Magnetic properties of patterned tunnel junctions

Abstract

Patterned magnetic tunnel junctions are being actively studied for their application in magnetic random access memory (MRAM) and read-heads. For MRAM application purposes, a clean magnetization reversal is one of the required properties. Various parameters such as junction size, shape or layer sequence are being investigated to optimize element properties. In this article, we report the results of Lorentztransmission electron microscopy used to study the magnetization reversal mechanism of ( Ta/NiFe/MnFe/NiFe/Al 2 O 3 / NiFeCo ) tunnel junction elements. Single layer NiFeCo element properties have also been investigated for comparison with the tunnel junctions. The results on tunnel junctions show the influence of size and aspect ratio of the patterned elements on magnetic properties. For the wider elements, domain formation and propagation is the dominant reversal mechanism and no asymmetry is observed between the antiparallel (AP) to parallel (P) and P–AP reversal measured as a function of aspect ratio. Single-domain reversal is the main process for narrower elements and there is an asymmetry in reversal field between the AP–P and P–AP reversals as a function of aspect ratio. Many energy terms (such as Néel coupling, stray field coupling, and the internal demagnetizing field) need to be taken into account to explain this behavior.