Electron Paramagnetic Resonance (EPR), also known as Electron Spin Resonance (ESR), is a spectroscopic technique used to study materials with unpaired electrons. These unpaired electrons create a magnetic moment, which can interact with an external magnetic field. When exposed to microwave radiation at a particular frequency, these magnetic moments can absorb energy, causing a transition between magnetic energy levels. This absorption is detected and analyzed in EPR spectroscopy.
