The time-dependent dielectric breakdown of Co/Al2O3/Co(-Fe) magnetic tunnel junctions is investigated. At voltages larger than 1.2 V, almost immediate breakdown of the junction is observed, leading to a decreased (magneto)resistance. The shorts, which are local hot spots, were visualized by making use of a liquid crystal film on top of the junction. The breakdown voltages of a series of nominally identical tunnel junctions measured in a voltage-ramp experiment are shown to increase with increasing ramp speed. The results are analyzed in the framework of several models for the voltage dependent breakdown probability.

Due to their very thin tunnel barrier layer, magnetic tunnel junctions show dielectric breakdown at voltages of the order of 1 V. At the moment of breakdown, a highly conductive short is formed in the barrier and is visible as a hot spot. The breakdown effect is investigated by means of voltage ramp experiments on a series of nominally identical Co/Al 2 O 3 /Co tunnel junctions. The results are described in terms of a voltage dependent breakdown probability, and are further analyzed within the framework of a general model for the breakdown probability in dielectric materials, within which it is assumed that at any time the breakdown probability is independent of the ͑possibly time-dependent͒ voltage that has been previously applied. The experimental data can be described by several specific forms of the voltage breakdown probability function. A comparison with the models commonly used for describing thin film SiO 2 breakdown is given, as well as suggestions for future experiments.

The magnetothermopower and magnetoresistance of two copper/cobalt multilayers grown on grooved indium phosphide were measured between 100 K and 295 K. One sample was deposited at an angle onto a grooved substrate such that transport properties are measured between layers rather than parallel to them (CPP); the other was deposited perpendicular to the substrate, so that the transport properties are measured at an angle to the planes (CAP). The data show the magnetothermopower to vary inversely with the resistivity, as predicted by the Mott formula if the magnetoresistance is determined by the ratio α of majority to minority densities of states at the Fermi energy EF in the magnetic metal. Using this result, we can collapse the thermopower data at various temperatures to find that α′/α is 0.6 eV−1 for the CPP sample and 0.7 eV−1 for the CAP sample, where α′≡(∂α/∂E)EF.

Document VersionPublisher's PDF, also known as Version of Record (includes final page, issue and volume numbers) Please check the document version of this publication:• A submitted manuscript is the author's version of the article upon submission and before peer-review. There can be important differences between the submitted version and the official published version of record. People interested in the research are advised to contact the author for the final version of the publication, or visit the DOI to the publisher's website.• The final author version and the galley proof are versions of the publication after peer review.• The final published version features the final layout of the paper including the volume, issue and page numbers. Link to publication Citation for published version (APA):Oepts, W., Gijs, M. A. M., Reinders, A., Jungblut, R., van Gansewinkel, R. M. J., & Jonge, de, W. J. M. (1996). Perpendicular giant magnetoresistance of Co/Cu multilayers on grooved substrates : systematic analysis of the temperature dependence of spin-dependent scattering. Physical Review B: Condensed Matter, 53(21), 14024-14027. DOI: 10.1103/PhysRevB.53.14024 General rightsCopyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from the public portal for the purpose of private study or research.• You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal ? Take down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. The giant magnetoresistance of Co/Cu multilayers deposited at an angle onto grooved substrates is measured with the current perpendicular to the layer plane. The spin-dependent scattering parameters due to magnetic bulk and interface scattering are determined as a function of temperature, which is done by comparing our experiments with the two-channel model. We find that the decrease of the magnetoresistance from 4.2 K to room temperature is mainly due to an increase of the bulk resistivities of the Co and Cu layers, while the temperature dependence of the interface resistance and the spin-asymmetry parameters for electron scattering is small.