Increase in perpendicular coercivity of Co-Ni ferrite-plated films by Zn ferrite underlayers

Abstract

The present article explains that Co-Ni ferrite-plated films with perpendicular coercivity H c⊥ of 3.8 kOe were obtained using Zn ferrite underlayers at the substrate temperature of 90°C without postannealing. Though a thinner recording layer is required for low noise media, perpendicular anisotropy of Co-Ni ferrite single-layer films of 50 nm in thickness is weak due to worse crystallinity in the initial growth region. Their reproduced waveforms were single pulses, as observed in the longitudinal recording media. Thus, the underlayers of a spinel type of Zn ferrite were used to improve the crystallinity in the Co-Ni ferrite layers, in particular, in the initial growth region. The thickness of the Co-Ni ferrite layer t CoNi was 50 nm, and that of the Zn ferrite underlayers t Zn was in the range of 25-110 nm. While H c⊥ of the Co-Ni ferrite single layers with t CoNi of 50 nm was 2.5 kOe, H c⊥ of the double-layer films increased with increasing t Zn, reaching 3.8 kOe at t Zn of 110 nm. The reproduced waveforms exhibited dipulses that are typical in the perpendicular recording media. These results will open the way to develop the perpendicular recording disks with high H c⊥ using plastic substrates at low temperature. © 2000 American Institute of Physics.