A magnetic field controlled transistor circuit includes a first electrode, a second electrode, and a channel including a magneto-resistive material. The channel is arranged between the first and second electrodes and electrically coupled to the first and second electrodes. The transistor circuit further includes a third electrode, a fourth electrode, and a control layer including an electrically conductive material. The control layer is arranged between the third and fourth electrodes and electrically coupled to the third and fourth electrodes. In addition, an insulating layer including an insulating material is provided. The insulating layer is arranged between the channel and the control layer and configured to electrically insulate the channel from the control layer. A related method for operating a transistor circuit and a corresponding design structure are also provided.