Ho Be 13 commensurate and incommensurate magnetic structures

Abstract

Neutron diffraction (λ = 1.140 Å) studies show that the cubic intermetallic compound Ho Be 13 exhibits an incommensurate helimagnetic structure in the temperature range between T N' = 4.5 K and T N = 6 ± 0.5 K and a commensurate magnetic structure below T N' ( a, a, 3 a tetragonal magnegnetic unit cell). The magnetic moments of the Ho 3+ ions lie in a plane perpendicular to the crystallographic c -axis. The propagation vector of the magnetic structure, parallel to the crystallographic c -axis, is a function of temperature: τ( T) = 1 3 c ∗ (1 − ϵ( T)), with ϵ( T)<5×10 −2 for T N'< T≤ T N and ϵ( T) = 0 for T≤ T N'. These magnetic structures results fro the competition between exchange interactions and magnetocrystalline anisotropy. A magnetic phase diagram has been obtained for the RE Be 13 intermetallics (RE = Rare Earth), within the frame of a Hamiltonian model incorporating isotropic exchange interactions (molecular field approximation) and fourth order magnetic anisotropy in the (001) plane. Theoretical and experimental results are then compared for RE = Gd (Incommensurate magnetic structure), Tb and Ho (Commensurate - Incommensurate), Dy and Er (Commensurate τ = 1 3 c ∗ magnetic structure).