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MgO-based magnetic tunnel junctions with up to 230% tunnel magnetoresistance ratio at room temperature and up to 345% at 13 K are prepared. The lower electrode is either exchange-biased or free, while the top electrode is free or an exchanged-biased artificial ferrimagnet, respectively. Additionally, a pseudo-spin-valve ͑hard-soft switching͒ design with two unpinned electrodes is used. Inelastic electron-tunneling spectra for each of these systems show a strong variation in the zero-bias anomaly with a reduced peak for some of the junctions. At voltages around 200 mV additional structures are found, which are not known from junctions with lower magneto resistance, such as alumina-based junctions. We discuss the spectra for the different electrode types and compare our findings with respect to barrier material and magnetoresistance ratio.

Articles you may be interested inComment on "Mapping of localized spin-wave excitations by near-field Brillouin light scattering" [Appl. Phys. Lett.97, 152502 (2010)] Appl. Phys. Lett. 99, 186101 (2011); 10.1063/1.3656967 Ferromagnetic and antiferromagnetic spin-wave dispersions in a dipole-exchange coupled bi-component magnonic crystal Appl. Phys. Lett. 99, 143118 (2011); 10.1063/1.3647952 Magnetic-field-orientation dependent magnetization reversal and spin waves in elongated permalloy nanorings J. Appl. Phys. 108, 053909 (2010); 10.1063/1.3475648High-intensity Brillouin light scattering by spin waves in a permalloy film under microwave resonance pumpingWe report on the experimental study of the spatial characteristics of high-frequency spin-wave modes localized at the edges of micrometer-size in-plane magnetized permalloy ellipses. Using a near-field Brillouin light scattering technique, we have mapped the modes with the spatial resolution of few tens of nanometers. We show that the width of the localization area strongly depends on the applied magnetic field and reduces to about 85 nm for high fields. We also demonstrate that the existing theoretical models do not appropriately describe spatial characteristics of the modes.

We have studied experimentally with high spatial resolution the nonlinear eigenmodes of microscopic Permalloy elliptical elements. We show that the nonlinearity affects the frequencies of the edge and the center modes in an essentially different way. This leads to repulsion of corresponding resonances and to nonlinear mode hybridization resulting in qualitative modifications of the spatial characteristics of the modes. We find that the nonlinear counterparts of the edge and the center modes simultaneously exhibit features specific for both their linear analogues.