Abstract: An electroplating apparatus and method reduces oxidation of thermodynamically unstable and oxidizable ionic species in an electroplating solution to deposit complex magnetic alloys onto substrates. In one embodiment, the electroplating apparatus comprises an electroplating cell in which oxidation of oxidizable anions and cations is reduced. The cell comprises (i) an anode compartment comprising an anode and anolyte solution; and (ii) a cathode compartment comprising a cathode and catholyte solution containing oxidizable plating anions. A cation-selective semi-permeable membrane separates the anode and cathode compartments. An electrical power supply is used to maintain a voltage across the anode and cathode. Upon application of the voltage to the anode and cathode, transport of the oxidizable plating anions, and to a lesser degree cations, to the anode is substantially blocked by the cation-selective semi-permeable membrane, thereby reducing oxidation of the oxidizable anions and cations at the anode.