THE HELIMAGNETIC STRUCTURE OF EU(AS0.20P0.80)(3) DETERMINED BY ZERO-FIELD NEUTRON POLARIMETRY

Zero-field neutron polarimetric measurements have been made on semi-me tallic phosphorus-rich Eu(As1-xPx)(3) with x = 0.80 to determine the m agnetic structure of the low-temperature helimagnetic phase. Unlike un polarized neutron diffraction, this technique allows an unambiguous de termination of the spin configuration. We show that the previous struc ture model derived from unpolarized neutron diffraction data in which the Eu magnetic moments were assumed to be confined to the a-c plane i s not correct. The zero-field neutron polarimetric data clearly demons trate the existence of a spin component parallel to the monoclinic b-a xis. The new model based on these observations is in better agreement with the diffraction intensities obtained from unpolarized neutron dif fraction. In this model the low-temperature helimagnetic phase in phos phorus-rich Eu(As1-xPx)(3) has two components, one parallel to the b-a xis and a second which lies in the a-c plane nearly perpendicular to t he propagation vector.