Further development of a scanned near-field optical microscope for magneto-optic Kerr imaging of magnetic domains with 10nm resolution

Abstract

Work is described on the development of a scanning near-field optical microscope (SNOM) for the primary purpose of imaging magnetic systems with resolution on the order of 10 nm. Since many magnetic materials are optically opaque, it is desired to have a probe which is appropriate for the reflection mode. The near-field probe must be linearly polarizable, since the magneto-optic kerr effect (MOKE) is utilized for magnetic imaging. Data will be presented on the characterization and use of ∼30 nm diameter Ag particles as probes for MOKE-sensitive SNOM. Such small metal particles exhibit a localized plasmon resonance in the visible, which greatly enhances their optical scattering cross-section. We have made a systematic study of the light scattering properties of single Ag particles from 20 to 30 nm in size with a high-sensitivity micro spectrophotometer system, for several reasons: (1) To compare the light scattering properties of individual particles with the predictions of Mie theory; (2) to understand the polarization sensitivity of the optical scattering properties of real aspherical particles; and (3) to optimize the probe-sample separation distance for various magnetic materials of interest Ag particles prepared by colloidal chemistry techniques have been deposited on Bi-doped YIG and silica-coated permalloy to measure the magnitude of near-field MOKE. Near-field MOKE polarization rotations of 1.5 and 6.5 milliradians were measured for permalloy and YIG, respectively.