In this work the influence of temperature during mechanical alloying (from 80 K up to 525 K) on the structural state and magnetic properties of alloys based on immiscible Cu-Co and Cu-Fe alloys with 3d-metal contents of up to 30 at. % was investigated. It was established that mechanical alloying of Cu-Co and Cu-Fe forms a heterogeneous nanophase structure, in a temperature range from 80 up to 400 K containing clusters or particles with various contents of a ferromagnetic element. The reversibility of structural changes for Cu-Co alloy was observed; in this case the final structural state does not depend on the sample prehistory, and is determined by the milling temperature for given parameters of the milling equipment. The mechanism for a change of critical temperature for magnetic phase transformation in the alloys is discussed taking into account the magnetic interaction between particles.