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The electrical and magnetic properties of slightly Cu-deficient BiOCu(0.94)S are investigated using neutron diffraction, ac magnetic susceptibility, magnetization and electrical resistivity measurements. The Cu spins order in a ferromagnetic arrangement below T(C) = 250 K. An antiferromagnetic component develops below 180 K when the crystalline unit cell experiences a sharp thermal contraction upon cooling, resulting in a canted ferromagnetic spin arrangement at low temperatures. In the magnetically ordered state the electrical transport can be described using three-dimensional variable range hopping conduction. An applied magnetic field can effectively reduce the hopping barrier. Spin-charge couplings are clearly revealed when the resistivity departs from the hopping conduction and begins to increase with increasing temperatures above 250 K where the Cu spins become disordered.

Neutron diffraction, magnetic susceptibility, specific heat, and dielectric constant measurements of single crystal Co 3 TeO 6 have been measured to study the interplay between the ferroelectricity and magnetic order. Long range incommensurate magnetic order develops below T M1 =26 K, which is followed by three additional zero-field phase transitions at T M2 =19.5 K, T M3 =18 K, and T M4 =16 K where the incommensurate order changes and commensurate order develops. In magnetic fields up to 14 T we find that the magnetic intensities and incommensurate wave vector are dramatically altered as ferroelectricity develops, with a fifth abrupt transition around 10 T. The overall behavior characterizes Co 3 TeO 6 as a type-II multiferroic.Ferroelectricity is a physical phenomenon where spontaneous electrical polarization P appears below a certain temperature T C . Ferroelectric order can arise in a number of ways, such as from a structural change, a spin-exchange interaction, or spin-orbit interaction that triggers relative displacements of the positive and negative ions. 1-6 Multiferroics, where both ferroelectric and magnetic order coexist, are quite uncommon, but are of particular interest both to understand the fundamental interactions between the two types of order as well as for the potential for practical applications. 7-9 For conventional (type-I, or proper) ferroelectrics the two types of order must be associated with different atoms, with generally a weak interaction between the two order parameters. For type-II (improper) ferroelectrics, on the other hand, the ferroelectric displacements