Investigation of weak interlayer exchange coupling in GaMnAs/GaAs superlattices with insulating nonmagnetic spacers

A robust long-range antiferromagnetic coupling between ferromagnetic Ga0.97Mn0.03As layers has previously been realized via insertion of nonmagnetic Be-doped GaAs spacers between the magnetic layers. In this paper we report the observation of weak antiferromagnetic coupling between Ga0.97Mn0.03As layers through undoped GaAs spacers with thicknesses as large as 25 monolayers. The field and the temperature dependences of the sample magnetization suggest that the interlayer coupling in these systems substantially deviates from typical ferromagnetic behavior. Polarized neutron reflectivity measurements reveal antiferromagnetic alignment between Ga0.97Mn0.03As layers when a weak field is applied perpendicular to the magnetic easy axis during cooling below TC. The strength of the observed coupling between the magnetic layers is estimated to be weaker than 0.05 mT. VC 2011 American Institute of Physics. [doi:10.1063/1.3609080]