ИСТИНА

The evolution of the domain structure (DS) of cubic magnetite particles of submicron and micron sizes has been modeled numerically during “cooling” of a particle from the Curie temperature Tc to room temperature Tr following by reverse “heating” to Tc in order to determine the degree of irreversibility of DS changes during heat treatment. It is shown that typical magnetic configurations are represented by the flower state at small sizes less than 100 nm. Grains up to 2 microns in size exhibit vortex mode with one or two vortices. A model of the formation of thermoremanent magnetization (TRM) in submicron pseudodomain particles (PSD) is proposed based on an expansion of single-domain Neel's thermofluctuation model of the TRM acquisition. According the model, the equality of blocking and non-blocking temperatures is kept for small submicron PSD grains. Consequently, for this fraction the Thellier laws of additivity and independence of pTRM must be also valid. This work is supported by the RFBR grant 20-05-00215 and the state program of the IPE RAS.