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Title: Magnetic and transport properties of sputtered iron-aluminium films under vacuum
Authors: Zayer, Nadhum K.
Issue Date: 1993
Publisher: © Nadhum Kadhum Zayer
Abstract: Sputter deposition is one of the vapour quenching methods used to produce alloying compounds in thin film form. The alloying compounds produced by this method have a chemically homogeneous, non-equilibrium structure which is dill'erent from that of alloys produced by solid quenching, liquid quenching, or mechanical alloying methods. In the present investigation the Fe 1-:x.A1x alloy thin films were prepared using multisource magnetron sputtering. The samples were deposited onto a water cooled substrate and their thickness was kept constant at t- 300nm. To investigate the effect of the deposition parameters on the properties of the films, the samples were deposited at various argon gas pressures PAr I, 3, or 4 mtorr. The effect of gas pressure is consistent with the thermalization of the deposited material by collisions with gas atoms in the chamber. The composition range of the samples varied from pure iron to pure aluminium. The composition, structure and morphology of the films was obtained using Transmission Electron Microscopy (TEM). X-ray diffraction patterns were also used to obtain the structure of the films. Structure analysis showed that a bcc crystalline structure was obtained in samples of composition range x= 0 to - 50%, an amorphous structure in samples of composition range x- 55% to - 83%, and a fcc crystalline structure in samples of composition range x- 85% to 100%. These composition ranges are affected by altering the deposition gas pressure. The morphology of the deposited films was observed to be affected by the deposition gas pressure. The samples deposited at low gas pressure Par=1 mtorr consist of a fibrous structure with densely packed boundaries, while the samples deposited at high gas pressure Par=4 mtorr consist of columnar structures separated by open boundaries. Room temperature resistivity measurements show a drop in resistivity in the composition range x- 30% to 50%. This drop is thought to be due to the formation of chemically ordered Fe3Al and FeAI compounds. Also the resistivity increases with increasing argon gas pressure. The effect of altering the argon gas pressure is to change the morphology of these alloys, and this has a significant effect on the magnetic properties. The effect of annealing on the magnetisation and morphology was also studied in the samples. A low temperature resistivity measurement system was constructed. A closed cycle helium refrigerator, which provided a working temperature range of T= l5°K to 3000K was used for the cooling process. The resistivity measurements revealed three distinct characteristics dependent on composition :- 1. x= 0 to 46%: The samples in this range exhibit a metallic behaviour, with the samples in the composition range x= 27% to 46% showing a resistivity minimum at low temperature which is thought to be due to spin glass formation. 2. x= 48% to 83%: These samples have a semiconductor or metallic glass-like behaviour. 3. x= 85% to 100%: These samples show a metallic behaviour. The above properties are associated with the change in the structure of the fiIrns as the composition varies. A computer controlled AC susceptometer was designed and constructed to measure the AC susceptibility of the samples in the temperature range T= 20 OK to T= 300 OK. A closed cycle helium refrigerator was used to provide the cooling process. The AC susceptibility measurements for the samples with resistivity minima show a sharp peak at low temperature which confirms the presence of spin glass in these samples at low temperature. The results of magnetic and transport properties can be related to the structure and morphology of the filrns. The results have been compared with those obtained from bulk samples with the same composition.
Description: A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.
URI: https://dspace.lboro.ac.uk/2134/21526
Appears in Collections:PhD Theses (Physics)

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