MINT Seminar Page

MINT seminars (EE 8192), Winter 1998

Title: Exchange Pinning and Ferromagnetic Domain Structure in FM/AFM Coupled Thin Films
Presenter: Mark T. Kief, Recording Heads Operations, Seagate Technology
Date: March 10, 1998, Tuesday
Time: 11:15 a.m.
Room: 102 Mech. Eng.

Abstract

Magnetic recording heads and magnetic sensors employing ferromagnetic thin films typically require that the ferromagnetic layers be single domain and highly oriented. This desired ferromagnetic domain configuration is achieved by many methods including shape anisotropy, hard and soft magnet biasing, and antiferromagnet pinning. The application of antiferromagnet pinning layers have been demonstrated for domain stabilization in AMR (Anisotropic MagnetoResistance) heads and for pinning layers for next generation GMR (Giant MagnetoResistance) based Spin Valve heads. Despite the technological importance of these pinning layers they are still not well understood. A simple model proposed by Meikeljohn and Bean 4 decades ago suggests a pinning field magnitude approximately 100 times greater than experimentally observed. Many theories including Mauri (1987) et. al, Malozemoff (1987) and Koon (1997) have attempted to explain this discrepancy and related observations such as increased coercivity, magnetic training and dependence upon interface structure. In this presentation, we experimentally investigate the prototypical system NiFe/NiO. We will discuss the effects of the antiferromagnet surface roughness and texture upon the pinning field. We will show through applications of Kerr microscopy that the ferromagnet domain structure need not undergo coherent rotation, as is often assumed, to display a strong uni-directional anisotropy. This result gives new insight into FM/AFM coupled layers. It explains the greatly increased coercivity often exhibited in this system and suggests a local dispersion in the antiferromagnetic pinning direction.

For more information on the seminars, please call Jack Judy at 612/625-7381 or email at judy@ece.umn.edu