Application of Magnetic Garnet Films for Magnetooptical Imaging of Magnetic Field Distributions

Abstract

Rare-earth iron garnet films of high quality can be grown by liquid phase epitaxy on paramagnetic substrates of gadolinium galliumgarnet. Such films are currently used for imaging of the spatial distribution of magnetic fields. This application is based on the Faraday rotation which can strongly be enhanced by bismuth incorporation.The physical properties of the films can be controlled by the chemical composition, the growth conditions and the crystallographic orientation. The sensor properties like sensitivity, dynamic range, signal linearity and unambiguity must be optimized according to the application desired. These properties, however, are not independent of each other. In addition, they strongly depend on the optical wavelength. Thus, it is necessary to find compromises.The influence of Faraday rotation, Faraday ellipticity, optical absorption, magnetic anisotropies and film thickness on the performance of a magnetooptical indicator film is investigated. Based on the swing of the photoresponse, a new optimization process is introduced. The process is experimentally verified and application examples are demonstrated.Furthermore, two methods are presented to enhance the sensitivity of magnetooptical sensors. Using specific crystallographic orientations, an easy plane of magnetization can be induced which is inclined with respect to the film plane. If the magnetization lies in this plane a very high sensitivity is achieved. The dependence of the geometrical orientation of the easy plane on the growth direction is calculated and the sensitivity and dynamic range are derived. Experimental results of a [112] oriented garnet film are in good agreement with calculations.Garnet films which are magnetized along the film normal due to a strong induced uniaxial anisotropy support magnetic domains. If the collapse field perpendicular to the film plane is small, such films can be used as very sensitive indicator films. Such films are easier to prepare than sensitive in-plane films. However, the spatial resolution is limited by the size of the domains. This disadvantage can be avoided by applying a bias field in the film plane. Directly at the in-plane collapse field the sensor film is in-plane magnetized yielding high spatial resolution at still high sensitivity. The variation of magnetooptical images with in-plane induction is demonstrated. Experimental results are in agreement with calculations.

Coercive Properties of Magnetic Garnet Films

“…The flexibility of ion substitution has led to promising applications of the magnetic garnet materials in microwave devices based on magnetostatic waves propagation [18], energy-independent information storage (bubble memory devices) [19,20], vertical Bloch line memory [21,22], a wide range of magneto-optic devices, i.e., shutters, modulators, deflectors, rotators [23][24][25][26][27]. As it can be seen from the above arguments, magnetic garnets still are among the most intensively studied magnetic dielectrics, and the last decade of the former century revealed many promising applications in sensors for epitaxial iron garnets having easy plane type magnetic anisotropy, for example, a magneto-optic visualization of the spatial distribution of magnetic field [28], for the non-destructive testing of high-temperature superconductors, eddy current imaging of defects in plated conducting materials, electric current topography in ICs, inductive and magneto-optical magnetic field sensors for different applications [29].…”

Asymmetric Magneto-Optical Rotation in Magnetoplasmonic Nanocomposites

“…It has been shown that the magneto-optical effects in magnetic iron-garnet films are very valuable in different applications of photonics, spintronics, sensorics, magnetometry, etc. [3][4][5]. In order to enhance the magneto-optical effect for these applications, various methods can be used.…”