Abstract
Shifted hysteresis loops characteristic of the exchange bias effect between a ferromagnet and an antiferromagnet are demonstrated in structures formed by a 2.5 nm Cr layer deposited on top of an array of Fe nanoislands (Cr/Fe-nanoislands). This effect evidences the persistence of antiferromagnetic (AF) order for Cr layers much thinner than the thickness reported in the literature. The field shift measured is found to increase for the smallest island sizes, which can be related with the enhancement of the Fe-nanoisland surface to volume ratio. The comparative study between superconducting proximity effects in Nb/Cr/Fe-nanoislands and Nb/normal metal/Fe-nanoisland hybrids (where the normal metals used are Al and Pt) confirms the presence of AF order in the 2.5 nm Cr spacer layer. A much shorter penetration depth of the Cooper pairs into the AF Cr layers than in the normal metal Pt and Al spacer layers is deduced.
Highlights
Thin film magnetism has long been a subject of interest and intense research activity since the magnetic properties of thin films present important differences from the properties of the bulk material
In this work we show how this complex Cr/Fe-nanoisland geometry is responsible for both the AF order and the exchange bias effect observed for Cr layer thickness much lower than the critical thickness reported in the literature
Taking into account the corrugation and strains of the Cr spacer layer induced by the Fe islands morphology, the number of magnetic defects in the interface increases as the Fe islands become smaller, resulting in an enhanced proximity effect and lower TC for small island sizes
Summary
Thin film magnetism has long been a subject of interest and intense research activity since the magnetic properties of thin films present important differences from the properties of the bulk material. In the present paper we have focused on the effect of disorder and roughness on the magnetic properties and on the exchange bias effect in Cr/Fe bilayers where the ferromagnetic film is replaced by a layer consisting of an assembly of Fe nanoislands. The second part of this work is dedicated to a comparative study of the superconducting proximity effects in Nb/Cr/Fe nanoislands and Nb/normal metal/Fe-nanoislands where the normal metals used are Pt and Al. By adjusting the deposition parameters of the Fe layer, island size can be modified in a controlled fashion, allowing the analysis of proximity effects as a function of the contact surface area between the superconductor and the ferromagnet. We show the different role that Cr plays from a normal metal, as an intermediate layer between Nb film and Fe islands
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