Probing Spin Dynamics in Thin CrCl₃ Flakes Using Cryogenic Nitrogen Vacancy Microscopy 

Here, we investigate spin noise in CrCl₃ nanoflakes across their magnetic phase transitions using shallow nitrogen vacancy (NV) centers in diamond, combined with cryogenic ferromagnetic resonance (FMR) spectroscopy. CrCl₃ undergoes two successive magnetic phase transitions upon cooling: paramagnetic-ferromagnetic (~17 K) and ferromagnetic-antiferromagnetic (~13 K) [1]. We measured optically detected magnetic resonance (ODMR) [2], Rabi oscillations, and longitudinal relaxation time (T₁) across the magnetic phase transitions under different magnetic fields and temperatures. Our results show a sharp reduction in ODMR contrast and total collapse of the and Rabi oscillations amplitude in the ferromagnetic state, while their revival in the paramagnetic and antiferromagnetic states indicates strong magnetic noise in the ferromagnetic phase [3]. The T₁ (spin-lattice relaxation time) measurements show an ~87-fold reduction in the ferromagnetic state, and a lambda-like anomaly in the relaxation rate (1/T₁) near the paramagnetic–ferromagnetic transition, evidence of enhanced GHz magnetic fluctuations near the critical regime of phase transition, as confirmed by FMR [3]. [1] Yu Liu al., Phys. Rev. B 102, 014424 (2020). [2] I. Fescenko, et al., Adv. Funct. Mat. 35 (38), e71467 (2025). [3] B. E. Hammons, et al., under preparation.