A neutron scattering and μSR investigation of the magnetic phase transitions of CuB2O4

We have investigated the magnetic ground state in CuB2O4, copper metaborate, by means of neutron diffraction and muSR measurements. At T-N = 21 K CuB2O4 undergoes a second-order phase transition from a paramagnetic to an antiferromagnetic commensurate state followed by a second transition at T* = 10 K where the two magnetic sublattices form a soliton lattice, as reported earlier. We give a detailed analysis of the magnetic structure in the commensurate phase which is found to be different from the one published recently. New experimental results are presented which show the existence of a third transition below T approximate to 1.8 K. The magnetic structure remains incommensurate at very low temperatures, but a re-distribution of the magnetic intensities is observed in the neutron diffraction data set which suggests that the phases between the Cu2+ spins are changed. (C) 2002 Elsevier Science B.V. All rights reserved.