Utilizing On-Chip Resonant Cavities for Magnetic Resonance Studies

We studied an Electron Spin Resonance (ESR) setup utilizing a balanced bridge in conjunction with a lock-in detector to be used at the low temperature attained by a dilution refrigerator. ESR measurements were performed on a spin 1/2 DPPH sample at room temperature. The setup uses a microstrip line, which has recently attracted a lot of interest due to its high sensitivity and low noise baseline. Electronic spin excitation of the sample was achieved through use of an ``omega'' shaped microstrip cavity with resonant frequency of 17.4 GHz, which concentrates the magnetic field in a small region where the sample is placed. A homemade heterodyne detector was used for signal detection with and without a balanced magic-T bridge and lock-in amplifier. Direct measurements were also performed using a fast digital acquisition card.