Strong biquadratic coupling and antiferromagnetic-ferromagnetic crossover in NiFe/Cu multilayers

       K. Pettit 
       Department of Physics, University of Illinois at Urbana Champaign, 1110 W. Green Street, Urbana, Illinois 61801-3080
       IBM Research Division, Almaden Research Center, 650 Harry Road, San Jose, California 95120-6099

       S. Gider and S. S. P. Parkin 
       IBM Research Division, Almaden Research Center, 650 Harry Road, San Jose, California 95120-6099

       M. B. Salamon 
       Department of Physics, University of Illinois at Urbana Champaign, 1110 West Green Street, Urbana, Illinois 61801-3080
       Center for Materials Science, Los Alamos National Laboratory, Los Alamos, New Mexico 87545

Received 4 November 1996; revised 22 May 1997

We report clear manifestations of biquadratic exchange in the magnetoresistance (MR) of (110) single-crystal NiFe/Cu multilayers. Magnetoresistance curves show a low-field
MR minimum which results from an asymmetric canting of the moments away from the applied magnetic field. The stability of these magnetic configurations indicates that the
biquadratic coupling can be significantly stronger than the bilinear coupling. In samples with ferromagnetic (F) bilinear coupling the strength of both the bilinear and
biquadratic coupling decays in the temperature range from 200 to 400 K. In samples that are coupled antiferromagnetically (AF) at room temperature, we observe a crossover
from AF to F bilinear coupling as the temperature is lowered below 200 K. We attribute the strong biquadratic coupling and temperature dependence of the bilinear coupling to
pinholes in the Cu spacer layers.

©1997 The American Physical Society

URL: http://publish.aps.org/abstract/PRB/v56/p7819
PACS: 75.70.Pa, 72.15.Gd