Ferrimagnetic 120∘^\circ magnetic structure in Cu2OSO4

We report magnetic properties of a 3d$^9$ (Cu$^{2+}$) magnetic insulator Cu2OSO4 measured on both powder and single crystal. The magnetic atoms of this compound form layers, whose geometry can be described either as a system of chains coupled through dimers or as a Kagom\'e lattice where every 3rd spin is replaced by a dimer. Specific heat and DC-susceptibility show a magnetic transition at 20 K, which is also confirmed by neutron scattering. Magnetic entropy extracted from the specific heat data is consistent with a $S=1/2$ degree of freedom per Cu$^{2+}$, and so is the effective moment extracted from DC-susceptibility. The ground state has been identified by means of neutron diffraction on both powder and single crystal and corresponds to a $\sim120$ degree spin structure in which ferromagnetic intra-dimer alignment results in a net ferrimagnetic moment. No evidence is found for a change in lattice symmetry down to 2 K. Our results suggest that \sample \ represents a new type of model lattice with frustrated interactions where interplay between magnetic order, thermal and quantum fluctuations can be explored.Comment: Published in Physical Review

Magnetic and structural properties of Ni-substituted magnetoelectric Co4Nb2O9

The magnetic and structural properties of polycrystalline Co4-xNixNb2O9 (x = 1, 2) have been investigated by neutron powder diffraction, magnetization and heat capacity measurements, and density functional theory (DFT) calculations. For x = 1, the compound crystallizes in the trigonal P (3) over bar c1 space group. Below T-N = 31 K it develops a weakly noncollinear antiferromagnetic structure with magnetic moments in the ab plane. The compound with x = 2 has crystal structure of the orthorhombic Pbcn space group and shows a hard ferrimagnetic behavior below T-C = 47 K. For this compound a weakly noncollinear ferrimagnetic structure with two possible configurations in the ab plane was derived from neutron diffraction study. By calculating magnetic anisotropy energy via DFT, the ground-state magnetic configuration was determined for this compound. The heat capacity study in magnetic fields up to 140 kOe provides further information on the magnetic structure of the compounds