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)