Unbiased microwave circulator based on ferromagnetic nanowires arrays of tunable magnetization state

A planar microwave circulator operating without biasing static magnetic field is presented, using bistable ferromagnetic nanowires embedded in a dielectric medium. We show that its circulation mechanism is strongly dependent on the magnetization state at zero external magnetic field. A theoretical model, yielding the permeability components of the magnetic nanowired composite at remanent or partially magnetized state and the transmission characteristics of the circulator, is proposed. It explains the essential role played by the magnetization. state on the circulation performances. Composites with very high remanence are necessary for an optimal circulation effect. It is also shown that the insertion losses can be significantly reduced by improving the matching between the access lines and the circulator.