David N. Lambeth

Effects of Ag underlayers on the microstructure and magnetic properties of epitaxial FePt thin films

In this work Ag underlayers, with a slightly larger unit cell than FePt, were found not only to induce epitaxial growth of the FePt films but also to reduce the FePt ordering temperature. Without using the Ag underlayer, the FePt film deposited onto the Si substrate was fcc disordered. By the use of the Ag underlayer, it was observed that the FePt unit cells were expanded in the film plane. This has caused the shrinkage of the FePt unit cells along the film normal direction and resulted in the in situ ordering of the FePt thin film at reduced temperatures. The microstructural and magnetic properties of the FePt/Ag films at varied substrate temperature and FePt thickness were studied to investigate the L10 FePt ordering.

Media for 10 Gb/in.2 hard disk storage: Issues and status (invited)

Future 10 Gb/in.2 recording densities represent submicron trackwidths and sub‐100 nm bit lengths. This requires extremely small magnetic switching units and very high coercivities of the media to satisfy the signal‐to‐noise ratio requirements. At the same time the question of magnetic thermal stability and the lack of transducers capable of performing at these densities makes it difficult to evaluate media. An uncoupled, highly uniform magnetic grain size of about 10 nm is a compromise toward maintaining an adequately low media noise and yet maintaining magnetic stability. Here we discuss current media construction, the detrimental role of substrate roughness, the role of new media structures and alloys on microstructure and magnetic properties as well as techniques for evaluating media performance prior to the availability of the required playback heads.

NiAl underlayers for CoCrTa magnetic thin films

CoCrTa films were sputter-deposited on either NiAl or Cr underlayers on glass substrates and their coercivities were compared. The NiAl film was found have the B2 structure with a lattice parameter of /spl sim/0.288 nm. The grain size of a 100 nm NiAl film is /spl sim/15 nm, which is about 50% smaller than a similarly deposited Cr film. As for the CoCrTa/Cr films the CoCrTa/NiAl films show a similar increase of the in-plane coercivity with thickening of the underlayer. X-ray diffraction studies showed that CoCrTa/NiAl films have a stronger (101~0) peak than CoCrTa/Cr films. Substrate heating and biasing during deposition of the NiAl underlayer are less helpful than in the case of Cr underlayer. >

Formation of crystallographic texture in rf sputter‐deposited Cr thin films

Although it is well known that Cr underlayers sputter deposited on glass or NiP/Al substrates have either the (002) or (110) textures, the mechanism of the formation of the crystallographic textures is not clear. A model is proposed for the formation of the crystallographic texture of sputter‐deposited Cr thin films. A systematic set of experiments has been carried out to test the model. It was found that the (110) texture, which is usually found in Cr thin films deposited on substrates without preheating, can form at elevated temperatures (250 °C) when deposited at low Ar pressure or by applying substrate bias. The initial stage of the texture formation was also investigated by using very thin Cr films. It was found that the (002) texture can be initiated directly on the substrate surface, while the (110) texture appears not to form directly on substrate surface, but rather as a result of film growth. The proposed model is consistent with the experimental results.

CoSm‐based high‐coercivity thin films for longitudinal recording

In order to produce thin media with high intrinsic coercivity, we studied a number of CoSm films produced by rf‐diode sputtering. We determined an optimized set of sputtering parameters for films sputtered both on glass and NiP‐coated Al substrates with and without Cr underlayers. While the coercivity of the films depended strongly on argon pressure, the 〈110〉 texture of the Cr underlayer remained unaffected by it. The 〈110〉 texture of Cr changed to 〈200〉 texture at temperatures ≥300 °C, and the coercivity of the film was significantly reduced. Under optimal conditions we obtained intrinsic coercivities ≳2400 Oe for films with thickness <20 nm.

Chemical sensing using nanostructured polythiophene transistors.

We show that the chemical sensing responses of organic field-effect transistors based on nanostructured regioregular polythiophene are strongly dependent upon the gate biasing field. With different applied gate voltages, the source-drain current response can be different both in sign and magnitude for the same analyte. This implies that multiple competing sensing mechanisms exist at the same time. We propose that the sensing mechanisms for polycrystalline semiconducting polymer thin films are mainly an intragrain effect, which yields a positive response, and a grain boundary effect, which yields a negative response.

Effects of Cr intermediate layers on CoCrPt thin film media on NiAl underlayers

Sputter-deposited NiAl underlayers can induce better in-plane c-axis textures in the overlying CoCrPt films and have a smaller grain size than Cr underlayers. However, it is found that the CoCrPt/NiAl films on glass substrates have on lower coercivity values than the CoCrPt/Cr films. A scheme which inserts a Cr intermediate layer, about 2.5 nm thick, between the CoCrPt and NiAl layers is found to greatly improve the in-plane magnetic properties of the CoCrPt/NiAl films. The existing (10.

High density recording on CoSm/Cr thin film media

SmCo/Cr thin films with coercivity up to 3000 Oe were prepared by RF-diode sputtering. Hard disks were fabricated using glass substrates and the recording properties, carrier-to-integrated-noise ratio, media noise, and overwritability were evaluated using conventional thin-film inductive heads. The influence of the thickness of the Cr underlayer, SmCo magnetic layer, and Cr overlayer on media noise was studied. The intergranular exchange and magnetostatic interaction effects present in SmCo/Cr media were measured from their remanence magnetization curves and correlated with media noise values obtained from recording measurements. The media noise in SmCo/Cr disks varied little with increasing linear density, and no supralinear increase in noise as explained by a transition noise model was observed. A thin Cr underlayer ( >

MgO seed layers for CoCrPt/Cr longitudinal magnetic recording media

Sputter deposited MgO thin films with the B1 crystal structure and (002) film texture are used as seed layers to improve the texture and magnetic properties of the CoCrPt/Cr magnetic thin films on glass substrates for longitudinal recording. The desired (002) textured Cr underlayers are usually obtained by sputtering Cr onto heated substrates. However, it is found that the MgO seed layers can induce the (002) film texture in the Cr underlayers without using a heated substrate and hence, the overlying CoCrPt films are formed with the (1120) texture. Vibrating‐sample magnetometry measurements show greatly improved in‐plane coercivities that are suitable for future high density recording media can be easily obtained.

The effects of Ag underlayer and Pt intermediate layers on the microstructure and magnetic properties of epitaxial FePt thin films

Abstract In this work, Ag underlayers, which have a slightly larger lattice parameter than FePt, were found not only to induce epitaxial growth of the FePt films but also to reduce the temperature at which the atomic ordering occurred. Without using the Ag underlayer, the FePt film deposited onto the hydrofluoric acid etched-Si substrate was FCC disordered. When Ag underlayers were used the FePt unit cells were expanded in the film plane. This caused the shrinkage of the FePt unit cells along the film normal direction and resulted in the in situ ordering of the FePt thin film at reduced temperatures. Furthermore, it was found that the degree to which the FePt unit cells contracted along the film normal varied when a Pt intermediate layer was added. This resulted in FePt thin films with different textures and magnetic properties. The microstructural and magnetic properties of the FePt films prepared at various substrate temperatures, FePt thicknesses, Ag underlayer thicknesses and with the use of the Pt intermediate layer were studied to investigate the L10 FePt ordering.