Effect of humidity and temperature on piezoresponse of single phase multiferroic thin films

D.K. Pradhan
The University of Tennessee, Knoxville TN 37996, USA and Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA,
United States

Keywords: multiferroic, piezoresponse, humidity

Summary:

Effect of humidity and temperature on piezoresponse of single phase multiferroic thin films Dhiren K. Pradhan1, Shalini Kumari2, Philip D. Rack1 1Department of Materials Science & Engineering, University of Tennessee, Knoxville, Tennessee 37996, USA. 2Department of Materials Science & Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802, USA. Piezoresponse Force Microscopy (PFM) has emerged as a powerful tool for experimental investigations of ferroelectric materials. In the imaging mode, PFM allows visualization of static domain structures with nanometer spatial resolution. Application of a sufficiently large voltage through a conductive scanning probe microscopy (SPM) tip can induce local polarization switching and can be extended for creation of tailored domain structures and ferroelectric data storage. Finally, acquisition of the piezoresponse signals during polarization reversal allows measurement of local hysteresis loops, which can be used for characterization of the switching process in the nanoscale area in the vicinity of the tip. The broad application of PFM for probing domain structures and polarization reversal in ferroelectrics demands deep understanding of the basic mechanisms involved. PFN (Pb(Fe0.5Nb0.5)O3) is a well-known multiferroic material with high dielectric constant, very good ferroelectric properties, low dielectric loss and low magnetization value at room temperature. PFN thin films were grown by optimized pulsed laser deposition (PLD) .The thicknesses of PFN thin films are found to be ~ 70 nm. The highly c-axis oriented growth containing only (00l) diffraction peaks of PFN films along with in plane epitaxial relationship were confirmed by high resolution X-ray diffraction measurements. From the atomic force micrographs, it was observed that all the films were densely packed, smooth, free from microcrack and particulates with uniform grain-size distributions. The existence of ferroelctricity confirmed by band excitation PFM. The local polarization reversal by an electric field produced by a conductive SPM tip as a function of the relative humidity and temperature in an SPM chamber has been studied. The decrease of piezoresponse is observed with increase of relative humidity and temperature. The observed phenomena are attributed to the existence of a water meniscus in the vicinity of the tip–surface contact. The ferroelectric phase transition is also probed by the temperature dependence of piezoresponse studies. In addition to the temperature dependence of piezoresponse studies the phase transition is also confirmed by temperature dependent dielectric spectra. Detailed studies on effect of humidity and temperature on piezoresponse of PFN thin film will be discussed in the meeting.