Kinetics of alloy formation at the interfaces in a Ni-Ti multilayer: X-ray and neutron reflectometry study

Abstract

Vacuum-deposited Ni/Ti multilayers on annealing at different temperatures exhibit formation of ordered alloy layers at interfaces. We have studied in detail the formation of alloy at interfaces of a Ni/Ti multilayer on annealing at $300\text{ }\ifmmode^\circ\else\textdegree\fi{}\text{C}$ and $400\text{ }\ifmmode^\circ\else\textdegree\fi{}\text{C}$ using powder x-ray diffraction, x-ray reflectometry, polarized neutron reflectometry, and off-specular x-ray reflectometry techniques. Correlation among structural, magnetic, and morphological properties in as-deposited Ni/Ti multilayer as well as in a sample annealed at $300\text{ }\ifmmode^\circ\else\textdegree\fi{}\text{C}$ and $400\text{ }\ifmmode^\circ\else\textdegree\fi{}\text{C}$ has been studied. X-ray diffraction technique was used to obtain crystal structure of the sample. Specular x-ray reflectometry and neutron reflectometry were used to determine the growth of alloy layers from density profile, as a function of depth in the sample. From off-specular x-ray reflectivity we found that the in-plane correlation lengths at the interfaces grew with annealing. This is associated with alloy crystallite growth obtained from x-ray reflectometry. Detailed magnetic-moment density profile of as-deposited as well as annealed multilayer sample has been determined by polarized neutron reflectometry measurements, which was used to determine the magnetic nature of the alloy layers. The results show formation of nonmagnetic alloy layers at the interfaces on annealing. From the Bragg-peak intensities of x-ray reflectivity and polarized neutron reflectivity measurements, we have estimated the diffusion lengths after annealing at $300\text{ }\ifmmode^\circ\else\textdegree\fi{}\text{C}$ and $400\text{ }\ifmmode^\circ\else\textdegree\fi{}\text{C}$.