Exchange effects in invar hardening: Fe0.65Ni0.35 as a test case

M. Molotskii, V. Fleurov

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An increase of the critical resolved shear stress of Invar alloys (Invar hardening) with a lowering temperature is explained. The effect is caused by a growth of the exchange interaction between dangling d-electron states of dislocation cores and paramagnetic obstacles (e.g., Ni atoms in FeNi alloys) that occurs below the Curie temperature. The spins of the two electrons align along the magnetization due to the exchange interaction with the surrounding atoms of the ferromagnetic. The exchange interaction between the dislocations and obstacles is enhanced in Invars due to a strong growth of the magnetic moments of atoms under the action of elastic strains near the dislocation cores. Parameters characterizing the exchange interaction are determined for the case of the Fe0.65Ni0.35 Invar. The influence of the internal magnetic field on the dislocation detachment from the obstacles is taken into account. The obtained temperature dependence of the critical resolved shear stress in the Fe0.65Ni0.35 Invar agrees well with the available experimental data. Experiments facilitating a further check of the theoretical model are suggested.

Original languageEnglish
JournalPhysical Review B - Condensed Matter and Materials Physics
Issue number18
StatePublished - 19 Apr 2001


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