W. K. Shen

Exchange coupled composite media for perpendicular magnetic recording

Exchange coupled composite (ECC) media has been shown to possess several major advantages relative to conventional perpendicular media, including a reduction in the switching field of approximately a factor two for the same thermal stability and greater insensitivity to easy axis distribution. In this paper, full magnetostatic interactions are included: this allows comparison between the behavior of multigrain thin films and that of isolated grains as presented earlier. Significant results include hysteresis loops for thin films under various conditions including inadequate and excessive intra granular exchange between the hard and soft materials. An important distinction is made between the coercivity and remnant coercivity as a function of angle between applied field and easy axis. A perpendicular magnetic recording head is used to compare the shape of effective fields for ECC and conventional perpendicular media. Written transitions in the ECC media appear to be similar to those written in perpendicular media at comparable densities.

Composite media (dynamic tilted media) for magnetic recording

We designed and fabricated a composite magnetic recording medium with exchange decoupled magnetic grains that consist of two vertically exchange-coupled magnetic regions (one is magnetically soft and one is magnetically hard) as an approach to alleviate the writing field limitation of perpendicular magnetic recording heads. A nonmagnetic layer with different thickness was put between the hard and soft layer to tune the exchange coupling. With proper coupling, significant drop of the coercivity field was observed for this composite medium while still maintaining good thermal stability. Better recording performance was obtained for such medium compared to perpendicular and longitudinal medium. The results have proved the possibility of fabricating a writable recording medium having an ultrahigh magnetic anisotropy constant (Ku) value.

Fabrication and Characterization of Exchange Coupled Composite Media

Magnetic hard and soft phases CoCrPt-SiO2 thin films were developed to fabricate exchange coupled composite (ECC) media. Domain wall nucleation and propagation from the soft regions to the hard regions in the composite grains was found to be the switching mechanism in the ECC media. ECC media on the disk substrate with soft underlayer was fabricated. Interlayer thickness dependence of saturation field and domain wall length in CoCrPt-SiO2 soft layer suggested that domain wall nucleation and propagation in ECC media. Spin-stand testing showed more than a six-times reduction of saturation writing current and more than a 10 dB increase of total signal-to-noise ratio (SNR) for ECC media. Time decay results of readback signals indicated that there is no thermal stability problem for ECC media. The roll-off curve of ECC media showed the same SNR level as a state-of-art reference perpendicular media targeted around 200 Gb/in2. With further optimizations, areal densities beyond 1 Tb/in2 seem achievable for ECC media

In situ epitaxial growth of ordered FePt (001) films with ultra small and uniform grain size using a RuAl underlayer

In situ epitaxial growth of ordered FePt thin films with small and uniform grain size using RuAl underlayer is reported. A transmission electron microscopy image of a 20-nm RuAl layer deposited on a glass substrate revealed small (D∼5.0nm) and uniform (ΔD∕D∼15%) grains. The (001) texture was formed in RuAl films at a substrate temperature higher than 100 °C. The FePt L10 (001) texture with mean grain size of 6.63 nm and narrow size distribution (17%) has been successfully induced using a RuAl underlayer at a substrate temperature of 400 °C. The influences of the RuAl composition ratio and Pt interlayer were studied.

Ferromagnetic interlayer coupling and switching process of exchange coupled composite media

The ferromagnetic coupling effects in the exchange coupled composite (ECC) magnetic recording media were studied by varying the interlayer thickness and the saturation magnetization (Ms) of the soft layer. A minimum coercivity was observed at a certain interlayer thickness for the ECC media with a low Ms soft layer. When the Ms of the soft layer was increased (700emu∕cm3 in this work), no interlayer was needed to get the lowest coercivity for the ECC media, which makes the ECC media practical for a manufacturing process. A method to characterize the ferromagnetic coupling strength for the ECC media was quantitatively proposed. The switching process of the ECC media was observed to consist of the reversible switching of the soft layer and the irreversible switching of the hard layer.

Composite perpendicular magnetic recording media using [Co∕PdSi]n as a hard layer and FeSiO as a soft layer

We fabricated the composite perpendicular magnetic recording (PMR) media successfully for the first time by combining a nanogranular FeSiO soft layer and a [Co∕PdSi]n hard layer. PdSi spacing layer (0–4nm) was used to study the exchange coupling effects between the FeSiO(5nm) and the [Co(0.26nm)∕Pd(1nm)]14 layers in the composite films. Proper coupling occurs when PdSi interlayer is ∼0.5nm. Significant lowering of the coercivity is observed for the composite PMR medium while still maintaining good thermal stability. The results prove the possibility to fabricate a writable PMR medium having an ultrahigh magnetic anisotropy constant Ku value.

Enhancement in Magnetic Anisotropy for hcp-Structured Co Alloy Thin Films Through Pt Addition

The addition effects of Pt in the (0002) Ru underlayer were studied. It was found that the lattice parameter can be tuned as desired through Pt addition in a (0002)-oriented Ru layer. The out-of-plane and in-plane lattice parameter of the RuPt can be increased by 2.3% and 0.44%, respectively. No phase segregation was apparently observed in RuPt films under these process conditions even with a very high Pt content (39%). The RuPt layer thus provides a good template layer to study the Pt addition effects in (0002)-textured hcp Co alloy perpendicular media with a very wide range of Pt content. CoCrPt-SiO2 films were deposited with a Pt addition level varying from 15% to 40% on an optimally designed RuPt underlayer. The magnetic results showed that Hk,Hc,Ku reached a plateau at about 19%-23% Pt content. The maximum values for H k,Hc, and Ku are 16.0 kOe, 6.6 kOe, and 3.1times106 erg/cm3, respectively

Recent Experimental Advances in Exchange Coupled Composite Media

Exchange coupled composite media (ECC) has been proposed and prototyped for 1 Terabit/in2 perpendicular magnetic recording [1,2]. Currently systematic experimental investigation is very necessary to guide and select a proper theory [1-5]. We will report our recent experimental advances on ECC media, including proper fabrication conditions, new fundamental findings and first spin-stand recording performance testing.

New perpendicular media by engineering the thermal stability and writing capability separately

We experimentally demonstrated two novel approaches to tune the thermal stability (K/sub u/V/k/sub B/T) and coercivity of perpendicular media separately to alleviate writing field limitation of perpendicular magnetic recording. The well-exchange decoupled magnetic grain is engineered into two parts: magnetic hard and magnetic soft. The first approach is to control the exchange coupling strength to a proper value thus the soft region of grain will switch first with an external field and apply a torque to help the switch of the hard region, which has been proposed theoretically and demonstrated experimentally. The second approach is to use the pure Zeeman energy from soft region of grain to help the switching of hard region of grain.

Magnetic Anisotropy Enhancement for hcp Structured Co Alloy Thin Films through Pt Doping

This study aims to investigate the Pt doping effects in Ru interlayer to adjust Ru lattice. A DC magnetron sputtering system is used to deposit the films. XRD and TEM are used to evaluate the film orientation and microstructure. Magnetic properties such as perpendicular hysteresis loops and coercivity are tested using a vibrating sample magnetometer. Results show that the highest value for CoCrPt-SiO2 film happens at around 24-28% Pt content, with magnetic anisotropy field of 16.0 kOe.