Date/Time
Date(s) - 17/09/2003
3:30 pm - 4:30 pm

Title: EXCHANGE-COUPLED FERROMAGNETIC/ANTIFERROMAGNETIC FILMS

Speaker: Dr. David Venus

Institute: Department of Physics and Astronomy
McMaster University

Location: ABB 102

Description:

Interface phenomena in ultrathin magnetic film systems
drive a rich variety of magnetic properties in these
materials, many of which have allowed advances in
magnetic recording technologies. A crucial element
in the design of magnetoresistive read heads is the
inclusion of an antiferromagnetic/ferromagnetic interface
that introduces a shift of the ferromagnetic hystersis loop.
This shift occurs through local exchange coupling across
the interface and is called the “exchange bias”. It is
understood to arise from the frustration of the exchange
coupling across an imperfect interface, when the system
is placed in a metastable state by cooling it below the
antiferromagnetic transition temperature in an applied field.
Traditionally, this phenomenon has been studied using
large fields (kOe) to trace a hysteresis loop of the
exchange-coupled films and determine the effective
“exchange field” from the offset of the loop from H=0.
Our more nuanced approach is to make small field (1 Oe)
measurements of the ac-susceptibility as a function of
temperature and to study the magnetic relaxation of the
metastable state and relate it to the activated processes
creating the exchange field.