Magnetoplastic Effect: From Spin Dynamics to Dislocation Mobility

Abstract

Microscopic elementary events responsible for magnetoplastic effect are studied in detail by means of photoluminescence, electron spin resonance and SQUID magnetometry in NaCl:Eu single crystals. The Eu2+ clusters being dislocation obstacles were used as a spin and luminescent labels allowed detecting simultaneous spin and atomic structure transitions in exchange-coupled few-atomic Eu2+ clusters under static magnetic field B = 5 T. Rearrangement of atomic structure of these clusters changes the lattice distortions around them and effectiveness of clusters interaction with moving dislocations during plastic flow. From the comparison of spectroscopic data and numerical calculations of aggregation pathways of small clusters it was concluded that magnetosensitive clusters contain two Eu2+ ions with parallel spins (dimers). Two different ways of creating of magnetosensitive dimers in the crystal lattice are found: (1) slow diffusion limited aggregation in freshly quenched crystals, and (2) fast aggregation stimulated by dislocations dynamical distortions of lattice provided by the plastic deformation of aged crystals.