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High-temperature moment-volume instability and anti-Invar of γ-Fe

1994; American Physical Society; Volume: 49; Issue: 9 Linguagem: Inglês

10.1103/physrevb.49.6012

1095-3795

M. Acet, H. Zähres, E. F. Wassermann, Werner Pepperhoff,

Magnetic Properties and Applications

Just as Invar describes a system with a smaller than ``normal'' thermal expansion in a magnetically ordered state, a system with a larger than ``normal'' thermal expansion in a magnetically disordered state can be described as anti-Invar. Anti-Invar had been already observed in a number of fcc binary and ternary alloys of the 3d series well above magnetic ordering temperatures. While Invar is characterized by low-temperature moment-volume instabilities, anti-Invar signifies the importance of high-temperature moment-volume instabilities. Both are closely related to the ground-state properties. We have reinvestigated the ${\mathrm{Fe}}_{50}$${\mathrm{Ni}}_{\mathit{x}}$${\mathrm{Mn}}_{50\mathrm{\ensuremath{-}}\mathit{x}}$ alloy system and confirmed the existence of enhanced thermal expansion at high temperatures, i.e., the anti-Invar effect. With the aid of the thermal properties of these alloys we deduce the temperature dependence of the thermal expansion of \ensuremath{\gamma}-Fe and show its anti-Invar nature. The enhanced volume expansion in \ensuremath{\gamma}-Fe amounts to 2.8%, which is larger than the Invar effect (2%) in ${\mathrm{Fe}}_{65}$${\mathrm{Ni}}_{35}$.