K. R. Mountfield

Ferromagnetic resonance studies of exchange biasing in Ni81Fe19/Pt10Mn90 bilayers

In-plane ferromagnetic resonance (FMR) has been used to study exchange anisotropy in Ni81Fe19/Pt10Mn90 bilayers at room temperature. A theoretical calculation for the FMR resonance field was carried out based on a simple model of the exchange bias in a polycrystalline bilayer that incorporates reversible as well as irreversible behavior of the antiferromagnetic layer. In addition to the expected cos φH contribution to the resonance field, where φH is the direction of the applied field, there is a negative shift of the resonance field. It is argued that the negative shift of the resonance related to the irreversible behavior of the antiferromagnetic moments is not isotropic. The linewidth broadening of in-plane resonance for the exchange biased bilayers is also discussed.

Design, fabrication, switching, and optical characteristics of new magneto‐optic spatial light modulator

A new reflected mode magneto‐optic spatial light modulator (R‐MOSLM) has been developed for miniature optical correlators and computers. A factor of 4 improvement in pixel switching sensitivity, compared to the conventional transmission mode magneto‐optic spatial light modulator, has been achieved by the use of narrower drive lines, and burying the conductor into the film. A factor of 3 higher resolution and a factor of 2 higher optical efficiency have also been achieved by the use of smaller pixels and narrower pixel gaps. The smaller pixels and improved switching sensitivity permit an order of magnitude reduction in optical path length and increase in frame rate, respectively. The progress that has been made in the design of the R‐MOSLM, issues concerning its fabrication, a comparison by finite element analysis of field modeling to experimentally determined current requirements to drive individual lines, and some optical characteristics are discussed.

Transmission electron microscopy of Co-Cr films for magnetic recording

The microstructure of Co‐Cr thin films for perpendicular magnetic recording has been examined by transmission electron microscopy in both conventional (bright field/dark field and selected area diffraction) and convergent beam electron diffraction modes. Results of as‐deposited samples indicate that the films consist of well‐oriented c axis structures. A range of microstructures (columnar morphology, transition layers, twins, etc.) have been observed. These and other results will be presented.

TEM investigation of Co-Cr film microstructure

Abstract Transmission electron microscopy (TEM) was used to reconstruct the microstructure of Co-Cr thin films. It was found that the initial layer consists of randomly oriented small crystal grains, that further growth favors well-aligned grains and that microstructural details may be correlated with inferences from ferromagnetic resonance (FMR).

Search for high moment soft magnetic materials: FeZrN

FeN materials exhibiting high moment, low coercivity and small magnetostriction have previously been reported. Zr has been known to reduce the magnetostriction in other Fe alloys. The criteria for an ideal recording head pole material as well as shields for magnetoresistive sensors include high moment, low coercivity, high permeability, and zero magnetostriction. We present here the properties of 0.3 μm thick rf sputtered FeZrN films measured as a function of the N2 partial pressure. The films were deposited at a pressure of 3 mT using a Perkin Elmer sputtering system. The target was composed of Fe with Zr chips covering approximately 2% of the surface area. The easy axis and hard axis coercivities show minima of 1.8 and 0.6 Oe, respectively, at 7–10 % N2 partial pressure with a saturation magnetization of about 18 kG. The magnetic anisotropy field is approximately 5 Oe yielding a dc permeability of approximately 4000 along the hard axis. X‐ray data reveal a systematic change in the ratio of α–Fe and γ–Fe...

Magnetic‐structural development in Co‐Cr films for perpendicular recording media

Transmission electron microscopy (TEM) was employed to examine the relation between microstructure and the corresponding magnetic domain structure in Co‐Cr films. Emphasis has been placed on the influence of crystallographic orientation on the magnetic domain morphology. Examination of thin samples (7.5–35 nm) reveals that randomly oriented small grains form in‐plane domain structures with cross‐tie walls, magnetic ripple structure, and Bloch lines. As the film thickness increases (40–50 nm), the grains become well oriented along their c axes and the corresponding domain structures are comprised of the stripe‐type characteristic of perpendicular domains. The magnetic domain structures will be discussed in terms of crystallographic orientation and microstructural defects.

Microstructural development in Co-Cr films for perpendicular recording media

A series of Co-Cr films have been examined using transmission electron microscopy (TEM) in bright/dark field imaging, and selected area diffraction (SAD) as well as convergent beam electron diffraction (CBED). Examination of the early stages of deposition by a DC magnetron provides evidence that amorphous Co-Cr films form prior to small randomly oriented equiaxed grains. Occasionally, a mixture of equiaxed and elongated grains were observed in the plane-view. Furthermore, microvoids are present running parallel to the columnar boundaries in cross-section view and at grain boundaries/edges in plane-view. In addition to conical and straight columnar grains, a mixture of small equiaxed and elongated grains were observed in cross-section view.

Micro/magnetic structural development in Co‐Ni‐Cr and Co‐Ni‐Cr/Cr films for longitudinal recording media

A series of Co‐Ni‐Cr and Co‐Ni‐Cr/Cr films have been examined using transmission electron microscopy in conventional bright/dark‐field imaging, selected‐area diffraction, convergent beam electron diffraction, as well as in Lorentz electron microscopy imaging mode. The crystallographic orientation and magnetic domain structure have been characterized as a function of film thickness. The results indicate that amorphous Co‐Ni‐Cr films form prior to the formation of small randomly oriented equiaxed grains during deposition on amorphous substrates. As the film thickness increases, some of the small grains grow preferentially with their c axis parallel to film plane, but others with their c axis at an angle of 62° from the film plane. Longitudinal domain structures of the films were found to consist of Neel walls associated with cross‐tie walls and Bloch lines. Each domain contains a large amount of the magnetic ripple‐type structure.

Thermomagnetic analysis, annealing effects, and Cr distribution in CoCr sputtered films

Thermomagnetic analyses (TMA) of rf‐sputtered CoCr films have shown unusual magnetization versus temperature behavior. On heating, magnetization persists to around 700 °C. After cooling from 800 °C, however, magnetization does not appear again until around 300 °C. On all subsequent heatings and coolings, such films retain a Curie temperature of around 300 °C. At the same time, room‐temperature Ms values decrease considerably. TMA of bulk samples of the same composition show a Curie temperature around 300 °C and no subsequent change of Curie temperature upon heating and cooling. These data cannot be explained on the basis of Cr‐rich oxide formation. Additional experiments have ruled out Cr segregation in a planar transition layer. X‐ray and electron diffraction measurements have shown no evidence of long‐range order‐disorder phenomenon. However, the data are consistent with explanations involving either Cr grain‐boundary segregation or atomic‐scale redistribution of the Cr. A simple model of grain‐boundary...

The effect of annealing on the transiton layer in Co-Cr thin films as inferred from FMR☆

Abstract Co-Cr films have been vacuum-annealed with and without the application of dc magnetic fields. A 30 GHz ferromagnetic resonance (FMR) spectrometer was used to assess changes in magnetic properties. When a structurally oriented bulk layer or applied magnetic field are present, annealing affects the transition layer through preferential grain growth.