Preparation and characterisation of magnetic single and double barrier junctions

ii Declaration I wrote this thesis by myself and used none but the indicated resources. Preface In recent years, a lot of new developments in solid state physics have been related to the field of spin electronics. The spin electronic or spintronic device not only uses the charge of electrons to carry information, but also their spin. For example, this allows one to use magnetic fields to manipulate the output in logic circuits. Because these magnetic fields can be induced by electric currents on the chip, it is possible to fully implement these new devices in conventional electronics. One can think of several ways to build spin electronic devices. One approach does not use conventional electronic such as transistors at all. Cowburn showed how to get all basic functions (a branch of one into two signal lines, a crossover of two signal lines, a NOT gate, and an OR gate) using only magnetic logics in specially structured Iron-Nickel lines. With these ingredients it is possible to build any logic circuit. The second more conventional approach uses spin polarised currents in CMOS environments. This is easier to implement, because only electrical signals are used. The challenge of this approach is to get and to manipulate spin polarised currents. The easiest way of getting these spin polarised currents is by using a device with an unpolarised current input and a polarised output. Therefore, this is called a spin filter device, often realised as a tunnel barrier with different opacity for each spin state. The approach investigated in this thesis is the use of a ferromagnetic electrode in tunnel barrier junctions. Because the density of states in ferromagnetic electrodes is not equal for spin up and spin down, the current after tunnelling through the barrier is spin polarised. The spin direction usually does not change during the tunnelling process. This method is a way to create spin polarised currents, but the question, how to manipulate them remains. To solve that problem, two ferromagnetic electrodes are used at both sides of the barrier. Then, two different alignments of the magnetisations of the two electrodes are possible: parallel and anti-parallel. Investigations of the density of states in both electrodes show that the resistance of this device is related to the orientation of the magnetisation of the ferromagnets. Usually the resistance is higher in the anti-parallel case. Because the resistance is an electrical signal, it is …