Using solution-gelation and the auto-combustion process, calcium (Ca)-doped cobalt ferrite (CoFe2O4) nanoparticles were synthesised. The synthesised nanomaterials were characterised by powder X-ray diffraction (PXRD), Fourier transform infrared (FTIR) spectroscopy, field-effect scanning electron microscopy (FESEM), energy dispersive X-ray (EDX), UV–Vis spectroscopy, and vibrating sample magnetometer (VSM) techniques. The PXRD analysis shows that the crystallite size reduces from 39 to 27 nm with increasing calcium content. UV–Vis spectroscopy reveals that the band gap is enhanced with calcium content. The VSM illustrates that coercivity and saturation magnetisation decrease with the concentration of calcium. The synthesised nanomaterials were first time applied to humidity sensing, and different sensing parameters were determined. The response and recovery times were 44.95 and 53.52 s, respectively. The designed sensor has a repeatability of 97% and a minute ageing effect.
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