Magnetic structural study of Co-doped barium ferrites by the RXMS method

Materials and Structures Laboratory, Tokyo Institute of Technology* Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, Japan** Photon Factory, Institute of Materials Structure Science, KEK, Japan*** Industrial Research Institute of Ishikawa, Japan****
â—‹Maki Okube* Seiji Ohsawa** Satoshi Sasaki* Takeharu Mori*** Takeshi Toyoda****

Resonant X-ray magnetic scattering (RXMS) has attracted much interest as a useful tool to determine the magnetic structures associated with specific electronic states. The magnetic resonance even at the K absorption edge is useful to arise from the spin-orbit coupling. We have carried out synchrotron RXMS studies for single crystals of ferrimagnetic M-type barium ferrites at the Fe K edge at the BL-3A of Photon Factory. Diffraction experiments at l = 1.7406 Å (E = 7122.8 eV) gave a magnetic satellite peak for 0 0 8+(2/3) of BaCoTiFe10O19 at T = 100 K, which disappeared at 200 K. It was interpreted from the neutron work as a magnetic helix propagated along the hexagonal c axis. This shows that magnetic intensity can be resonantly excited at the Fe K.
M-type barium ferrite has five independent Fe sites in a hexagonal-ferrite structure, which are well described as a sequence of spinel fcc block of (Fe6O8)2+ and hcp block of (BaFe6O11) 2-. In this study, the crystal structure with spin orientation has been determined based on the difference between observed and calculated asymmetry ratios. Diffraction profiles were measured with right- and left-circularly polarized X-rays at l = 1.7406 and 1.7390 Å. A diamond (001) phase retarder was used to produce the circular polarization near the 111 Bragg condition in the asymmetric Laue case. The observed asymmetrical ratios DRobs were obtained through the RXMS measurements. The structure factors and DRcalc was estimated through magnetic structural models by related to the charge, resonant, magnetic and resonant magnetic scatterings for more than 30 Bragg reflections. Finally, the spin orientations were evaluated through the difference of DRobs - DRcalc.