Measurement of the magnetization in thin films using magneto-optical effects

Many sensors of magnetic field and the electric current sensors are based on the magneto-optical (MO) effects. MO Kerr effects in reflection are widely used for thin film magnetization study. A magneto-optical hysteresis loop measurement and an observation of the magnetic domain (MO microscopy) have an important advantage for the study of the magnetism of thin and ultrathin films. The observation and careful separation of three magnetization components (sometimes called vectorial magnetometry) are the tasks for a precise MO measurement. The paper is devoted to the influences of various magnetization components on the ellipsometric observables. The component separation is discussed including both linear and quadratic terms in magnetization. Presented theory is based on a solution of the wave equation in MO medium described by the permittivity tensor. The eigenmode (characteristic) equation is solved for a general magnetization direction in the linear and quadratic approximations using both numeric and symbolic methods. The boundary conditions for the electric and magnetic fields at interfaces are written in compact form based on 4 X 4 Yeh's matrix formalism. Three basic magnetization configurations are usually distinguished -- polar, longitudinal and transversal. The component perpendicular to the plane of incidence (transversal) affects only the rpp reflection coefficient in the linear approximation. The components lying in the plane of incidence (polar component is normal and longitudinal one is parallel to the interface) affect the conversion reflection coefficients rsp, rps and the ellipsometric angles (Kerr rotation and ellipticity). The quadratic effects are observed when both the transversal magnetization component (perpendicular to the plane of incidence) and the longitudinal one (parallel to the plane of incidence) are present simultaneously. These quadratic effects are observed as a product of the magnetization components in the conversion reflection coefficients.

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