Robust magneto-optical temperature sensing using harmonics of magnetic loop characteristics

Temperature measurements are essential in laboratory and industrial applications. We demonstrate a contactless magneto-optical measurement scheme that directly relates magnetization loop shape to temperature. The scheme relies on the characteristic temperature-dependent loop shapes associated with domain wall motion, domain wall nucleation, and annihilation. The magnetization response characteristics are defined by the harmonics of the magnetic field responses, where temperature can be derived from the ratio of the frequency components of the magnetization reversal for a given modulation field amplitude. This enables the temperature to be determined independently of the signal amplitude, eliminating the need for recurring calibrations. Multiple harmonic ratios can be combined for a more unambiguous and robust determination of physical quantities. The temperature measurement method is demonstrated in magneto-optically active iron garnet films. The shown scheme is extendable to the measurements of other quantities, e.g., magnetic field strength and electric current sensing capabilities as well as enabling mechanical stress sensing, empowering further and multi-functional sensor applications. Other magnetic materials, which exhibit temperature-dependent magnetization reversal properties and magneto-optical measurements based on the magneto-optical Kerr effect or detection schemes, are also compatible with the proposed measurement scheme.