The role of interfaces in CoFe/IrMn exchange biased systems

A trilayer system consisting of an IrMn layer exchanged coupled to two CoFe layers of equal thickness has been studied. A single stage reversal was observed over a wide range of temperatures. Two bilayers with the same thicknesses of the pinning layer but different ferromagnetic thicknesses were also studied. By comparing the magnetic properties of these three stacks the effect of the interfacial area on the exchange field and the coercivity has been determined. We find that the interfacial area has a very minor effect on the exchange field H-ex and the blocking temperature (T-B) but causes a doubling of the coercivity (H-c). This indicates that H-c is dominated by the interface whereas the exchange bias is controlled by volumetric effects

Novel sputtering-technology for grain-size control

In this paper, we present a description of a novel high-rate plasma sputtering system that allows the control of grain size in sputtered films. Additionally, the system has the advantage of a better utilization of the target material (around 80% to 90%) by eliminating the race track at the target as in conventional plasma magnetron sputtering systems. The potential and capabilities of this novel plasma sputtering device are demonstrated in this paper by the deposition of a number of different Cr thin films suitable for underlayers in thin-film media and for which we have performed a systematic X-ray and TEM analysis to determine the grain-size histograms, mean grain diameters, and their relationship to the sputtering processes

Noncontact GMR measurements of synthetic spin valves using IR reflection spectroscopy

The magnetorefractive effect has been used in infrared reflection spectroscopy to study the magnetotransport properties of synthetic spin valves. This optical noncontact technique shows excellent correlation with the electrical giant magnetoresistance data

Growth rate effects in soft CoFe films

We report on growth rate effects in sputter-deposited CoFe films prepared using high target utilization sputtering technology (HiTUS). We find that the grain structure of these polycrystalline films is closely related to the growth rate. By changing the growth rate, samples were prepared with different grain structure, which in turn had the effect of changing the magnetic properties of the films. We demonstrate control of the coercivity, which varied by a factor of more than ten. This was achieved via grain size control in CoFe films of thickness 20 nm. Furthermore, by employing a two-step sputtering process, in which two extreme growth rates are used sequentially, we were able to tune the saturation magnetization

Study of roughness effect in Fe and Co thin films prepared by plasma magnetron sputtering

We report the experimental and theoretical study of a substrate roughness surface induced magnetic anisotropy in thin films of Fe and Co. The experimental results confirm previously reported data on NiFe thin films and indicate that rough substrates increase the magnetic coercive fields in magnetic thin films. This effect is most prominent in films of thickness comparable to the surface roughness values and materials of small volume magnetic anisotropy. We determined the coercive field of 15 nm Fe thin film sample deposited onto rough PVDF to be 256 Oe, which is more than doubled the value of the coercive field of 15 nm Fe films coated under identical conditions, onto smooth Si substrates. The effect is visible for Co films but weaken by its increased volume magneto-crystalline anisotropy. These results are important for applications based on magnetic thin film where the magnetic properties could be adjusted via substrate roughness engineering

Anisotropy and texture. Studies in magnetic media Magnetic anisotropy

The rapid development of magnetic materials for recording media applications increased the demands for new and more precise experimental investigation techniques. In respect with these demands, this project is focused on experimental analyses of advanced particulate media and magnetic thin film samples. A new extended rotational remanence technique for anisotropy field measurements was developed. The technique is suitable for samples that contain aligned or partially aligned particles and provides both: in-plane anisotropy field distributions and the in-plane anisotropy field. This technique was also extended to out-of-plane anisotropy field measurements. Rotational hysteresis was introduced as an alternative method for anisotropy field measurements. This applies well in the case of samples without texture or samples having very small magnetic moment (i.e. thin films). The two techniques for anisotropy field measurement compare well and the experimental results were interpreted in terms of inter-particles interactions. Two measurement methods for determination of the demagnetizing field acting perpendicular to a sample plane were also developed. The first method is based on the in-plane and out-of-plane anisotropy field determination using an extended rotational remanence technique. The second method can provide the demagnetizing field starting from in-plane and out-of-plane transverse hysteresis loops. Comparison between the results from the two methods showed good agreement. Furthermore, the demagnetizing field values were used to calculate the magnetic coating thickness, so the two methods provide a non-destructive method for magnetic thickness measurements in film samples. The in-plane easy axis distribution (EAD) was experimentally determined using vector VSM techniques. Correlations between in-plane tape texture and magnetic thickness were obtained for a series of advanced MP tapes. A theoretical approach was used in order to relate the orientation ratio to EAD. The out-of-plane EAD was derived from numerical calculations. The out-of-plane distribution also showed a variation with the magnetic thickness. In addition, the microstructure and particle morphology of the advanced MP tapes, as well as the out-of-plane component of magnetization, have been investigated using Moessbauer Spectroscopy. Finally, 3D - EAD maps were produced. All VSM experiments were fully computer controlled and the routines were designed in the LabView environment as part of this project. (author)SIGLEAvailable from British Library Document Supply Centre- DSC:dxn059003 / BLDSC - British Library Document Supply CentreGBUnited Kingdo