Magnetic anisotropy and magnetoresistance of sputtered [(FeTaN)/(TaN)](n) multilayers

TL;DR

This study investigates how varying TaN layer thickness in sputtered [(FeTaN)/(TaN)](n) multilayers influences magnetic anisotropy, coercivity, grain size, and magnetoresistance, revealing a transition from uniaxial to biaxial anisotropy and oscillatory behavior with layer number.

Contribution

It demonstrates the interlayer coupling effects on magnetic properties and anisotropy evolution in multilayers, highlighting differences from single-layer FeTaN films.

Findings

Coercivity, grain size, and MR amplitude decrease then increase with TaN thickness.

Transition from uniaxial to biaxial anisotropy occurs around 4.0 nm of TaN.

Magnetoresistance effects are mainly due to anisotropic MR (AMR).

Abstract

We studied the in-plane magnetic anisotropy of rf (radio frequency) sputtered [(FeTaN)/(TaN)](n) multilayers synthesized on Si substrates. In the multilayers where n=5, the FeTaN thickness is fixed at 30 nm and the thickness of TaN, t(TaN), is varied from 0 to 6.0 nm, we observed a clear trend that, with increasing t(TaN), the values of coercivity, grain size, and amplitude of maximum magnetoresistance (MR) of the samples all decrease first and then increase after reaching a minimum when t(TaN) is around 2.0-4.0 nm. This trend is also associated with an evolution of in-plane magnetic anisotropy, where the multilayers change from uniaxial anisotropy to biaxial at t(TaN) around 4.0 nm and above. We attribute the phenomena to the interlayer coupling effect of FeTaN films as a function of the coupling layer (TaN) thickness, rather than to the thickness dependence observed in single-layered FeTaN films, where the direction of easy axis switches 90degrees when the film is thicker than 300 nm. The in-plane anisotropy of the [(FeTaN)/(TaN)](n) multilayers also shows signs of oscillation when the number of coupling layers varies. The MR effects observed are mainly due to anisotropy MR (AMR), while the grain size and exchange coupling may also contribute to the change of maximum MR ratios in the multilayers with changing t(TaN).