THICKNESS AND GRAIN-SIZE DEPENDENCE OF THE COERCIVITY IN PERMALLOY THIN-FILMS

This paper reports the effect of thickness and grain size on the coerc ivity of Ni81Fe19 permalloy thin films (2.5-30 nm) sputtered on glass substrates for their application in magnetoresistive sensors. Coercivi ty was systematically investigated as a function of underlayer materia ls, thickness, and substrate temperature. Lateral grain size of the sp uttered films was investigated, The grain size reduced very quickly in the thinner films. It was also found that the coercivity of the films with very small lateral grain size is much lower than those with a no rmal grain size, The lowest coercivity (H-c=0.8 Oe) was observed in 7. 5 nm thick film and having a grain size of 4 nm. When an underlayer is used, its crystallinity affects the lateral grain size in the permall oy and correlates with the observed coercivity variation [P. Galtier, R. Jerome, and T. Valet, Mater. Res. Sec. Symp. Proc. 313, 417 (1993). ] It was also observed that the coercivity of the permalloy is depende nt on the nature of the underlayer. It was established that the coerci vity of Ni81Fe19 films increases when the thickness increased from a c ritical film thickness and grain size. The variation of the coercivity in thin Ni81Fe19 films with lateral grain size and relationship with domain-wall width is discussed and compared with other theories for ma gnetization reversal. (C) 1997 American Institute of Physics.