Magnetic order in YbMn2Si2 — Neutron scattering investigation

Abstract

Several mechanisms have been proposed to account for the structural and magnetic behaviour of the rare earth intermetallic compound YbMn2Si2 below the transition that occurs around ∼30 K. We have carried out detailed neutron diffraction measurements over the temperature range ∼0.3–52 K and confirm both an antiferromagnetic structure with ferromagnetic Mn (001) planes coupled antiferromagnetically along the c-axis above ∼30 K and the absence of ordering of the Yb sublattice down to 0.3 K. The decrease in intensity of the (111) reflection around ∼30 K together with the appearance of satellite reflections of propagation vector \(k = 00\tfrac{1} {2}\) confirm that the magnetic unit cell doubles along the c axis below TN2. The resultant molecular field acting on half of the ions below ∼30 K removes the degeneracy of the Kramers doublets of the Yb3+ ions and accounts for the additional excitations observed below ∼30 K compared with the inelastic neutron scattering above ∼30 K.