Camelia Das, Jumal Das, Thiruvengadam Vijayabaskaran, Subhankar Bedanta, Abhishek Talapatra, Jyoti Ranjan Mohanty and Perumal Alagarsamy
We report systematic investigation of thickness dependent surface topography, magnetic properties and magnetic domain structures of amorphous Fe80Ta8C12 (x nm) films with x=5–100 nm. All the as-deposited films fabricated directly on thermally oxidized Si substrate at ambient temperature using magnetron sputtering technique exhibit amorphous structure. The structural studies reveal that island-like structure in ultra-thin films transforms into continuous one with increasing x>10. In addition, the average surface roughness increases with increasing x, but without any systematic dependency on x. Room temperature magnetic properties illustrate that the paramagnetic nature observed for films with x<10 changes into ferromagnetic one with rectangular loops having high remanence ratio (MR/MS>97%), low coercivity (HC<1.77 kA/m), low saturation field (HS<2.2 kA/m) and simple magnetization reversal behavior for x up to 40 nm. Upon increasing x ≥ 50, the loop shape again changes into transcritical one with increased HC (>3.5 kA/m) and HS (>40 kA/m) and reduced MR/MS (<45%). The magnetic domain studies not only reveal that the domains change from in-plane magnetization to dense stripe domain pattern with increasing x due to enhancement of effective magnetic anisotropy caused by stress quenched in during deposition, but also confirm that films with 12<x<40 exhibit in-plane magnetization with uniaxial anisotropy. High temperature thermomagnetization reveal a clear magnetic phase transition from ferromagnetic to paramagnetic state at relatively higher temperature of about 530 K. The observed results are elucidated on the basis of enhanced effective magnetic anisotropy, change in the magnetic domain structure and magnetic disorder with increasing FeTaC film thickness.
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