Experimental investigation of Fe-(SiO2) granular films

Abstract

Fe-(SiO2) granular films were fabricated by sputtering with a mosaic target. The fractional area of iron on the target was varied from 0.29 to 0.42. The volume fraction of iron was found from the saturation magnetization to be within 0.03 of that predicted by the target composition. The sample coercivities ranged from Hc = 130 to 950 Oe at room temperature and 690 to 2390 Oe at 77 K. Characteristics relevant for recording media were investigated for the highest-coercivity sample. The squareness values for hysteresis loops measured in and out of the plane of the film, Mr/Ms = 0.54 and 0.43, respectively, indicate that the granules have a uniaxial anisotropy and the easy axes tend to lie more in the plane of the film. The rotational hysteresis was measured at room temperature; the rotational hysteresis integral was calculated to be Ir = 1.56. Because the magnetization reversal is assisted by thermal fluctuation, the low temperature value of Ir was estimated by scaling the measured value by the ratio of the coercivities measured at 77 K and at room temperature. The value of Ir ≊ 0.6 is closest to the theoretical value for the coherent rotation mechanism. The relative decay of magnetization between 30 and 3600 s had a maximum value of ΔM/Ms = 0.10 for a reversal field near Hc. This value falls within the range of the values reported for conventional particulate media, which suggests that a stable transition can be recorded in this material.