Coupling of terahertz split-ring resonators to antiferromagnetic resonances in CaFe₂O₄

Most terahertz (THz) metamaterial studies have focused on their electromagnetic response without considering their interaction with the substrate. We study the possible interaction between split-ring resonator metamaterials grown on the novel antiferromagnet CaFe₂O₄ to the antiferromagnetic resonances in CaFe₂O₄. This material exhibits two resonances at low temperature around ~600GHz and ~700GHz for different crystal orientations, which are detected with THz spectroscopy by properly polarizing the electromagnetic wave along the different crystal axes. We design and match the resonant frequency of the split-ring resonators to those of the magnons in CaFe₂O₄. We test the interaction between the magnetic split-ring resonator response and the antiferromagnetic resonances by varying the distance between the antiferromagnet and the metamaterial. This is done by adding an insulating layer of photoresist in between them. We report on the results of these tests.