Structural and magnetic properties of Ru/Ni multilayers

K Mergia,I Panagiotopoulos,F Ott,A Tomou

doi:10.1088/0022-3727/44/7/075001

Abstract

Ru/Ni multilayers of different Ni thicknesses have been fabricated using magnetron sputtering. The structure of the multilayers has been determined by grazing incidence x-ray diffraction and x-ray reflectivity and their magnetic properties by magnetization and polarized neutron reflectivity measurements. The presence of Ru leads to the formation of a hexagonal Ni structure within an interfacial layer ∼1 nm above each Ru layer, while the rest of the Ni layer relaxes to the equilibrium fcc structure. The hcp Ni interfacial layer has a substantially increased cell volume, and is ferromagnetic with an atomic magnetic moment that increases with Ni layer thickness but remains lower than the value predicted from ab initio calculations.

Highlights

Layered magnetic structures are the basis for several technological applications from spin valves and magnetic random access memories to ultra high density recording hard disk media
The grazing incidence X-ray diffraction (GIXRD) patterns for all the Ru/Ni multilayers are presented in figure 1 together with the spectrum from the 12 nm Ru single layer which was deposited under the same conditions
In the GIXRD patterns from Ru/Ni multilayers, hexagonal Ru Bragg peaks arise from two sources, the one attributed in the 9 nm Ru buffer layer and the other arising from the Ru layers in the multilayer structure

Summary

Introduction

Layered magnetic structures are the basis for several technological applications from spin valves and magnetic random access memories to ultra high density recording hard disk media. It has been demonstrated that the incorporation of lattice mismatched or structurally incoherent layers between soft magnetic layers can lead to a significant reduction in saturation and coercive fields [5] due to suppression of stripe domains. Soft magnets as permalloys and iron-cobalt alloys crystallize in cubic structures and are structurally incompatible with hexagonal Ru. The existence of interfacial magnetically “dead” [6] or “weak” layers has been reported in NiFe/Ru multilayers [7] but their origin remains unclear. It is found that the use of Ru interlayers leads to the formation of hexagonal Ni at the interfaces which disrupts the coupling between the magnetic layers and can be used to reduce the saturation and coercive fields

Experimental

Experimental results

Discussion and Conclusions

Ni hexagonal 0 o Ni cubic * *