Effect of 100 MeV Ag⁺⁷ ion irradiation on the bulk and surface magnetic properties of Co-Fe-Si thin films

Thin films of Co-Fe-Si were vacuum evaporated on pre-cleaned float glass substrates employing thermal evaporation. The films were subsequently irradiated with 100 MeV Ag⁺⁷ ions at fluences of 1×10¹¹, 1×10¹² and 1×10¹³ ions/cm². The pristine and irradiated samples were subjected to surface analysis using Atomic Force Microscopy (AFM), Vibrating Sample Magnetometry (VSM) and Magneto Optic Kerr Effect (MOKE) measurements. The as deposited film has a root mean square roughness (Rq) of 8.9 nm and an average roughness of (Ra) 5.6 nm. Irradiation of the as deposited films with 100 MeV Ag⁷⁺ ions modifies the surface morphology. Irradiating with ions at fluences of 1×10¹¹ ions/cm² smoothens the mesoscopic hill-like structures, and then, at 1×10¹² ions/cm² new surface structures are created. When the fluence is further increased to 1×10¹³ ions/cm ² an increase in the surface roughness is observed. The MOKE loop of as prepared film indicated a squareness ratio of 0.62. As the film is irradiated with fluences of 1×10¹¹ ions/cm², 1×10 ¹² ions/cm² and 1×10¹³ ions/cm ² the squareness ratio changes to 0.76, 0.8 and 0.86 respectively. This enhancement in squareness ratio towards 1 is a typical feature when the exchange interaction starts to dominates the inherent anisotropies in the system. The variation in surface magnetisation is explained based on the variations in surface roughness with swift heavy ion (SHI) irradiation.