Münster 1999 – wissenschaftliches Programm

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PV: Plenarvorträge

PV II

PV II: Plenarvortrag

Dienstag, 23. März 1999, 08:30–09:15, H1

Coming of Age of Magnetic Multilayers: Giant Magnetoresistance Field Sensors and Magnetic Tunnel Junction Memory Elements — •Stuart S. P. Parkin — IBM Almaden Research Center, 650 Harry Road, San Jose, CA 95120-6099, USA

During the past decade major advances in our understanding and our ability to prepare magnetic multilayered thin film structures using simple sputter-deposition techniques have led to important applications of these materials. Multilayers of thin ferromagnetic layers separated by thin non-magnetic conducting or insulating layers display unusual properties. In particular, metallic magnetic multilayers and magnetic tunnel junctions (MTJ) exhibit, respectively, giant magnetoresistance (GMR) and giant magneto-tunneling (GMT) effects, namely very large changes in resistance when subjected to magnetic field. The magnetoresistance (MR) is related to changes in the magnetic structure of the multilayer with field. In metallic structures the ferromagnetic layers are exchange coupled via the intervening non-magnetic layers. The exchange coupling oscillates from ferromagnetic to anti-ferromagnetic coupling with increasing spacer layer thickness with oscillation periods of ∼ 5 − 20 Å, determined by quantization of the electronic states in the multilayer. This leads to related oscillations in the GMR: GMR effects as large as 110% are observed at room temperature in relatively large magnetic fields (∼ 20 kOe). In MTJs, GMT effects as large as ∼ 42% are found at 300 K in much smaller magnetic fields (∼ 1 − 5 Oe). By engineering GMR and MTJ materials useful structures can be constructed for advanced magnetic recording read heads and for building non-volatile magnetic memories (MRAM). Indeed many tens of millions of GMR read heads have been incorporated into hard disk drivers in the past year and many hundreds of millions of such devices will be manufactured in the coming years. MRAM using MTJ storage elements promises truly non-volatile random access memory with the high speed of SRAM and the high density of DRAM. This talk will describe the evolution of magnetic thin film multilayered structures over the past ten years and their current usage and future potential.