Magnetostrictive behavior of pure nickel core: A study on the effects of annealing and magnetization using VSM and optical microscopy techniques

•Exposing the samples to electro-polishing solution cause to appear the grain boundaries.•The maximum input magnetic hysteresis decreases with annealing.•Magnetization increases the maximum input magnetic hysteresis.•Annealing reduces the maximum output magnetic hysteresis.•Annealing reduces the coercive field and increases the magnetostriction effect. This study investigates the impact of annealing and magnetization on the magnetostrictive behavior of pure nickel, which is used as the core of an ultrasonic transducer. Pure metals are not commonly used as magnetic materials due to their limited magnetic and non-magnetic properties. Analyzing the effects of alloying on different characteristics of pure elements is a complex process. Improving the efficiency of magnetostrictive transducers by enhancing their properties is an area of interest for researchers. Grain size, in particular, is a significant parameter that affects the properties of ferromagnetic materials. This study reveals that exposing pure nickel and magnetized samples to an electro-polishing solution with 10 % oxalic acid for 60 s results in the appearance of grain boundaries. Furthermore, the study finds that the 90° domain wall energy is higher than the 180° domain wall energy, impacting the radial magnetostrictive force more than the longitudinal magnetostrictive force. The results show that annealing reduces the maximum output magnetic hysteresis, while magnetization has little effect. Additionally, annealing significantly reduces the coercive field, increasing the magnetostriction effect. Therefore, annealed nickel is a promising candidate for use as the core of an ultrasonic transducer for removing residual chemicals from fruits and vegetables.