Neutron diffraction study of the magnetic structure of ErSi

Abstract

The compound ErSi is known to be antiferromagnetic below T N = 11.5 K and to undergo at T IC a lock-in transition from a sine-wave modulated magnetic structure incommensurate with the crystal lattice (above T IC) characterized by the wave vector K = (k x,0, 1 2 ) to a commensurate one with the wave vector ( 1 2 , 0, 1 2 )(below T IC ). This magnetic behaviour has been revisited by means of powder neutron diffraction. Evidence is given for the existence of a two-component incommensurate wave vector K = ( k x , 0, k z ) above T IC = 5.75 K. The erbium magnetic moments are colinear and aligned along the a-axis. Two orderings are compatible with the experiment and with group theory calculations, namely ( + + + + ) and ( + + + − ) for the four of the chemical unit cell. Finally, the coexistence of the two transforming magnetic phases is put in evidence near T C thus showing the first-order character of the transition. Hysteresis effects are observed near T C and in the whole incommensurate domain.