Mossbauer studies of helimagnetic FeAs

The Mossbauer studies on helimagnetic intermetallic compound FeAs are reported over a temperature range of 30 to 525K. The spectrum in the paramagnetic state is found to be a well defined single quadrupole doublet and the quadrupole splitting has been found to decrease with increase in temperature. The spectrum in the magnetic state is, however, found to be a complex asymmetric pattern. It is argued that in this system, the complexities in the spectrum are arising because of the helimagnetic spin ordering and not due to the presence of different local principal EFG axes for the four crystallographically equivalent Fe atoms in a unit cell.