The relationship between coercivity and grain diameter was investigated for pure Fe, Ni, and Co metals. The grain diameter of samples was varied from 200Å to 5μm by preparing sputtered films and rapidly quenched ribbons. For all the metals, the coercivity was roughly proportional to the sixth power of the grain diameter below a certain diameter (200Å, 400Å, and 300Å for Fe, Ni, and Co, respectively) and to the inverse of the grain diameter above that diameter. The behavior can be satisfactorily explained by the random anisotropy model proposed by Herzer and Alben et al.
The magnetic and structural properties of sputtered Fe-Al-Ti, Fe-Si-Ti, and Fe-Co-Ti ternary films were investigated. The samples were annealed at 673 K for one hour. The crystal structures were bcc for the Fe-Si-Ti and Fe-Co-Ti ternary films, and a mixture of bcc and bcc+Fe2Ti for the Fe-Al-Ti ternary films. The addition of Ti reduces the grain size to a minimum of about 10 nm. Addition of Al, Si, or Ti to Fe reduces the saturation magnetic flux density for Fe-Al-Ti and Fe-Si-Ti films, and addition of Co increases the saturation magnetic flux density for Fe-Co-Ti. Zero magnetostriction samples were obtained for each ternary system. Low coercivity (less than 5 Oe) and high initial permeability (about 1000) were obtained with zero magnetostriction for Fe-Al-Ti ternary films by adding a small amount of Ti. For Fe-Co-Ti ternary films, low coercivity and high permeability were obtained with a small grain size of about 10 nm. For films with low magnetostriction (λs<3×10-6), the coercivity was roughly proportional to the third power of the grain diameter.