Continuously tuning effective refractive index based on thermally controllable magnetic metamaterials

By employing a thermally active magnetic material, we theoretically design a kind of electromagnetic metamaterial with intrinsic magnetic response, termed magnetic metamaterial (MM). The retrieved effective electric permittivity ε(eff) and magnetic permeability μ(eff) exhibit a nearly continuous transition from double negative to double zero, and then to double positive by controlling the temperature, indicating a flexible tunability of the effective refractive index. The beam splitting, collimation, focusing, and total reflection are achieved at different typical temperatures. Most importantly, with the MM implemented under a gradient temperature, a gradient negative-zero-positive index metamaterial (NZPIM) can possibly be realized, thus providing a new platform to study wave features in NZPIM.