Yingguo Peng

HAMR Areal Density Demonstration of 1+ Tbpsi on Spinstand

Heat-assisted magnetic recording (HAMR) is being developed as the next-generation magnetic recording technology. Critical aspects of this technology, such as plasmonic near-field transducer (NFT) and high anisotropy granular FePt media, have been demonstrated and reported. However, progress with areal density was limited until recently. In this paper, we report a basic technology demonstration (BTD) of HAMR, at 1.007 Tbpsi with a linear density of 1975 kBPI and track density of 510 kTPI, resulting from advances in magnetic recording heads with NFT and FePtX media. This demonstration not only shows significant areal density improvement over previously reported HAMR demos, more significantly, it shows HAMR recording at a much higher linear density compared to previous reports. It is an important milestone for the development of such a new technology. Many challenges still remain to bring this technology to market, such as system reliability and further advancement of areal density.

Well-isolated L10 FePt–SiNx–C nanocomposite films with large coercivity and small grain size

FePt–SiNx–C films on TiN/CrRu/glass substrate with large coercivity, (001) texture, and small isolated grains were obtained by co-sputtering FePt, Si3N4, and C targets at 380 °C. It was found that when C was doped into the FePt–SiNx films, the out-of-plane coercivity increased while the small in-plane coercivity remained unchanged. Grain size decreased and grain size distribution became more uniform with increasing the C doping concentration. The x-ray photoelectron spectroscopy (XPS) depth profile showed a uniform depth distribution of Si in the FePt layer. The Si2p XPS spectrum implied the existence of Fe–Si bonds, indicating that SiNx was located at the FePt grain boundaries and was stable against diffusion to the surface, thus favoring grain isolation. Well-isolated FePt (001) granular films with coercivity higher than 21.5 kOe and an average grain size of 5.6 nm were obtained by doping 40 vol. % of SiNx and 20 vol. % of C.

High coercive FePt and FePt-SiNx(001) films with small grain size and narrow opening- up of in-plane hysteresis loop by TiN intermediate layer

The effects of a TiN intermediate layer on the epitaxial growth and magnetic properties of FePt films were investigated. It was found that 5 nm TiN can effectively block the diffusion of a CrRu underlayer into a FePt magnetic layer and the magnetic dead layer on the TiN layer was negligible. Compared with an FePt film grown on a MgO intermediate layer, FePt film grown on a TiN interlayer exhibited very high out-of-plane coercivity and very narrow opening-up of in-plane hysteresis loop. With doping 40 vol. % SiNx in FePt film the grain size was reduced to 5.5 nm and the magnetic properties, such as high out-of-plane coercivity and line-like in-plane hysteresis loop, were retained.

Control of Microstructure and Magnetic Properties of FePt Films With TiN Intermediate Layer

The effects of a TiN intermediate layer on the microstructure and magnetic properties of the FePt films were investigated. It was found that the TiN layer could effectively block the diffusion of Cr into the FePt film. The good epitaxial relationships among these layers were revealed from the transmission electron microscopy (TEM) results. With introducing TiN intermediate layer the chemical ordering and magnetic properties of FePt films significantly improved. The FePt film with 5 nm TiN exhibited a high perpendicular coercivity of 13.7 kOe and a low in-plane coercivity of 0.24 kOe, resulting from the combined contribution of TiN (200) orientation, TiN layer roughness and the effective block of Cr diffusion. Moreover, with doping C into the FePt-SiNx films, the out-of-plane coercivity increased due to the decrease of the exchange coupling, the grain size of FePt films decreased, and well-separated FePt grains and uniform size were formed. By optimizing the sputtering process, the [FePt (4 nm)-SiNx 40 vol·% ]- 20 vol·% C (001) film with coercivity higher than 21.5 kOe, a single layer structure, and small FePt grain size of 5.6 nm in average diameter was obtained, which are suitable for ultrahigh density perpendicular recording.

Nanogranular TiN-ZrO2 intermediate layer induced improvement of isolation and grain size of FePt thin films

The effects of TiN-ZrO2 intermediate layer on the microstructures and magnetic properties of FePt films were investigated. The TiN-ZrO2 intermediate layer was granular consisting of grains of solid solution of Ti(Zr)ON segregated by amorphous ZrO2. By doping ZrO2 into TiN intermediate layer, the FePt grains became better isolated from each other and the FePt grain size was reduced. For 20 vol. % ZrO2 doping into TiN, the grain size decreased dramatically from 11. 2 nm to 6. 4 nm, and good perpendicular anisotropy was achieved simultaneously. For the FePt 4nm-SiO2 35 vol. % -C 20 vol. % films grown on top of the TiN-ZrO2 20 vol. % intermediate layer, well isolated FePt (001) granular films with coercivity higher than 18. 1 kOe and an average size as small as 6. 4 nm were achieved.

L10 FePt-ZrO2 (001) nanostructured films with high aspect ratio columnar grains

In order to increase the signal-to-noise ratio of heat assisted magnetic recording, it is desirable to fabricate high magnetic anisotropy FePt media with small grain size and high aspect ratio (grain height to size ratio). In the present paper, we report that FePt media with small grain size and high aspect ratio were achieved by doping ZrO2 into FePt film grown on TiON intermediate layer. The grain size was around 5.6 nm, and the aspect ratio was as high as 2.6. It is believed that this originated from the ZrO2 (002) tetragonal crystalline phase epitaxially grown on TiON intermediate layer. With a 5 vol. % carbon doping into FePt-ZrO2 films, the perpendicular anisotropy was improved and the out-of-plane coercivity was around 23.2 kOe. Doping of crystalline phase material with certain required crystal structure may offer a method for fabrication of nanostructured thin films with high aspect ratio grains at high processing temperature.

Cluster size and exchange dispersion in perpendicular magnetic media

A computational study of the effects of the intergranular exchange field and its dispersion on the cluster size in perpendicular recording media is presented. The dispersion arises from the grain size dispersion and the dispersion of intrinsic exchange coupling between individual grains. It is found that increasing the degree of dispersion reduces the cluster size due to weakly coupled grains acting as pinning sites against the expansion of the clusters. A simple semi-analytical model is proposed which gives good agreement with the numerical calculations in the limit of the large anisotropy constant.

Effect of gradient alignment in heat assisted magnetic recording

Heat assisted magnetic recording (HAMR) is one of the leading technologies to extend magnetic storage. Significant progress has been achieved in head and media fabrication [M. Seigler et al., IEEE Trans. Magn. 44, 119 (2008); Y. Peng et al., TMRC, Seagate Research, 2008], resulting in a basic technology demonstration (C. Hardie et al., ODS Conference Proceedings, 2008) of HAMR. Both field and field-gradient limitations of a conventional perpendicular recording are overcome by engineering the thermal profile (notably the gradient) and recording at a temperature near Tc (thus requiring a smaller head field). We have used a micromagnetic recording model to study the effect of thermal and field-gradient alignment in HAMR by varying the separation between the thermal spot and the leading edge of the head field. The output of the recording model includes transition jitter, which is based on Monte Carlo simulations of isolated transitions. We use a realistic granular medium with HK∼50–80 kOe and a grain size of ...

Areal-Density Limits for Heat-Assisted Magnetic Recording and Perpendicular Magnetic Recording

Differences in the areal-density capability limits for heat-assisted magnetic recording (HAMR) and conventional perpendicular magnetic recording (PMR) are explored using spinstand measurements, drive footprinting, and micromagnetic modeling. The written track curvature is measured with a special technique that mitigates the cross-track averaging effects due to a finite read sensor width. Tracks written with HAMR heads are shown to have more curvatures compared with those written with modern PMR writers. Mitigation of written track curvature is demonstrated with two different HAMR writer designs. The curvature effect appears to challenge not only the downtrack bit resolution during readback, but also the cross-track written width with increased linear density (LD). Experimental measurements of a constant bit error rate for different LDs and track densities (TDs) indicate a significant opportunity for high TD recording using HAMR. The difference appears to be related to the ability for HAMR to address high track pitches with a minimal increase in risk of adjacent track interference compared with PMR.

Crystalline ZrO2 doping induced columnar structural FePt films with larger coercivity and high aspect ratio

Columnar (001) FePt-ZrO2-C films with large coercivity, small grain size, and high aspect ratio were obtained. By doping ZrO2 into FePt film at high sputtering temperature, tetragonal (002) textured ZrO2 was formed and distributed at the grain boundaries of FePt grains, resulting in the formation of columnar structured FePt films. The perpendicular anisotropy of FePt films was degraded since some (200) FePt grains were formed directly on the (002) textured ZrO2. With a small amount of carbon doping into FePt-ZrO2 35 vol. % films, the perpendicular anisotropy was improved. However, FePt grains were still interconnected. Upon further increasing concentration of ZrO2, (001) textured FePt-ZrO2 40 vol. %-C 5 vol. % films with well isolated grains in average diameter of 5.5 nm and very good columnar structure were obtained.