Thermally-controlled interlayer exchange and field-induced anisotropy in synthetic antiferromagnets

Interlayer exchange in synthetic antiferromagnets incorporating thin paramagnetic spacers can be controlled thermally. The spacer provides an additional ferromagnetic contribution that renormalizes the otherwise temperature-independent interlayer coupling. As a result, the system shows antiferromagnetic alignment at high temperatures and ferromagnetic alignment at low temperatures. This behavior is observed in Fe(2 nm)/Cr(0.4 nm)/Fe${}_{17.5}$Cr${}_{82.5}$(0.9 nm)/Cr(0.4 nm)/Fe(2 nm) multilayers with the inner spacer Fe${}_{17.5}$Cr${}_{82.5}$ paramagnetic at and above room temperature, and is shown to be due to the spacer being significantly magnetically polarized on lowering the temperature toward its Curie point. Although the Fe layers lack intrinsic magnetocrystalline anisotropy, the magnetization reversal demonstrates a field-induced uniaxial anisotropy of antiferromagnetic character. The resulting reversal process resembles that of a metamagnet with a spin-flip transition.