Evolution of magnetic and microstructural properties of thick sputtered NdFeB films with processing temperature

TL;DR

This study investigates how processing temperature and heating rate affect the magnetic and microstructural properties of thick sputtered NdFeB films, revealing optimal conditions for high coercivity and grain development.

Contribution

It provides new insights into the effects of deposition and annealing parameters on NdFeB film microstructure and magnetic properties, especially the influence of heating rate.

Findings

High annealing temperatures (>650°C) are necessary for coercivity.

Faster heating rates (≥2000°C/h) promote higher coercivity.

Grain shape and size are strongly affected by heating rate.

Abstract

Ta (100 nm) / NdFeB (5 $\mu$m) / Ta (100 nm) films have been deposited onto Si substrates using triode sputtering (deposition rate ~ 18 $\mu$m/h). A 2-step procedure was used : deposition at temperatures up to 400 C followed by ex-situ annealing at higher temperatures. Post-deposition annealing temperatures above 650 C are needed to develop high values of coercivity. The duration of the annealing time is more critical in anisotropic samples deposited onto heated substrates than in isotropic samples deposited at lower temperatures. For a given set of annealing conditions (750 C/ 10'), high heating rates (≥ 2000 C / h) favour high coercivity in both isotropic and anisotropic films. The shape and size of Nd2Fe14B grains depend strongly on the heating rate.