Pulsed laser deposition of CoCrFeMnNi High Entropy Alloy and its stability

KARRI, SRI NAGA SESHA and Ramadurai, Ranjit and Bhattacharjee, Pinaki Prasad (2018) Pulsed laser deposition of CoCrFeMnNi High Entropy Alloy and its stability. Masters thesis, Indian Institute of Technology Hyderabad.

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Abstract

CoCrFeMnNi High Entropy Alloy is a single phase solid solution with FCC crystal structure which has shown very novel properties in its bulk form. Present study investigates the stability of these alloys in thin film form deposited by pulsed laser deposition. For this purpose depositions are done on two different substrates namely glass and platinized silicon at three different temperatures (room temperature, 2500C and 4000C). XRD studies have shown that the required phased formation is observed on films deposited at room temperature and no phase formation is observed on films deposited at 4000C and 2500C. Energy dispersive x-ray analysis (EDAX) analysis has shown that the composition of the bulk target materials is maintained in the thin films as well. The thickness of the deposited films was found to be around 100 nm which was studied by Ellipsometry. Reexamination of the films after 3 months of deposition by SEM analysis have shown a new phase formation and pores on the films. however, no extra phase could be detected within the limits of x-ray diffraction studies. To analyze the phase segregation if any, the samples were subjected to heat treatment studies. These samples were heat treated at 1500C for 1 hour to enhance the new phase observed under microstructural studies. however no enhancement of the phase was observed under x-ray diffraction studies. Suspecting the formation of metal oxide (mainly Mn and Cr) oxidation studies were attempted. An oxygen annealing was performed at a steady state of 50 mTorr of oxygen ambience at 3000C. But no oxide peaks or any new phase peaks was noticed in XRD analysis. however, EDAX analysis has shown that the new phase formed is mainly due to the formation of manganese oxide. Magnetic studies carried out using MFM studies before and after oxidation of the films have showed that films are paramagnetic which may be attributed to nano grain size of the film.VSM studies carried out on oxidized and heat treated samples have shown that these alloy films are weakly ferromagnetic at room temperature. This ferromagnetic nature could be attributed to oxide impurities mainly manganese oxides.

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