Berlin 2008 – wissenschaftliches Programm

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MA: Fachverband Magnetismus

MA 24: FV Internal Symposium in honour of Nobelprice 2007 to Peter Grünberg and Albert Fert

MA 24.1: Hauptvortrag

Donnerstag, 28. Februar 2008, 09:30–10:00, EB 301

Physics and applications of tunneling magnetoresistance effect — •Shinji Yuasa — National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8568, Japan

A magnetic tunnel junctions (MTJ), which consists of an ultra-thin insulator (a tunnel barrier) sandwiched by two ferromagnetic electrode layers, exhibits tunneling magnetoresistance (TMR) effect due to spin-dependent electron tunneling. Since the discovery of room-temperature TMR effect in 1995, MTJs with an amorphous Al-O tunnel barrier have been extensively studied and are currently used in magnetoresistive random-access-memory (MRAM) and read head of hard disk drive (HDD). These conventional MTJs show magnetoresistance (MR) ratios of up to about 70% at room temperature. However, MTJs with much higher magnetoresistance are desired for next-generation MRAM and HDD. In 2001, first-principle theories predicted the MR ratios above 1,000% in epitaxial Fe(001)/MgO(001)/Fe(001) MTJs with a crystalline MgO(001) tunnel barrier as a result of coherent spin-dependent tunneling. In 2004, giant MR ratios of about 200% at room temperature (RT) were experimentally achieved in fully epitaxial MgO-based MTJs and (001)-oriented poly-crystalline (textured) MgO-based MTJs. Novel CoFeB/MgO(001)/CoFeB MTJ structure, which is highly compatible with mass-manufacturing processes of MRAM and HDD read head, was also developed, and giant MR ratios above 200% up to 500% at RT have been achieved. Giant TMR effect in MgO-based MTJs is of great importance not only for developing various spintronic devices but also for clarifying the physics of spin-dependent tunneling.