Short-range helical magnetic order in FeP1-xAsx (x = 0.33 and 0.5)

Although the FeP 1-x As x solid solution compounds are isostructural with the binary helimagnets FeP and FeAs with MnP-type structure (sp. gr. Pnma ) of the B31 family, their magnetic structure remained unclear. We studied two members of this family ( x = 0.33 and 0.5) via microscopic site-selective techniques such as Mössbauer and NMR spectroscopy. Our results indicate that the helimagnetic nature of the ground state is preserved, but undergoes significant modifications. In particular, its ordering range seems to become drastically shorter, so that the local fields on the non-magnetic phosphorus atoms decrease several times compared to those in FeP, and even local fields on iron slightly decrease compared to FeP and FeAs. The ordering temperature for these fragmented structures is suppressed down to 20–30 K, which is significantly lower than the T N values for FeP and FeAs. Additionally, both compounds demonstrate higher sustainability to the external field than the parent compound FeP.