Abstract
We present the alternative approach to study the thermodynamics of Kerr-Newman-Kasuya spacetime (rotating dyon black hole) through deflection angle. We first compute the deflection angle of the considered model by using the Gauss Bonnet theorem. After calculating the thermodynamical quantities, we observe that temperature fluctuations in the deflection angle can be used to deduce the stable and unstable phases. Then, looking into the Gibbs free energy optical dependency to the Hawking-Page transition. We demonstrate, among other things, that the transition between a large to a small black hole takes place at a particular deflection angle value. Moreover, we also observe that heat capacity against deflection angle plays a vital role in the local stability of the Kerr-Newman-Kasuya spacetime.