Growth and Characterization of Magnetooptic Garnet Films with Planar Uniaxial Anisotropy

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Growth and Characterization of Magnetooptic Garnet Films with Planar Uniaxial Anisotropy Vincent J. Fratello, Irina Mnushkina, Steven J. Licht and Robert R. Abbott Integrated Photonics, Inc., 132 Stryker Lane Hillsborough, NJ 08844-1937, U.S.A. ABSTRACT Thick film garnet Faraday rotators with perpendicular anisotropy have limited utility for variable polarization rotation applications because multi-domain effects result in large effective insertion losses in device applications. Thick film growth of (BiGdLu)3(FeGaAl)5O12 on (100) substrates yields growth-induced anisotropies ranging from positive anisotropy perpendicular domains to negative anisotropy in-plane domains. Planar domains show variable magnetization by domain rotation with a uniform projection of magnetization along the axis of light propagation. This can produce low-loss devices when operated in sub-saturation applications such as magnetic field sensors, variable optical attenuators and polarization controllers. INTRODUCTION Liquid phase epitaxy (LPE) of single crystal films of magnetic garnets has been developed since the 1970’s for a wide variety of magnetic and optical devices for memory, display, signal processing and optical communications. The technique has been perfected for growth of thick bismuth-doped rare earth iron garnet (Bi:RIG) films for Faraday rotator applications. Thick-film garnet Faraday rotators with perpendicular anisotropy are widely used in the photonics industry [1]. They are the principal component in such non-reciprocal devices as magnetooptic isolators, circulators, interleavers and low speed switches. In operation they are customarily magnetically saturated in a single direction perpendicular to the major face of the garnet and approximately parallel to the direction of propagation of light through the garnet. When the magnetic field is removed, standard garnets revert to a demagnetized state of serpentine domains as seen in Figure 1a. This mixture of “up” and “down” perpendicular stripe domains depicted schematically in Figure 1b is the lowest energy configuration for a material with perpendicular anisotropy. When a perpendicular magnetic field is applied, the domains parallel to the field will expand and the domains anti-parallel to the field will contract as in Figure 1c. In this way, the average magnetization of the film varies continuously as in the Vibrating Sample Magnetometer (VSM) curve in Figure 2. The effective Faraday rotation of the film varies somewhat differently. A light beam passing through the garnet will be rotated in accord with the domains it samples with each domain providing full rotation according to the magnetooptic coefficient and direction of magnetization. A beam that is small compared to the domain size would experience essentially a Faraday rotation according to the orientation of the specific domains it passes through, with the overall effect of being random for any beam location with a statistical distribution around the proportional distribution of domains. A beam that is large compar