Interlayer coupling and magnetoresistance of MnGa-based trilayers with semiconducting, antiferromagnetic, and ferrimagnetic spacer layers

We have studied the influence of the magnetic structure of the spacer layer on the interlayer exchange coupling and on the correlation between the coupling and magnetoresistance in MnGa-based trilayers with antiferromagnetic (Mn2As), ferrimagnetic (Mn2Sb), and semiconducting (GaAs) spacer layers. The samples are grown epitaxially on GaAs(001) substrates using molecular beam epitaxy. We can control both the period of the magnetic long-range order in the spacer layers and the orientation of their easy axis with respect to the MnGa easy axis. Magnetic measurements show that the period of the interlayer coupling is not related to the magnetic long-range order of the spacer layer. The strength of the coupling does depend on the orientation of the easy axis of the spacer, with strong coupling when it is collinear with the easy axis of MnGa and weak coupling when it is orthogonal. GaAs spacer layers grown using an optimized procedure to eliminate any Mn contamination still show metalliclike behavior. This is attributed to a large defect density caused by the low-temperature growth. The sign and magnitude of the magnetoresistance show a direct correlation with the interlayer coupling. The proportionality constant is universal for all spacer layer materials under investigation. This behavior is discussed in terms of two models based on quantum interference effects and on a frustration magnetoresistance mechanism