Magnetic Order-Order Transition in Tetragonal ErB₂C₂

Abstract

We have investigated magnetic properties of ErB₂C₂ which is an isostructural compound of the antiferroquadrupolar ordering materials, DyB₂C₂ and HoB₂C₂, by magnetisation and neutron diffraction measurements. ErB₂C₂ shows magnetic transitions at T_N = 15.9 K and T_t = 13.0 K. The magnetic structure of the ground state is a simple Ising-type antiferromagnetic one with a propagation vector of k=(1, 0, 0). The intermediate phase between T_N and T_t under zero magnetic field is a long range magnetic ordered state with a transverse sinusoidal modulation with a propagation vector of (1+δ, δ, 0), where δ=0.1120(2) which is nearly the same as that in phase IV in HoB₂C₂.