[19a-P1-1~17] 7 Beam Technology and Nanofabrication（Poster）

[19a-P1-9] Time-resolved XMCD study of ferromagnetic insulating BaFeO₃ thin films

〇Hiroki Wadati^1,2, Tomoyuki Tsuyama^1,2, Suvankar Chakraverty³, Niko Pontius⁴, Christian Schussler⁴, Harold Hwang^3,5, Yoshinori Tokura^2,3 (1.ISSP Univ. of Tokyo, 2.Dept. of Appl. Phys. Univ. of Tokyo, 3.RIKEN CEMS, 4.HZB BESSYII, 5.Stanford Univ.)

Keywords:XMCD,BaFeO3,time-resolved measurement

Fe⁴⁺ oxides have attracted great attention due to their various magnetic phases. While metallic SrFeO₃ thin films show helical magnetic ordering below T_N = 115 K, insulating BaFeO₃ thin films show ferromagnetism below T_C = 111 K by reducing the Fe 3d - O 2p hybridization through the lattice expansion. We performed time resolved x-ray magnetic circular dichroism (XMCD) measurement on BaFeO₃ thin films in order to investigate the spin dynamics in this material. A Ti-Sapphire laser (800 nm, 1.55 eV) was employed as a pump laser.
Main results are the XMCD and reflectivity evolutions with the delay time by the pump fluence of 3.3 - 10 mJ/cm². The time resolution is ~ 70 ps. With the low pump power, we observed slow demagnetization of ~ 150 ps, corresponding to the typical demagnetization time scale in insulators. There was no change in reflectivity intensity. In higher fluence, we observed fast changes about ~ 70 ps in both reflectivity and XMCD. The unusual fast changes in reflectivity and XMCD intensities for an insulator clearly suggest photo-induced insulator-to-metal transitions in BaFeO₃ thin films.