNi-type chemical order in FeesNiss films grown by evaporation Implications regarding the Invar problem. Phys Rev B 62 978-985 Lagarec K, Rancourt DG, Bose SK, Sanyal B, Dunlap RA (2001) Observation of a composition-controlled high-moment/low-moment transition in the face centered cubic Fe-Ni system Invar effect is an expansion, not a contraction. J Magnet Magnetic Mater (in press)... 

One of the most interesting effects is the so-called Invar-effect, which is observed in FeNi alloys. This was noted already 1897 by Guillaume [148], and consists of a vanishing of the thermal expansion coefficient of FeNi steels at Ni concentrations around 35%, the alloy does not expand when heated. In recent years theoretical as well as experimental communities have expressed an increased interest in the problem [149, 150, 151, 152, 153, 154, 155, 156, 157], because of new suggestions of the origin of the Invar effect in the FeNi system related to an observation of noncollinear magnetic structures in the alloy [158]. 

D. D. Johnson and W. A. Shelton, in The Invar effect A Centennial Symposium, edited by J. Wittenauer, (The Minerals, Metals Materials Society, 1997). 

Thermal expansion curves and magnetic properties of amorphous Cr Fe9o xZrio alloys have been investigated by [1994Lu] providing experimental evidence that the invar effect of these alloys is also related to the instabiUty of the ferromagnetism. 

It is possible to prepare, in the two-phase domain, composite alloys consisting of a high conductivity copper rich phase and a low expansivity Invar rich phase [1998Cot] provided that the ratio Fe/Ni be maintained near by 64/36 (in mass%) because the Invar effect occurs only in a narrow composition range. 

Thermal Properties. Selected data of thermal conductivity and thermal expansion of PGM and PgAg alloys are given in Tables 3.1-212-3.1-215, Fig. 3.1-273. FePd-alloys exhibit around the Fes Pd stoechiometry in the disordered state zero coefficient of thermal expansion (Invar effect) [1.281,282]. 

The Invar effect, which was discovered by Guillaume [14] at the end of the 19th century, refers to the anomalously low coefficient of thermal expansion of certain alloys [23, 36], FeesNiss being the archetype. Different compositions of these alloys also show related effects, such as a constant modulus of elasticity with tranperature [12],... 

The two main types of model [26] for explaining the Invar effect are those [34] based on a high local magnetic moment-low local magnetic moment transition (HM/LM), and those involving a frustrated local magnetic order [23,27],... 

Although there have been a number of different attempts at experimentally determining the mechanism behind the Invar effect, the problem is yet to be conclusively resolved [21, 22]. A consideration of how the models extend into the liquid state, particularly with respect to magnetic correlations, may allow for certain possibilities to be excluded. 

Entel P, Hoffmann E, Mohn P, Schwarz K, Moruzzi VL (1993) First-principles calculations of the instabdity leading to the Invar effect. Phys Rev B 47(14) 8706-8720... 

Weiss RJ (1963) The origin of the Invar effect. Proc Phys Soc Lond 82(526) 281-288... 

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