Revealing complex magnetic interactions in Fe2P-based compounds: a study using Mössbauer spectroscopy and neutron diffraction

The magnetic properties of Fe_2−2xMn_2xP_1−xSi_x (0 ≤ x ≤ 0.5) compounds are studied by neutron diffraction, Mössbauer spectroscopy, and magnetometry. DC magnetization measurements indicate that compounds with 0.2 ≤ x ≤ 0.5 undergo a paramagnetic to ferromagnetic transition, with the Curie temperature increasing as x increases. In contrast, compounds with 0 < x ≤ 0.15 show unclear magnetic ordering in DC magnetization measurements, while AC magnetization measurements display frequency-dependent peaks, indicating glassy spin dynamics. For the x = 0.125 sample, AC magnetization measurements under applied DC fields suggest that the transition at 150 K corresponds to a complex antiferromagnetic (AFM) structure. Mössbauer spectroscopy reveals four distinct regions of hyperfine interactions for different x values, suggesting extreme sensitivity in the magnetic behaviour with Mn and Si substitutions. For 0 < x < 0.15, a drop in the magnetic hyperfine field supports the existence of a complex AFM structure. Neutron diffraction on the x = 0.1 sample confirms an incommensurate AFM structure with a propagation vector q_x = 0.2204(4), consistent with the Mössbauer and magnetization results.