Bunsen Y. Wong

The crystallography and texture of Co-based thin film deposited on Cr underlayers

Some of the evidence for the effect of Cr orientation on the crystallographic orientation of Co-based thin films is presented. The authors review four experimental techniques that can be used to investigate the orientation relationships (OR) between the magnetic Co-based film and the Cr underlayer. These techniques are X-ray diffraction, selected area (electron) diffraction (SAD), electron microdiffraction, and atomic resolution electron microscopy of cross sections of the bi-layer films. The authors focus on the crystallographic orientation relationships between the grains in the magnetic film and those in the Cr (BCC) underlayer. The magnetic films discussed are all alloys of Co, usually with HCP structure. >

Microstructural origin of the perpendicular anisotropy in M-type barium hexaferrite thin films deposited by RF magnetron sputtering

Barium hexaferrite thin films deposited by RF magnetron sputtering have exhibited saturation magnetization 90% of that of bulk single crystals, whereas the perpendicular uniaxial anisotropy is only 60% of that of the bulk. X-ray diffraction spectra suggest good c-axis orientation perpendicular to the film plane. However, M-H hysteresis loops show a fairly large in-plane hysteresis. Scanning electron microscopy and transmission electron microscopy show that the films are made of a mixture of platelet-shaped grains and acicular grains. Microdiffraction studies in a transmission electron microscope indicate that the platelets have their c-axis oriented perpendicular to the plane and that the acicular grains have c-axis orientation in the plane. Preferential grain growth in the basal plane of the crystal is believed to be responsible for these grain geometries. >

Crystallography of Co/Cr bilayer magnetic thin films

Various crystallographic textures of Co‐alloy/Cr bilayer thin films are discussed based on microdiffraction and selected‐area diffraction (SAD) results. In order to understand the origin of the crystallographic texture of the Co thin films, the orientation relationships between the Co and Cr grains were determined by the electron microdiffraction technique. From this information, we suggest that the {110} Cr underlayer texture may not necessarily be required to obtain the highest in‐plane coercivity in Co films. In order to evaluate the crystallographic texture of the film by SAD patterns, normalized intensity of SAD patterns for various thin‐film textures have been calculated. Using these calculations, we interpret the SAD patterns taken from various Co and Cr thin films.

Study of the growth characteristics of sputtered Cr thin films

The crystallographic texture of Cr film deposited on glass substrates is found to depend on the film thickness dCr and the substrate temperature Ts. Without substrate preheating, only the Cr {110} peak was observed in the x‐ray diffraction spectra for films between 60 and 400 nm in thickness. With increasing Ts (by substrate preheating), the Cr{200} peak became observable at progressively increasing intensity, whereas the intensity of the {110} peak decreased. Consequently the 170‐nm‐thick films deposited at Ts ≥200 °C are predominantly {100} textured. However, even for these high Ts values (≥200 °C), the {110} peak intensity increases with increasing film thickness. Larger film thickness values are required at higher Ts for the {110} texture to overcome the {100} texture. The grain size of the Cr films deposited on glass increases with film thickness and with substrate temperature.

Investigation of CoNiCr thin films deposited on

This paper reports on Co{sub 62.5} Ni{sub 30}Cr{sub 7.5} thin films that were sputtered onto (100) and (110) Cr single crystals as well as polycrystalline Cr TEM folls. VSM measurements have revealed the existence of an anisotropy in the in-plane coercivity. This stems from the development of a crystallographic texture in the plane of the film. TEM investigations have found the presence of crystallographic variants in the direction of the hcp c-axis in the CoNiCr films deposited on (100) and (110) Cr surfaces. Lorentz microscopy studies have found relatively straight domain walls which lie parallel to the specific crystallographic directions. The direction of magnetization within each domain is along the c-axis.

Microstructural investigations of barium ferrite longitudinal thin‐film media

Crystalline barium ferrite films with in‐plane magnetic anisotropy have been obtained by postdeposition annealing of amorphous sputtered films. The magnetic properties, the crystallographic texture, and the microstructure are very sensitive to the sputtering and postdeposition annealing conditions. It was found that both Hc and the grain size decrease with the addition of Co and Ti ions. However, an excessive amount of dopants leads to a loss in the in‐plane anisotropy. Barium ferrite films produced by this technique contain physical voids or channels separating the grains which help to decrease the exchange coupling between grains.

The dependence of the microstructure and magnetic properties of CoNiCr/Cr thin films on the substrate temperature

Thin CoNiCr/Cr films (candidates for longitudinal recording media) were deposited on Corning 7059 glass substrate by RF diode sputtering. The CoNiCr layer thickness was fixed at 40 nm; the Cr layer thickness, d/sub Cr/, ranged between 60 and 400 nm. At d/sub Cr/=170 nm, when the substrate temperature before deposition, T/sub s/, was set below 100 degrees C, both the Cr underlayer and the CoNiCr layer were more or less randomly oriented. When specimens were deposited at T/sub s/>or=200 degrees C, the Cr layer was strongly [100] textured and the CoNiCr layer exhibited a strongly preferred texture. This CoNiCr texture is epitaxially favored by the Cr [100] texture. With increasing d/sub Cr/ the Cr [110] texture increased and the CoNiCr texture decreased. The grain size increased with T/sub s/ and d/sub Cr/. In-plane coercivity, H/sub c/, initially increased with T/sub s/ to peak at T/sub s/=200 degrees C. As T/sub s/ was increased further from 200 to 260 degrees C, H/sub c/ decreased. The squareness and saturation magnetization were not sensitive to T/sub s/. >

Structural origin of magnetic biased field in NiMn/NiFe exchange coupled films

The factors which determine the strength of the magnetic biased field in NiMn/NiFe exchange biased system have been examined. It was found that a strong NiFe (111) texture and columnar growth are essential to obtaining a high exchange field as they facilitate epitaxy between the NiFe and NiMn layers. The application of an amorphous Ta nucleation layer and substrate biasing during NiFe deposition have been found to promote these structures. Fcc NiMn replicates the (111) texture through epitaxial growth on NiFe according to a cube on cube orientation relationship. Upon annealing, atomic ordering takes place in the NiMn layer and gives rise to an exchange biased field. However, a fully L10 ordered structure cannot be achieved at the NiMn/NiFe interface due to the stabilizing effect of fcc NiFe. Away from the interface, the transformation proceeds and the ordered tetragonal unit cell creates a lattice strain within the NiMn film. This strain is relieved by twinning within the NiMn grains of the film. The stre...

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.

An investigation on the fine defect structure of CoCrTa/Cr magnetic thin films

The fine defect structure inside the CoCrTa grains in a CoCrTa/Cr bilayer film has been investigated by high‐resolution transmission electron microscopy. A high density of stacking faults bound by partial dislocations has been observed. The origin of these stacking faults and the nucleation and growth of CoCrTa on Cr columns have been discussed. It is suggested the surface morphology of the Cr column could play an important role in determining the number of CoCrTa nuclei and consequently the size of the individual CoCrTa crystallographic variants. In addition, plates of face‐centered cubic CoCrTa separating the hexagonal‐close‐packed regions have been found and we believe that the existence of these plates could lead to coercivity enhancement.