Patrick Matthes

Adsorption of α-helical polyaniline self-assembled monolayers onto magnetic substrates containing a thin Co layer determines the magneto-optical response.

We have investigated ferroelectric charged domains in polycrystalline hexagonal yttrium manganite thin films (Y₁Mn₁O₃, Y_0.95Mn_1.05O₃, Y₁Mn_0.99Ti_0.01O₃, and Y_0.94Mn_1.05Ti_0.01O₃) by scanning electron microscopy (SEM) in secondary electron emission mode with a small acceleration voltage. Using SEM at an acceleration voltage of 1.0 kV otherwise homogenous surface charging effects are reduced, polarization charges can be observed and polarization directions (±P_z) of the ferroelectric domains in the polycrystalline thin films can be identified. Thin films of different chemical composition have been deposited by pulsed laser deposition on Pt/SiO₂/Si structures under otherwise same growth conditions. Using SEM it has been shown that different charged domain density networks are existing in polycrystalline yttrium manganite thin films.

We report the optical and magneto-optical properties of amorphous and crystalline Co₆₀Fe₂₀B₂₀ films with thicknesses in the range of 10 nm to 20 nm characterized using spectroscopy ellipsometry (SE) and magneto-optical Kerr effect (MOKE) spectroscopy. We derived the spectral dependence of the dielectric tensor from experimental data for samples prior and after annealing in vacuum. The features of the dielectric function can be directly related to the transitions between electronic states and the observed changes upon annealing can be ascribed to an increase of the crystalline ordering of CoFeB.

We report unipolar resistive switching in polycrystalline, hexagonal yttrium manganite thin films grown on unpatterned Pt metal coated SiO₂/Si substrates with circular Al top electrodes. Electroforming-free or electroforming-based resistive switching is observed, depending on the chemical composition (Y₁Mn₁O₃, Y_0.95Mn_1.05O₃, Y₁Mn_0.99Ti_0.01O₃, and Y_0.94Mn_1.05Ti_0.01O₃). The number of loading cycles measured at room temperature for samples with Y₁Mn₁O₃ and Y_0.95Mn_1.05O₃ composition is larger than 10³. The dominant conduction mechanism of the metal–insulator–metal structures between 295 K and 373 K in the high resistance state is space charge limited conduction and in the low resistance state is ohmic conduction. Activation energies in Ohm's law region in the high resistance state are calculated from the Arrhenius equation and are evaluated to be 0.39 ± 0.01 eV (Y₁Mn₁O₃), 0.43 ± 0.01 eV (Y_0.95Mn_1.05O₃), 0.34 ± 0.01 eV (Y₁Mn_0.99Ti_0.01O₃), and 0.38 ± 0.02 eV (Y_0.94Mn_1.05Ti_0.01O₃).

The performance of CoFeB/MgO tunnel junctions is strongly dependent on an annealing step at the end of the fabrication process to first, set a reference magnetization through the exchange bias effect and second, to crystallize the MgO/CoFe layers while boron diffuses out, in order to maximize the magnetoresistance ratio. In this regard, a laser-induced annealing process presents several advantages against traditional oven annealing techniques, providing a scalable approach with no limitations regarding the defined reference magnetization that can be aligned in different directions on a wafer. This paper concentrates on the mechanisms and dependences of laser annealing on the magnetic properties in comparison to the standard vacuum oven annealing, providing a first insight for the applicability of laser annealing for CoFeB-/MgO-based magnetic tunnel junctions with all concomitant needs.