Novel Approach to Electron Spin Resonance Spectroscopy Powered by Free Electron Laser*

Pulsed electron spin resonance (ESR) spectroscopy is crucial for obtaining information on spin dynamics for the understanding and development of molecular qubits and single molecular magnets [1], antiferromagnetic spintronics [2], and fractionalized magnets [3]. In the last decade, ESR moved to high fields and frequencies (HF-ESR) to achieve better resolution and sensitivity, and to get access to high-spin systems with large zero field splitting (also called single ion anisotropy). The aim of our work is to set up and develop a general-purpose state-of-the-art broadband pulsed HF-ESR spectrometer. Our design uses UCSB’s free electron laser (FEL) [6] as the source of frequency-agile kW power that operates at frequencies from 120 GHz to 500 GHz, sample temperatures in the range of 1.6 K to 300 K, and at magnetic fields up to 16 T. More importantly, we present a novel approach of rapid scan ESR, which is capable of providing T₁ relaxation time via imaging spin saturation recovery by combining a high-power pulse from the FEL together with continuous sample irradiation by low power microwave source. Such a design will allow multi-frequency relaxation studies of a variety of samples ranging from bulk materials, powders, single crystals, and air-sensitive samples in liquid solutions. 

[1] E. Coronado, Nat Rev Mater 5, 87–104 (2020)

[2] L. Junxue, et all., Nature 578, 70–74 (2020)

[3] Y. Wan, et all., Phys. Rev. Lett., 122, 257401-257407 (2019)

[4] S. Takahashi, et all., Nature 489, 409–413 (2012)