Novel Magneto-Optic Layers Based on Semiconductor Nanostructures for Kerr Microscopy.
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J6.3.1
Novel Magneto-Optic Layers Based on Semiconductor Nanostructures for Kerr Microscopy. C. Gourdon1, V. Jeudy1, G. Karczewski2, R. André3, E.L. Ivchenko4 1
Groupe de Physique des Solides, Universités Paris 6 et 7, CNRS UMR 7588, Campus Boucicaut 140 rue de Lourmel, F-75015 Paris, France 2 Institute of Physics, Polish Academy of Sciences, Warsaw, Poland 3 Laboratoire de Spectrométrie Physique, Université Joseph Fourier-Grenoble I, Saint Martin d’Hères F-38402, France 4 A.F. Ioffe Physico-Technical Institute, Russian Academy of Sciences, St Petersburg, Russia
ABSTRACT A novel type of magneto-optic layers based on CdMnTe quantum wells is used to image the magnetic flux pattern at the surface of type I superconductors. The magneto-optic layer is designed as an anti-reflecting optical cavity. The quantum wells are arranged in a Bragg structure and placed at maxima of the electric field in the cavity in order to enhance Faraday rotation. INTRODUCTION Imaging the magnetic flux structure at the surface of a non-magnetic material like a superconductor requires the use of a magneto-optic layer (MOL) [1]. Using Kerr (Faraday) microscopy the mapping of the magnetic field amplitude at the surface of the sample can be achieved owing to Faraday effect in the MOL. Depending on the need for either high spatial resolution or high field sensitivity various kinds of MOL have been used, mainly Eu semiconductor compounds in the first case and Bi-doped yttrium iron garnets in the second case [1]. Since all these materials show ferro- or ferrimagnetism their magnetic influence on the sample under study might not be negligible although this point is rarely addressed. We have recently developed a novel type of MOL based on diluted magnetic semiconductor (DMS) quantum wells (QW). These materials have a paramagnetic behaviour that cannot disturb the magnetic properties of the studied sample. DMS like CdMnTe exhibit a large Faraday rotation due to the giant Zeeman splitting of the valence and conduction band states. The giant Zeeman splitting results from the strong sp-d exchange coupling between the localized Mn2+ spins and the carriers. In QWs the confinement lifts the degeneracy of light and heavy holes states and the oscillator strength of excitonic transitions is enhanced. This leads to an increase of the Faraday effect. When the MOL is used on top of a material with a high reflection coefficient like a metal, a metal/MOL/vacuum optical cavity is formed. One must consider the thickness of the MOL with respect to the wavelength of light. The Faraday rotation angle can be greatly enhanced due to multiple reflections in the cavity. In order to further increase Faraday rotation the QWs can be placed at anti-nodes of the electric field inside the cavity. EXPERIMENTAL SETUP AND SAMPLES
J6.3.2
The MOLs were grown by molecular beam epitaxy. Sample 1 and 2 were grown in Warsaw. Sample 1 consists of a ~ 6 µm thick CdMgTe buffer grown on a (001) GaAs substrate without rotation of the sample holder, resulting in a slight gradient of both th
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