L1(0) iron-platinum on nanocrystalline HITPERM soft magnetic underlayers for perpendicular recording media

L10 phase Fe-Pt thin films with the (002) crystallographic orientation have been prepared on HITPERM (pronounced hiteperm) soft magnetic underlayer thin films for double-layered perpendicular magnetic recording media. The HITPERM thin film alloy (composition (Fe, Co)88Zr7B4Cu1) displayed excellent soft magnetic properties (Hc ∼ 3--4 Oe; 4piMs ∼ 19--20 kG) when prepared in the nanocrystalline phase wherein magnetic nanoparticles of Fe-Co are suspended in a ferromagnetic amorphous matrix. This selective crystallization of the Fe-Co nanoparticles (as against secondary phase crystallization involving non-magnetic phases) was achieved by sputtering at higher power densities under ambient conditions. Once formed, the nanocrystals were stable and thus the excellent soft magnetic properties were maintained even oil post-annealing at elevated temperatures of ∼250°C. These thin films also exhibited an anisotropy in the plane of the medium which is of interest as far as application in a soft magnetic underlayer is concerned. Large magnetic stripe-domains, of size ≃30m were observed, and magnetization reversal was seen to occur by domain wall motion.; Cr seed layers films with the (200) texture were successful in inducing the perpendicular (002) texture desired in the Fe-Pt recording layer films. However, the ordering of the Fe-Pt to L10 phase was only moderate under in situ conditions. Expanding the Cr lattice by alloying it with heavy elements such as Pt and W, with the idea of promoting the strain-induced transformation to the L1 0 phase was, in addition also seen to degrade the strength of the perpendicular texture. Post-annealing the as-deposited films, pursued as an alternative approach to cause ordering, in fact resulted in merging of the layers through inter-diffusion.; The magnetic properties of the double-layered perpendicular thin film media were studied using the anomalous Hall effect. Conventional techniques utilizing the Vibrating Sample Magnetometer fail in this regard because they sample the combined magnetic moment from all the layers of film, and often the signals from the soft underlayer overwhelm those from the recording layer. With respect to the Hall technique, a methodology has been developed that enables us to exclusively investigate the magnetization process of the recording layer in such double-layered perpendicular media. The end results of using this methodology compared well when matched up against that measured using other techniques, indicating its potential as a valuable tool in the future. Magnetic characterization thus performed, indicated enhanced hysteresis properties (coercivity, Hc ∼ 7000 Oe; loop squareness, S ∼ 0.80) in the Fe-Pt recording layer films that exhibited better quality of the perpendicular texture.