Magnetization‐induced optical second harmonic generation from the surface of Co‐doped rutile TiO₂(110)

Abstract

We have investigated the surface magnetism of 5 at% Co-doped rutile TiO 2 (110) using magnetization-induced optical second harmonic generation (MSHG) in the longitudinal Kerr configuration with the incident beam angle of 4• . MSHG is observed at both 2 ω = 2.33 eV and 2 ω = 4.20 eV. MSH intensity showed a hysteresis as a function of the external magnetic field for the second harmonic photon energy of 2 ω = 4.20 eV at which the absorption length limits the MSHG origin to the surface layer of 10 nm due to the TiO 2 bulk. Since 5 at% Co: TiO 2 (110) is judged to have no metallic Co near the top surface by XPS, the hysteresis is attributed to a carrier-induced ferromagnetism at the surface of this material.

Anisotropy of magnetization-induced surface optical second harmonic generation from Co doped rutile TiO2

“…We have found that the surface magnetization showed an anisotropic two-lobed pattern and suggest that this two-lobed pattern reflects the anisotropy of the magnetization of the surface Co ions due to the ligand field of oxygen. Hence the judgment made in our previous paper [9], that 5 at% Co:rutile TiO 2 (1 1 0) is a ferromagnetic dilute magnetic semiconductor at its surface, has been reconfirmed in this study.…”

“…2 demonstrate superparamagnetic behavior. In our previous paper [9] we reported that with a different SH photon energy, this sample showed hysteresis in SH intensity as a function of the applied magnetic field. Therefore, the surface of this sample is ferromagnetic.…”

“…The majority of Co species in 5 at% Co:rutile TiO 2 (1 1 0) grown by the combinatorial laser molecular beam epitaxy technique in an oxygen atmosphere has been found to be Co 2+ ions [9]. If the surface ferromagnetism originates from Co 2+ ions, the ions should feel the ligand field of neighboring oxygen in their magnetization.…”

“…In our previous study we tried to clarify the origin of the ferromagnetism of the Co:rutile TiO 2 surface by using magnetization-induced optical second harmonic generation (MSHG) [9]. SH intensity showed a hysteresis as a function of the external magnetic field at the second harmonic photon energy of 2 hv ¼ 4:20 eV.…”

“…This phenomenon is called magnetizationinduced second harmonic generation. MSHG has been used to detect ferromagnetism and antiferromagnetism at surfaces and interfaces [9,[16][17][18]. The second-order nonlinear polarization as a function of the magnetic field is written by using the nonlinear susceptibility and the fundamental field as…”