57Fe Mössbauer and magneto-optical Kerr effect (MOKE) study of transcritical state in permalloy (FexNi100-x) thin films.

The present work reports the study of transcritical state of magnetic anisotropy in Fe_xNi_100-x films as a function of film thickness and composition. The transcritical state is a manifestation of weak perpendicular magnetic anisotropy resulting in peculiar hysteresis loop and stripe magnetic domains above a critical thickness of film. Signatures of transcritical state, corroborated by the formation of stripe domains, are observed in the magneto optical Kerr effect(MOKE) data and magnetic force microscopy (MFM) data of Fe_xNi_100-x films with ≈ 75 nm thickness for x = 7. The effect of thickness on the formation of transcritical state is studied for Fe₉Ni₉₁ films and it is observed that films with thickness ≥ 105 nm exhibit transcritical state. Further a quantitative analysis of magnetic texture is carried out by ⁵⁷Fe conversion electron Mössbauer spectroscopy (CEMS) measurements for the thickness variation samples. The CEMS data show a systematic variation in the area ratio of second and third line intensity as a function of thickness corroborating the MOKE data. The films are studied as a function of thermal annealing and it is observed that the transcritical state still preserved for Fe₉Ni₉₁ films of higher thickness even after annealing at 300 ^∘C. [ABSTRACT FROM AUTHOR]