Weak antiferromagnetic coupling in sputtered NiCo/Cu multilayers

Small-angle neutron scattering has been used to study the magnetic ordering of Ni80Co20/Cu multilayers, a system which exhibits giant magnetoresistance. This system was selected for study because of its near-zero magnetic anisotropy, so that the exchange coupling may be determined with minimal interference from anisotropic effects. For a Cu thickness around 20 Å, clear antiferromagnetic order is seen, which may be suppressed by an external field of only 160 Oe. Combining the neutron data with magnetization data yields a value of 5.8×10-3 erg/cm2 for the exchange coupling, considerably less than values quoted hitherto for Cu/transition-metal multilayers.