Magnetic ordering induced Raman scattering in FePS3 and NiPS3 layered compounds

Abstract

Systematic investigation of the phonon Raman scattering efficiency in FePS3 as a function of temperature in the vicinity of the magnetic phase transition temperature T demonstrates three levels of enhancement of the Raman peaks: i) in the low frequency region the appearance, and strong enhancement in the antiferromagnetic phase, of peaks not observable in the paramagnetic phase; ii) in the intermediate frequency region the enhancement and narrowing of peaks which are only weak in the paramagnetic phase; iii) in the high frequency region the enhancement of phonon Raman peaks. All of these manifestations can be explained by the Brillouin Zone folding due to the appearance, below TN, of a magnetic superstructure in the c direction with a magnetic unit cell which is double that of the crystallographic cell. In NiPS3 the antiferromagnetic in-plane ordering along the b axes conserves the same magnetic unit cell as the crystallographic cell. The magnetic ordering in the c and a directions is ferromagnetic. Only slight enhancements are observed in this case near TN, but there also appear a broad continuum in the Raman spectrum and Fano interferences on top of this continuum. © 1987 IUPAC