The spinel series CuxFe3-xO4+delta,0 less than or equal to delta less than or equal to 0.4 (where x = 0.2, 0.3, 0.4, 0.5, 0.6, 0.8 and 1.0) has been investigated by means of X-ray diffraction and Barkhausen jumps. Analysis of X-ray intensity data showed that this system separates into two phases at x < 1. The percentage of phase separation decreases with increasing copper content. The system shows a single phase at x = 1. The mean potential difference, V-B, and the frequency, F-B, of Barkhausen jumps were measured as a function of the magnetizing current. Addition of copper enhances the irreversible motion of domain walls. The sample with x = 1 shows the highest values of V-B and F-B. The potential energy of the walls increases with increasing copper content.