Magnetic switching field and giant magnetoresistance effect of multilayers with synthetic antiferromagnet free layers

Synthetic antiferromagnets (SyAF) made of ${\mathrm{Co}}_{90}{\mathrm{Fe}}_{10}({\mathrm{t}}_1\mathrm{)/}\mathrm{Ru}(\mathrm{d}\mathrm{)/}{\mathrm{Co}}_{90}{\mathrm{Fe}}_{10}({\mathrm{t}}_2)$ trilayers and spin-valve type multilayers using a SyAF free layer were deposited on a buffer layer of Cu(2.5 nm)/Ru(10 nm) on a ${\mathrm{SiO}}_2/\mathrm{Si}$ substrate by using an ultrahigh vacuum sputtering system and a metal mask. The magnetization switching field of the SyAF in both trilayers and multilayers was independent of the Ru thickness, suggesting that the switching field is independent of the magnitude of the antiferromagnetic interlayer exchange coupling, and was proportional to $t_1\mathrm{/\Delta t}$ ${\mathrm{(\Delta t=|t}}_1{\mathrm{-t}}_2\mathrm{|),}$ which is in good agreement with the model of coherent rotation with perfect antiparallel alignment during magnetization reversal of the SyAF. Giant magnetoresistance of the multilayers exhibited two types of curves depending on $t_1{\mathrm{>t}}_2$ or $t_1{\mathrm{<t}}_2.$