Incommensurate magnetic structure in copper metaborate

Based on the experimental data on copper metaborate single crystals obtained in X-ray and neutron diffraction studies and heat capacity, magnetic susceptibility, and muon spin relaxation measurements, a phenomenological theory of the incommensurate magnetic structure of this crystal was developed. Considering the space group of the crystal, I (4) over bar 2d, Lifshits invariants were included into its thermodynamic potential. An analysis showed that magnetic structure formation at 10-20 K was dominated by the subsystem of copper spins in 4b unit cell sites. Below 10 K, the role played by the magnetic subsystem of copper spins in 8d unit cell sites in the formation of the magnetic structure of copper metaborate substantially increased. This caused a sharp increase in the wave vector of the incommensurate structure as temperature lowered. Numerical simulation of the temperature dependence of the wave vector of the helix and the heat capacity of the crystal gave a satisfactory description of the experimental data. This simulation was used to estimate the parameters of the phenomenological thermodynamic potential of the magnetic system of copper metaborate. (C) 2001 MAIK "Nauka/Interperiodica".