Indirect Exchange Coupling in Sputtered Magnetic Multilayers

This thesis describes the design, construction, and use of a sputter deposition facility at the University of Leeds for the growth of magnetic multilayer samples. Now completed, the machine is a UHV sputtering facility, capable of growing up to 15 samples of arbitrary complexity under computer control in a single vacuum cycle. The system currently has five sputter targets.
The system was used to grow Co/Cu multilayers. It was found that the level of residual gas in the chamber is of primary importance in determining the final quality of the samples. A good vacuum is required to achieve good antiferromagnetic coupling between adjacent Co layers in the multilayer stack. Consequentially the giant magnetoresistance of such samples is very high. A poor vacuum leads to poor coupling between Co layers, and the magnetoresistance of such samples is minimal.
When grown under clean conditions the giant magnetoresistance of the Co/Cu multilayers was very high - as much as 75% at room temperature, rising to 130% at 4.2K. Coupling oscillations as the Cu spacer thickness was varied were strong, whilst none were detected as a function of Co thickness.
It was found that the >< Cu spacer layer was the part of the multilayer where the effects of damage by residual gases were most severe, and that damage to this area could cause biquadratic coupling. This form of the coupling arranges spins in adjacent layers at 90° to one another, rather than antiparallel, reducing the giant magnetoresistance response of the sample. The saturation magnetisation, bilinear and biquadratic coupling energies of 180° and 90° coupled samples were measured. These three quantities were found to scale as a function of temperature.