Origin of the magnetostructural coupling inFeMnP0.75Si0.25

Abstract

The strong coupling between the crystal structure and magnetic state (ferromagnetic or helical antiferromagnetic) of FeMnP 0.75 Si 0.25 is investigated using density functional theory in combination with atomistic spin dynamics. We find many competing energy minima for drastically different ferromagnetic and noncollinear magnetic configurations. We also find that the appearance of a helical spin-spiral magnetic structure at finite temperature is strongly related to one of the crystal structures reported for this material. Shorter Fe-Fe distances are found to lead to a destabilized ferromagnetic coupling, while out-of-plane Mn-Mn exchange interactions become negative with the shortening of the interatomic distances along the c axis, implying an antiferromagnetic coupling for the nearest-neighbor Mn-Mn interactions. The impact of the local dynamical correlations is also discussed.

Kinetic-arrest-induced phase coexistence and metastability in(Mn,Fe)2(P,Si)

“…The magnetic transition is strongly coupled to variations in the lattice parameters. The FM configuration is in competition with an incommensurate magnetic configuration in the (Mn,Fe) 2 (P,Si) compounds, and the relative stability of the two configurations strongly depends on the c/a ratio [29]. The stability of the incommensurate magnetic configuration is enhanced with the increase in c/a ratio [29].…”

“…The FM configuration is in competition with an incommensurate magnetic configuration in the (Mn,Fe) 2 (P,Si) compounds, and the relative stability of the two configurations strongly depends on the c/a ratio [29]. The stability of the incommensurate magnetic configuration is enhanced with the increase in c/a ratio [29]. As a result, a metastable 094426-7 incommensurate magnetic configuration forms in S1 and S3 with large c/a ratios at low temperature.…”

“…These two phases transform into a FM and an incommensurate magnetic phase upon cooling [28]. However, theoretical calculations revealed that the coexistence of a FM and an incommensurate magnetic phase may be a result of competing magnetic configurations [29,30]. The incommensurate magnetic phase is considered to be an intermediate metastable phase, which is formed due to the kinetic arrest of the PM-FM transition [30].…”

Short-range magnetic correlations and spin dynamics in the paramagnetic regime of(Mn,Fe)2(P,Si)

“…In contrast, the magnetic moment of the Mn atoms (about 2.6 μ B ) is preserved when crossing the FM-PM transition [2,7]. The local magnetic field exerted on the Fe atoms by the Mn atoms triggers the moment formation and magnetic order [7,22]. Therefore, magnetic correlations between Mn atoms in the PM state will enhance the local magnetic field, promote the formation of Fe magnetic moment, and will finally result in long-range magnetic order.…”

“…It should be noted that the AFM intermediate phase has only been found in certain (Mn,Fe) 2 (P,Si) compositions [21]. The formation of the AFM phase is due to the competing magnetic configurations and strong magnetoelastic coupling in (Mn,Fe) 2 (P,Si) compounds, as revealed by recent theoretical [22] and experimental [21] studies.…”