Abstract
Low-dimensional magnetic heterostructures are a key element of spintronics, where magnetic interactions between different materials often define the functionality of devices. Although some interlayer exchange coupling mechanisms are by now well established, the possibility of direct exchange coupling via proximity-induced magnetization through non-magnetic layers is typically ignored due to the presumed short range of such proximity effects. Here we show that magnetic order can be induced throughout a 40-nm-thick amorphous paramagnetic layer through proximity to ferromagnets, mediating both exchange-spring magnet behaviour and exchange bias. Furthermore, Monte Carlo simulations show that nearest-neighbour magnetic interactions fall short in describing the observed effects and long-range magnetic interactions are needed to capture the extent of the induced magnetization. The results highlight the importance of considering the range of interactions in low-dimensional heterostructures and how magnetic proximity effects can be used to obtain new functionality.
Highlights
Low-dimensional magnetic heterostructures are a key element of spintronics, where magnetic interactions between different materials often define the functionality of devices
When two ferromagnetic layers are separated by a nonmagnetic layer, proximity effects arise at both interfaces, which can give rise to long-range interlayer exchange coupling[16], changes in ordering temperature[17] and/or non-oscillatory alignment of the magnetic layers[15,18]
We provide experimental evidence that such a proximity effect can result in direct exchange coupling across a 40-nm-thick paramagnetic layer, which is more than an order of magnitude longer than previously demonstrated
Summary
Low-dimensional magnetic heterostructures are a key element of spintronics, where magnetic interactions between different materials often define the functionality of devices. The need for such assumptions is removed if longer-range (beyond nearest-neighbour) magnetic interactions are allowed[3,4,5,6,7] This approach is rarely used due to its computational complexity, it has been employed successfully to capture finite size effects on the magnetic ordering and describe the spatial variation of the magnetization in very thin, freestanding films[8]. When two magnetic materials are in direct contact, the influence of the proximity effects is mutual, leading to a variation in the coupling strength across the interface, which has been modelled previously using mean field theory[11] This can for example give rise to changes in the ordering temperature of the two materials[12] or even result in a single singularity in the susceptibility[11]. We show how such a proximity effect can be rationalized using an atomistic spin model with long-range magnetic interactions and move beyond the common assumption of only nearest-neighbour magnetic interactions
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