Study of fractal dimension and power spectral density analysis of superconductor/ferromagnetic bilayer

Highlights: • C-axis oriented YBCO and YBCO/LSMO films were grown successfully using PLD. • YBCO particle is about 70 nm and with fluence the particle size decreases. • Crack width increases with increase of fluence and is more prominent in bilayer films. • PSD analysis confirms surface & volume diffusion modify the film properties. • Experimental data well agreed with the Fractal model and K-correlation model. Atomic force microscopy investigations through power spectral density analysis and fractal dimension analysis of crack surface due to swift heavy ion (897.6 MeV Xe) irradiation on YBa₂Cu₃O_7−δ and YBa₂Cu₃O_7−δ/La_0.67Sr_0.33MnO₃ PLD thin films have presented. Lattice disorder and suppression of crystallinity of the film has been reported through Ion irradiation. The grain size reduction coupled with development of cracks at higher fluence ∼3 × 10¹² ions/cm² has been observed. The width of the cracks has increased with increase of fluences and is more prominent in bilayer films. The grain size decreased with increasing ion fluence, which led to reduced surface roughness. Swift heavy ion irradiation causes surface diffusion, volume diffusion and strain relaxation in nanoparticles thin films which appear to be responsible for the pragmatic particle size reduction. Power spectral density analyses of AFM data followed by fractal model and K-correlation model have been explained. The crack formation in the above thin films due to irradiation is responsible for the above related phenomena along with the tensile stress which causes surface instability.