The Study of Structural, Magnetic and Ferroelectric Properties of Bi-Fe-O （Bi/Fe=3/7, 4/6, 5/5, 6/4, 7/3）Epitaxial Films Grown by Molecular Beam Epitaxy

• Main Authors: Ching-Yen Tsai, 蔡清彥
• Other Authors: Gung Chern
• Format: Others
• Language: zh-TW
• Published: 2007
• Online Access: http://ndltd.ncl.edu.tw/handle/65979255935933545974

碩士 === 國立中正大學 === 物理所 === 95 === Using oxygen-plasma-assisted molecular beam epitaxy, a series of Bi-Fe-O films are synthesized directly on SrTiO3(001) and with Ta buffer layer on Si(001) substrates. These films were grown with Bi/Fe ratio = 7/3, 6/4, 5.5/4.5, 5/5, 4/6, 3/7 respectively in the environment of plasma oxygen pressure ~ 5×10-5 torr. and with growth temperature 650°C. X-ray diffraction perpendicular to the film surface reveals epitaxial quality of all films grown on SrTiO3(001) with lattice parameters match Bi3Fe5O12(001) peaks. The magnetic hysteresis curves of the films with (001) plane show that the magnetic easy axis is in the film plane if Fe content is rich. However, the magnetic anisotropy gradually changes from in-plane to perpendicular direction when Bi/Fe is 7/3. The saturation magnetization is between 600 (emu/cm3) to 150 (emu/cm3) and shows a minimum for the film with Bi/Fe = 6/4. The ferroelectric measurements are carried out for the film with Ta electrodes. A ferroelectric hysteresis, with P = 6 (uC/cm2), is observed for the film with Bi/Fe = 6/4, which is the one has the lowest magnetization. It is believed that the chemical formula for the film with Bi/Fe = 6/4 should be close to BiFeO3 because Bi is more volatile during the growth. The present observation indicates that if Fe ion is evenly distributed in d and a Site, an antiferromagnetic state may be formed and a possible ferroelectric phase is induced.