Polarized light in structures with magnetic ordering

Modeling of the light interaction in magnetic structures represents a problem of optics of anisotropic media based on solution of the Maxwell's equations. Magneto-optic medium is described using permittivity and permeability tensors, however, the permeability tensor is mostly set to its vacuum value for optical frequencies. The permittivity tensor can be expanded into a power series as a function of magnetization components. Linear and quadratic effects of the magnetization are characterized by linear and quadratic magneto-optic tensors, respectively. A complexity of the tensors and a number of the independent tensor components are reduced by including the crystal symmetry and the Onsager's principle. We describe, how the magnetic ordering affects eigenmode polarizations in magneto-optic media. Magneto-optic angles dependence on the magnetization components is discussed in details. Quadratic or second-order terms also affect significantly the magnetization measurement. Particular attention is devoted to magneto-optic effects in cubic crystals. While the optical and linear magneto-optic properties of cubic crystals are independent on the direction of crystal axes, the quadratic effects exhibit strong anisotropy. The theory was completed by an experimental observation of the quadratic effect anisotropy in an epitaxial Fe layer prepared on a MgO substrate. The influence of the magnetization components on the magneto-optic vector magnetometry is discussed for a general magnetization direction.

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