The present article describes CoxFe3−xO4 films, which were fabricated at 90 °C by the ferrite-plating method and have the excellent perpendicular magnetic anisotropy and the perpendicular coercivity Hc⊥ above 2 kOe. The films were composed of Co ferrite and Fe3O4 grains. The highest Hc⊥ reached 3 kOe at the composition of Co0.43Fe2.57O4 and the saturation magnetization Ms was 500–550 emu/cc. Hc⊥ was over 2 kOe even for a film thickness of 35 nm without any underlayers. ΔM⊥ evaluation that is measured in the perpendicular direction to the film plane showed that the interactions in the films supported the magnetized state, stabilizing the direct current remanent state. The Mössbauer analyses revealed that the Co0.43Fe2.57O4 films have excellent perpendicular magnetic anisotropy and the magnetization direction inclined from the perpendicular axis due to the demagnetization field. This achievement will open the way to develop the high-density perpendicular recording media even when plastic disks and sheets are used as substrates.

Abstruct-The influence of Ni-Zn ferrite plated underlayers on grain size and magnetic characteristics of sputter-deposited Co-Cr-Ta layers was investigated. These properties were found to be strongly influenced by the surface texture of the underlayers. When the grain size of the underlayers was large (200-300 nm), the grains in the Co-Cr-Ta layers seemed to aggregate and were not isolated clearly. When the grain size of the underlayers was small (50-70 nm), the grain size in the Co-Cr-Ta layers decreased and the perpendicular coercivity increased to over 2 kOe. Further studies showed RE sputter-etching of the underlayers reduced grain size (30-50 nm), and increased perpendicular coercivity (3.0 kOe), presumably through a reduction of surface roughness and a formation of many fine nodules on the underlayers, which play a role of nucleation sites for the CO-Cr-Ta grains.

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Co-Cr-Ta perpendicular magnetic recording media with Ni-Zn ferrite backlayers are promising candidates to improve high frequency performance in extremely high linear density applications. Though ferrite plating facilitates to fabricate polycrystalline Ni-Zn ferrite films even at low temperature below 100 QC, the films have disadvantages oflarge grain size (200~300 nm) and roughness (4~5 nm). Such surface texture caused aggregating grains without clear magnetic isolations in Co-Cr-Ta layers deposited on them, resulting in low perpendicular coercivity Hd (1.3 kOe). These properties will lead poor recording density characteristics and high media noise. RF sputter-etching of the Ni-Zn ferrite backlayers was attempted in order to improve their surface texture. It reduced grain size (30~50 nm), and increased Hd (3.0 kOe) in the Co-Cr-Ta layers, presumably through a reduction of surface roughness and a formation of many fine nodules on the Ni-Zn ferrite-plated backlayers, which play a role of nucleation sites for the Co-Cr-Ta grains.

Abstract-In order to develop good backlayer for the Co-Cr perpendicular magnetic recording media, crystalline films of spinel, (Fe, Mi30AM=Ni and Zn) were prepared on glass substrates by spin-spray ferrite plating method. Reaction and oxidizing solution were sprayed in the reaction chamber in which the substrate is rotating. The reaction was influenced by concentration of reaction solution(R c ) and oxidizing solution(Oc), the flow rates of the reaction solution(R f ) and oxidizing so!ution(Oc), reaction temperature (T) and rotation speed of substrate(Sr). Under the condition where R r , OF60[rnQ/min], T=90(C] and Sr=150 [rpm], effect of Rc and Oc on the ferrite plating reaction were studied in aspect of chemical composition, crystallographic and magnetic properties. In the composition of Nio.34ZnO.6~e204' we have the stable crystaUographic and magnetic properties. I . INTRODUCTIONThere are several methods to perform ferrite plating to prepare the films with crystalline spinel structure in an aqueous solution at low temperature( < 90 "C) [1,2].Among them, "Spin-spray" method, in which a reaction solution and oxidizing solution are simultaneously sprayed onto a spinning substrate which is kept at 90 ["(:], is the most excellent technique for getting good quality films[3J.Ferrite films prepared in this method will be used of backlayer under Co-Cr films for inhabitation eddy current loss and improvement the high frequency properties of CoCr perpendicular magnetic recording media.Previously, the same process of the aspect using ferrite single-crystal substrate was studied, but we consider that using ferrite film is desirable from the practical view.In this paper, we report the crystallographic and magnetic properties of the Ni-Zn ferrite films which are deposited for spin-spray ferrite plating method. IT . EXPERIMENTAL METHODThe ferrite plating was performed by spin-spray method on glass substrates [4,5]. We used a reaction solution(pR=5.2) which contains FeCh4H 2 0, NiClz6H 2 0 and ZnCh and an oxidizing solution(pH=6.9) which contains NaN0 2 and CH 3 COONH 4 , simultaneously sprayed these two solutions for 30 min. The substrate was kept at 90rC] and spun at 150rpm during plating.We have performed magnetic properties(perpendicular to film plane) using VSM and crystalIographic properties using XRD. The surface and thickness in each layer were observed and measured by AFM and SEM, respectively. Also, the chemical composition of samples plated on the substrates were analyzed by ICP.