Toward Magneto‐Optical Cryogenic Thermometers with High Sensitivity: A Magnetic Circular Dichroism Based Thermometric Approach

Remote temperature probing at the cryogenic range is of utmost importance for the advancement of future quantum technologies. Despite the notable achievements in luminescent thermometers, accurately measuring temperatures below 10 K remains a challenging endeavor. In this study, we propose a novel magneto‐optical thermometric approach based on the magnetic‐circular dichroism (MCD) technique, which offers unprecedented capabilities for meticulous temperature variation analysis at cryogenic temperatures. The inherent temperature sensitivity of the MCD C ‐term, in conjunction with both positive and negative signals, enables highly sensitive magneto‐optical temperature probing. Additionally, a groundbreaking relative thermal sensitivity value of 95.3 % K −1 at 2.54 K can be achieved using a mononuclear lanthanide complex, [[Ho(acac) 3 (phen)], in the presence of a 0.25 T applied magnetic field and using a combination of multiparametric thermal read‐out with multiple regression. These results unequivocally demonstrate the viability and effectiveness of our methodology for cryogenic temperature sensing.