Growth and characterisation of multiferroic BiFeO_3 films with fully saturated ferroelectric hysteresis loops and large remanent polarisations

摘要

Multiferroic BiFeO_3 films have been deposited on a number of substrates by RF magnetron sputtering. Two routes were adopted in order to obtain the films of high phase purity and accurate stoichiometry. The first was to sputter films at room temperature and then the BiFeO_3 phase was formed after sintering at various temperatures under controlled ambient atmosphere. The second was to grow BiFeO_3 in-situ at high temperature during sputtering. Although the sintered films grown on SrTiO_3 substrates were epitaxial and showed better texture than the in-situ films, they had much poorer ferroelectric properties, due to the residual traces of intermediate phases formed during heating. Under right growth parameters, the in-situ films grown on the LaNiO_(3-x) buffered SrTiO_3 showed fully saturated ferroelectric hysteresis loops with large remanent polarisation of 64 mu C/cm~2. Piezoresponse force microscopy (PFM) was used to examine the ferroelectric domain structures. When scanned without DC bias, fine spontaneous domains were observed. Under + -10 V DC bias, PFM confirmed that the domains could be poled and switched.