AVS 50th International Symposium
    Magnetic Interfaces and Nanostructures Monday Sessions
       Session MI-MoA

Paper MI-MoA4
Atomistic Simulations of Metal/Metal Oxide Heterostructures

Monday, November 3, 2003, 3:00 pm, Room 316

Session: Magnetic Recording and Magnetoresistive Structures
Presenter: X.W. Zhou, University of Virginia
Authors: X.W. Zhou, University of Virginia
H.N.G. Wadley, University of Virginia
Correspondent: Click to Email
A thin aluminum oxide layer sandwiched between a pair of ferromagnetic metal layers forms a spin-dependent tunnel junction that can be used to construct random access memory. Atomistic simulations based upon interatomic potentials provide a way to identify the best conditions to synthesize these structures. However, unlike the approaches that have been successfully used to simulate metal multilayer deposition, atomic simulation methods for metal and metal oxide heterostructures are poorly developed. Metal oxides involve a significant ionic interaction between constituent cations and anions. Traditional fixed charge ionic potentials do not allow the introduction of different oxidation states and cannot ensure charge neutrality during simulation of oxide vapor deposition. They also significantly overestimate the cohesive energy of oxides. Because their charges are designated (for a given bulk oxide), they are not applicable to metal oxide heterostructures and cannot address metal/oxide interfaces. A charge transfer ionic potential (CTIP) model proposed by Streitz and Mintmire has attempted to overcome these deficiencies. However, we found that this charge transfer model is unstable and can only be applied to single metal-oxygen binary systems. By incorporation of the physical principle of elemental valency we have found an expedient solution to the limitations of the original CTIP model. The improved CTIP potential has been combined with an existing embedded atom method (EAM) metal potential to dynamically address both ionic and metallic components of the interatomic interactions in an O-Al-Ni-Co-Fe system during atomistic simulations. Application of this novel approach in the oxidation of aluminum layer in Ni65Co20Fe15/Al2O3/Ni65Co20Fe15 spin-dependent tunnel junction multilayer is reported and the roles of processing conditions used to synthesis the aluminum oxide layer are discussed.