The crystal and magnetic structure relationship in Cu(W1-xMOx)O4 compounds with wolframite-type structure

The magnetic structures of Cu(W1-xMox)O-4 compounds with wolframite-type structure at 1.5 K have been determined by neutron powder diffraction for average composition <x> = 0.15, 0.25 and 0.35. For <x> = 0.15 the magnetic structure is antiferromagnetic with a magnetic unit cell doubled along the a-axis, (k) over right arrow = (1/2, 0, 0), i.e. the same magnetic structure as for CuWO4. For <x> = 0.25 and 0.35 two magnetic structures are observed: one is identical to that for <x> 0.15, while the other is doubled with respect to the c-axis, (k) over right arrow = (0, 0, 1/2), i.e. the same magnetic structure as for the high-pressure modification CuMoO4 III. The coexistence of these two magnetic arrangements is interpreted as reflecting a slightly inhomogeneous contribution of Mo and W in different crystallites together with a sharp transition between the stability ranges of the two types of magnetic structure with respect to x. The specific Mo:W distributions in the grains of the powdered samples were deduced from a profile analysis based on high-resolution synchrotron powder diffraction data. No additional, intermediate magnetic phase with (k) over right arrow = (1/2, 1/2, 0) was found in Cu(W0.75Mo0.25)O-4, in contrast to predictions in the framework of extended Huckel calculations based on the precise crystal structure.