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Optimization of Embedded Fast Magnetic Memory Cells

Materials Science Seminar
Georg Wolf, New York University and Technische Universitat Kaiserslautern, Germany
January 22, 2013 11:00AM to 12:00PM
Building 223, Room S105
Tunneling magneto resistance (TMR) structures are promising candidates for novel fast non-volatile memory cells. The magnetization reversal of the free layer on a nanosecond time scale is a crucial aspect on the way to a potential application. The present work addresses the switching behavior of a micro-sized TMR structure under the influence of two mutually orthogonal magnetic field pulses. The aim of the investigation is to define a suitable parameter space for fast and above all stable switching of the magnetization of the free layer. The parameter space includes amplitude, and duration of the magnetic field pulses, as well as their relative temporal delay.

The experiments were carried out on a full TMR layer stack based on CoFeB/MgO/CoFeB tunneling structure using time‐resolved magneto-optical Kerr effect (MOKE) microscopy. The obtained time profile of the switching behavior of the free layer magnetization is compared to a simple macro spin model and an extensive micromagnetic simulation. The experimental findings are discussed in terms of chances and limitations for potential applications. The second part of the work focuses on the magneto-optical properties of Co‐based Heusler compounds. Due to their high spin polarization they are potential materials for TMR structures. The control of the material properties is a key aspect with regards to potential industrial applications.

Especially the crystal order plays an important role to achieve the favored properties. Besides some of these materials exhibited a very large quadratic magneto-optical Kerr effect (QMOKE). Subject of the investigation are thin films of several Heusler compounds with different material compositions and different degrees of crystal ordering, achieved through post-deposition annealing at different temperatures. All materials investigated show remarkably large QMOKE. It was found that the magnitude of the QMOKE signal correlates with the crystal structure of the materials. This opens up the possibility to use the optical technique of QMOKE as an indicator for the crystal order of these materials.