Origin of the modulus anomaly over a wide temperature range of Mn_0.70Fe_0.25Cu_0.05 alloy

To reveal the origin of modulus anomaly over a wide temperature range (about 240 K) observed in Mn_0.70Fe_0.25Cu_0.05 alloy, a phase-field model considering antiferromagnetic (AF) transition with doping Fe was established, in which the average modulus is considered as a functional of order parameter. Simulation reveals that the pining effect by doping Fe leads to the increase of low spin non-collinear AF domain walls (LS), meanwhile, the LS domain walls gradually evolve to high spin collinear AF domains (HS) with lowering temperature, accompanying the growth of HS domains and the decrease of modulus, and vice versa. Such a dynamic antiferromagnetic domain size (DAFDZ) effect gives rise to modulus anomaly, while the proper volume ratio of LS and HS is a crucial factor for the wide temperature range of modulus anomaly.