*

We report on the magnetic excitations of the antiferromagnet CaFe₂O₄ as measured with time-domain terahertz spectroscopy via an on-chip device. This material has been previously measured with a free-space terahertz apparatus, showing a magnon excitation at ~725 GHz below the material’s Neel temperature of 200 K. We have observed a possible first-order phase transition between 60 K and 120 K, indicating the coexistence of two different magnetic phases. For this experiment the material was measured with a device that generates a terahertz pulse confined to a transmission line. We report on the results of this experiment.