Microstructure, magnetic properties and TMR effect of Fe-SiO2 granular films investigated by Mossbauer spectroscopy

Fe-SiO2 granular films with various metal volume fractions (f(v)) were fabr icated by RF co-sputtering. The microstructure and magnetic properties as w ell as the tunneling magneto resistance (TMR) were systematically investiga ted. The TMR exists in the samples with f(v) < 0.5, and the Fe-0.33(SiO2)(0 .67) film exhibits the largest TMR value of -3.3% at room temperature under 1.3 T magnetic field. The transmission electron microscopy images indicate that these samples consist of small Fe particles with the size range from 1.0 to 15.0 mn. separated by insulating SiO2 matrix and exhibit TMR effect. Mossbauer measurement reveals that more superparamagnetic Fe component and less paramagnetic Fe2SiO4 are in favor of the higher probability of spin-d ependent tunneling, thus larger TMR value. For the samples with f(v)<greate r than or equal to>0.43, Mossbauer study shows the existence of perpendicul ar magnetic anisotropy, and the strongest perpendicular magnetic anisotropy was observed in the sample of Fe-0.47(SiO2)(0.53). This phenomenon may be ascribed to the stress anisotropy in this film. (C) 2001 Elsevier Science B .V. All rights reserved.