Magnetic tunnel junctions that utilize perpendicular magnetic anisotropy have attracted growing attention due to their potential for higher storage densities in future high capacity magnetic memory applications. In this study, we present an experimental demonstration of magnetic tunnel junctions composed of perpendicularly magnetized Co∕Pt multilayer electrodes and an AlOx tunnel barrier. The emphasis has been on how to maximize the thickness of the Co layers adjacent to the tunnel barrier while still magnetized perpendicularly for possible spin torque utilization in future applications. It is found that the thickness ratio between the Co and Pt layers and the number of bilayers were significant parameters to customize the magnetic properties. The difference between the switching fields of the soft and the hard layers can be adjusted by the number of repeats of the Co∕Pt bilayers. The measured hysteresis shows virtually zero exchange coupling between the two layers through the tunnel barrier. Measured tunneling magnetoresistance ratio of the fabricated submicron-size tunnel junctions ranges from 10% to 15% at room temperature.

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We demonstrate spin-transfer switching of nanomagnetic devices composed of Co/Pt multilayer electrodes with perpendicular magnetic anisotropy. In order to obtain highly spin-polarized current, we have proposed the adoption of thick Co adjacent layers. The film stack has been optimized so that two different Co/Pt multilayer electrodes switch separately, with each having narrow switching field distribution. Detrimental effects of surface roughness have been observed and minimized to achieve well-defined switching behavior. Diverse nanopillar devices fabricated by e-beam lithography and subsequent processes show well-defined single step switching in both perpendicular field and injected current applications. The critical current density obtained is comparable to that of Co/Ni electrode based devices, indicating enhanced spin-transfer efficiency.

This paper presents vibration characteristics of magnetorheological(MR) elastomer, whose elastic modulus are controllable by applied magnetic field. By using this property, the material can be applied to vibration absorber, so that the stiffness of the absorber can be changed and actively controlled according to the magnetic flux density. However, the various performances of MR elastomer depends on different polarized direction of particles by applied magnetic field and dimension during the manufacturing process. In this paper, in order to obtain the optimal characteristics of MR elastomer, MR elastomers with different types and dimensions are prepared for a series tests. Using this test setup, extent of natural frequency shifted against magnetic field at various excitation frequencies can be measured. Specimens are prepared with 3 types, as cylinder samples exposed to magnetic field vertically, horizontally and unexposed during cure, respectively. Also, a set of design variables are considered to produce MR elastomers. Through the modal tests of mass structure with MR elastomer, the optimal design as well as the polarization direction of MR elastomer is obtained among the various dimensions and 3 directional types of MR elastomers.

Low-resistance magnetic tunnel junctions utilizing perpendicular magnetic anisotropy of Co/Pt multilayer electrodes have been investigated. In these junctions, AlO x tunnel barrier has been prepared by repeated natural oxidation processes. Each natural oxidation process has been optimized by varying the thickness of pre-oxidized Al layer prior to oxidation. The perpendicular magnetic anisotropy of Co/Pt multilayer has been found to be dependent on the degree of oxidation at the interface of tunnel barrier and Co adjacent layer. It has been observed that magnetization of Co/Pt multilayer is tilted when Co layer adjacent to tunnel barrier is relatively thick, which is attributed to the lack of interfacial anisotropy contribution near the interface of Co adjacent layer and AlO x barrier. Interfacial oxidation treated on the monolayer thick Co adjacent layer has enhanced perpendicular magnetic anisotropy of the entire Co/Pt multilayer electrodes, enabling sharp transition between well-defined parallel and anti-parallel states at micro-fabricated perpendicular magnetic tunnel junctions of 100 m 2 resistance-area product.