Investigation of size effects in magnetoelectric BiFeO3

Abstract

Magnetoelectric materials may be applicable in magnetic and ferroelectric devices, because they exhibit both magnetic and electrical ordering over a range of temperatures. One of the few magnetoelectic materials is BiFeO3. Large particles of (bulk) BiFeO3 have a perovskite structure, a Neel temperature (TN) of 380 °C, and a ferroelectric transition temperature (TC) of 810 °C. Changing the particle size of BiFeO3, to nanometer scale has been demonstrated to affect the magnetoelectric properties of this material. These changes may result from the small particle size of the nanoparticulate BiFeO3 or may be due to local structural changes caused by the decrease in particle size. Nanoparticles of BiFeO3 with a narrow size distribution are not easy to prepare. Nanoparticles were synthesized by using wet chemical techniques and were characterized by x-ray diffraction and scanning electron microscopy. Fe K-edge x-ray-absorption fine structure (XAFS) measurements were made of bulk and nanoparticulate BiFeO3 to determine the local atomic structure about Fe. The XAFS results from the nanoparticulate BiFeO3 show that the local structure about the Fe atoms to approximately 4.0 Å is the same as in the bulk BiFeO3 sample. This result indicates that the decrease in the Neel Temperature (400 to 339 °C for these samples) with the decrease in particle size (1.4 μm to 20 nm) is not due to local structural changes about the Fe atoms as a result of the decrease in particle size.