Y.C. Feng

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.

The control of microstructural features of thin films for magnetic recording

Abstract Extrinsic magnetic properties play a major role in determining the performance of magnetic thin films used as magnetic recording media. These extrinsic properties are the ones which are largely determined by the microstructure of the thin magnetic films. In this paper we discuss various ways that the crystallographic texture of thin films can be controlled. We begin with a discussion of the origin of crystallographic texture of underlayers. Next, the origin of crystallographic texture of magnetic thin films by means of epitaxy with the underlayer is discussed. The control of other microstructural features such as grain size and perfection by means of underlayers and interlayers is briefly introduced. Examples from recent research are included.

Interdiffusion and grain isolation in Co/Cr thin films

In this work, interdiffusion and grain isolation in Co/Cr films have been investigated by studying the dependence of the magnetic properties on the substrate preheating temperature as well as on post-deposition annealing processes. By choosing pure Co instead of a Co-alloy, the possibility of grain isolation caused by the segregation of solute atoms from within the magnetic layer has been eliminated. It is found that both post-deposition thermal annealing and substrate preheating can effectively increase the isolation of the Co grains. >

Design and crystallography of multilayered media

Abstract In this paper several different schemes for multilayered longitudinal magnetic recording media are presented and discussed. We will focus the discussion on those schemes on which we have worked over the past several years, emphasizing the role of new underlayers, seed layers, intermediate layers and interlayers. In each case we discuss the role that each of the layers plays in determining the important magnetic properties and recording performance of the Co based hcp thin film media. Included in the paper is a review of the role of new underlayers (NiAl and MgO), seed layers (MgO), intermediate layers (Cr, Co alloys) and interlayers (Cr, Al, Cu and Ag). Throughout we discuss the role of epitaxy between the various layers and demonstrate that the resulting microstructure and crystallographic texture of the films depends strongly on such epitaxy. These characteristics, in turn, control the resulting magnetic properties of the Co based films such as in plane coercivity H c and squareness ratio, S ∗ .

Electron diffraction patterns of fibrous and lamellar textured polycrystalline thin films. II. Applications

Electron diffraction patterns of a sputter-deposited poly crystalline MgO thin film on an SiO2 substrate, of a Ta thin film and of CoCrTa/Cr bilayer films on glass substrates are presented and analyzed based on the theory developed in Paper I [Tang & Laughlin (1996). J. Appl. Cryst. 29, 411–418]. It is found that the MgO film is [001] textured with a distribution angle of 13°. The Ta film is composed both of randomly oriented grains and [011] textured grains. The [011] texture axis distribution angle of the Ta film is determined to be 11° (11{\bar 2}O)CoCrTa/(001)Cr and (10{\bar 1}1)CoCrTa/(011)Cr polycrystalline epitaxy are identified in the CoCrTa/Cr bilayer films. Both the bilayer films have a texture axis distribution angle of 6°.

The role of Ta and Pt in segregation within Co‐Cr‐Ta and Co‐Cr‐Pt thin film magnetic recording media

Polarization dependent extended x‐ray absorption fine structure (PD‐EXAFS) and magnetic circular dichroism (MCD) measurements of CoCrTa and CoCrPt films, sputter deposited at varying substrate temperatures, were performed to investigate the average local structure and chemistry about the Ta, Pt, and Co atoms and the average magnetic moment of the Co and Cr atoms within these films. Results from the MCD measurements indicate the average net magnetic moment of the Cr atoms is opposite in direction and five percent in amplitude relative to the Co moments. Inspection of the Fourier transforms of the XAFS data from these samples shows an increase in structural disorder around the Ta and Pt atoms with increasing substrate deposition temperature. A further comparison between the Ta and Pt edge EXAFS results show that the temperature‐dependent increase in structural disorder is greater around the Ta atoms in the CoCrTa system than it is around the Pt atoms in the CoCrPt system.

Preferential site distribution of Pt and Ta in CoCr-based films: An extended x-ray absorption fine structure study

Co86Cr12Ta2, and Co86Cr12Pt2 films were made to investigate the local structure and chemistry around Ta and Pt atoms to determine their site distributions in these alloys. Comparisons between the measured data and data collected from experimental standards and calculated using theoretical EXAFS simulation codes indicate that the Ta atoms are preferentially distributed to the Cr-enriched regions of the CoCr media, and the Pt atoms have an effect on the local environment of the Co atoms. Both Ta and Pt introduce a large amount of local structural disorder to the local environments in which they reside. The presence of Ta atoms in the Cr-enriched regions further reduces the magnetization of these regions, which enhances the magnetic isolation of the Co regions from each other. This helps improve the noise characteristics of the films. The portion of the Pt atoms residing in the Co-enriched regions increases the magnetic anisotropy of the films, thereby increasing their coercivity.

Magnetic properties and crystallography of double-layer CoCrTa thin films with various interlayers

In this work, the hysteretic properties and remanence curves of double-layer CoCrTa thin films with various interlayers (Al, Cu, Ag, and Cr) are investigated. It is found that the double-layer CoCrTa films with Cu or Ag interlayers have narrower switching field distributions but similar high coercivities, compared with the films with Cr interlayers. To understand the effects of interlayers on the magnetic properties, the crystallography of these multilayer thin films are studied. The results from this work show that Ag and Cu are strong candidates as interlayer materials in multilayer magnetic-recording media. >

Direct observation of Cr magnetic order in CoCrTa and CoCrPt thin films

Magnetic circular dichroism measurements of room temperature, sputter deposited Co86Cr12Ta2 and Co86Cr12Pt2 films were performed to investigate the local magnetic ordering of the Co and Cr atoms. The results demonstrate that the Cr has a net magnetic moment and that a small fraction of the Cr is magnetically oriented opposite to the Co moment.

Multilayer CoCrTa thin film media with Cr or Ag interlayers

The magnetic properties and recording performance of multilayer CoCrTa thin film media with Cr or Ag interlayers are investigated. It is found that the coercivities and coercivity squareness of the films with Ag interlayers could be higher than that of the films with Cr interlayers. Recording tests show that the disks with Ag interlayers are noisier than the disks without an interlayer and the disks with a Cr interlayer. It is proposed that the increase in media noise when Ag was used as an interlayer is due to the RKKY coupling among magnetic grains through Ag.