Effect of preannealing on the kinetics of the reorientation of the field-induced anisotropy in CoZr thin films (abstract)

Abstract

In this paper, we will analyze the changes in the kinetics of the induced anisotropy due to preannealing in 300-Å and 1-μm-thick Co94Zr6 amorphous films. Samples were prepared by a dc sputtering method. A silicon wafer with SiO2 overcoat was used as a substrate material, and a field of 200 Oe was applied during the deposition to induce uniaxial anisotropy. Based on x-ray data and resistivity measurements, the films were considered amorphous. The samples were annealed in a magnetic field at temperatures up to 500 °C, and the annealing time was varied from 0.5 to 400 h. As previously reported, the anisotropy, Ku, in as-deposited samples is a function of sample thickness and varied from 1.6×104 ergs/cm3 for 300-Å film to ∼1×104 ergs/cm3 for 1-μm films [T. Jagielinski, J. Appl. Phys. 61, 3237 (1987)]. It was found that the Ku in thick films is reversible, and the kinetics can be fully explained by the anelasticity model [T. Egami, Rep. Prog. Phys. 47, 1601 (1984)]. The mean value of the activation energy is ∼2 eV for samples preanneled at 375 °C. However, in the case of thin films, an additional irreversible component of anisotropy, always along the direction of the field applied during the deposition, is observed. The magnitude is a growing function of annealing temperature, and is as large as 3×104 ergs/cm3 for a 300-Å sample preanneled at 400 °C. The origin of the irreversible component of the anisotropy is not well understood. Based on x-ray data, we concluded that this effect is not related to crystallization. However, since anisotropy is thickness dependent, the structure of the film-substrate interface seems to be responsible for the irreversible part. The reversible parts of anisotoropy behave similarly in both thin and thick films and are 1.6×104 ergs/cm3 and 8×103 ergs/cm3 for 300-Å and 1-μm films, respectively.