Spintronics applications use ferromagnetic(F)/antiferromagnetic(AF) exchange bias (EB) interactions to set the reference direction required for the spin of conduction electrons. They therefore may involve layers intermixing originating from F/AF interfaces. As a consequence of intermixing, interfacial spin-glass-like phases (frustrated spin configurations) with reduced EB properties and increased dispersions form and may lower the devices performances. It is thereby necessary to limit intermixing. Diffusion barriers have been commonly implemented in the field of electronics. The science of diffusion barriers involves many aspects which often lead to compromise and one of the major difficulties is that the barrier must not corrupt the surrounding materials that it is supposed to be protecting. Some barriers may consist of multiple layers to accommodate such a need for non-reactivity. Here, we implemented diffusion barrier and in particular dual barriers for the F/AF building block of spintronics devices. We focus on F/AF cobalt/iridium-manganese (Co/IrMn) based stacks with (Cu/Pt) dual barriers.
Our method uses blocking temperature distributions (DTB) to quantify the interfacial quality of the F/AF interface - TB is the temperature over which the AF is no longer thermally stable when cycling the F magnetization. Via the combination of a specific procedure commonly carried out for measurements of DTB above room-temperature (room-T) and the alternative use of a sufficiently low reference-T (usually 4K), we recently provided a simple method for quantifying the magnetic interfacial quality of F/AF bilayers (ie the interfacial glassy character). The method is fairly easy to implement in laboratories: hysteresis loops measurements at 4K following various field cooling from incremental T up to room-T or above, and it provides data usually obtained via large scale facilities experiments. For example, x-ray magnetic circular dichroism results obtained from synchrotron radiation experiments give the amount of stable AF spins, at room-T usually, when our laboratory method provides the complement, ie the amount of unstable spins at and above room-T.
Inserting a (Cu/Pt) dual barrier between Co and IrMn fulfilled the manifold requirements of limiting Co-Mn, Co-Pt and Cu-Mn intermixing which take place when using either no or single Pt and Cu barriers respectively. Although inserting the dual barrier was beneficial for the EB properties dispersions, it weakened the EB absolute values by taking the F away from the AF. However, some encouraging data suggested that it is in principle possible to find barriers for which the benefits of intermixing limitations overcome the disadvantages of spacing augment between the F and the AF thus validating the overall positive impact of adding diffusion barriers for the specific case of EB based spintronics devices.
This work was performed under the bilateral agreement SPINTEC-CROCUS Technology.
Last update : 10/14 2013 (860)